Aboveground tree growth varies with belowground carbon allocation in a tropical rainforest environment

Rainforest transformation reallocates energy from green to brown food webs

Terrestrial animal biodiversity is increasingly being lost because of land-use change1,2. However, functional and energetic consequences aboveground and belowground and across trophic levels in megadiverse tropical ecosystems remain largely unknown. To fill this gap, we assessed changes in energy fluxes across 'green' aboveground (canopy arthropods and birds) and 'brown' belowground (soil arthropods and earthworms) animal food webs in tropical rainforests and plantations in Sumatra, Indonesia. Our results showed that most of the energy in rainforests is channelled to the belowground animal food web. Oil palm and rubber plantations had similar or, in the case of rubber agroforest, higher total animal energy fluxes compared to rainforest but the key energetic nodes were distinctly different: in rainforest more than 90% of the total animal energy flux was channelled by arthropods in soil and canopy, whereas in plantations more than 50% of the energy was allocated to annelids (earthworms). Land-use change led to a consistent decline in multitrophic energy flux aboveground, whereas belowground food webs responded with reduced energy flux to higher trophic levels, down to -90%, and with shifts from slow (fungal) to fast (bacterial) energy channels and from faeces production towards consumption of soil organic matter. This coincides with previously reported soil carbon stock depletion3. Here we show that well-documented animal biodiversity declines with tropical land-use change4-6 are associated with vast energetic and functional restructuring in food webs across aboveground and belowground ecosystem compartments.

First assessment of root biomass and root carbon and nitrogen stocks in Turkish floodplain forests

Estimation of whole root biomass including coarse and larger roots and root balls can provide better understanding of carbon and nitrogen stocks in floodplain forests. Whole root systems of nine ash trees (Fraxinus angustifolia Vahl.) and six alder trees (Alnus glutinosa L.) trees ranging in diameter breast height (dbh) from 29.1 to 72.0 cm for ash and from 29.1 to 44.3 cm for alder were excavated, and their small < 1 cm, medium 1-4 cm, larger > 4 cm and root-ball biomass, and root carbon and nitrogen stocks were determined in Karacabey floodplain forest in Bursa, Turkey. In addition, for the method comparison, small root biomass (< 1 cm) was also determined using soil-core method. The whole root biomass of ash trees varied from 167.7 to 186.8 Mg ha^-1. Alder trees had lower whole root biomass than ash trees ranging from 49.0 to 63.6 Mg ha^-1. The determination of small root biomass by soil excavation method was nearly two-fold higher than by soil core method. Both root carbon and nitrogen stocks showed an increase with increasing root diameter. Among the tree characteristics (dbh, age, height, and volume), the dbh showed the highest correlation with whole root biomass and root carbon and nitrogen stocks for both tree species. It is concluded that young trees can have higher small, medium, and large root biomass and store more C and N in those roots, whereas older trees can have higher root-ball biomass and root-ball carbon and nitrogen stocks in Karacabey floodplain forests.

The biodiversity and ecosystem service contributions and trade-offs of forest restoration approaches

Forest restoration is being scaled-up globally to deliver critical ecosystem services and biodiversity benefits, yet we lack rigorous comparison of co-benefit delivery across different restoration approaches. In a global synthesis, we use 25,950 matched data pairs from 264 studies in 53 countries to assess how delivery of climate, soil, water, and wood production services as well as biodiversity compares across a range of tree plantations and native forests. Carbon storage, water provisioning, and especially soil erosion control and biodiversity benefits are all delivered better by native forests, with compositionally simpler, younger plantations in drier regions performing particularly poorly. However, plantations exhibit an advantage in wood production. These results underscore important trade-offs among environmental and production goals that policymakers must navigate in meeting forest restoration commitments.

Different Urban Forest Tree Species Affect the Assembly of the Soil Bacterial and Fungal Community

The selection of tree species used for the afforestation of urban forests is very important for maintaining the urban ecosystem, while soil microbe is one of the driving factors of material cycling in the urban forest ecosystem and for health of forests. In this study, the characteristics of surface soil bacterial and fungal community structure in four urban forests (primarily composed of Fraxinus mandshurica (Fm), Quercus mongolica (Qm), Pinus sylvestris var. mongolica (Ps), and Pinus tabulaeformis var. Mukdensis (Pt) as the main dominant tree species, respectively) were investigated by high-throughput sequencing. Our results showed that the alpha diversity of the soil microbial community in the Fm urban forest was the highest, while the lowest was in the Ps urban forest. In the bacterial community, Proteobacteria was the most predominant phylum in soils from Fm, Ps, and Pt urban forests. The most relatively abundant phylum of the Qm urban forest soil was Acidobacteria. The relative abundances of the bacterial communities at the genus level in the soil of four urban forests were significantly different. The soil bacterial communities in Ps and Pt urban forests were more similar, and Qm and Fm were also more similar. In the fungal community, Basidiomycota was the most predominant phylum in soils from Qm, Ps, and Pt urban forests. The phylum with the greatest relative abundance in the Fm urban forest soil was Ascomycota. There were differences in the fungal community between Qm, Fm, Ps, and Pt urban forests. Soil microbial community composition was affected by environmental factors: soil bacterial and fungal community compositions were significantly related to soil electrical conductivity (EC), alkali hydrolysable nitrogen (AHN), total nitrogen (TN), and total phosphorus (TP). In conclusion, the soil microbial community structure was related to both forest's tree species and soil properties.

Root mass carbon costs to acquire nitrogen are determined by nitrogen and light availability in two species with different nitrogen acquisition strategies

Plant nitrogen acquisition requires carbon to be allocated belowground to build roots and sustain microbial associations. This carbon cost to acquire nitrogen varies by nitrogen acquisition strategy; however, the degree to which these costs vary due to nitrogen availability or demand has not been well tested under controlled conditions. We grew a species capable of forming associations with nitrogen-fixing bacteria (Glycine max) and a species not capable of forming such associations (Gossypium hirsutum) under four soil nitrogen levels to manipulate nitrogen availability and four light levels to manipulate nitrogen demand in a full-factorial greenhouse experiment. We quantified carbon costs to acquire nitrogen as the ratio of total root carbon to whole-plant nitrogen within each treatment combination. In both species, light availability increased carbon costs due to a larger increase in root carbon than whole-plant nitrogen, while nitrogen fertilization generally decreased carbon costs due to a larger increase in whole-plant nitrogen than root carbon. Nodulation data indicated that G. max shifted relative carbon allocation from nitrogen fixation to direct uptake with increased nitrogen fertilization. These findings suggest that carbon costs to acquire nitrogen are modified by changes in light and nitrogen availability in species with and without associations with nitrogen-fixing bacteria.

Biotic and Abiotic Determinants of Soil Organic Matter Stock and Fine Root Biomass in Mountain Area Temperate Forests—Examples from Cambisols under European Beech, Norway Spruce, and Silver Fir (Carpathians, Central Europe)

Forest ecosystems significantly contribute to the global organic carbon (OC) pool, exhibiting high spatial heterogeneity in this respect. Some of the components of the OC pool in a forest (woody aboveground biomass (wAGB), coarse root biomass (CRB)) can be relatively easily estimated using readily available data from land observation and forest inventories, while some of the components of the OC pool are very difficult to determine (fine root biomass (FRB) and soil organic matter (SOM) stock). The main objectives of our study were to: (1) estimate the SOM stock; (2) estimate FRB; and (3) assess the relationship between both biotic (wAGB, forest age, foliage, stand density) and abiotic factors (climatic conditions, relief, soil properties) and SOM stocks and FRB in temperate forests in the Western Carpathians consisting of European beech, Norway spruce, and silver fir (32 forest inventory plots in total). We uncovered the highest wAGB in beech forests and highest SOM stocks under beech forest. FRB was the highest under fir forest. We noted a considerable impact of stand density on SOM stocks, particularly in beech and spruce forests. FRB content was mostly impacted by stand density only in beech forests without any discernible effects on other forest characteristics. We discovered significant impacts of relief-dependent factors and SOM stocks at all the studied sites. Our biomass and carbon models informed by more detailed environmental data led to reduce the uncertainty in over- and underestimation in Cambisols under beech, spruce, and fir forests for mountain temperate forest carbon pools.

A Comparative Study of Pyrolysis Liquids by Slow Pyrolysis of Industrial Hemp Leaves, Hurds and Roots

This study assessed the pyrolysis liquids obtained by slow pyrolysis of industrial hemp leaves, hurds, and roots. The liquids recovered between a pyrolysis temperature of 275-350 °C, at two condensation temperatures 130 °C and 70 °C, were analyzed. Aqueous and bio-oil pyrolysis liquids were produced and analyzed by proton nuclear magnetic resonance (NMR), gas chromatography-mass spectrometry (GC-MS), and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). NMR revealed quantitative concentrations of the most abundant compounds in the aqueous fractions and compound groups in the oily fractions. In the aqueous fractions, the concentration range of acetic acid was 50-241 gL^-1, methanol 2-30 gL^-1, propanoic acid 5-20 gL^-1, and 1-hydroxybutan-2-one 2 gL^-1. GC-MS was used to compare the compositions of the volatile compounds and APPI FT-ICR MS was utilized to determine the most abundant higher molecular weight compounds. The different obtained pyrolysis liquids (aqueous and oily) had various volatile and nonvolatile compounds such as acetic acid, 2,6-dimethoxyphenol, 2-methoxyphenol, and cannabidiol. This study provides a detailed understanding of the chemical composition of pyrolysis liquids from different parts of the industrial hemp plant and assesses their possible economic potential.

Soil physicochemical properties drive the variation in soil microbial communities along a forest successional series in a degraded wetland in northeastern China

The Sanjiang Plain is the biggest freshwater wetland locating in northeastern China. Due to climate change and human activities, that wetland has degraded to a successional gradient from the original flooded wetland to dry shrub vegetation and a forest area with lower ground water level, which may result in changes in soil microbiologic structure and functions. The present study investigated the microbial diversity and community structure in relation to soil properties along that successional gradient. The soil physico-chemical properties changed significantly with degradation stage. The Shannon diversity index of both soil bacteria (5.90-6.42) and fungi (1.7-4.19) varied significantly with successional stage (both p < .05). The community structures of soil bacteria and fungi in the early successional stages (i.e., the wetland) were significantly determined by water content, total nitrogen, and available nitrogen concentrations in soils, while those in the later successional stages (i.e., forests) were significantly structured by soil organic carbon, soil pH, and available phosphorus concentrations. These results suggest that the soil microbial structure is mainly determined by soil properties rather than by plant community such as plant species composition along successional stages.

Effects of terracing on root distribution of Pinus tabulaeformis Carr. forest and soil properties in the Loess Plateau of China

Terracing is one of the most effective ecological engineering practices that improve soil anti-erosivity properties and support plant growth in the dryland loess hilly area and other similar regions. The objective of the study was to understand the vertical distribution of root in different terraces and their relationships with soil environmental factors in the Loess Plateau of China. The vertical root distribution in the 0-400 cm soil profile, fine root distribution and soil moisture, soil nutrients (soil organic carbon, total nitrogen, and total phosphorus) and soil anti-erosivity in 0-160 cm soil profiles (every 20 cm for one layer) were investigated using the ground-penetrating radar and soil coring methods in a Pinus tabulaeformis Carr. forest under three terrace types during the growing season of 2018. We highlight several key findings here. First, level benches had the highest root density (18.14 kg m^-2), followed by fish-scale pits (13.95 kg m^-2) and reverse-slope terraces (9.84 kg m^-2), as well as the highest soil water content, nutrients and soil stability. Second, terracing caused significant differences in root distribution (P < 0.05), leading to the variation of soil moisture, nutrients, anti-erosivity (explained over 80% variation) and reduced spatial heterogeneities of soil water content and nutrients. Third, fine root density parameters attained the highest values in the topsoil (0-40 cm soil layer) and decreased with increasing soil depth in all the three terrace types (P < 0.05). Finally, fine roots contributed to soil water improvement, nutrient promotion and soil stabilization, while higher density of coarse roots might consume soil nutrients and reduce soil anti-erosivity. We thus suggest that level benches could be a more suitable terracing measure for plantation of P. tabulaeformis Carr., and to achieve soil melioration and fixation during the ecosystem restoration process in the Loess Plateau and other arid and semiarid regions.

Estimating the full greenhouse gas emissions offset potential and profile between rehabilitating and established mangroves

Mangrove forests are extremely productive, with rates of growth rivaling some terrestrial tropical rainforests. However, our understanding of the full suite of processes underpinning carbon exchange with the atmosphere and near shore-waters, the allocation of carbon in mangroves, and fluxes of non-CO₂ greenhouse gases (GHGs) are limited to a handful of studies. This constrains the scientific basis from which to advocate for greater support for and investment in mangrove restoration and conservation. Improving understanding is urgently needed given the on-going landuse pressures mangrove forests face, particularly throughout much of Southeast Asia. The current study reduces uncertainties by providing a holistic synthesis of the net potential GHG mitigation benefits resulting from rehabilitating mangroves and established forests. Rehabilitating sites from two contrasting locations representative of high (Tiwoho) and low (Tanakeke) productivity systems on the island of Sulawesi (Indonesia) were used as case studies to compare against established mangroves. A carbon budget, allocation and pathways model was developed to account for inputs (carbon sequestration) and outputs (GHG emissions of CO₂, N₂O and CH₄) to estimate Net Ecosystem Production (NEP) and Net Ecosystem Carbon Balance (NECB). Our results indicate that while Tiwoho's rehabilitating sites and established mangroves represent a significant carbon sink (-10.6 ± 0.9 Mg CO₂e ha^-1 y^-1 and 16.1 Mg CO₂e ha^-1 y^-1 respectively), the low productivity of Tanakeke has resulted in minimal reductions to date (0.7 ± 0.3 Mg CO₂e ha^-1 y^-1). Including NEP from mangrove-allied primary producer communities (e.g. benthic algae) and the portion of dissolved inorganic carbon exported from mangroves (EX_DIC) that remains within the water column may drive overall removals considerably upwards in established forests to -37.2 Mg CO₂e ha^-1 y^-1. These values are higher than terrestrial forests and strengthen the evidence base needed to underpin the use of forest carbon financing mechanisms for mangrove restoration.

From the High Arctic to the Equator: Do Soil Metagenomes Differ According to Our Expectations?

Comparing the functional gene composition of soils at opposite extremes of environmental gradients may allow testing of hypotheses about community and ecosystem function. Here, we were interested in comparing how tropical microbial ecosystems differ from those of polar climates. We sampled several sites in the equatorial rainforest of Malaysia and Brunei, and the high Arctic of Svalbard, Canada, and Greenland, comparing the composition and the functional attributes of soil biota between the two extremes of latitude, using shotgun metagenomic Illumina HiSeq2000 sequencing. Based upon "classical" views of how tropical and higher latitude ecosystems differ, we made a series of predictions as to how various gene function categories would differ in relative abundance between tropical and polar environments. Results showed that in some respects our predictions were correct: the polar samples had higher relative abundance of dormancy related genes, and lower relative abundance of genes associated with respiration, and with metabolism of aromatic compounds. The network complexity of the Arctic was also lower than the tropics. However, in various other respects, the pattern was not as predicted; there were no differences in relative abundance of stress response genes or in genes associated with secondary metabolism. Conversely, CRISPR genes, phage-related genes, and virulence disease and defense genes, were unexpectedly more abundant in the Arctic, suggesting more intense biotic interaction. Also, eukaryote diversity and bacterial diversity were higher in the Arctic of Svalbard compared to tropical Brunei, which is consistent with what may expected from amplicon studies in terms of the higher pH of the Svalbard soil. Our results in some respects confirm expectations of how tropical versus polar nature may differ, and in other respects challenge them.

Temporal and Spatial Variation of Soil Bacteria Richness, Composition, and Function in a Neotropical Rainforest

The high diversity of tree species has traditionally been considered an important controller of belowground processes in tropical rainforests. However, soil water availability and resources are also primary regulators of soil bacteria in many ecosystems. Separating the effects of these biotic and abiotic factors in the tropics is challenging because of their high spatial and temporal heterogeneity. To determine the drivers of tropical soil bacteria, we examined tree species effects using experimental tree monocultures and secondary forests at La Selva Biological Station in Costa Rica. A randomized block design captured spatial variation and we sampled at four dates across two years to assess temporal variation. We measured bacteria richness, phylogenetic diversity, community composition, biomass, and functional potential. All bacteria parameters varied significantly across dates. In addition, bacteria richness and phylogenetic diversity were affected by the interaction of vegetation type and date, whereas bacteria community composition was affected by the interaction of vegetation type and block. Shifts in bacteria community richness and composition were unrelated to shifts in enzyme function, suggesting physiological overlap among taxa. Based on the observed temporal and spatial heterogeneity, our understanding of tropical soil bacteria will benefit from additional work to determine the optimal temporal and spatial scales for sampling. Understanding spatial and temporal variation will facilitate prediction of how tropical soil microbes will respond to future environmental change.

Temporal Variation of Wood Density and Carbon in Two Elevational Sites of Pinus cooperi in Relation to Climate Response in Northern Mexico

Forest ecosystems play an important role in the global carbon cycle. Therefore, understanding the dynamics of carbon uptake in forest ecosystems is much needed. Pinus cooperi is a widely distributed species in the Sierra Madre Occidental in northern Mexico and future climatic variations could impact these ecosystems. Here, we analyze the variations of trunk carbon in two populations of P. cooperi situated at different elevational gradients, combining dendrochronological techniques and allometry. Carbon sequestration (50% biomass) was estimated from a specific allometric equation for this species based on: (i) variation of intra-annual wood density and (ii) diameter reconstruction. The results show that the population at a higher elevation had greater wood density, basal area, and hence, carbon accumulation. This finding can be explained by an ecological response of trees to adverse weather conditions, which would cause a change in the cellular structure affecting the within-ring wood density profile. The influence of variations in climate on the maximum density of chronologies showed a positive correlation with precipitation and the Multivariate El Niño Southern Oscillation Index during the winter season, and a negative correlation with maximum temperature during the spring season. Monitoring previous conditions to growth is crucial due to the increased vulnerability to extreme climatic variations on higher elevational sites. We concluded that temporal variability of wood density contributes to a better understanding of environmental historical changes and forest carbon dynamics in Northern Mexico, representing a significant improvement over previous studies on carbon sequestration. Assuming a uniform density according to tree age is incorrect, so this method can be used for environmental mitigation strategies, such as for managing P. cooperi, a dominant species of great ecological amplitude and widely used in forest industries.

Tree species, spatial heterogeneity, and seasonality drive soil fungal abundance, richness, and composition in Neotropical rainforests

Tropical ecosystems remain poorly understood and this is particularly true for belowground soil fungi. Soil fungi may respond to plant identity when, for example, plants differentially allocate resources belowground. However, spatial and temporal heterogeneity in factors such as plant inputs, moisture, or nutrients can also affect fungal communities and obscure our ability to detect plant effects in single time point studies or within diverse forests. To address this, we sampled replicated monocultures of four tree species and secondary forest controls sampled in the drier and wetter seasons over 2 years. Fungal community composition was primarily related to vegetation type and spatial heterogeneity in the effects of vegetation type, with increasing divergence partly reflecting greater differences in soil pH and soil moisture. Across wetter versus drier dates, fungi were 7% less diverse, but up to four-fold more abundant. The combined effects of tree species and seasonality suggest that predicted losses of tropical tree diversity and intensification of drought have the potential to cascade belowground to affect both diversity and abundance of tropical soil fungi.

Comparisons of allometric and climate-derived estimates of tree coarse root carbon stocks in forests of the United States

BACKGROUND

Refined estimation of carbon (C) stocks within forest ecosystems is a critical component of efforts to reduce greenhouse gas emissions and mitigate the effects of projected climate change through forest C management. Specifically, belowground C stocks are currently estimated in the United States' national greenhouse gas inventory (US NGHGI) using nationally consistent species- and diameter-specific equations applied to individual trees. Recent scientific evidence has pointed to the importance of climate as a driver of belowground C stocks. This study estimates belowground C using current methods applied in the US NGHGI and describes a new approach for merging both allometric models with climate-derived predictions of belowground C stocks.

RESULTS

Climate-adjusted predictions were variable depending on the region and forest type of interest, but represented an increase of 368.87 Tg of belowground C across the US, or a 6.4 % increase when compared to currently-implemented NGHGI estimates. Random forests regressions indicated that aboveground biomass, stand age, and stand origin (i.e., planted versus artificial regeneration) were useful predictors of belowground C stocks. Decreases in belowground C stocks were modeled after projecting mean annual temperatures at various locations throughout the US up to year 2090.

CONCLUSIONS

By combining allometric equations with trends in temperature, we conclude that climate variables can be used to adjust the US NGHGI estimates of belowground C stocks. Such strategies can be used to determine the effects of future global change scenarios within a C accounting framework.

Controlling Factors of Soil CO2 Efflux in Pinus yunnanensis across Different Stand Ages

The characteristics of soil respiration (Rs) across different stand ages have not been well investigated. In this study, we identified temporal variation of Rs and its driving factors under three nature forest stands (e.g. 15-yr-old, 30-yr-old, and 45-yr-old) of Pinus yunnanensis in the Plateau of Mid-Yunnan, China. No consistent tendency was found on the change of Rs with the stand ages. Rs was ranked in the order of 30-yr-old > 45-yr-old >15-yr-old. Rs in 15-yr-old stand was the most sensitive to soil temperature (Ts) among the three sites. However, Ts only explained 30-40% of the seasonal dynamics of Rs at the site. Soil water content (Sw) was the major controlling factor of temporal variation at the three sites. Sw explained 88-93% of seasonal variations of Rs in the 30-yr-old stand, and 63.7-72.7% in the 15-yr-old and 79.1-79.6% in the 45-yr-old stands. In addition, we found that pH, available nitrogen (AN), C/N and total phosphorus (TP) contributed significantly to the seasonal variation of Rs. Sw was significantly related with pH, total nitrogen (TN), AN and TP, suggesting that Sw can affect Rs through improving soil acid-base property and soil texture, and increasing availability of soil nutrient. The results indicated that besides soil water, soil properties (e. g. pH, AN, C/N and TP) were also the important in controlling the temporal variations of Rs across different stand ages in the nature forestry.

Correction: aboveground tree growth varies with belowground carbon allocation in a tropical rainforest environment

[This corrects the article DOI: 10.1371/journal.pone.0100275.].