Effect of manure co-digestion on methane production, carbon retention, and fertilizer value of digestate

Anaerobic digestion can provide benefits not only from the perspective of renewable energy production but also in the form of fertilization effect and increased retention of C in soils after digestate application. This study consisted of two phases, where the first phase assessed the suitability of carbon-rich co-feedstocks for methane production via laboratory testing. The second phase assessed the balance and stability of C before and after anaerobic digestion by systematic digestate characterization, and by evaluating its carbon retention potential using a modeling approach. The results indicated that pyrolysis chars had a negligible effect on the methane production potential of cattle manure, while wheat straw expectedly increased methane production. Thus, a mixture of cattle manure and wheat straw was digested in pilot-scale leach-bed reactors and compared with undigested manure and straw. Although the total amount of C in the digestate was lower than in the untreated feedstocks, the digestion process stabilized C and was modeled to be more effective in retaining C in the soil than untreated cattle manure and wheat straw. In addition, digestion converted 23-27 % of the C into valuable methane, increasing the valorization of the total C in the feedstock. Considering anaerobic digestion processes as a strategy to optimize both carbon and nutrient valorization provides a more holistic approach to addressing climate change and improving soil health.

Aging microplastics and coupling of "microplastic-electric fields" can affect soil water-stable aggregates' stability

As plastic waste continues to accumulate in natural environments, the impact of aged microplastics (MPs) on soil ecosystems is increasingly becoming a matter of global concern. However, the effects of aged MPs on the stability of water-stable soil aggregates have not been clearly elucidated. Therefore, we investigated the influence of two types of aged MPs, namely, polystyrene and polypropylene, on soil aggregate stability. We found that MPs have a notable effect on the fundamental structural units of soil aggregates, including organic matter and microorganisms. Consequently, reducing the structural stability of soil aggregates by disrupting the bonding mechanisms of soil particles affects the erosion resistance of coarse aggregates. Furthermore, we investigated the coupled effects of "soil electric field-MPs" on aggregate stability. The results showed that the critical potential for aggregate explosive fragmentation corresponds to an electric field intensity at an electrolyte concentration of 10-2 mol·L-1. In this study, we have clarified the primary factors through which MPs affect the stability of water-stable soil aggregates, providing new insights for a more accurate assessment of the impact of MPs on soil aggregates.

Assessment of land use management and its effect on soil quality and carbon stock in Ebonyi State, Southeast Nigeria

Evaluating soil quality (SQ) resulting from land management use impact is important for soil carbon (C) monitoring, land sustainability and suitability. However, the data in less developed regions of Africa like Nigeria is scarce, limiting our understanding at global scale. The study evaluated land management use on soil quality in Ebonyi State, Nigeria, a representative region of Africa. Soil samples were collected in 2021 and resampled in 2022 from regions including five land use managements (FS = forest soil; GLS = grass land soil; ACS = alley cropping Soil; SDS = sewage dump-soils; CCS = continuously cultivated soil). Soil physical and chemical properties were analyzed and discussed. The results shows that soil physical properties (bulk density, hydraulic conductivity, aggregate stability) were significantly (P < 0.05) influenced by land use management. Moderate to high bulk density, very low hydraulic conductivity (HC), and low aggregate stability were observed across land management, suggesting potential inhibition to root penetration, poor aeration, and water infiltration. Improved land management practices such as planting of cover crops either for re-grassing or addition of crop residues could be adopted as conservative options for increasing soil quality and encourage additional soil C. Soil pH decreased with the increase in soil depth in all land uses for both years. A higher soil pH of 6.78 (slightly acidic) was seen in SDS and lower mean 6.0 (moderately acidic) was obtained in CCS at 0-20 cm in 2021. The average mean nitrogen content was rated "very high" (0.81 g kg-1 and 0.69 g kg-1) in 2021 and 2022 respectively, suggesting nitrogen might not be a limiting factor for plant growth in the region. During the 2021 and 2022 study periods, the overall average mean C stock were 12.71 g kg-1 and 15.87 g kg-1 respectively suggesting 3.1 g kg-1 C stock increment in 2022. Soil inorganic C also increased by 9.86 g cm-2 in 2022. The study provided crucial information about how land management use affected soil physico-chemical properties including C stock and suggested that C stock could be improved by adopting appropriate land management use practices. The results fill a data gap in under-studied regions, but also facilitate potential land management practices.

Decadal soil total carbon loss in northern hinterland of Tibetan Plateau

As the largest and highest plateau in the world, ecosystems on the Tibetan Plateau (TP) imply fundamental ecological significance to the globe. Among the variety, alpine grassland ecosystem on the TP forms a critical part of the global ecosystem and its soil carbon accounts over nine tenths of ecosystem carbon. Revealing soil carbon dynamics and the underlying driving forces is vital for clarifying ecosystem carbon sequestration capacity on the TP. By selecting northern TP, the core region of the TP, this study investigates spatiotemporal dynamics of soil total carbon and the driving forces based on two phases of soil sampling data from the 2010s and the 2020s. The research findings show that soil total carbon density (STCD) in total-surface (0-30 cm) in the 2010s (8.85 ± 3.08 kg C m-2) significantly decreased to the 2020s (7.15 ± 2.90 kg C m-2), with a decreasing rate (ΔSTCD) of -0.17 ± 0.39 kg C m-2 yr-1. Moreover, in both periods, STCD exhibited a gradual increase with soil depth deepening, while ΔSTCD loss was more apparent in top-surface and mid-surface than in sub-surface. Spatially, ΔSTCD loss in alpine desert grassland was -0.41 ± 0.48 kg C m-2 yr-1, which is significantly higher than that in alpine grassland (-0.11 ± 0.31 kg C m-2 yr-1) or alpine meadow (-0.04 ± 0.28 kg C m-2 yr-1). The STCD in 2010s explained >30 % of variances in ΔSTCD among the set of covariates. Moreover, rising temperature aggravates ΔSTCD loss in alpine desert grassland, while enhanced precipitation alleviates ΔSTCD loss in alpine meadow. This study sheds light on the influences of climate and background carbon on soil total carbon loss, which can be benchmark for predicting carbon dynamics under future climate change scenarios.

Interactive effects of grassland utilization and climatic factors govern the plant diversity-soil C relationship in steppe of North China

The relationship between plant diversity and the ecosystem carbon pool is important for understanding the role of biodiversity in regulating ecosystem functions. However, it is not clear how the relationship between plant diversity and soil carbon content changes under different grassland use patterns. In a 3-year study from 2013 to 2015, we investigated plant diversity and soil total carbon (TC) content of grasslands in northern China under different grassland utilization methods (grazing, mowing, and enclosure) and climatic conditions. Shannon-Wiener and Species richness index of grassland were significantly decreased by grazing and mowing. Plant diversity was positively correlated with annual precipitation (AP) and negatively correlated with annual mean temperature (AMT). AP was the primary regulator of plant diversity. Grazing and mowing decreased TC levels in grasslands compared with enclosures, especially in topsoil (0-20 cm). The average TC content was decreased by 58 % and 36 % in the 0-10 cm soil layer, while it was decreased by 68 % and 39 % in 10-20 cm soil layer. TC was positively correlated with AP and negatively correlated with AMT. Principal component analysis (PCA) showed that plant diversity was positively correlated with soil TC, and the correlation decreased with an increase in the soil depth. Overall, this study provides a theoretical basis for predicting soil carbon storage in grasslands under human disturbances and climate change impacts.

Topsoil porosity prediction across habitats at large scales using environmental variables

Soil porosity and its reciprocal bulk density are important environmental state variables that enable modelers to represent hydraulic function and carbon storage. Biotic effects and their 'dynamic' influence on such state variables remain largely unknown for larger scales and may result in important, yet poorly quantified environmental feedbacks. Existing representation of hydraulic function is often invariant to environmental change and may be poor in some systems, particularly non-arable soils. Here we assess predictors of total porosity across two comprehensive national topsoil (0-15 cm) data sets, covering the full range of soil organic matter (SOM) and habitats (n = 1385 & n = 2570), using generalized additive mixed models and machine learning. Novel aspects of this work include the testing of metrics on aggregate size and livestock density alongside a range of different particle size distribution metrics. We demonstrate that porosity trends in Great Britain are dominated by biotic metrics, soil carbon and land use. Incorporating these variables into porosity prediction improves performance, paving the way for new dynamic calculation of porosity using surrogate measures with remote sensing, which may help improve prediction in data sparse regions of the world. Moreover, dynamic calculation of porosity could support representation of feedbacks in environmental and Earth System Models. Representing the hydrological feedbacks from changes in structural porosity also requires data and models at appropriate spatial scales to capture conditions leading to near-saturated soil conditions. Classification. Environmental Sciences.

Invasive Japanese beetle (Popillia japonica Newman) larvae alter structure and carbon distribution in infested surface soil

Invasive macrofauna influence the biophysical state and function of soil, helping to drive ecological changes over time. Many soil-dwelling invertebrates affect soil stability by facilitating or hindering the soil aggregation process, changing the availability of plant and soil organic matter (SOM) for aggregate incorporation, and shifting the predominant mechanisms by which carbon is incorporated into soil aggregates. Using mass fractionation and stable carbon isotope techniques, this 17-month experimental study examined silt-clay-loam mesocosms either infested or not infested with soil-dwelling larvae of the invasive Japanese beetle, Popillia japonica Newman (JB). We hypothesized that larval root-herbivory would promote a pathway of large aggregate formation that features the mixing of digested root tissue with mineral soil and subsequent fecal deposition. These newly deposited, large soil aggregates will then grow by agglomeration of particles, thereby occluding a larger pool of fresh organic carbon, or be broken apart, exposing fresh organic inputs to microbial activity and mineralization processes, depending on soil conditions. Findings show a proportional increase of larger soil size fractions (2- 8 mm) in the rhizosphere of infested soil after 1½ life cycles of the beetle, but a decrease in the smaller soil size fractions (0.053-2 mm). In infested bulk surface soil (0-2.5 cm) carbon increased, primarily due to greater carbon content in the largest size fractions. Carbon also increased in all size fractions, although the proportion of total carbon in fractions was greater only in the largest fractions due to their greater relative abundance. There may also be an increase of microbially derived carbon in the largest size fractions, possibly indicating significant priming effects associated with JB larval herbivory. The implications of these findings for relative stabilization of the bulk surface soil carbon pool in JB-infested soil likely depends on the residence time of, and stable microaggregate formation within these large size fractions.

Agent-Based Life Cycle Assessment enables joint economic-environmental analysis of policy to support agricultural biomass for biofuels

Production of agricultural biofuels is expected to rise due to increasing climate change mitigation ambitions. Policy interventions promoting targeted bioenergy solutions can be motivated by the large environmental externalities present in agricultural systems and the local context of biomass production co-benefits. Introducing energy crops in crop rotations in arable land with depleted Soil Organic Carbon (SOC) levels offers the potential to increase SOC stocks and future crop yields as a step towards more sustainable agricultural systems. However, the environmental performance of a policy incentive for energy crops with SOC co-benefits is less evident when considering its land-use effects within and outside of the target agricultural system. We study the potential impacts of a change in agricultural policy on regional agricultural structure and production, and the environment with an Agent-Based Life Cycle Assessment approach. We simulate a policy payment that would achieve adoption of grass leys in crop rotations corresponding to 25 % of the highly productive land in an intensive farming region of southern Sweden. Although enhancing soil health in SOC-depleted farming regions is a desirable environmental objective, its significance is limited within the life-cycle performance of the payment. Instead, crop-displacement impacts and the grass potential as biofuel feedstock are the main drivers. The active utilisation of grasses for biofuel purposes is key in reaching a positive environmental evaluation of the policy instrument. Our environmental evaluation is likely generalisable to other regions with similar technological levels and farming intensity, while our analysis on structural shifts is specific to the policy instrument and agricultural production system under study. Overall, our work provides a method to contrast regional effects and global environmental impacts of policy instruments supporting agricultural biomass for biofuels prior to implementation. This contributes to the environmental assessment of land-based biofuels at a time when their sustainability is highly debated.

Land use change and forest management effects on soil carbon stocks in the Northeast U.S

BACKGROUND

In most regions and ecosystems, soils are the largest terrestrial carbon pool. Their potential vulnerability to climate and land use change, management, and other drivers, along with soils' ability to mitigate climate change through carbon sequestration, makes them important to carbon balance and management. To date, most studies of soil carbon management have been based at either large or site-specific scales, resulting in either broad generalizations or narrow conclusions, respectively. Advancing the science and practice of soil carbon management requires scientific progress at intermediate scales. Here, we conducted the fifth in a series of ecoregional assessments of the effects of land use change and forest management on soil carbon stocks, this time addressing the Northeast U.S. We used synthesis approaches including (1) meta-analysis of published literature, (2) soil survey and (3) national forest inventory databases to examine overall effects and underlying drivers of deforestation, reforestation, and forest harvesting on soil carbon stocks. The three complementary data sources allowed us to quantify direction, magnitude, and uncertainty in trends.

RESULTS

Our meta-analysis findings revealed regionally consistent declines in soil carbon stocks due to deforestation, whether for agriculture or urban development. Conversely, reforestation led to significant increases in soil C stocks, with variation based on specific geographic factors. Forest harvesting showed no significant effect on soil carbon stocks, regardless of place-based or practice-specific factors. Observational soil survey and national forest inventory data generally supported meta-analytic harvest trends, and provided broader context by revealing the factors that act as baseline controls on soil carbon stocks in this ecoregion of carbon-dense soils. These factors include a range of soil physical, parent material, and topographic controls, with land use and climate factors also playing a role.

CONCLUSIONS

Forest harvesting has limited potential to alter forest soil C stocks in either direction, in contrast to the significant changes driven by land use shifts. These findings underscore the importance of understanding soil C changes at intermediate scales, and the need for an all-lands approach to managing soil carbon for climate change mitigation in the Northeast U.S.

The importance of accounting method and sampling depth to estimate changes in soil carbon stocks

BACKGROUND

As interest in the voluntary soil carbon market surges, carbon registries have been developing new soil carbon measurement, reporting, and verification (MRV) protocols. These protocols are inconsistent in their approaches to measuring soil organic carbon (SOC). Two areas of concern include the type of SOC stock accounting method (fixed-depth (FD) vs. equivalent soil mass (ESM)) and sampling depth requirement. Despite evidence that fixed-depth measurements can result in error because of changes in soil bulk density and that sampling to 30 cm neglects a significant portion of the soil profile's SOC stock, most MRV protocols do not specify which sampling method to use and only require sampling to 30 cm. Using data from UC Davis's Century Experiment ("Century") and UW Madison's Wisconsin Integrated Cropping Systems Trial (WICST), we quantify differences in SOC stock changes estimated by FD and ESM over 20 years, investigate how sampling at-depth (> 30 cm) affects SOC stock change estimates, and estimate how crediting outcomes taking an empirical sampling-only crediting approach differ when stocks are calculated using ESM or FD at different depths.

RESULTS

We find that FD and ESM estimates of stock change can differ by over 100 percent and that, as expected, much of this difference is associated with changes in bulk density in surface soils (e.g., r = 0.90 for Century maize treatments). This led to substantial differences in crediting outcomes between ESM and FD-based stocks, although many treatments did not receive credits due to declines in SOC stocks over time. While increased variability of soils at depth makes it challenging to accurately quantify stocks across the profile, sampling to 60 cm can capture changes in bulk density, potential SOC redistribution, and a larger proportion of the overall SOC stock.

CONCLUSIONS

ESM accounting and sampling to 60 cm (using multiple depth increments) should be considered best practice when quantifying change in SOC stocks in annual, row crop agroecosystems. For carbon markets, the cost of achieving an accurate estimate of SOC stocks that reflect management impacts on soils at-depth should be reflected in the price of carbon credits.

Effects of forest fire smoke deposition on soil physico-chemical properties and bacterial community

The number of forest fires has increased globally, together with considerable smoke emission that significantly impacts the atmospheric environment and associated ecosystems. Most current studies have focused on the in situ effects of fire on the forest ecosystem. However, the mechanisms by which smoke particles affect adjacent ecosystems are largely unexplored. In this study, a simulated forest fire combustion system was developed to evaluate the effect of different smoke concentrations (control, low and high) on soil physico-chemical properties of adjacent farmland at two soil depths. The abundance and diversity of bacterial community were also determined. The results showed that smoke deposition increased the contents of total carbon (TC), total nitrogen (TN), and total phosphorus (TP) in the 0-10 cm soil layer; however, no significant changes in soil water content (SWC) and pH values was observed. The ACE(Abundance Coverage-based Fastimator) and Chao1 diversity indices of bacterial community generally showed a downward trend whereas the PD_whole_ tree diversity index increased after 180 d of smoke deposition. The relative abundance of Proteobacteria remained stable, while abundance of Firmicutes in soil decreased after 180 d of smoke deposition. Smoke deposition slightly affected the physical and chemical properties of the 10-20 cm soil, but the range of variation of the relative abundance and diversity dominant bacteria exceeded that of the 0-10 cm soil. A significant positive correlation was found between the soil properties and the alpha diversity indices during the first 30 d after smoke deposition; the correlation then decreased gradually. Redundancy analysis revealed that Proteobacteria, Firmicutes, and Actinobacteria were generally positively correlated with TC, TN, and SWC. As a whole, the study reveals that the effects of smoke deposition on soil physico-chemical properties and bacterial community depends on smoke concentration where relatively low concentration appears to be beneficial to soil bacterial community.

The fate of rice crop residues and context-dependent greenhouse gas emissions: Model-based insights from Eastern India

Crop residue burning is a common practice in many parts of the world that causes air pollution and greenhouse gas (GHG) emissions. Regenerative practices that return residues to the soil offer a 'no burn' pathway for addressing air pollution while building soil organic carbon (SOC). Nevertheless, GHG emissions in rice-based agricultural systems are complex and difficult to anticipate, particularly in production contexts with highly variable hydrologic conditions. Here we predict long-term net GHG fluxes for four rice residue management strategies in the context of rice-wheat cropping systems in Eastern India: burning, soil incorporation, livestock fodder, and biochar. Estimations were based on a combination of Tier 1, 2, and 3 modelling approaches, including 100-year DNDC simulations across three representative soil hydrologic categories (i.e., dry, median, and wet). Overall, residue burning resulted in total direct GHG fluxes of 2.5, 6.1, and 8.7 Mg CO2-e in the dry, median, and wet hydrologic categories, respectively. Relative to emissions from burning (positive values indicate an increase) for the same dry to wet hydrologic categories, soil incorporation resulted in a -0.2, 1.8, or 3.1 Mg CO2-e change in emissions whereas use of residues for livestock fodder increased emissions by 2.0, 2.1, or 2.3 Mg CO2-e. Biochar reduced emissions relative to burning by 2.9 Mg CO2-e in all hydrologic categories. This study showed that the production environment has a controlling effect on methane and, therefore, net GHG balance. For example, wetter sites had 2.8-4.0 times greater CH4 emissions, on average, than dry sites when rice residues were returned to the soil. To effectively mitigate burning without undermining climate change mitigation goals, our results suggest that geographically-target approaches should be used in the rice-based systems of Eastern India to incentivize the adoption of regenerative 'no burn' residue management practices.

Environment and agricultural practices regulate enhanced biochar-induced soil carbon pools and crop yield: A meta-analysis

Using biochar in agriculture to enhance soil carbon storage and productivity has been recognized as an effective means of carbon sequestration. However, the effects on crop yield and soil carbon and nitrogen can vary depending on environmental conditions, field management, and biochar conditions. Thus, we conducted a meta-analysis to identify the factors contributing to these inconsistencies. We found that biochar application significantly increased soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized carbon (EOC), particulate organic carbon (POC), total nitrogen (TN), and the C:N ratio in topsoil (0-20 cm) and crop yields. Biochar was most effective in tropical regions, increasing SOC, Soil TN, and crop yield the most, with relatively moderate pyrolysis temperatures (550-650 °C) more conducive to SOC accumulation and relatively low pyrolysis temperatures (<350 °C) more conducive to increasing soil carbon components and crop yields. Biochar made from manure effectively increased soil carbon components and TN. Soil with low fertility (original SOC < 5 g kg-1; original TN < 0.6 g kg-1), coarse texture, and acidity (pH < 5.5) showed more effective results. However, biochar application rates should not be too high and should be combined with appropriate nitrogen fertilizer. And biochar application had long-term positive effects on soil carbon storage and crop yield. Overall, we recommend using small amounts of biochar with lower pyrolysis temperatures in soils with low fertility, coarse texture, and tropical regions for optimal economic and environmental benefits.

Trends in soil organic matter and topsoil thickness under regenerative practices at the University of Washington student farm

Conventional methods of agriculture, especially tillage, are often accompanied by soil degradation in the form of erosion and organic matter depletion. Regenerative agricultural methods seek to repair soil ecosystems by building topsoil and soil organic matter (SOM), decreasing reliance on chemical fertilizers and increasing both water retention capacity and the diversity and quantity of soil microbial and fungal communities. The University of Washington (UW) student farm is an organic and regeneratively managed site on the UW Seattle campus. Over the past 20 years the farm gradually expanded so locations on the farm encompass both unimproved topsoil and soils managed regeneratively for periods of 5 to 20 years. This arrangement allows a time-trend analysis of soil development under regenerative methods. Measurements of topsoil thickness (defined as the distance from the ground surface to the base of the soil A horizon) and organic matter content were collected across 14 distinct plots on the farm to quantify trends over time and estimate net change in SOM (and soil organic carbon, or SOC). While SOM content weakly increased by 0.5% per year, topsoil thickness exhibited a significant linear increase of 0.86 cm per year. Over a twenty-year period under the management practices of the UW Farm total organic carbon storage in soils, determined using topsoil thickness, density, and SOC content, increased by between 4 and 14 t ha-1 yr-1. The general increases in topsoil thickness, SOM content, and total soil carbon demonstrate the potential of soil-health-focused practices to help maintain a productive and efficient urban growing space.

Effects of co-applied biochar and plant growth-promoting bacteria on soil carbon mineralization and nutrient availability under two nitrogen addition rates

In the background of climate warming, the demand for improving soil quality and carbon (C) sequestration is increasing. The application of biochar to soil has been considered as a method for mitigating climate change and enhancing soil fertility. However, it is uncertain whether the effects of biochar application on C-mineralization and N transformation are influenced by the presence or absence of plant growth-promoting bacteria (PGPB) and soil nitrogen (N) level. An incubation study was conducted to investigate whether the effects of biochar application (0 %, 1 %, 2 % and 4 % of soil mass) on soil respiration, N status, and microbial attributes were altered by the presence or absence of PGPB (i.e., Sphingobium yanoikuyae BJ1) under two soil N levels (N0 and N1 soils as created by the addition of 0 and 0.2 g kg-1 urea- N, respectively). The results showed that biochar, BJ1 strain and their interactive effects on cumulative CO2 emissions were not significant in N0 soils, while the effects of biochar on the cumulative CO2 emissions were dependent on the presence or absence of BJ1 in N1 soils. In N1 soils, applying biochar at 2 % and 4 % increased the cumulative CO2 emissions by 141.0 % and 166.9 %, respectively, when BJ1 was absent. However, applying biochar did not affect CO2 emissions when BJ1 was present. In addition, the presence of BJ1 generally increased ammonium contents in N0 soils, but decreased nitrate contents in N1 soils relative to the absence of BJ1, which indicates that the combination of biochar and BJ1 is beneficial to play the N fixation function of BJ1 in N0 soils. Our results highlight that biochar addition influences not only soil C mineralization but also soil available N, and the direction and magnitude of these effects are highly dependent on the presence of PGPB and the soil N level.

Soil carbon content prediction using multi-source data feature fusion of deep learning based on spectral and hyperspectral images

Visible near-infrared reflectance spectroscopy (VNIR) and hyperspectral images (HSI) have their respective advantages in soil carbon content prediction, and the effective fusion of VNIR and HSI is of great significance for improving the prediction accuracy. But the contribution difference analysis of multiple features in the multi-source data is inadequate, and there is a lack of in-depth research on the contribution difference analysis of artificial feature and deep learning feature. In order to solve the problem, soil carbon content prediction methods based on VNIR and HSI multi-source data feature fusion are proposed. The multi-source data fusion network under the attention mechanism and the multi-source data fusion network with artificial feature are designed. For the multi-source data fusion network based on the attention mechanism, the information are fused through the attention mechanism according to the contribution difference of each feature. For the other network, artificial feature are introduced to fuse multi-source data. The results show that multi-source data fusion network based on the attention mechanism can improve the prediction accuracy of soil carbon content, and multi-source data fusion network combined with artificial feature has better prediction effect. Compared with two single-source data from the VNIR and HSI, the relative percent deviation of Neilu, Aoshan Bay and Jiaozhou Bay based on multi-source data fusion network combined with artificial feature are increased by 56.81% and 149.18%, 24.28% and 43.96%, 31.16% and 28.73% respectively. This study can effectively solve the problem of the deep fusion of multiple features in the soil carbon content prediction by VNIR and HSI, so as to improve the accuracy and stability of soil carbon content prediction, promote the application and development of soil carbon content prediction in spectral and hyperspectral image, and provide technical support for the study of carbon cycle and the carbon sink.

Variations of methane fluxes and methane microbial community composition with soil depth in the riparian buffer zone of a sponge city park

Riparian buffers benefit both natural and man-made ecosystems by preventing soil erosion, retaining soil nutrients, and filtering pollutants. Nevertheless, the relationship between vertical methane fluxes, soil carbon, and methane microbial communities in riparian buffers remains unclear. This study examined vertical methane fluxes, soil carbon, and methane microbial communities in three different soil depths (0-5 cm, 5-10 cm, and 10-15 cm) within a riparian buffer of a Sponge City Park for one year. Structural equation model (SEM) results demonstrated that vertical methane fluxes varied with soil depths (λ = -0.37) and were primarily regulated by methanogenic community structure (λ = 0.78). Notably, mathematical regression results proposed that mcrA/pmoA ratio (R² = 0.8) and methanogenic alpha diversity/methanotrophic alpha diversity ratio (R² = 0.8) could serve as valid predictors of vertical variation in methane fluxes in the riparian buffer of urban river. These findings suggest that vertical variation of methane fluxes in riparian buffer soils is mainly influenced by carbon inputs and methane microbial abundance and community diversity. The study's results quantitatively the relationship between methane fluxes in riparian buffer soils and abiotic and biotic factors in the vertical direction, therefore contributing to the further development of mathematical models of soil methane emissions.

Slash and burn management and permanent or rotation agroforestry systems: A comparative study for C sequestration by century model simulation

Understanding the effects of agroforestry systems (AFs) on soil organic carbon (SOC) requires long-term experiments, but scenarios simulations can anticipate the potential of these systems to sequester or lose carbon (C). This study aimed to simulate the SOC dynamics in slash and burn management (BURN) and AFs using the Century model. Data from a long-term experiment implemented in the Brazilian semiarid region were used to simulate SOC dynamics under BURN and AFs situations, and the natural vegetation (NV) "Caatinga" as a reference. BURN scenarios considered different fallow periods (0, 7, 15, 30, 50 and 100 years) among cultivation of the same area. The two types of AFs (agrosilvopastoral-AGP and silvopastoral-SILV) were simulated in two contrasting conditions: (i) each one of the AFs and also NV area were permanently conducted with no rotation among these areas; and (ii) the two AFs and NV rotated among them every 7 years. The correlation coefficients (r), coefficients of determination (CD) and coefficients of residual mass (CRM) showed adequate performance, meaning that the Century model is able to reproduce the SOC stocks in the slash and burn management and AFs situations. The equilibrium points of NV SOC stocks stabilized around 30.3 Mg ha^-1, as similar to the measured average of 28.4 Mg ha^-1 at field conditions. The adoption of BURN without a fallow period (0 years) resulted in a reduction of 50% of SOC, approximately 20 Mg ha^-1, after the first 10 years. Permanent (p) and rotating (r) AFs management systems recovered (in 10 years) fast to the original SOC stocks, resulting in higher SOC stocks than NV SOC at equilibrium. The fallow period of 50 years is necessary to recovery SOC stocks in the Caatinga biome. The simulation shows that the AFs systems increase more SOC stocks than observed in natural vegetation in long-term.

Estimating biomass and soil carbon change at the level of forest stands using repeated forest surveys assisted by airborne laser scanner data

BACKGROUND

Under the growing pressure to implement mitigation actions, the focus of forest management is shifting from a traditional resource centric view to incorporate more forest ecosystem services objectives such as carbon sequestration. Estimating the above-ground biomass in forests using airborne laser scanning (ALS) is now an operational practice in Northern Europe and is being adopted in many parts of the world. In the boreal forests, however, most of the carbon (85%) is stored in the soil organic (SO) matter. While this very important carbon pool is "invisible" to ALS, it is closely connected and feeds from the growing forest stocks. We propose an integrated methodology to estimate the changes in forest carbon pools at the level of forest stands by combining field measurements and ALS data.

RESULTS

ALS-based models of dominant height, mean diameter, and biomass were fitted using the field observations and were used to predict mean tree biophysical properties across the entire study area (50 km²) which was in turn used to estimate the biomass carbon stocks and the litter production that feeds into the soil. For the soil carbon pool estimation, we used the Yasso15 model. The methodology was based on (1) approximating the initial soil carbon stocks using simulations; (2) predicting the annual litter input based on the predicted growing stocks in each cell; (3) predicting the soil carbon dynamics of the annual litter using the Yasso15 soil carbon model. The estimated total carbon change (standard errors in parenthesis) for the entire area was 0.741 (0.14) Mg ha^-1 yr^-1. The biomass carbon change was 0.405 (0.13) Mg ha^-1 yr^-1, the litter carbon change (e.g., deadwood and leaves) was 0.346 (0.027) Mg ha^-1 yr^-1, and the change in SO carbon was - 0.01 (0.003) Mg ha^-1 yr^-1.

CONCLUSIONS

Our results show that ALS data can be used indirectly through a chain of models to estimate soil carbon changes in addition to changes in biomass at the primary level of forest management, namely the forest stands. Having control of the errors contributed by each model, the stand-level uncertainty can be estimated under a model-based inferential approach.

Impacts of land-use change on carbon dynamics in China's coastal wetlands

The impact of land-use and land-cover change (LULCC) on ecosystem carbon (C) dynamics has been previously documented at local and global scales, but uncertainty persists for coastal wetlands due to geographical variability and field data limitations. Field-based assessments of plant and soil C contents and stocks of various LULCC types were conducted in nine regions along the coastline of China (21°-40°N). These regions cover natural coastal wetlands (NWs, including salt marshes and mangroves) and former wetlands converted to different LULCC types, including reclaimed wetlands (RWs), dry farmlands (DFs), paddy fields (PFs) and aquaculture ponds (APs). The results showed that LULCC generally decreased the C contents and stocks of the plant-soil system by 29.6 % ± 2.5 % and 40.4 % ± 9.2 %, respectively, while it slightly increased the soil inorganic C contents and stocks. Wetlands converted to APs and RWs lost greater ecosystem organic C stocks (EOC, sum of plants and top 30 cm of soil organic C stocks) than other LULCC types. The annual potential CO₂ emissions estimated from EOC loss depended on the LULCC type, with an average emission of 7.92 ± 2.94 Mg CO₂-eq ha^-1 yr^-1. The change rate of EOC in all LULCC types showed a significantly deceasing trend with increasing latitude (p < 0.05). The loss of EOC due to LULCC was larger in mangroves than in salt marshes. The results showed that the response of plant and soil C variables to LULCC was mainly related to differences in plant biomass, median grain size, soil water content and soil NH₄⁺-N content. This study emphasized the importance of LULCC in triggering C loss in natural coastal wetlands, which strengthens the greenhouse effect. We suggest that the current land-based climate models and climate mitigation policies must account for specific land-use types and their associated land management practices to achieve more effective emission reduction.

Soil C/N ratios cause opposing effects in forests compared to grasslands on decomposition rates and stabilization factors in southern European ecosystems

Soils store an important amount of carbon (C), mostly in the form of organic matter in different decomposing stages. Hence, understanding the factors that rule the rates at which decomposed organic matter is incorporated into the soil is paramount to better understand how C stocks will vary under changing atmospheric and land use conditions. We studied the interactions between vegetation cover, climate and soil factors using the Tea Bag Index in 16 different ecosystems (eight forests, eight grasslands) along two contrasting gradients in the Spanish province of Navarre (SW Europe). Such arrangement encompassed a range of four climate types, elevations from 80 to 1420 m.a.s.l., and precipitation (P) from 427 to 1881 mm year^-1. After incubating tea bags during the spring of 2017, we identified strong interactions between vegetation cover type, soil C/N and precipitation affecting decomposition rates and stabilization factors. In both forests and grasslands, increasing precipitation increased decomposition rates (k) but also the litter stabilization factor (S). In forests, however, increasing soil C/N ratio raised decomposition rates and the litter stabilization factor, while in grasslands higher C/N ratios caused the opposite effects. In addition, soil pH and N also affected decomposition rates positively, but for these factors no differences between ecosystem types were found. Our results demonstrate that soil C flows are altered by complex site-dependent and site-independent environmental factors, and that increased ecosystem lignification will significantly change C flows, likely increasing decomposition rates in the short term but also increasing the inhibiting factors that stabilizes labile litter compounds.

Selective sorption and desorption of DOM in Podzol horizons - DOC and aluminium contents of leachates from a column experiment

Complexation of dissolved organic matter (DOM) with cations and minerals contributes to the stabilization of carbon in soils, and can enable the transport of metals in the environment. Hence, a proper understanding of mechanisms that control DOM binding properties in the soil is important for major environmental challenges, such as climate change and stream pollution. However, the role of DOM source in those mechanisms remains understudied. Here, we consider poorly drained tropical Podzols as a model environment to isolate effects of aluminium and DOM on sorption and desorption processes in podzolisation. We collected E- and Bh-horizons from a Brazilian coastal Podzol under tropical rainforest to conduct a column experiment, and percolated the columns with DOM collected from a stream (Stream), peat water (Peat), litter (Litter) and charred litter (Char). To quantify sorption and desorption from the columns, leachates were analysed for DOC content, aluminium content, pH, and the amount of fulvic acid relative to humic acid. The results showed large differences in DOC retention between DOM-types, which were consistent over all columns. Retention of DOC in the column varied between 25 % and 92 % for DOM-type Stream, between 33 % and 63 % for DOM-type Peat, between 22 % and 47 % for DOM-type Litter, and between 8 % and 49 % for DOM-type Char. Similarly, desorption from columns with B-horizon material highly differed between DOM-types. Percolation with DOM-types Stream and Peat caused a release of native DOC from B columns that was higher than in those percolated with water only. On the other hand, percolation of B columns with DOM-types Litter and Char caused a net DOC retention. These differences reflect that certain DOM-types hindered desorption, while other DOM-types caused active desorption. The large differences in sorption/desorption between DOM-types implies that changes in environmental conditions may highly influence the fate of soil carbon in Podzols.

The inverted forest: Aboveground and notably large belowground carbon stocks and their drivers in Brazilian savannas

Savannas contribute to ca. 30 % of the total terrestrial net primary productivity and are responsible for significant carbon storage. Savannas in South America are mostly found within the Cerrado Domain, which is very threatened and presents remarkable carbon pools. Herein, we used a unique dataset of 21 Cerrado sites spanning 144 permanent field plots in Southeastern Brazil to assess the general patterns of above and belowground carbon stocks. We identified the main environmental and tree diversity drivers of aboveground wood carbon and productivity, belowground carbon stocks (roots and soil), carbon ratios (root:shoot and above:below) and total carbon stocks in the Cerrado through a combination of climatic estimates, fire frequency data, field measurements of vegetation, roots, soil carbon, nutrients and texture, and assessment of different components of diversity (species, functional and phylogenetic). Our findings reveal average aboveground, root, and soil carbon stocks of 20.4, 14.24, and 123.13 Mg.ha^-1, respectively. Average Root:Shoot and Above:Below confirm the "inverted forest" concept with values of 1.58 and 0.21, respectively. Total carbon was 145.62 Mg.ha^-1, reinforcing the great amount of carbon storage in the Cerrado and its role in the carbon cycle and dynamics. Tree diversity variables (mainly species diversity and functional composition variables) had more significant effects over aboveground variables, whereas environmental variables had more significant effects over belowground variables. Ratios and total carbon mixed up these effects. The impressive values of carbon storage, especially belowground, point out the need to better manage and protect the Cerrado. Moreover, our findings might be particularly relevant for discussions on restoration programs focused on the trees-for‑carbon idea that do not consider species diversity and belowground carbon stocks.

Degradation Reduces Microbial Richness and Alters Microbial Functions in an Australian Peatland

Peatland ecosystems cover only 3% of the world's land area; however, they store one-third of the global soil carbon (C). Microbial communities are the main drivers of C decomposition in peatlands, yet we have limited knowledge of their structure and function. While the microbial communities in the Northern Hemisphere peatlands are well documented, we have limited understanding of microbial community composition and function in the Southern Hemisphere peatlands, especially in Australia. We investigated the vertical stratification of prokaryote and fungal communities from Wellington Plains peatland in the Australian Alps. Within the peatland complex, bog peat was sampled from the intact peatland and dried peat from the degraded peatland along a vertical soil depth gradient (i.e., acrotelm, mesotelm, and catotelm). We analyzed the prokaryote and fungal community structure, predicted functional profiles of prokaryotes using PICRUSt, and assigned soil fungal guilds using FUNGuild. We found that the structure and function of prokaryotes were vertically stratified in the intact bog. Soil carbon, manganese, nitrogen, lead, and sodium content best explained the prokaryote composition. Prokaryote richness was significantly higher in the intact bog acrotelm compared to degraded bog acrotelm. Fungal composition remained similar across the soil depth gradient; however, there was a considerable increase in saprotroph abundance and decrease in endophyte abundance along the vertical soil depth gradient. The abundance of saprotrophs and plant pathogens was two-fold higher in the degraded bog acrotelm. Soil manganese and nitrogen content, electrical conductivity, and water table level (cm) best explained the fungal composition. Our results demonstrate that both fungal and prokaryote communities are shaped by soil abiotic factors and that peatland degradation reduces microbial richness and alters microbial functions. Thus, current and future changes to the environmental conditions in these peatlands may lead to altered microbial community structures and associated functions which may have implications for broader ecosystem function changes in peatlands.

Greenhouse gas mitigation potential in smallholder agroecosystem of southern Ethiopia

In developing countries, it is critical that novel and swift strategies are devised to help direct and prioritize potential greenhouse gas (GHG) mitigation activities. The Carbon Benefit Project (CBP) analysis tool is a modular, web-based system that allows a consistent comparison of various projects by providing a standardized GHG benefits protocol. In this study, we used the CBP tool to estimate the GHG mitigation potential of the agriculture, forestry, and other land uses (AFOLU) sector and prioritize components for their GHG benefits in three districts of Wolaita Zone, southern Ethiopia. The study area is 90,731 ha of which about 2% was covered by forest, 7% by grassland, 78% by annual crops, 12% by home garden and 1% by settlements. The livestock population in the study area was 512,622 heads. Using the CBP's Detailed Assessment, we estimated mitigation potential in the AFOLU consisting of different managements strategies for a period between 2016 and 2030 in the smallholder agricultural landscape. The results showed an overall GHG benefit of 1,725,052 (±5%) Mg CO₂e from the projected scenario in the study area. The GHG benefit was in the order of biomass C (683,757 Mg CO₂e) > soil C (619,210 Mg CO₂e) > livestock (408,981 Mg CO₂e) illustrating the greater mitigation potential of trees in different systems. The soil C plus biomass C was high in agroforestry systems, and this component had the highest priority for GHG mitigation. This was followed by high enteric methane emission reduction in the livestock category. The GHG emission from manure increased by 71,633 Mg CO₂e in the project because manure was not managed. The surprisingly low GHG benefit of the forest was primarily because of its low land cover (i.e., about 2%) in the agroecosystem. Despite the low GHG benefit in the cropland from best management practices, the improved soil quality in it can affect GHG benefits from other land uses by contributing to their conservation through food security. Thus, a comprehensive project may be a viable strategy in a mitigation effort at the agroecosystem level because of the interactions amongst the components. The CBP analysis tool is useful in prioritizing mitigation activities and may be an option to quantify GHG benefits if studies collate Teir 2 factors in data scarce areas.

Recycling paper to recarbonise soil

Soil organic carbon can be increased through sympathetic land management and/or directly by incorporating carbon rich amendments. Herein, a field experiment amended paper crumble (PC) to soil at a normal deployment rate of 50 t ha^-1, and at higher rates up to 200 t ha^-1. The nominal 50 t ha^-1 PC amendment resulted a mean increase in soil carbon of 12.5 g kg^-1. Using a modified Roth-C carbon fate model, the long-term (50 years) carbon storage potential of a 50 t ha^-1 PC amendment was determined to be 0.36 t_OC ha^-1. Modelling a rotational (4 yearly) 50 t ha^-1 PC amendment indicated 6.65 t_OC ha^-1 uplift would accrue after 50 years. Contextualised for the average farm in the East of England (~120 ha, with 79 % as arable), PC derived increases in SOC would be equivalent to 2310 t CO₂e. These results support the use of PC to deliver significant levels of soil recarbonisation. Beyond carbon, PC was observed to influence other soil properties. Benefits observed included, decreased bulk density, increased water holding capacity, and increased cation exchange capacity. While PC amendment did not significantly increase wheat (Triticum aestivum) crop yield, manifold benefits in terms of increased SOC, long-term carbon storage potential, and improved soil quality sustain PC as a beneficial soil conditioner.

The carbon sequestration response of aboveground biomass and soils to nutrient enrichment in boreal forests depends on baseline site productivity

Nutrient enrichment can alleviate productivity limitations and thus substantially increase carbon (C) uptake in northern coniferous forests. Yet, factors controlling stand-to-stand variation of forest ecosystem responses to nutrient enrichment remain unclear. We used five long-term (13 years) nutrient-enrichment experiments across Sweden, where nitrogen (N), phosphorus, and potassium were applied annually to young Norway spruce forests that varied in their baseline ecosystem properties. We measured tree biomass and soil C and N stocks, litterfall C inputs, soil CO₂ efflux, and shifts in composition and biomass of soil microbial communities to understand the links between above and belowground responses to nutrient enrichment. We found that the strongest responses in tree biomass occurred when baseline site productivity was lowest. High increases in tree biomass C stocks were generally balanced by weaker responses in organic soil C stocks. The average ecosystem C-N response rate was 35 kg C kg^-1 N added, with a nearly five-fold greater response rate in tree biomass than in soil. The positive nutrient enrichment effects on ecosystem C sinks were driven by a 95% increase in tree biomass C stocks, 150% increase in litter production, 67% increase in organic layer C stocks, and a 46% reduction in soil CO₂ efflux accompanied by compositional changes in soil microbial communities. Our results show that ecosystem C uptake in spruce forests in northern Europe can be substantially enhanced by nutrient enrichment; however, the strength of the responses and whether the enhancement occurs mainly in tree biomass or soils are dependent on baseline forest productivity.

Rotation age extension synergistically increases ecosystem carbon storage and timber production of Chinese fir plantations in southern China

Afforestation is an effective method to increase carbon (C) sinks and address climate change. It is crucial to understand how the stand growth affects C sequestration capacity, especially when the trade-offs with timber production from plantations have not been fully examined. We used a chronosequence approach to estimate C storage in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations (including the trees, understory, litter, and soils) at seven stand ages (3, 8-11, 16, 21, 25, 29, and 32 years). Ecosystem C storage increased nonlinearly from 76.4 to 282.2 t ha^-1 with stand age and was fitted with a logistic model that had a maximum C storage and age of 271.9 t ha^-1 and 33 years, respectively, to reach 95% of the maximum stored C. The C increment was mainly contributed by an increase in tree biomass, which ranged from 2.8 to 177.7 t ha^-1 and comprised 4-64% of the total ecosystem C. Live root C (sum of the stump, coarse, and fine root C) showed a logistic increase from 2.0 to 26.3 t ha^-1 with stand age and constituted 2.5-9.3% of ecosystem C. Understory plants and litter represented a small pool (<2% of ecosystem C). The C storage in shrubs and litter slightly increased, while that in herbs decreased as the stands aged. Soil C storage was an important and relatively stable pool, ranging from 69.6 to 130.1 t ha^-1. Stand volume was also best fitted with a logistic model with a maximum value of 552.6 m³ ha^-1. Additionally, the time needed to reach 95% of the maximum volume was 25 years. Hence, extending the rotation age to over 30 years for Chinese fir plantations could potentially maximize the synergistic benefits of C storage to mitigate climate change and obtain timber products for economic profit.

Different drivers of soil C accumulation in aggregates in response to altered precipitation in a semiarid grassland

Soil carbon (C) stabilization partially depends on its distribution within soil structural aggregates, and on the physicochemical processes of C within these aggregates. Changes in precipitation can alter the size distribution of aggregate classes within soils, and C input and output processes within these aggregates, which have potential consequences for soil C storage. However, the mechanisms underlying C accumulation within different aggregates under various precipitation regimes remain unclear. In this study, we conducted a 3-year field manipulation experiment to test the effects of a gradient of altered precipitation (-70%, -50%, -30%, 0%, +30%, and +50% amounts compared with ambient rainfall) on soil aggregate distribution and C accumulation in aggregates (53-250 μm, microaggregates; < 53 μm, silt and clay fractions) in a meadow steppe of northeastern China. Our results revealed that the distribution of soil microaggregates decreased along the precipitation gradient, with no detectable discrepant responses with respect to soil C accumulation within the microaggregates to precipitation treatments. In contrast, higher precipitation amounts coupled with a greater proportion of silt and clay fractions enhanced the accumulation of soil C. Importantly, structural equation models revealed that the pathways by which changes in precipitation control the accumulation of soil C varied across aggregate size fractions. Plant biomass was the main direct factor controlling the accumulation of C within soil microaggregates, whereas soil aggregate distribution and enzyme activities strongly interacted with soil C accumulation in the silt and clay fractions. Our findings imply that identifying how plant and soil aggregate properties respond to precipitation changes and drive C accumulation among soil particles will enhance the ability to predict responses of ecosystem processes to future global change.

Plant diversity enhances soil fungal network stability indirectly through the increase of soil carbon and fungal keystone taxa richness

Plant diversity is critical to the stability of ecosystems. However, our knowledge about the plant diversity effect on the stability of belowground communities is limited. Here, we characterized soil fungal diversity and co-occurrence network across a plant diversity gradient in a diversity manipulation experiment. We found that higher plant diversity resulted in higher fungal diversity, network complexity and stability. The positive plant diversity effect on fungal network stability was indirect via the increase of soil carbon and fungal keystone taxa richness based on structural equation modeling analysis. The model explained 44% variations of network stability when combining soil carbon and fungal keystone taxa richness, but explained approximate 30% variations of network stability when considering either one of the two factors, indicating that environmental filtering and biotic interaction processes play comparable roles in mediating the plant diversity effect on soil fungal network stability. The plant diversity-induced fungal network stability was significantly correlated with community-level functions including community resistance and enzyme activities. This study, from the view of networks, provides new insights into the plant diversity effect on the stability of soil microbial communities, which have implications for biodiversity conservation and policy development.

Interactive impacts of climate change and agricultural management on soil organic carbon sequestration potential of cropland in China over the coming decades

Cropland plays an important role in Soil Organic Carbon (SOC) sequestration. Although the SOC stock and its dynamic in the past decades have been extensively investigated, the information as to where, how much, and how SOC could be potentially sequestered in the coming decades has rarely been available. Here, the Rothamsted Carbon model was applied to investigate the spatiotemporal pattern of SOC sequestration potential for China's cropland in 2021-2040 at 1 km resolution, as well as the interactive impacts of climate change and agricultural management on SOC sequestration. Under the combined impacts of climate change and C input, the SOC sequestration of China's cropland in 2021-2040 would be about 0.56 Mg C ha^-1 (0.06% yr^-1), 1.33 Mg C ha^-1 (0.15% yr^-1), 2.10 Mg C ha^-1 (0.24% yr^-1), and 3.65 Mg C ha^-1 (0.41% yr^-1), with no increase, 5%, 10%, and 20% increase of C input, respectively. Therefore, a >20% increase in C input would be necessary to realize the promise of the '4 per 1000' initiative. Climate change would decrease SOC sequestration by 26.6-27.6 Tg yr^-1 (or 60.4-62.7%). An increase of C input by 0%, 5%, 10%, and 20% relative to business as usual (BAU) would increase SOC sequestration by 4.8 (or 10.8%), 6.6 (or 14.9%), 13.1 (or 29.8%), and 26.2 (or 59.6%) Tg yr^-1, respectively. The contributions of temperature, precipitation, and C input to SOC sequestration will be averagely 18.6%, 22.4%, and 59.0%, respectively. Our findings quantify the SOC sequestration in 2021-2040 at a high spatial resolution under the interactive impacts of climate change and agricultural management, which help to identify potential foci and develop region-specific measures to increase SOC sequestration efficiently.

Review: biological engineering for nature-based climate solutions

Nature-based Climate Solutions are landscape stewardship techniques to reduce greenhouse gas emissions and increase soil or biomass carbon sequestration. These mitigation approaches to climate change present an opportunity to supplement energy sector decarbonization and provide co-benefits in terms of ecosystem services and landscape productivity. The biological engineering profession must be involved in the research and implementation of these solutions-developing new tools to aid in decision-making, methods to optimize across different objectives, and new messaging frameworks to assist in prioritizing among different options. Furthermore, the biological engineering curriculum should be redesigned to reflect the needs of carbon-based landscape management. While doing so, the biological engineering community has an opportunity to embed justice, equity, diversity, and inclusion within both the classroom and the profession. Together these transformations will enhance our capacity to use sustainable landscape management as an active tool to mitigate the risks of climate change.

The coupling interaction of soil organic carbon stock and water storage after vegetation restoration on the Loess Plateau, China

Vegetation restoration may increase the soil organic carbon stock (SOCS) but decrease the soil water storage (SWS) of terrestrial ecosystems in arid and semiarid regions. To guarantee the sustainability of restoration, it is critical to evaluate the coupling interaction of SOCS and SWS. Here, we examined the spatial distributions of SOCS and SWS across a 0-200 cm soil profile in a grassland, forestland and shrubland on the Loess Plateau and determined the driving factors that affected their variations. Our results showed that SOCS and SWS varied across the 0-200 cm soil profile and considerably accumulated in the deep soil layers (100-200 cm). In comparison to SOCS, SWS generally had higher relative benefits in most studied plant communities, which ensured sustainable restoration. In addition, land use played a less important role than local environmental conditions in determining the variations in SOCS and SWS. Specifically, the interaction between SOCS and SWS was mainly strong in the surface soil layers (0-20 cm). Topography was a predominant factor that affected SOCS and SWS in the deep soil layers (100-200 cm), while soil texture was a stable driving factor influencing their variations across the whole soil profile (0-200 cm). Given the low moisture consumption of grasslands and the lowest root mean square deviation (RMSD) of Hippophae rhamnoides, we proposed an advanced scenario for ecological restoration on the Loess Plateau: establishing reasonably large Hippophae rhamnoides patches with fewer edges in a contiguous grassland matrix. Furthermore, this scenario should be tailored to local environmental conditions, such as soil water, texture and topography, followed by natural vegetation succession.

Initial soil conditions outweigh management in a cool-season dairy farm's carbon sequestration potential

Pastures and rangelands are a dominant portion of global agricultural land and have the potential to sequester carbon (C) in soils, mitigating climate change. Management intensive grazing (MIG), or high density grazing with rotations through paddocks with long rest periods, has been highlighted as a method of enhancing soil C in pastures by increasing forage production. However, few studies have examined the soil C storage potential of pastures under MIG in the northeastern United States, where the dairy industry comprises a large portion of agricultural use and the regional agricultural economy. Here we present a 12-year study conducted in this region using a combination of field data and the denitrification and decomposition (DNDCv9.5) model to analyze changes in soil C and nitrogen (N) over time, and the climate impacts as they relate to soil carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes. Field measurements showed: (1) increases in soil C in grazed fields under MIG (P = 0.03) with no significant increase in hayed fields (P = 0.55); and (2) that the change in soil C was negatively correlated to initial soil C content (P = 0.006). Modeled simulations also showed fields that started with relatively less soil C had significant gains in C over the course of the study, with no significant change in fields with higher initial levels of soil C. Sensitivity analyses showed the physiochemical status of soils (i.e., soil C and clay content) had greater influence over C storage than the intensity of grazing. More extensive grazing methods showed very little change in soil C storage or CO₂ and N₂O fluxes with modeled continuous grazing trending towards declines in soil C. Our study highlights the importance of considering both initial system conditions as well as management when analyzing the potential for long-term soil C storage.

Enzymic moderations of bacterial and fungal communities on short- and long-term warming impacts on soil organic carbon

Microbial communities play critical roles in soil carbon-warming feedback, but our understanding of their linkages to soil carbon (C) pools in response to short- and long-term warming is deficient. Here, by conducting a meta-analysis of 150 studies, we show that short-term (<5 years) warming mainly affects soil labile carbon (LC) pools by changing bacterial community structure, while long-term (≥5 years) warming promotes the decomposition of recalcitrant C (RC) pools by increasing fungal biomass and decreasing actinobacterial biomass. Specifically, under short-term warming, significant increases in actinobacterial biomass (+15.9%) and the G+/G- ratio (+8.0%) were accompanied by an increase in carbon-degrading enzyme activities and a decrease in LC (-5.9%). Under long-term warming, the fungal biomass (+20.4%) and related POX (phenol oxidase) activity (+34.9%) increased significantly, while actinobacterial biomass (-20.1%), RC (-18.8%) and SOC (-6.7%) decreased. Meanwhile, we observed that warming impacts on soil microbial communities can be predicted by ecosystem type, the magnitude of warming, pH and elevation. Latitude and warming duration contributed the most to explaining the responses of LC and RC, respectively, across studies. Given that RC accounts for a substantial fraction of global soil C pools, the decline in RC pools greatly contributes to soil C degradation. Our findings suggest that different microbial groups may mediate the temporal dynamics of the decomposition of different soil C components and highlight that incorporating the temporal responses of soil microorganisms will improve predictions of the long-term dynamics of soil C pools in a warmer world.

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Soil carbon supplementation is known to stimulate plant growth by improving soil fertility and plant nutrient uptake. However, the underlying process and chemical mechanism that could explain the interrelationship between soil carbon supplementation, soil micro-ecology, and the growth and quality of plant remain unclear. In this study, we investigated the influence and mechanism of soil carbon supplementation on the bacterial community, chemical cycling, mineral nutrition absorption, growth and properties of tobacco leaves. The soil carbon supplementation increased amino acid, carbohydrates, chemical energy metabolism, and bacterial richness in the soil. This led to increased content of sugar (23.75%), starch (13.25%), and chlorophyll (10.56%) in tobacco leaves. Linear discriminant analysis revealed 49 key phylotypes and significant increment of some of the Plant Growth-Promoting Rhizobacteria (PGPR) genera (Bacillus, Novosphingobium, Pseudomonas, Sphingomonas) in the rhizosphere, which can influence the tobacco growth. Partial Least Squares Path Modeling (PLS-PM) showed that soil carbon supplementation positively affected the sugar and starch contents in tobacco leaves by possibly altering the photosynthesis pathway towards increasing the aroma of the leaves, thus contributing to enhanced tobacco flavor. These findings are useful for understanding the influence of soil carbon supplementation on bacterial community for improving the yields and quality of tobacco in industrial plantation.

Predicting forested wetland soil carbon using quantitative color sensor measurements in the region of northern Virginia, USA

Forested wetland soils within the Piedmont and Coastal Plain physiographic provinces of Northern Virginia (NOVA) were investigated to determine the utility of a handheld colorimeter, the Nix Pro Color Sensor ("Nix"), for predicting carbon contents (TC) and stocks (TC stocks) from on-site color measurements. Both the color variables recorded with each Nix scan ("Nix color variables"; n = 15) and carbon contents significantly differed between sites, with redder soils (higher a and h) at Piedmont sites, and higher TC at sites with darker soils (lower values of L, or lightness; p < 0.05). Nix-carbon correlation analysis revealed strong relationships between L (lightness), X (a virtual spectral variable), R (additive red), and K_K (black) and log-transformed TC (Ln[TC]; |r| = 0.70; p < 0.01 for all). Simple linear regressions were conducted to identify how well these four final Nix variables could predict soil carbon. Using all color measurements, about 50% of Ln(TC) variability could be explained by L, X, R, or K_K (p < 0.01), yet with higher predictive power obtained for Coastal Plain soils (0.55 < R² < 0.65; p < 0.01). Regression model strength was maximized between Ln(TC) and the four final Nix variables using simple linear regressions when color measurements observed at a specific depth were first averaged (0.66 < R² < 0.70; p < 0.01). While further study is warranted to investigate Nix applicability within various soil settings, these results demonstrate potential for the Nix and its soil color measurements to assist with rapid field-based assessments of soil carbon in forested wetlands.

Long-term monitoring of Vermont's forest soils: early trends and efforts to address innate variability

Long-term monitoring of forest soils is necessary to understand the effects of continued environmental change, including climate change, atmospheric deposition of metals, and, in many regions, recovery from acidic precipitation. A monitoring program was initiated in 2002 at five protected forest sites, primarily Spodosol soils, in Vermont, northeastern USA. Every 5 years, ten soil pits were sampled from random subplots in a 50 × 50-m plot at each site. Samples were taken by genetic horizon and, to reduce variability and improve comparability, from four specific layers: the combined Oi/Oe layer, the combined Oa/A layer, the top 10 cm of the B horizon, and 60-70 cm below the soil surface (usually the C horizon). The samples were archived and a subset analyzed for carbon, nitrogen, and exchangeable cations. After four sampling campaigns, the average coefficients of variation (CVs) at each site had a broad range, 10.7% for carbon in the Oa/A horizon to 84.3% for exchangeable Ca²⁺ in the B horizon. An investigation of variability within the upper 10 cm of the B horizon across a 90-cm soil pit face showed similar CVs to the entire site, emphasizing the need for consistent and careful sampling. After 15 years, temporal trends were significant in the Oa/A and B horizons at two of the five sites, with one site showing an increase in carbon concentration in both layers along with increases in both exchangeable Ca²⁺ and Al³⁺ in the B horizon, perhaps linked to recovery from acidification. The monitoring program plans to continue at 5-year intervals for the next century.

Biomass, carbon stock and sequestration potential of Oxytenanthera abyssinica forests in Lower Beles River Basin, Northwestern Ethiopia

BACKGROUND

Given the large bamboo resource base with considerable potential to act as an important carbon sink, Ethiopia has included bamboo in the national Reducing Emissions from Deforestation and Forest Degradation and enhancing forest carbon stocks (REDD+) and Clean Development Mechanisms (CDM) programs. However, little is known about the carbon stock and sequestration potential of bamboo forests. As a result, this research was conducted to quantify the carbon sequestration and storage capacity of Oxytenanthera abyssinica forests in the Lower Beles River Basin, northwestern Ethiopia. To this end, a total of 54 circular plots, each measuring 100 m² with a radius of 5.64 m, were established to conduct the inventory in Assitsa and Eddida bamboo forests, the typical bamboo sites in Lower Beles River Basin. Biomass accumulation of bamboo was estimated using an allometric equation based on diameter at breast height (DBH) and age. Soil samples were taken from two different soil depths (0-15 and 15-30 cm) to determine soil organic carbon.

RESULTS

Results indicate that the mean biomass of the bamboo forests in the study area accounted for about 177.1 [Formula: see text] 3.1 Mg ha^-1. The mean biomass carbon and soil organic carbon stock of the bamboo forests were 83.2 [Formula: see text] 1.5 Mg C ha^-1 and 70 [Formula: see text] 1.7 Mg C ha^-1, respectively. Therefore, the mean carbon stock of the O. abyssinica bamboo forests was 152.5 [Formula: see text] 2.5 Mg C ha^-1 to 559.8 [Formula: see text] 9.0 ton CO₂ ha^-1.

CONCLUSION

This study highlights the importance of assessing bamboo's carbon stock and sequestration potential for enhancing its role in climate change mitigation and sustainable resource management. The O. abyssinica bamboo forests of the study area have significant carbon stock and sequestration potential. Therefore, sustainable management of these crucial vegetation resources will enhance their role in providing ecosystem services, including climate change mitigation.

Soil organic matter turnover rates increase to match increased inputs in grazed grasslands

Managed grasslands have the potential to store carbon (C) and partially mitigate climate change. However, it remains difficult to predict potential C storage under a given soil or management practice. To study C storage dynamics due to long-term (1952-2009) phosphorus (P) fertilizer and irrigation treatments in New Zealand grasslands, we measured radiocarbon (¹⁴C) in archived soil along with observed changes in C stocks to constrain a compartmental soil model. Productivity increases from P application and irrigation in these trials resulted in very similar C accumulation rates between 1959 and 2009. The ∆¹⁴C changes over the same time period were similar in plots that were both irrigated and fertilized, and only differed in a non-irrigated fertilized plot. Model results indicated that decomposition rates of fast cycling C (0.1 to 0.2 year^-1) increased to nearly offset increases in inputs. With increasing P fertilization, decomposition rates also increased in the slow pool (0.005 to 0.008 year^-1). Our findings show sustained, significant (i.e. greater than 4 per mille) increases in C stocks regardless of treatment or inputs. As the majority of fresh inputs remain in the soil for less than 10 years, these long term increases reflect dynamics of the slow pool. Additionally, frequent irrigation was associated with reduced stocks and increased decomposition of fresh plant material. Rates of C gain and decay highlight trade-offs between productivity, nutrient availability, and soil C sequestration as a climate change mitigation strategy.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10533-021-00838-z.

Influence of arboreal components on the physical-chemical characteristics of the soil under four silvopastoral systems in northeastern Peru

Silvopastoral systems (SPS) are presented as an alternative for the protection and recovery of soils; however, the relationship between the tree component and the physical-chemical characteristics of the soil is unknown. Thus, the objective of this study was to evaluate the physical-chemical characteristics of the soil under four silvopastoral systems (SPS), alder (Alnus acuminata), pine (Pinus patula), cypress (Cupressus macrocarpa), and pona (Ceroxylon quindiuense), and a treeless system (TS) in the Amazonas region. A completely randomized design (CRD) with five treatments and three replicates was used. The experimental units were sampled at two depths, 0–15 and 15–30 cm. The parameters evaluated were pH, electrical conductivity (dS/m), organic matter (%), phosphorus (ppm), potassium (ppm), cation exchange capacity (meq/100 g), porosity (%), mechanical resistance (kg/cm²), bulk density (gr/cm³), moisture (%) and total carbon (t/ha). The results were analyzed by analysis of variance (α = 0.05 %) and Tukey's test of means (p ≤ 0.05). The systems presented strong acidic pH values (4.11–5.61), which resulted in high organic matter contents in all systems (6.74–9.99 %). The highest phosphorus content was in the SPS with alder (12.64 ppm), and the highest potassium content was in the SPS with cypress (382.33 ppm). Porosity in all systems was higher than 60 %. The highest bulk density was between 15 and 30 cm, and the highest percentage of moisture was in the surface layer (0–15 cm). The mechanical strength was higher in the SPS with cypress (2.62 kg/cm²). For all the systems evaluated, the highest carbon stock was found in the first 15 cm. The SPS with pine had the best soil characteristics and carbon sequestration (149.05 t/ha).

New pedotransfer approaches to predict soil bulk density using WoSIS soil data and environmental covariates in Mediterranean agro-ecosystems

For the estimation of the soil organic carbon stocks, bulk density (BD) is a fundamental parameter but measured data are usually not available especially when dealing with legacy soil data. It is possible to estimate BD by applying pedotransfer function (PTF). We applied different estimation methods with the aim to define a suitable PTF for BD of arable land for the Mediterranean Basin, which has peculiar climate features that may influence the soil carbon sequestration. To improve the existing BD estimation methods, we used a set of public climatic and topographic data along with the soil texture and organic carbon data. The present work consisted of the following steps: i) development of three PTFs models separately for top (0-0.4 m) and subsoil (0.4-1.2 m), ii) a 10-fold cross-validation, iii) model transferability using an external dataset derived from published data. The development of the new PTFs was based on the training dataset consisting of World Soil Information Service (WoSIS) soil profile data, climatic data from WorldClim at 1 km spatial resolution and Shuttle Radar Topography Mission (SRTM) digital elevation model at 30 m spatial resolution. The three PTFs models were developed using: Multiple Linear Regression stepwise (MLR-S), Multiple Linear Regression backward stepwise (MLR-BS), and Artificial Neural Network (ANN). The predictions of the newly developed PTFs were compared with the BD calculated using the PTF proposed by Manrique and Jones (MJ) and the modelled BD derived from the global SoilGrids dataset. For the topsoil training dataset (N = 129), MLR-S, MLR-BS and ANN had a R² 0.35, 0.58 and 0.86, respectively. For the model transferability, the three PTFs applied to the external topsoil dataset (N = 59), achieved R² values of 0.06, 0.03 and 0.41. For the subsoil training dataset (N = 180), MLR-S, MLR-BS and ANN the R² values were 0.36, 0.46 and 0.83, respectively. When applied to the external subsoil dataset (N = 29), the R² values were 0.05, 0.06 and 0.41. The cross-validation for both top and subsoil dataset, resulted in an intermediate performance compared to calibration and validation with the external dataset. The new ANN PTF outperformed MLR-S, MLR-BS, MJ and SoilGrids approaches for estimating BD. Further improvements may be achieved by additionally considering the time of sampling, agricultural soil management and cultivation practices in predictive models.

Effects of moisture and physical disturbance on pore-scale oxygen content and anaerobic metabolisms in upland soils

Soils are the largest dynamic stock of carbon (C) on Earth, and microbial respiration of soil organic C accounts for over 25% of global carbon dioxide (CO₂) emissions. Zones of oxygen depletion in upland soils (anaerobic microsites) are increasingly recognized as an important control on soil microbial respiration rates, but the factors governing the volume and distribution of anaerobic microsites are relatively unknown. We measured the dissolved oxygen (DO) content of porewater from incubated soil cores of varying moisture contents (<80% and >80% water saturation) and degrees of disturbance (undisturbed, conventionally tilled, and physically disturbed). Porewater was extracted sequentially from pores constrained by three effective pore diameters, ≥3.0 μm, 3.0-1.0 μm, and 1.0-0.6 μm, from cores incubated for 7, 14, or 28 days, using a modified Tempe cell extraction system. We observed a parabolic pattern in mean dissolved oxygen (DO) concentrations across pore sizes, independent of soil moisture and degree of disturbance. Specifically, DO values within the largest and smallest pore domains were relatively depleted (155 ± 10 μM and 160 ± 11 μM, respectively), while DO values within medium pores were closer to saturation (214 ± 8 μM). The observed DO pattern provides insight into the balance of microbial oxygen demand versus oxygen supply across pore domains within upland soils. Additionally, we observed iron and manganese reduction in all soils except samples subjected to disturbance and incubated at <80% water saturation, suggesting that disturbance enhances aeration and diminishes anaerobic metabolisms within upland soils. Our findings highlight the influence of soil moisture and management on soil redox and CO₂ efflux rates.

Soil carbon and plant richness relationships differ among grassland types, disturbance history and plant functional groups

Understanding the relationship of soil carbon storage and species diversity in grasslands can provide insights into managing these ecosystems. We studied relationships among soil C and plant species richness within ~ 9700 ha of grasslands in Colorado, US. Using 141 grassland transects, we tested how soil C was related to plant species richness, grassland type, soil texture, and prairie dog presence. Soil C was significantly, positively related to plant species richness, while native perennial graminoid species richness exhibited an even stronger positive relationship. However, the relationship of soil C and plant richness was not found in all three grassland types studied, but instead was unique to the most common grassland type, mixed grass prairie, and absent from both xeric tallgrass and mesic tallgrass prairie. The presence of a single indicator species, Andropogon gerardii, showed a significant, positive relationship with soil carbon. Our best possible model explained 45% of the variance in soil C using species richness, grassland type, and their interaction. Surprisingly, soil C was negatively related to soil clay, suggesting that surface clays amplify evaporation and water runoff rather than protecting soil organic matter from decomposition. Soil C was negatively related to prairie dog presence, suggesting that prairie dogs do not enhance soil carbon sequestration; in fact, prairie dog occupied sites had significantly lower soil C, likely related to loss of topsoil from prairie dog colonies. Our results suggest that management for species richness provides the co-benefit of soil C storage, and high clay and prairie dog disturbance compromises both.

Estimating blue carbon sequestration under coastal management scenarios

Restoring and protecting "blue carbon" ecosystems - mangrove forests, tidal marshes, and seagrass meadows - are actions considered for increasing global carbon sequestration. To improve understanding of which management actions produce the greatest gains in sequestration, we used a spatially explicit model to compare carbon sequestration and its economic value over a broad spatial scale (2500 km of coastline in southeastern Australia) for four management scenarios: (1) Managed Retreat, (2) Managed Retreat Plus Levee Removal, (3) Erosion of High Risk Areas, (4) Erosion of Moderate to High Risk Areas. We found that carbon sequestration from avoiding erosion-related emissions (abatement) would far exceed sequestration from coastal restoration. If erosion were limited only to the areas with highest erosion risk, sequestration in the non-eroded area exceeded emissions by 4.2 million Mg CO₂ by 2100. However, losing blue carbon ecosystems in both moderate and high erosion risk areas would result in net emissions of 23.0 million Mg CO₂ by 2100. The removal of levees combined with managed retreat was the strategy that sequestered the most carbon. Across all time points, removal of levees increased sequestration by only an additional 1 to 3% compared to managed retreat alone. Compared to the baseline erosion scenario, the managed retreat scenario increased sequestration by 7.40 million Mg CO₂ by 2030, 8.69 million Mg CO₂ by 2050, and 16.6 million Mg CO₂ by 2100. Associated economic value followed the same patterns, with large potential value loss from erosion greater than potential gains from conserving or restoring ecosystems. This study quantifies the potential benefits of managed retreat and preventing erosion in existing blue carbon ecosystems to help meet climate change mitigation goals by reducing carbon emissions.

Plant succession and geochemical indices in immature peatlands in the Changbai Mountains, northeastern region of China: Implications for climate change and peatland development

Peatlands cover a small portion of the Earth's land surface but hold ~30% of soil carbon (C) globally. However, few studies have focused on the early stage of peatland development, which is a key stage in the initial C sink function of peatlands. An immature peatland is vulnerable to changes in environmental conditions, e.g., temperature and water conditions, as the peat accumulation process can be easily interrupted by such changes. It is important to understand how immature peatlands develop, what conditions are beneficial to this process, and the present status of these important peatlands. Plant macrofossil analysis and geochemical characteristics of peat were used to determine the plant succession and the degree of decomposition at two peatlands developing in the Changbai Mountain region of northeastern China. The results show that during the entire plant community succession, plants in the two studied peatlands are mainly characterized by sedges (Cyperaceae) and mosses (mainly Sphagnum). Plant macrofossil analysis reveals a wetter trend in the Yuan Lake (YL) peatland in the most upper part of peat layer, which provides favorable conditions for peat accumulation and peatland development. The C/N ratios of core Chi Lake (CL) show a steady peat decomposition and accumulation process in the CL peatland. Additionally, there was a clear impact of presence of Sphagnum on the variations in the C/N ratio. In the YL peatland, macro-charcoal pieces indicated that fire events during dry hydrological conditions had great effects on biogeochemical processes within the peatland, affecting peat decomposition and the succession of the local plant community. An increase in major and trace elements suggests only weak disturbance due to the considerable distance to human settlements. This study determines the characteristics of pristine mountainous peatlands and highlights the importance of understanding the regular plant community in the early stage of peatland formation, as well as its potential effects on C sinks.

Effects of a nutrient enrichment pulse on blue carbon ecosystems

Coastal ecosystems are under increasing pressure from land-derived eutrophication in most developed coastlines worldwide. Here, we tested for 277 days the effects of a nutrient pulse on blue carbon retention and cycling within an Australian temperate coastal system. After 56 days of exposure, saltmarsh and mangrove plots subject to a high-nutrient treatment (~20 g N m^-2 yr^-1 and ~2 g P m^-2 yr^-1) had ~23% lower superficial soil carbon stocks. Mangrove plots also experienced a ~33% reduction in the microbe Amplicon Sequence Variant richness and a shift in community structure linked to elevated ammonium concentrations. Live plant cover, tea litter decomposition, and soil carbon fluxes (CO₂ and CH₄) were not significantly affected by the pulse. Before the end of the experiment, soil carbon- and nitrogen-cycling had returned to control levels, highlighting the significant but short-lived impact that a nutrient pulse can have on the carbon sink capacity of coastal wetlands.

Soil microbial CO2 fixation plays a significant role in terrestrial carbon sink in a dryland ecosystem: A four-year small-scale field-plot observation on the Tibetan Plateau

Assessment of the global terrestrial carbon (C) sink remains uncertain, and the uncertainty is largely derived from dryland ecosystems. Here we investigated the uncertainty and dynamics of gross primary productivity (GPP) by distinguishing the contributions of soil microbial primary producers and plants to CO₂ fixation during four sequential growing seasons in a fragile dry grassland on the Tibetan Plateau. The results demonstrated that soil microbial GPP consistently accounted for a high proportion of plant GPP (18.2%), and both exhibited similar seasonal patterns during the four-year observation. Soil microbial GPP demonstrated a much greater interannual variation (76.1%) than plant GPP (15.1%), indicating that the interannual GPP uncertainty could be largely from microbial primary producers. Regression analysis indicated that plant GPP had higher sensitivity (demonstrated by slope) than soil microbial GPP to both soil water content and temperature. The GPP ratio of soil microbes to plants also demonstrated a clear seasonal change, and peaked in July in the four-year observation, with a minimum interannual variation (6.8%). The GPP ratio enhanced with increasing soil water content (P < 0.001), but did not correlate with soil temperature. Our findings suggest the great potential of soil microbial GPP, and challenge the plant-oriented models of terrestrial C estimation, which account for plant GPP but ignore soil microbial GPP. Thus, a more robust framework needs to incorporate both soil microbial and plant GPPs for accurately assessing C balance.

Canopy mitigates the effects of nitrogen deposition on soil carbon-related processes in a subtropical forest

The rapid increases in atmospheric nitrogen (N) deposition have greatly affected the carbon (C) cycles of terrestrial ecosystems. Most studies concerning on the effects of N deposition have simulated N deposition by directly applying N to the understory and have therefore not accounted for the possibility of N absorption, retention, and transformation by the canopy. In this study, we compared the effects of understory addition of N (UN), canopy addition of N (CN) at 25 and 50 kg N ha^-1 yr^-1, and ambient addition of N (CK) on soil carbon-related processes in a subtropical forest. After seven years of addition, the contribution of new C from litter (F_new) was more than 2× greater with UN treatments than with CN treatments. UN treatments significantly increased the activity of β-1,4-glucosidase (BG) but reduced the activities of β-1,4-N-acetylglucosaminidase (NAG), polyphenol oxidase (PPO), and peroxidase (PER). CN treatments, in contrast, did not alter the activities of extracellular enzyme. Compared to CN, UN treatments significantly enhanced soil organic carbon (SOC) and mean weight diameter (MWD, represents soil aggregate stability). Differences in the responses of SOC and MWD to CN and UN treatments were positively correlated with F_new but negatively correlated with the activities of PPO and PER. The results imply that forest canopy mitigates the effects of atmospheric N inputs on SOC, and that conventional understory N addition might overestimate the positive effects of N deposition on forest soil C-related processes. We suggest that CN rather than UN should be used to simulate the effects of atmospheric N deposition on soil C dynamics in subtropical forests.

Soil carbon and nitrogen data during eight years of cover crop and compost treatments in organic vegetable production

Data presented are on carbon (C) and nitrogen (N) inputs, and changes in soil C and N in eight systems during the first eight years of a tillage-intensive organic vegetable systems study that was focused on romaine lettuce and broccoli production in Salinas Valley on the central coast region of California. The eight systems differed in organic matter inputs from cover crops and urban yard-waste compost. The cover crops included cereal rye, a legume-rye mixture, and a mustard mixture planted at two seeding rates (standard rate 1x versus high rate 3x). There were three legume-rye 3x systems that differed in compost inputs (0 versus 7.6 Mg ha⁻¹ vegetable crop⁻¹) and cover cropping frequency (every winter versus every fourth winter). The data include: (1) changes in soil total organic C and total N concentrations and stocks and nitrate N (NO₃–N) concentrations over 8 years, (2) cumulative above ground and estimated below ground C and N inputs, cover crop and crop N uptake, and harvested crop N export over 8 years, (3) soil permanganate oxidizable carbon (POX-C) concentrations and stocks at time 0, 6 and 8 years, and (4) cumulative, estimated yields of lettuce and broccoli (using total biomass and harvest index values) over the 8 years. The C inputs from the vegetables and cover crops included estimates of below ground inputs based on shoot biomass and literature values for shoot:root. The data in this article support and augment information presented in the research article “Winter cover crops increase readily decomposable soil carbon, but compost drives total soil carbon during eight years of intensive, organic vegetable production in California”.