Litter quality versus soil microbial community controls over decomposition: a quantitative analysis

Warming alters cascading effects of a dominant arthropod predator on fungal community composition in the Arctic

Rapid climate change in the Arctic is altering microbial structure and function, with important consequences for the global ecosystem. Emerging evidence suggests organisms in higher trophic levels may also influence microbial communities, but whether warming alters these effects is unclear. Wolf spiders are dominant Arctic predators whose densities are expected to increase with warming. These predators have temperature-dependent effects on decomposition via their consumption of fungal-feeding detritivores, suggesting they may indirectly affect the microbial structure as well. To address this, we used a fully factorial mesocosm experiment to test the effects of wolf spider density and warming on litter microbial structure in Arctic tundra. We deployed replicate litter bags at the surface and belowground in the organic soil profile and analyzed the litter for bacterial and fungal community structure, mass loss, and nutrient characteristics after 2 and 14 months. We found there were significant interactive effects of wolf spider density and warming on fungal but not bacterial communities. Specifically, higher wolf spider densities caused greater fungal diversity under ambient temperature but lower fungal diversity under warming at the soil surface. We also observed interactive treatment effects on fungal composition belowground. Wolf spider density influenced surface bacterial composition, but the effects did not change with warming. These findings suggest a widespread predator can have indirect, cascading effects on litter microbes and that effects on fungi specifically shift under future expected levels of warming. Overall, our study highlights that trophic interactions may play important, albeit overlooked, roles in driving microbial responses to warming in Arctic terrestrial ecosystems.

IMPORTANCE

The Arctic contains nearly half of the global pool of soil organic carbon and is one of the fastest warming regions on the planet. Accelerated decomposition of soil organic carbon due to warming could cause positive feedbacks to climate change through increased greenhouse gas emissions; thus, changes in ecological dynamics in this region are of global relevance. Microbial structure is an important driver of decomposition and is affected by both abiotic and biotic conditions. Yet how activities of soil-dwelling organisms in higher trophic levels influence microbial structure and function is unclear. In this study, we demonstrate that predicted changes in abundances of a dominant predator and warming interactively affect the structure of litter-dwelling fungal communities in the Arctic. These findings suggest predators may have widespread, indirect cascading effects on microbial communities, which could influence ecosystem responses to future climate change.

Residue quality drives SOC sequestration by altering microbial taxonomic composition and ecophysiological function in desert ecosystem

Plant residues are important sources of soil organic carbon in terrestrial ecosystems. The degradation of plant residue by microbes can influence the soil carbon cycle and sequestration. However, little is known about the microbial composition and function, as well as the accumulation of soil organic carbon (SOC) in response to the inputs of different quality plant residues in the desert environment. The present study evaluated the effects of plant residue addition from Pinus sylvestris var. mongolica (Pi), Artemisia desertorum (Ar) and Amorpha fruticosa (Am) on desert soil microbial community composition and function in a field experiment in the Mu Us Desert. The results showed that the addition of the three plant residues with different C/N ratios induced significant variation in soil microbial communities. The Am treatment (low C/N ratio) improved microbial diversity compared with the Ar and Pi treatments (medium and high C/N ratios). The variations in the taxonomic and functional compositions of the dominant phyla Actinobacteria and Proteobacteria were higher than those of the other phyla among the different treatments. Moreover, the network links between Proteobacteria and other phyla and the CAZyme genes abundances from Proteobacteria increased with increasing residue C/N, whereas those decreased for Actinobacteria. The SOC content of the Am, Ar and Pi treatments increased by 45.73%, 66.54% and 107.99%, respectively, as compared to the original soil. The net SOC accumulation was positively correlated with Proteobacteria abundance and negatively correlated with Actinobacteria abundance. These findings showed that changing the initial quality of plant residue from low C/N to high C/N can result in shifts in taxonomic and functional composition from Actinobacteria to Proteobacteria, which favors SOC accumulation. This study elucidates the ecophysiological roles of Actinobacteria and Proteobacteria in the desert carbon cycle, expands our understanding of the potential microbial-mediated mechanisms by which plant residue inputs affect SOC sequestration in desert soils, and provides valuable guidance for species selection in desert vegetation reconstruction.

'Fertile island' effects on the soil microbial community beneath the canopy of Tetraena mongolica, an endangered and dominant shrub in the West Ordos Desert, North China

BACKGROUND

The fertile islands formed by shrubs are major drivers of the structure and function of desert ecosystems, affecting seedling establishment, plant-plant interactions, the diversity and productivity of plant communities, and microbial activity/diversity. Although an increasing number of studies have shown the critical importance of soil microbes in fertile island formation, how soil microbial community structure and function are affected by the different fertile island effect intensities is still unknown. As an endangered and dominant shrub species in the West Ordos Desert, Tetraena mongolica was selected for further exploration of its fertile island effect on the soil microbial community in the present study to test the following two hypotheses: (1) T. mongolica shrubs with different canopy sizes exert fertile island effects of different strengths; (2) the soil microbial community structure and function beneath the T. mongolica canopy are affected by the fertile island, and the strength of these effects varies depending on the shrub canopy size.

RESULTS

The contents of soil total nitrogen (TN) and available phosphorus (AVP) were significantly greater beneath T. mongolica shrub canopy than outside the shrub canopy. With increasing shrub canopy size, the enrichment of soil TN and AVP increased, indicating a stronger fertile island effect. The structure and function of soil microbial communities, including fungal, archaeal and bacterial communities, are affected by the fertile island effect. An increase in canopy size increased the relative abundance of Ascomycota (Fungi) and Thaumarchaeota (Archaea). For the soil microbial functional groups, the relative abundance of endophytes in the fungal functional groups; steroid hormone biosynthesis, sphingolipid metabolism, and steroid biosynthesis genes in the bacterial functional groups; and nonhomologous end-joining and bisphenol degradation functional genes in the archaeal functional groups increased significantly with increasing T. mongolica canopy size.

CONCLUSIONS

These results revealed that T. mongolica had a fertile island effect, which affected the soil microbial community structure and functions, and that the fertile island effect might increase with increasing shrub canopy size. The fertile island effect may strengthen the interaction between T. mongolica shrubs and microbes, which may be beneficial to the growth and maintenance of T. mongolica.

Crop residue heterogeneity: Decomposition by potential indigenous ligno-cellulolytic microbes and enzymatic profiling

The continuous depletion of fossil resources, energy-crisis and environmental pollution has gained popularity for careful selection of suitable microbial consortium to efficiently decompose crop residue and facilitate nutrient cycling. While crop residue is commonly incorporated into soil, the impact of the heterogeneity of residue on decomposition and biological mechanisms involved in extracellular carbon (C) cycle related enzyme activities remain not fully understood. To address this problem, an incubation study was conducted on chemical heterogeneity of straw and root residue with indigenous ligno-cellulolytic microbial consortium on extracellular enzymes as their activity is crucial for making in-situ residue management decisions under field condition. The activity of extracellular enzymes in different substrates showed differential variation with the type of enzyme and ranged from 16.9 to 77.6 µg mL-1, 135.7 to 410.8 µg mL-1, 66.9 to 177.1 µg mL-1 and 42.1 to 160.9 µg mL-1 for cellulase, xylanase, laccase and lignin peroxidase, respectively. Extracellular enzyme activities were sensitive to heterogeneity of biochemical constituent's present in straw and root residues and enhanced the decomposition processes with indigenous ligno-cellulolytic microbial consortium (Bacillus altitudinis, Streptomyces flavomacrosporus and Aspergillus terreus). Correlation matrix elucidated A. terreus and B. altitudinis as potential indigenous ligno-cellulolytic microbial inoculant influencing soil enzymatic activity (p < 0.001). This research work demonstrates a substantial impact of chemically diverse crop residues on the decomposition of both straw and root. It also highlights the pivotal role played by key indigenous decomposers and interactions between different microorganisms in governing the decomposition of straw and root primarily through release of extracellular enzyme. Consequently, it is novel bio-emerging strategy suggested that incorporation of the crop residues under field conditions should be carried out in conjunction with the potential indigenous ligno-cellulolytic microbial consortium for efficient decomposition in the short period of time under sustainable agriculture system.

Bacterial community structure and assembly dynamics hinge on plant litter quality

Litter decomposition is a fundamental ecosystem process controlling the biogeochemical cycling of energy and nutrients. Using a 360-day lab incubation experiment to control for environmental factors, we tested how litter quality (low C/N deciduous vs. high C/N coniferous litter) governed the assembly and taxonomic composition of bacterial communities and rates of litter decomposition. Overall, litter mass loss was significantly faster in soils amended with deciduous (DL) rather than coniferous (CL) litter. Communities degrading DL were also more taxonomically diverse and exhibited stochastic assembly throughout the experiment. By contrast, alpha-diversity rapidly declined in communities exposed to CL. Strong environmental selection and competitive biological interactions induced by molecularly complex, nutrient poor CL were reflected in a transition from stochastic to deterministic assembly after 180 days. Constraining how the diversity and assembly of microbial populations modulates core ecosystem processes, such as litter decomposition, will become increasingly important under novel climate conditions, and as policymakers and land managers emphasize soil carbon sequestration as a key natural climate solution.

Long-term mitigation of drought changes the functional potential and life-strategies of the forest soil microbiome involved in organic matter decomposition

Climate change can alter the flow of nutrients and energy through terrestrial ecosystems. Using an inverse climate change field experiment in the central European Alps, we explored how long-term irrigation of a naturally drought-stressed pine forest altered the metabolic potential of the soil microbiome and its ability to decompose lignocellulolytic compounds as a critical ecosystem function. Drought mitigation by a decade of irrigation stimulated profound changes in the functional capacity encoded in the soil microbiome, revealing alterations in carbon and nitrogen metabolism as well as regulatory processes protecting microorganisms from starvation and desiccation. Despite the structural and functional shifts from oligotrophic to copiotrophic microbial lifestyles under irrigation and the observation that different microbial taxa were involved in the degradation of cellulose and lignin as determined by a time-series stable-isotope probing incubation experiment with 13C-labeled substrates, degradation rates of these compounds were not affected by different water availabilities. These findings provide new insights into the impact of precipitation changes on the soil microbiome and associated ecosystem functioning in a drought-prone pine forest and will help to improve our understanding of alterations in biogeochemical cycling under a changing climate.

The Invasive Tradescantia zebrina Affects Litter Decomposition, but It Does Not Change the Lignocellulolytic Fungal Community in the Atlantic Forest, Brazil

Invasive plants affect ecosystems across various scales. In particular, they affect the quality and quantity of litter, which influences the composition of decomposing (lignocellulolytic) fungal communities. However, the relationship among the quality of invasive litter, lignocellulolytic cultivated fungal community composition, and litter decomposition rates under invasive conditions is still unknown. We evaluated whether the invasive herbaceous Tradescantia zebrina affects the litter decomposition in the Atlantic Forest and the lignocellulolytic cultivated fungal community composition. We placed litter bags with litter from the invader and native plants in invaded and non-invaded areas, as well as under controlled conditions. We evaluated the lignocellulolytic fungal communities by culture method and molecular identification. Litter from T. zebrina decomposed faster than litter from native species. However, the invasion of T. zebrina did not alter decomposition rates of either litter type. Although the lignocellulolytic fungal community composition changed over decomposition time, neither the invasion of T. zebrina nor litter type influenced lignocellulolytic fungal communities. We believe that the high plant richness in the Atlantic Forest enables a highly diversified and stable decomposing biota formed in conditions of high plant diversity. This diversified fungal community is capable of interacting with different litter types under different environmental conditions.

Contrasting geochemical and fungal controls on decomposition of lignin and soil carbon at continental scale

Lignin is an abundant and complex plant polymer that may limit litter decomposition, yet lignin is sometimes a minor constituent of soil organic carbon (SOC). Accounting for diversity in soil characteristics might reconcile this apparent contradiction. Tracking decomposition of a lignin/litter mixture and SOC across different North American mineral soils using lab and field incubations, here we show that cumulative lignin decomposition varies 18-fold among soils and is strongly correlated with bulk litter decomposition, but not SOC decomposition. Climate legacy predicts decomposition in the lab, and impacts of nitrogen availability are minor compared with geochemical and microbial properties. Lignin decomposition increases with some metals and fungal taxa, whereas SOC decomposition decreases with metals and is weakly related with fungi. Decoupling of lignin and SOC decomposition and their contrasting biogeochemical drivers indicate that lignin is not necessarily a bottleneck for SOC decomposition and can explain variable contributions of lignin to SOC among ecosystems.

Decomposition Characteristics of Lignocellulosic Biomass in Subtropical Rhododendron Litters under Artificial Regulation

The nutrient turnover of subtropical rhododendron forests is slow, natural regeneration is difficult, and the decomposition of litter is slow. Lignin, cellulose, and hemicellulose are the key factors affecting the decomposition rate of litters. In this study, the litters of three forest stands, namely evergreen broadleaf Rhododendron delavayi, evergreen broadleaf Rhododendron agastum, and deciduous broadleaf mixed forest, were taken as the research objects to explore the dynamic changes and effects of lignin, cellulose, and hemicellulose contents in litters of different stands under indoor artificial control measures. Exogenous nitrogen, phosphorus, alkaline substances, and microbial agents were added to decompose litters in the laboratory for 140 days. Our results showed that (1) the contents of lignin and cellulose in the litters of the three stands decreased significantly in the early stage of decomposition and the content of hemicellulose was stable, and (2) low concentrations of nitrogen and phosphorus can accelerate the degradation of lignin, cellulose, and hemicellulose in litters of the three stands and thus promote the decomposition of litters. This study provides basic data for the nutrient return of artificial intervention in subtropical rhododendron forests in China.

Local conditions matter: Minimal and variable effects of soil disturbance on microbial communities and functions in European vineyards

Soil tillage or herbicide applications are commonly used in agriculture for weed control. These measures may also represent a disturbance for soil microbial communities and their functions. However, the generality of response patterns of microbial communities and functions to disturbance have rarely been studied at large geographical scales. We investigated how a soil disturbance gradient (low, intermediate, high), realized by either tillage or herbicide application, affects diversity and composition of soil bacterial and fungal communities as well as soil functions in vineyards across five European countries. Microbial alpha-diversity metrics responded to soil disturbance sporadically, but inconsistently across countries. Increasing soil disturbance changed soil microbial community composition at the European level. However, the effects of soil disturbance on the variation of microbial communities were smaller compared to the effects of location and soil covariates. Microbial respiration was consistently impaired by soil disturbance, while effects on decomposition of organic substrates were inconsistent and showed positive and negative responses depending on the respective country. Therefore, we conclude that it is difficult to extrapolate results from one locality to others because microbial communities and environmental conditions vary strongly over larger geographical scales.

Solar radiation explains litter degradation along alpine elevation gradients better than other climatic or edaphic parameters

Organic matter (OM) decomposition has been shown to vary across ecosystems, suggesting that variation in local ecological conditions influences this process. A better understanding of the ecological factors driving OM decomposition rates will allow to better predict the effect of ecosystem changes on the carbon cycle. While temperature and humidity have been put forward as the main drivers of OM decomposition, the concomitant role of other ecosystem properties, such as soil physicochemical properties, and local microbial communities, remains to be investigated within large-scale ecological gradients. To address this gap, we measured the decomposition of a standardized OM source - green tea and rooibos tea - across 24 sites spread within a full factorial design including elevation and exposition, and across two distinct bioclimatic regions in the Swiss Alps. By analyzing OM decomposition via 19 climatic, edaphic or soil microbial activity-related variables, which strongly varied across sites, we identified solar radiation as the primary source of variation of both green and rooibos teabags decomposition rate. This study thus highlights that while most variables, such as temperature or humidity, as well as soil microbial activity, do impact decomposition process, in combination with the measured pedo-climatic niche, solar radiation, very likely by means of indirect effects, best captures variation in OM degradation. For instance, high solar radiation might favor photodegradation, in turn speeding up the decomposition activity of the local microbial communities. Future work should thus disentangle the synergistic effects of the unique local microbial community and solar radiation on OM decomposition across different habitats.

Responses of soil respiration and microbial community structure to fertilizer and irrigation regimes over 2 years in temperate vineyards in North China

Fertilizer and irrigation regimes can profoundly affect soil carbon (C) emissions, which influence soil organic carbon (SOC) storage. However, information regarding the effects of fertilizer and irrigation management on the components of soil respiration (Rs) and the underlying microbial community characteristics in vineyard ecosystems remains limited. Therefore, a 2-year field experiment was conducted in a wine-grape vineyard (WGV) and a table-grape vineyard (TGV). Each vineyard included two fertilizer and irrigation regimes: farmers' practice (FP) and recommended practice (RP). The trenching method was employed to separate Rs into heterotrophic respiration (Rh) and autotrophic respiration (Ra). Additionally, the SOC storage and soil microbial community structure at 0-20 cm soil depth were determined after the 2-year experiment. The results showed that the fertilizer and irrigation regimes caused no effect on Ra. Compared with the FP treatment in WGV and TGV, the RP treatment significantly (P < 0.05) decreased the average daily Rh by 15.13 % and 17.11 %, which contributed to the annual Rs values at the whole-vineyard scale decreased by 8.93 % and 11.78 %, respectively. Besides, compared with the initial value, the SOC storage under RP treatment were effectively increased by 6.39 % and 6.33 % in WGV and TGV, respectively. Low annual total Rh was partially ascribed to the significant (P < 0.05) decline in Proteobacteria and Bacteroidetes relative abundance, thus reducing the decomposition rate of SOC. Compared with WGV, the fertilizer and water input was higher in the TGV, which resulted in the annual total Rs and Rh values at the whole-vineyard scale was increased by 11.53 % and 15.74 %, respectively, while the annual total Ra was decreased by 18.83 % due to the lower grapevine density and more frequent summer pruning. Overall, RP treatment was found to be a suitable strategy for reducing soil C emissions and benefiting SOC storage in vineyards around North China.

Drought changes litter quantity and quality, and soil microbial activities to affect soil nutrients in moso bamboo forest

Drought would significantly influence the forest soils through changing the litterfall production and decomposition process. However, comprehensive in situ studies on drought effects in subtropical forests, especially in bamboo forests, have rarely been conducted. Here, we conducted a throughfall exclusion experiment with a rainfall reduction of ~80% in moso bamboo (Phyllostachys edulis) forests to investigate effects of drought on litter quantity, quality, soil microbial and enzyme activities, and soil nutrients across two years in subtropical China. We observed that throughfall exclusion (TE) treatment significantly decreased soil moisture by 63% compared to ambient control treatment (CK). Drought significantly decreased the annual litterfall in the second treatment year, and the leaf litter decomposition rate (-30% relative to CK) over 2 years of decomposition. TE treatment significantly decreased net release rate of litter carbon (C) and the amount of litter nitrogen (N) immobilization during a 360-day decomposition period, leading an increased litter C: N ratio in TE compared to CK. There was a distinct difference in soil microbial community composition between TE and CK treatments, showing higher bacteria biomass in TE but no difference in fungal biomass between TE and CK. Structural equation modelling revealed that drought decreased the contribution of litter quantity to soil nutrients but increased that of litter quality and soil microbial community to soil nutrients. Our results suggest that increasing drought events in subtropical China will directly reduce litterfall quantity and quality on the one hand, and alter the soil enzyme activities and microbial composition on the other hand, all of which will consequently decrease litter decomposition rate, soil nutrient availability, growth rate and productivity, leading to changes in the functioning and services of subtropical bamboo forests.

A quantitative analysis of microbial community structure-function relationships in plant litter decay

Soil microbes play a central role in ecosystem element cycling. Yet a central question in microbial ecology remains unanswered: to what extent does the taxonomic composition of soil microbial communities mediate biogeochemical process rates? In this quantitative review, we explore the mechanisms that lead to variation in the strength of microbial community structure-function relationships over space and time. To evaluate these mechanisms, we conduct a meta-analysis of studies that have monitored the decomposition of sterilized plant litter inoculated with different microbial assemblages. We find that the influence of microbial community composition on litter decay is pervasive and strong, rivalling in magnitude the influence of litter chemistry on decomposition. However, no single environmental or experimental attribute was correlated with variation in the inoculum effect. These results emphasize the need to better understand ecological dynamics within microbial communities, particularly emergent features such as cross-feeding networks, to improve predictions of soil biogeochemical function.

Rock structures improve seedling establishment, litter catchment, fungal richness, and soil moisture in the first year after installation

Grasslands are essential natural and agricultural ecosystems that encompass over one-third of global lands. However, land conversion and poor management have caused losses of these systems which contributed to a 10% reduction of net primary production, a 4% increase in carbon emissions, and a potential loss of US $42 billion a year. It is, therefore, important to restore, enhance and conserve these grasslands to sustain natural plant communities and the livelihoods of those that rely on them. We installed low cost rock structures (media lunas) to assess their ability to restore grasslands by slowing water flow, reducing erosion and improving plant establishment. Our treatments included sites with small and large rock structures that were seeded with a native seed mix as well as sites with no seed or rock and sites with only seed addition. We collected summer percent cover for plants, litter, and rock and spring seedling count data. We also collected soil for nutrient, moisture, and microbial analysis. Within the first year, we found no change in plant cover between rock structures of two rock sizes. We did find, however, an increase in soil moisture, litter, fungal richness, and spring seedling germination within the rock structures, despite a historic drought. This work demonstrates that rock structures can positively impact plants and soils of grasslands even within the first year. Our results suggest that managers should seriously consider employing these low-cost structures to increase short-term plant establishment and possibly, soil health, in grasslands.

Dynamics of Dissolved Carbon in Subalpine Forest Streams

Dissolved carbon (DC) in forest streams plays a crucial role in maintaining the structure and productivity of adjoining aquatic ecosystems as well as informing biogeochemical links between mountain forests and adjoining rivers. Nevertheless, the functions of forest stream DC dynamics are rarely incorporated into river management. To better understand the biogeochemical links between subalpine forests and adjoining streams, the seasonal dynamics of DC in 15 representative forest streams were investigated in a geographically fragile subalpine-gorge catchment in the upper reaches of the Yangtze River. Depending on stream characteristics and critical periods, the DC stocks in the streams ranged from 0.22 to 2.35 mg m−2 for total DC, from 0.10 to 1.66 mg m−2 for dissolved inorganic carbon (DIC), and from 0.12 to 1.27 mg m−2 for dissolved organic carbon (DOC). Moreover, the annual stocks of DC, DIC, and DOC were 1.01, 0.56, and 0.45 mg m−2, respectively. Correspondingly, the averaged export rates for DC, DIC, and DOC from the forest streams ranged from 0.27 to 1.98 mg s−1, from 0.24 to 1.48 mg s−1, and from 0.18 to 0.90 mg s−1, respectively, in the subalpine forest catchment. The annual export rates of total DC, DIC, and DOC were 1.06, 0.75, and 0.31 mg C s−1, respectively. In particular, the highest rates of export were 4.67, 3.53, and 1.34 mg s−1 for DC, DIC, and DOC, respectively, in the snowmelt period. The average ratios of DOC to DIC stock in the export water ranged from 0.23–2.41 for the 15 streams, and the average value was 0.85 during this one-year investigation. In addition, the maximum and minimum values of the DC stocks, their exports, and the DIC:DOC ratio were consistently observed during the snowmelt season and the late growing period. In summary, precipitation, temperature, water discharge rate, and sediment depth regulated the stocks and export rates of DC and its components. In general, forest streams are important links between the carbon biogeochemical cycle of subalpine forests and adjoining streams.

Characteristics of prokaryotic and fungal communities emerged in eco-engineered waste rock - Eucalyptus open woodlands at Ranger uranium mine

Diverse prokaryotic and fungal communities in soil and litters are the structural basis for driving tree litter decomposition and inherent nutrient cycling in infertile Eucalyptus open woodlands. The present investigation characterized the composition and co-occurrence network of prokaryotic and fungal communities in litter and surface soil layers in 9-year old revegetated trial landforms at Ranger uranium mine, Northern Territory, Australia. The revegetated landforms consisted of soil-subsystems engineered from waste rocks and plant-subsystems of young, novel and native Eucalyptus open woodlands. The analysis of litters and surface soil layer revealed highly diverse microbial communities in the young Eucalyptus open woodland systems, which were composed of an average 1155 prokaryotic and 236 fungal OTUs. In the microbial communities, abundant bacterial communities were affiliated to Actinobacteria (30.2%), Proteobacteria (25.3%) and Chloroflexi (16.9%); and fungal communities were highly dominated by Ascomycota (63.4%) and Basidiomycota (23.6%). These OTUs were highly connected, forming microbial modules with >50% of predicted genes associated with metabolism of organics in the open woodland. Soil microbial communities present in the wet season contained a relatively high abundance of ammonium oxidizing archaea, plant associated bacteria, and fungal groups adapted to higher N availability, particularly those from the laterite + waste rock site. The elevated microbial activities in the litters and surface soil of lateritic soil + waste rock landform were attributed to the improved water and nutrient availability by increased fine fraction of laterites. Our study provides evidence that the features of prokaryotic and fungal communities in this eco-engineered and young waste rock - open Eucalyptus woodland systems are consistent with characteristics of microbial communities of native Eucalyptus woodlands to drive the decomposition of low N tree litters.

Climate-Driven Legacies in Simulated Microbial Communities Alter Litter Decomposition Rates

The mechanisms underlying diversity-functioning relationships have been a consistent area of inquiry in biogeochemistry since the 1950s. Though these mechanisms remain unresolved in soil microbiomes, many approaches at varying scales have pointed to the same notion—composition matters. Confronting the methodological challenge arising from the complexity of microbiomes, this study used the model DEMENTpy, a trait-based modeling framework, to explore trait-based drivers of microbiome-dependent litter decomposition. We parameterized DEMENTpy for five sites along a climate gradient in Southern California, United States, and conducted reciprocal transplant simulations analogous to a prior empirical study. The simulations demonstrated climate-dependent legacy effects of microbial communities on plant litter decomposition across the gradient. This result is consistent with the previous empirical study across the same gradient. An analysis of community-level traits further suggests that a 3-way tradeoff among resource acquisition, stress tolerance, and yield strategies influences community assembly. Simulated litter decomposition was predictable with two community traits (indicative of two of the three strategies) plus local environment, regardless of the system state (transient vs. equilibrium). Although more empirical confirmation is still needed, community traits plus local environmental factors (e.g., environment and litter chemistry) may robustly predict litter decomposition across spatial-temporal scales. In conclusion, this study offers a potential trait-based explanation for climate-dependent community effects on litter decomposition with implications for improved understanding of whole-ecosystem functioning across scales.

P is for persistence: Soil phosphorus remains elevated for more than a decade after old field restoration

Understanding constraints to ecological restoration on former agricultural land has become increasingly important due to agricultural land degradation in the developed world, and growing evidence for enduring agricultural legacies that limit native species recovery. In particular, the removal of native plant biomass and subsequent disturbance of soil properties through farming activities can alter soil ecosystem processes. Planting of native plant species is a common approach to restoring native vegetation on agricultural land and is assumed to benefit soil ecosystem processes, but the degree to which altered soil chemical processes recover is poorly documented. We investigated recovery of soil chemical properties after restoration in semiarid Western Australia, hypothesizing that elevated nutrient concentrations would gradually decline post planting, but available phosphorus (P) concentrations would remain higher than reference conditions. We used a space-for-time substitution approach, comparing 10 planted old field plots with matched fallow cropland and reference woodlands. Sampling on planted old fields and reference woodland plots was stratified into open patches and under tree canopy to account for consistent differences between these areas. The most prominent legacy of cropping was significantly and substantially higher concentrations of soil available P in fallow croplands and restored old fields compared with reference woodlands. Soil mineral nitrogen (N) concentrations were elevated in fallow croplands compared to open patches in reference woodlands (ammonium and nitrate) and under the tree canopy (ammonium). However, in restored old fields, mineral N concentrations were similar to woodland sites, providing evidence for amelioration over time. No significant differences in nutrient concentrations under tree canopies compared with open patches had developed in the planted old fields, despite a distinction between open patches and he under ttree canopy in reference woodlands for total N. We conclude that soil P legacies in old fields may inhibit the recolonization of native species that are sensitive to, or uncompetitive at, elevated P concentrations. To achieve full recovery, further research is required to test restoration practices aimed at reducing soil P concentrations to facilitate native plant establishment and persistence.

Mowing Facilitated Shoot and Root Litter Decomposition Compared with Grazing

Shoot and root litter are two major sources of soil organic carbon, and their decomposition is a crucial nutrient cycling process in the ecosystem. Altitude and land use could affect litter decomposition by changing the environment in mountain grassland ecosystems. However, few studies have investigated the effects of land use on litter decomposition in different altitudes. We examined how land-use type (mowing vs. grazing) affected shoot and root litter decomposition of a dominant grass (Bromus inermis) in mountain grasslands with two different altitudes in northwest China. Litterbags with 6 g of shoot or root were fixed in the plots to decompose for one year. The mass loss rate of the litter, and the environmental attributes related to decomposition, were measured. Litter decomposed faster in mowing than grazing plots, resulting from the higher plant cover and soil moisture but lower bulk density, which might promote soil microbial activities. Increased altitude promoted litter decomposition, and was positively correlated with soil moisture, soil organic carbon (SOC), and β-xylosidase activity. Our results highlight the diverse influences of land-use type on litter decomposition in different altitudes. The positive effects of mowing on shoot decomposition were stronger in lower than higher altitude compared to grazing due to the stronger responses of the plant (e.g., litter and aboveground biomass) and soil (e.g., soil moisture, soil bulk density, and SOC). Soil nutrients (e.g., SOC and soil total nitrogen) seemed to play essential roles in root decomposition, which was increased in mowing plots at lower altitude and vice versa at higher altitude. Therefore, grazing significantly decreased root mass loss at higher altitude, but slightly increased at lower altitude compared to mowing. Our results indicated that the land use might variously regulate the innate differences of the plant and edaphic conditions along an altitude gradient, exerting complex impacts in litter decomposition and further influencing carbon and nutrient cycling in mountain grasslands.

Litter Decomposition in Wet Rubber and Fruit Agroforests: Below the Threshold for Tropical Peat Formation

Peatlands are shaped by slow litter decomposition, but threshold decomposition rates that allow peat formation remain unclear. Can agroforestry in the tropics be compatible with paludiculture that allows peat formation? We explored the determinants of litter decomposition in wet agroforests adjacent to tropical peatlands in Central Kalimantan (Indonesia) by litterbag studies (up to 16 weeks) with standing litter sources to estimate rate constants, characterize litter quality (especially lignin (L), polyphenolics (Pp) and nitrogen (N)), and monitor temperature and groundwater levels. In litter transfer experiments we tested for home-field advantage (HFA) effects between land cover types. Mean residence times around 85 weeks at 27 °C were associated with a high (L + Pp)/N ratio. However, in the crossover treatments, mean residence times varied from 30 to 180 weeks and strong HFA effects (up to 80% faster decomposition at “home”) were found when litter from other sources was tested in old fruit-based agroforests. HFA indicates a local decomposer community well-adapted to its normal litter diet. Litter residence times of around two years are below the apparent peat formation threshold. Maintaining wet agroforest conditions adjacent to peat domes supports peatland rewetting and restoration but does not contribute to on-site peat formation processes.

Microbial community composition controls carbon flux across litter types in early phase of litter decomposition

Leaf litter decomposition is a major carbon input to soil, making it a target for increasing soil carbon storage through microbiome engineering. We expand upon previous findings to show with multiple leaf litter types that microbial composition can drive variation in carbon flow from litter decomposition and specific microbial community features are associated with synonymous patterns of carbon flow among litter types. Although plant litter type selects for different decomposer communities, within a litter type, microbial composition drives variation in the quantity of dissolved organic carbon (DOC) measured at the end of the decomposition period. Bacterial richness was negatively correlated with DOC quantity, supporting our hypothesis that across multiple litter types there are common microbial traits linked to carbon flow patterns. Variation in DOC abundance (i.e. high versus low DOC) driven by microbial composition is tentatively due to differences in bacterial metabolism of labile compounds, rather than catabolism of non‐labile substrates such as lignin. The temporal asynchrony of metabolic processes across litter types may be a substantial impediment to discovering more microbial features common to synonymous patterns of carbon flow among litters. Overall, our findings support the concept that carbon flow may be programmed by manipulating microbial community composition.

Water table depth, experimental warming, and reduced precipitation impact on litter decomposition in a temperate Sphagnum-peatland

The Tea Bag Index (TBI) method was used to estimate the litter decomposition rate in peatland exposed for climate manipulation (increased temperature and reduced precipitation) at two contrasting sites differing in water table depth (WTD) dynamics. To manipulate climate on peatland, the prototyped Open Top Chambers (OTC) and automated rain-out shelters were used. OTCs increased daytime air temperatures by ~1.7 °C at the driest plots exposed for an increase of air temperature and reduced precipitation, while the increase of the average daily air temperature was lower than 0.9 °C. However, OTCs cooled down the peat temperature even by 0.8 °C and this effect was most pronounced for daytime rather than night-time conditions. The precipitation amount was reduced by 26%. The tea bags were buried at 8 cm depth for 83 and 172 days starting from the 19th of April 2019. Our observation proved that although decomposition rates were dependent on temperature, WTD and its fluctuations are the main factors controlling the rates of litter decomposition in waterlogged ecosystems like ours. At waterlogged Sphagnum-dominated peatlands, the interrelation between different environmental factors may mitigate the impact of warming and reduced precipitation on litter decomposition.

The Additions of Nitrogen and Sulfur Synergistically Decrease the Release of Carbon and Nitrogen from Litter in a Subtropical Forest

Atmospheric nitrogen (N) and sulfur (S) deposition in subtropical forests has increased rapidly and the current level is very high, thus seriously affecting nutrient (e.g., N and phosphorus (P)) release from litter. However, the specific effects of S addition and its interaction with N on the release of carbon (C), N, and P from litter in subtropical evergreen broadleaved forests are unclear. Therefore, a two-year field experiment was performed using a litterbag method in a subtropical evergreen broadleaved forest in western China to examine the responses of litter decomposition and nutrient release to the control (CK), added N (+N), added S (+S), and added N and S (+NS) treatments. The results showed that the remaining litter mass, lignin, cellulose, C, N, P, and litter N/P ratio were higher, whereas the litter C/N ratio and soil pH were lower in the fertilization treatments than in CK. The annual decomposition coefficients (k-values) in the +N, +S, and +NS treatments were 0.384 ± 0.002, 0.378 ± 0.002, and 0.374 ± 0.001 year−1, respectively, which were significantly lower than the k-values in CK (0.452 ± 0.005 year−1, p < 0.05). The remaining mass, lignin, cellulose, C, and litter N/P ratio were higher, whereas the soil pH was lower in the +NS treatment than in the +N and +S. The interactive effects of N addition and S addition on the remaining litter lignin, cellulose, C, N, and P; the litter C/N, C/P, and N/P ratios; and the soil pH were significant (p < 0.05). In conclusion, the addition of N and S synergistically decreased the degradation of lignin and cellulose and the release of C and N and increased the litter N/P ratio, suggesting that external N and S inputs synergistically slowed the release of C and N from litter and exacerbated litter P limitation during decomposition in this forest.

Combined forest and soil management after a catastrophic event

At the end of October 2018, a storm of unprecedented strength severely damaged the forests of the eastern sector of the Italian Alps. The affected forest area covers 42,500 ha. The president of one of the damaged regions asked for help from the University of Padua. After eight months of discussion, the authors of this article wrote a consensus text. The sometimes asper debate brought to light some crucial aspects: 1) even experienced specialists may have various opinions based on scientific knowledge that lead to conflicting proposals for action. For some of them there is evidence that to restore a destroyed natural environment it is more judicious to do nothing; 2) the soil corresponds to a living structure and every ecosystem's management should be based on it; 3) faced with a catastrophe, people and politicians find themselves unarmed, also because they rarely have the scientific background to understand natural processes. Yet politicians are the only persons who make the key decisions that drive the economy in play and therefore determine the near future of our planet. This article is an attempt to respond directly to a governor with a degree in animal production science, who formally and prudently asked a university department called "Land, Environment, Agriculture and Forestry" for help before taking decisions; 4) the authors also propose an artistic interpretation of facts (uncontrolled storm) and conclusions (listen to the soil). Briefly, the authors identify the soil as an indispensable source for the renewal of the destroyed forest, give indications on how to prepare a map of the soils of the damaged region, and suggest to anchor on this soil map a series of silvicultural and soil management actions that will promote the soil conservation and the faster recovery of the natural dynamic stability and resilience.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available for this article at 10.1007/s11629-019-5890-0 and is accessible for authorized users.

Mass loss and nutrient release during the decomposition of sixteen types of plant litter with contrasting quality under three precipitation regimes

Mass loss and nutrient release during litter decomposition drive biogeochemical cycling in terrestrial ecosystems. However, the relationship between the litter decomposition process and the decomposition stage, precipitation, and litter quality has rarely been addressed, precluding our understanding of how litter decomposition regulates nutrient cycling in various ecosystems and their responses to climate change. In this study, we measured mass loss as well as carbon and nutrient releases during the decomposition of 16 types of leaf litter under three precipitation treatments over 12 months in a common garden experiment (i.e., using standardized soil and climatic conditions). Sixteen types of leaves were divided into three functional groups (evergreen, deciduous, and herbaceous). The objectives were to understand the effects of decomposition stages and precipitation regimes on litter decomposition and to examine the relationship between this effect and chemical properties. The mass loss and release of nitrogen and potassium were significantly higher in the 6- to 12-month stage of decomposition (high temperature and humidity) than in the 0- to 6-month stage. Phosphorus was relatively enriched in evergreen leaves after 6 months of decomposition. The rates of mass loss and nutrient release were significantly greater in herbaceous than in deciduous and evergreen leaves. Increasing precipitation from 400 to 800 mm accelerated mass loss and potassium release but decreased phosphorus release in the 0- to 6-month stage of decomposition. These results highlighted the contribution to and complexity of litter chemical properties in litter decomposition.

Constraints on microbial communities, decomposition and methane production in deep peat deposits

Peatlands play outsized roles in the global carbon cycle. Despite occupying a rather small fraction of the terrestrial biosphere (~3%), these ecosystems account for roughly one third of the global soil carbon pool. This carbon is largely comprised of undecomposed deposits of plant material (peat) that may be meters thick. The fate of this deep carbon stockpile with ongoing and future climate change is thus of great interest and has large potential to induce positive feedback to climate warming. Recent in situ warming of an ombrotrophic peatland indicated that the deep peat microbial communities and decomposition rates were resistant to elevated temperatures. In this experiment, we sought to understand how nutrient and pH limitations may interact with temperature to limit microbial activity and community composition. Anaerobic microcosms of peat collected from 1.5 to 2 meters in depth were incubated at 6°C and 15°C with elevated pH, nitrogen (NH4Cl), and/or phosphorus (KH2PO4) in a full factorial design. The production of CO2 and CH4 was significantly greater in microcosms incubated at 15°C, although the structure of the microbial community did not differ between the two temperatures. Increasing the pH from ~3.5 to ~5.5 altered microbial community structure, however increases in CH4 production were non-significant. Contrary to expectations, N and P additions did not increase CO2 and CH4 production, indicating that nutrient availability was not a primary constraint in microbial decomposition of deep peat. Our findings indicate that temperature is a key factor limiting the decomposition of deep peat, however other factors such as the availability of O2 or alternative electron donors and high concentrations of phenolic compounds, may also exert constraints. Continued experimental peat warming studies will be necessary to assess if the deep peat carbon bank is susceptible to increased temperatures over the longer time scales.

Extracellular enzyme activity in grass litter varies with grazing history, environment and plant species in temperate grasslands

Long-term livestock grazing (here after 'grazing') affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0-18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands.

Microbial succession on decomposing root litter in a drought-prone Scots pine forest

Decomposition is a major flux of the carbon cycle in forest soils and understanding the involved processes is a key for budgeting carbon turnover. Decomposition is constrained by the presence of biological agents such as microorganisms and the underlying environmental conditions such as water availability. A metabarcoding approach of ribosomal markers was chosen to study the succession of bacterial and fungal decomposers on root litter. Litterbags containing pine roots were buried in a pine forest for two years and sequentially sampled. Decomposition and the associated communities were surveyed under ambient dry and long-term irrigation conditions. Early decomposition stages were characterized by the presence of fast-cycling microorganisms such as Bacteroidetes and Helotiales, which were then replaced by more specialized bacteria and litter-associated or parasitic groups such as Acidobacteria, white rots, and Pleosporales. This succession was likely driven by a decrease of easily degradable carbohydrates and a relative increase in persistent compounds such as lignin. We hypothesize that functional redundancy among the resident microbial taxa caused similar root decomposition rates in control and irrigated forest soils. These findings have important implications for drought-prone Alpine forests as frequent drought events reduce litter fall, but not litter decomposition, potentially resulting in lower carbon stocks.

Soil Organic Carbon Chemical Functional Groups under Different Revegetation Types Are Coupled with Changes in the Microbial Community Composition and the Functional Genes

Different revegetatiom types can affect the chemical composition of soil organic carbon (SOC), soil microbial community and the functional genes related to carbon cycle. However, the relationships between SOC chemical functional groups and soil microbial communities and the functional genes remains poorly unclear under different revegetation types. Using the solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, we examined changes in the SOC chemical composition of five soils (0–10 cm depth) from Larix gmelinii Rupr. (LG), Pinus koraiensis Sieb. (PK), Quercus mongolica Fisch. (QM), Juglans mandshurica Maxim. (JM), and conifer-broadleaf forest (CB). And the soil microbial community genes related to metabolism of macro-molecular compounds were determined via whole genome shotgun based on Illumina HiSeq. Our results indicated that broadleaf forests (JM, QM) had increased the contents of soil total carbon (C), total nitrogen (N), dissolved organic carbon (DOC), and microbial biomass carbon (MBC), compared with coniferous forests (LG, PK) and the conifer-broadleaf forest (CB). While, the coniferous forests generated a lower O-alcoxyl C, a higher alkyl C, and the ratio of alkyl C/O-alkyl C than broadleaf forests. A total of four kingdoms were identified via whole metagenome shotgun sequencing, including eight archaea, 55 bacteria, 15 eukaryota, and two viruses, giving a total 80 phyla. The contents of alkyne C, phenolic C, methoxyl C, COO/NC=O, and alkyl C were strong related to the composition of soil microbial community and their contents illuminated a major part of the variation in soil microbial composition. We detected seven corresponding macro-molecular compounds of different organic carbon functional group, and 244 genes related to metabolism across all samples, and soil total C, total N, and DOC could be the main factors for microbial functional gene composition. Interestingly, the relative abundances of different SOC chemical functional groups, the phylogenetic distance for microbes, the genes of C cycling based on the KEGG database, and the relative abundance of genes related to metabolism of macro-molecular compounds of different SOC chemical functional groups under different revegetation types all could be divided into three groups, including PK plus LG, JM plus QM, and CB. Our results also illustrated that variations in SOC chemical functional groups were strongly associated with changes of soil microbial community taxa and functional genes, which might be affected by the changes of soil characteristics.

Drought increases the frequencies of fungal functional genes related to carbon and nitrogen acquisition

Although water is a critical resource for organisms, microbially-mediated processes such as decomposition and nitrogen (N) transformations can endure within ecosystems even when water is scarce. To identify underlying mechanisms, we examined the genetic potential for fungi to contribute to specific aspects of carbon (C) and N cycling in a drought manipulation in Southern California grassland. In particular, we measured the frequency of fungal functional genes encoding enzymes that break down cellulose and chitin, and take up ammonium and amino acids, in decomposing litter. Furthermore, we used "microbial cages" to reciprocally transplant litter and microbes between control and drought plots. This approach allowed us to distinguish direct effects of drought in the plot environment versus indirect effects via shifts in the microbial community or changes in litter chemistry. For every fungal functional gene we examined, the frequency of that gene within the microbial community increased significantly in drought plots compared to control plots. In contrast, when plot environment was held constant, frequencies of these fungal functional genes did not differ significantly between control-derived microbes versus drought-derived microbes, or between control-derived litter versus drought-derived litter. It appears that drought directly selects for fungi with the genetic capacity to acquire these specific C- and N-containing compounds. This genetic trait may allow fungi to take advantage of ephemeral water supplies. Altogether, proliferation of fungi with the genetic capacity for C and N acquisition may contribute to the maintenance of biogeochemical cycling under drought.

Decomposition responses to climate depend on microbial community composition

Bacteria and fungi drive decomposition, a fundamental process in the carbon cycle, yet the importance of microbial community composition for decomposition remains elusive. Here, we used an 18-month reciprocal transplant experiment along a climate gradient in Southern California to disentangle the effects of the microbial community versus the environment on decomposition. Specifically, we tested whether the decomposition response to climate change depends on the microbial community. We inoculated microbial decomposers from each site onto a common, irradiated leaf litter within "microbial cages" that prevent microbial exchange with the environment. We characterized fungal and bacterial composition and abundance over time and investigated the functional consequences through litter mass loss and chemistry. After 12 months, microbial communities altered both decomposition rate and litter chemistry. Further, the functional measurements depended on an interaction between the community and its climate in a manner not predicted by current theory. Moreover, microbial ecologists have traditionally considered fungi to be the primary agents of decomposition and for bacteria to play a minor role. Our results indicate that not only does climate change and transplantation have differential legacy effects among bacteria and fungi, but also that bacterial communities might be less functionally redundant than fungi with regards to decomposition. Thus, it may be time to reevaluate both the role of microbial community composition in its decomposition response to climate and the relative roles of bacterial and fungal communities in decomposition.

Bacterial Succession Decreases Network Complexity During Plant Material Decomposition in Mangroves

In this study, 16S rRNA gene amplicon sequencing was used to assess bacterial diversity and dynamics throughout different stages of leaves decomposition of three plant species (Rhizophora mangle, Laguncularia racemosa, and Avicennia schaueriana) in three distinct mangroves of São Paulo state, Brazil. The experiments were conducted in microcosms. Phylogenetic diversity (Faiths' PD) index showed differences between samples and suggested that some treatments like R. mangle increased their bacterial diversity through time. Principal coordinate analysis revealed that community's profile varied based on mangroves, followed by plant species and time. A clear succession patterns was observed in this study, i.e., some microorganisms with low abundance in the initial phases gradually became dominant (e.g., Alphaproteobacteria), whereas microbes that were initially predominant became low (e.g., Gammaproteobacteria). Co-occurrence analyses were performed for all times of plant degradation aiming to better understand the relationships between bacterial populations. The c-score index was done to test the randomness of the community assemblage during the stages of decomposition. For all degradation time points, the values of the observed c-score were higher than the values of the simulated c-score. This result indicated that during plant decomposition, the bacterial communities presented less co-occurrence than expected by chance and that these communities were not randomly assembled but instead they are driven by species interactions. Network analyses results showed that in the conditions presented in this experiment, the initial stages of leaf decomposition formed more connected and complex networks than the later stages. These results suggest that resource competition was a determinant in these specific mangroves during plant degradation, mainly in the initial periods.

Bacterial contributions to delignification and lignocellulose degradation in forest soils with metagenomic and quantitative stable isotope probing

Delignification, or lignin-modification, facilitates the decomposition of lignocellulose in woody plant biomass. The extant diversity of lignin-degrading bacteria and fungi is underestimated by culture-dependent methods, limiting our understanding of the functional and ecological traits of decomposers populations. Here, we describe the use of stable isotope probing (SIP) coupled with amplicon and shotgun metagenomics to identify and characterize the functional attributes of lignin, cellulose and hemicellulose-degrading fungi and bacteria in coniferous forest soils from across North America. We tested the extent to which catabolic genes partitioned among different decomposer taxa; the relative roles of bacteria and fungi, and whether taxa or catabolic genes correlated with variation in lignocellulolytic activity, measured as the total assimilation of ¹³C-label into DNA and phospholipid fatty acids. We found high overall bacterial degradation of our model lignin substrate, particularly by gram-negative bacteria (Comamonadaceae and Caulobacteraceae), while fungi were more prominent in cellulose-degradation. Very few taxa incorporated ¹³C-label from more than one lignocellulosic polymer, suggesting specialization among decomposers. Collectively, members of Caulobacteraceae could degrade all three lignocellulosic polymers, providing new evidence for their importance in lignocellulose degradation. Variation in lignin-degrading activity was better explained by microbial community properties, such as catabolic gene content and community structure, than cellulose-degrading activity. SIP significantly improved shotgun metagenome assembly resulting in the recovery of several high-quality draft metagenome-assembled genomes and over 7500 contigs containing unique clusters of carbohydrate-active genes. These results improve understanding of which organisms, conditions and corresponding functional genes contribute to lignocellulose decomposition.

Decomposing litter and associated microbial activity responses to nitrogen deposition in two subtropical forests containing nitrogen-fixing or non-nitrogen-fixing tree species

Atmospheric nitrogen (N) deposition has caused concern due to its effects on litter decomposition in subtropical regions where N-fixing tree species are widespread. However, the effect of N deposition on litter decomposition in N-fixing plantations remains unclear. We investigated the effects of a 2-year N deposition treatment on litter decomposition, microbial activity, and nutrient release in two subtropical forests containing Alnus cremastogyne (AC, N-fixing) and Liquidambar formosana (LF, non-N-fixing). The decomposition rate in AC was faster than in LF when there was no experimental N deposition. In AC, the initial decomposition rate was faster when additional N was applied and was strongly linked to higher cellulose-degrading enzyme activities during the early decomposition stage. However, N deposition reduced litter decomposition and inhibited lignin-degrading enzyme activities during the later decomposition stage. Nitrogen deposition enhanced carbohydrate and alcohol utilization, but suppressed amino acid and carboxylic acid uptake in the AC plantation. However, it did not significantly affect litter decomposition and microbial activity in the LF plantation. In conclusion, N deposition could inhibit litter decomposition by changing microbial enzyme and metabolic activities during the decomposition process and would increase carbon accumulation and nitrogen retention in subtropical forests with N-fixing tree species.

Identity of plant, lichen and moss species connects with microbial abundance and soil functioning in Maritime Antarctica

BACKGROUND AND AIMS

We lack studies evaluating how the identity of plant, lichen and moss species relates to microbial abundance and soil functioning on Antarctica. If species identity is associated with soil functioning, distributional changes of key species, linked to climate change, could significantly affect Antarctic soil functioning.

METHODS

We evaluated how the identity of six Antarctic plant, lichen and moss species relates to a range of soil attributes (C, N and P cycling), microbial abundance and structure in Livingston Island, Maritime Antarctica. We used an effect size metric to predict the association between species (vs. bare soil) and the measured soil attributes.

RESULTS

We observed species-specific effects of the plant and biocrust species on soil attributes and microbial abundance. Phenols, phosphatase and β-D-cellobiosidase activities were the most important attributes characterizing the observed patterns. We found that the evaluated species positively correlated with soil nutrient availability and microbial abundance vs. bare soil.

CONCLUSIONS

We provide evidence, from a comparative study, that plant and biocrust identity is associated with different levels of soil functioning and microbial abundance in Maritime Antarctica. Our results suggest that changes in the spatial distribution of these species linked to climate change could potentially entail changes in the functioning of Antarctic terrestrial ecosystems.

Direct and legacy effects of plant-traits control litter decomposition in a deciduous oak forest in Mexico

Background

Litter decomposition is a key process in the functioning of forest ecosystems, because it strongly controls nutrient recycling and soil fertility maintenance. The interaction between the litter chemical composition and the metabolism of the soil microbial community has been described as the main factor of the decomposition process based on three hypotheses: substrate-matrix interaction (SMI), functional breadth (FB) and home-field advantage (HFA). The objective of the present study was to evaluate the effect of leaf litter quality (as a direct plant effect, SMI hypothesis), the metabolic capacity of the microbial community (as a legacy effect, FB hypothesis), and the coupling between the litter quality and microbial activity (HFA hypothesis) on the litter decomposition of two contiguous deciduous oak species at a local scale.

Methods

To accomplish this objective, we performed a litterbag experiment in the field for 270 days to evaluate mass loss, leaf litter quality and microbial activity in a complete factorial design for litter quality and species site.

Results

The litter of Quercus deserticola had higher rate of decomposition independently of the site, while the site of Quercus castanea promoted a higher rate of decomposition independently of the litter quality, explained by the specialization of the soil microbial community in the use of recalcitrant organic compounds. The Home-Field Advantage Index was reduced with the decomposition date (22% and 4% for 30 and 270 days, respectively).

Discussion

We observed that the importance of the coupling of litter quality and microbial activity depends on decomposition stage. At the early decomposition stage, the home-advantage hypothesis explained the mass loss of litter; however, in the advanced decomposition stage, the litter quality and the metabolic capacity of the microbial community can be the key drivers.

Large herbivores influence plant litter decomposition by altering soil properties and plant quality in a meadow steppe

Large herbivores act as a major driver of plant litter decomposition in grasslands. The modifications of soil biotic and abiotic properties, as well as the changes in quality (C/N ratio) of plant litter, are two key pathways by which large herbivores can affect litter decomposition. Yet we know little about the relative role of these two mechanisms in mediating decomposition. Here, by combining a large-scale and a small-scale field manipulative experiment, we examined how livestock (cattle and sheep) grazing affects standing litter decomposition of a dominant grass, Leymus chinensis in grasslands in northeast China. We found that livestock grazing affected litter decay rate both by its influences on soil property (soil moisture, nutrient content, and microbial communities) and on plant litter quality (C/N ratio). Due to their distinct body size and diet preference, cattle and sheep affected soil property and litter quality, thus litter decay rate, differently by causing varying disturbance regimes and by feeding on different dominant species. Our study provides evidence that herbivore grazing can influence litter decomposition by modifying soil conditions and litter quality independently. Therefore, choosing the proper large herbivore(s) in grazing regimes may be important in maintaining nutrient cycling in grassland ecosystems.

Decoupling the direct and indirect effects of climate on plant litter decomposition: Accounting for stress-induced modifications in plant chemistry

Decomposition of plant litter is a fundamental ecosystem process that can act as a feedback to climate change by simultaneously influencing both the productivity of ecosystems and the flux of carbon dioxide from the soil. The influence of climate on decomposition from a postsenescence perspective is relatively well known; in particular, climate is known to regulate the rate of litter decomposition via its direct influence on the reaction kinetics and microbial physiology on processes downstream of tissue senescence. Climate can alter plant metabolism during the formative stage of tissues and could shape the final chemical composition of plant litter that is available for decomposition, and thus indirectly influence decomposition; however, these indirect effects are relatively poorly understood. Climatic stress disrupts cellular homeostasis in plants and results in the reprogramming of primary and secondary metabolic pathways, which leads to changes in the quantity, composition, and organization of small molecules and recalcitrant heteropolymers, including lignins, tannins, suberins, and cuticle within the plant tissue matrix. Furthermore, by regulating metabolism during tissue senescence, climate influences the resorption of nutrients from senescing tissues. Thus, the final chemical composition of plant litter that forms the substrate of decomposition is a combined product of presenescence physiological processes through the production and resorption of metabolites. The changes in quantity, composition, and localization of the molecular construct of the litter could enhance or hinder tissue decomposition and soil nutrient cycling by altering the recalcitrance of the lignocellulose matrix, the composition of microbial communities, and the activity of microbial exo-enzymes via various complexation reactions. Also, the climate-induced changes in the molecular composition of litter could differentially influence litter decomposition and soil nutrient cycling. Compared with temperate ecosystems, the indirect effects of climate on litter decomposition in the tropics are not well understood, which underscores the need to conduct additional studies in tropical biomes. We also emphasize the need to focus on how climatic stress affects the root chemistry as roots contribute significantly to biogeochemical cycling, and on utilizing more robust analytical approaches to capture the molecular composition of tissue matrix that fuel microbial metabolism.

Sediment anoxia limits microbial-driven seagrass carbon remineralization under warming conditions

Seagrass ecosystems are significant carbon sinks, and their resident microbial communities ultimately determine the quantity and quality of carbon sequestered. However, environmental perturbations have been predicted to affect microbial-driven seagrass decomposition and subsequent carbon sequestration. Utilizing techniques including 16S-rDNA sequencing, solid-state NMR and microsensor profiling, we tested the hypothesis that elevated seawater temperatures and eutrophication enhance the microbial decomposition of seagrass leaf detritus and rhizome/root tissues. Nutrient additions had a negligible effect on seagrass decomposition, indicating an absence of nutrient limitation. Elevated temperatures caused a 19% higher biomass loss for aerobically decaying leaf detritus, coinciding with changes in bacterial community structure and enhanced lignocellulose degradation. Although, community shifts and lignocellulose degradation were also observed for rhizome/root decomposition, anaerobic decay was unaffected by temperature. These observations suggest that oxygen availability constrains the stimulatory effects of temperature increases on bacterial carbon remineralization, possibly through differential temperature effects on bacterial functional groups, including putative aerobic heterotrophs (e.g. Erythrobacteraceae, Hyphomicrobiaceae) and sulfate reducers (e.g. Desulfobacteraceae). Consequently, under elevated seawater temperatures, carbon accumulation rates may diminish due to higher remineralization rates at the sediment surface. Nonetheless, the anoxic conditions ubiquitous to seagrass sediments can provide a degree of carbon protection under warming seawater temperatures.