Soil Carbon Decomposition Research Articles

Effects of application of horticultural soil amendments on decomposition, quantity, stabilisation and quality of soil carbon

Application of organic soil amendments is commonplace in horticulture to improve soil fertility. Whether this practice can also augment the soil carbon (C) pool has been of increasing interest in recent years. We used a controlled field experiment that has received annual applications of six different horticultural soil amendments for seven consecutive years. Each amendment was examined in terms of its contribution to bulk C and the distribution of C between theoretical pools, as defined by physical fractionation. Physical fractionation was combined with 13C nuclear magnetic resonance spectroscopy with cross-polarization and magic angle spinning (CPMAS NMR) analysis. Results indicated that the difference in total C concentration between treatments resulted from an increase in unprotected, free, particulate organic matter (fOM), rather than an increase in soil organic matter being occluded in aggregates or in organo-mineral complexes, and that C persisted in the fOM fraction as a result of accumulation in the alkyl C region. Unlike fresh litter or plant residues, organic amendments have undergone decomposition during the composting process (or during formation in the case of peat), in the absence of mineral soil components. This ex situ decomposition (and possible stabilization through acquired recalcitrance) could reduce the opportunity to become physically or chemically protected through association with the soil mineral phase following addition to soil. Carbon:Nitrogen (C:N) of amendment material likely influenced the rate of amendment decomposition. In addition, C:N determines the decomposition of plant litter inputs, as determined by the tea bag index.

The Grain-for-Green project offsets warming-induced soil organic carbon loss and increases soil carbon stock in Chinese Loess Plateau.

The dynamics of soil organic carbon (SOC) stock is a vital element affecting the climate, and ecological restoration is potentially an effective measure to mitigate climate change by enhancing vegetation and soil carbon stocks and thereby offsetting greenhouse gas emissions. The Grain-for-Green project (GFGP) implemented in Chinese Loess Plateau (LP) since 1999 is one of the largest ecological restoration projects in the world. However, the contributions of ecological restoration and climate change to ecosystem soil carbon sequestration are still unclear. In this study, we improved a soil carbon decomposition framework by optimizing the initial SOC stock based on full spatial simulation of SOC and incorporating the priming effect to investigate the SOC dynamics across the LP GFGP region from 1982 through 2017. Our results indicated that SOC stock in the GFGP region increased by 20.18 Tg C from 1982 through 2017. Most portion (15.83 Tg C) of the SOC increase was accumulated when the GFGP was initiated, with a SOC sink of 16.12 Tg C owing to revegetation restoration and a carbon loss of 0.29 Tg C due to warming during this period. The relationships between SOC and forest canopy height and investigations on the SOC dynamics after afforestation revealed that the accumulation rate of SOC could be as high as 24.68 g C m-2 yr-1 during the 70 years following afforestation, and that SOC could decline thereafter (-8.89 g C m-2 yr-1), which was mainly caused by warming. This study provides a new method for quantifying the contribution of ecological restoration to SOC changes, and also cautions the potential risk of LP SOC loss in the mature forest soil under future warming.

Edge effects increase soil respiration without altering soil carbon stocks in temperate broadleaf forests

AbstractAnthropogenic disturbance has left the world's forests highly fragmented, with a significant proportion of edge‐affected area. Abiotic changes at forest edges are likely to affect forest soil carbon cycling, as higher temperatures and lower moisture availability in edge environments have well‐documented effects on soil respiration. The present study sought to quantify persistent changes in soil carbon cycling in the fragmented broadleaf forests of southeastern Pennsylvania. At three sites with >80‐year‐old forest‐field edges, three 100‐m transects perpendicular to the edge were established. Monthly measurements of soil respiration, temperature, and moisture were made at fixed distances along each transect throughout the growing season. Soil carbon storage from 0 to 20 cm depth, litter biomass, and decomposition rates were also assessed. Soil respiration was significantly higher at forest edges, relative to the interior, and this effect penetrated 60 m into the forest. Significantly elevated surface soil temperature and decreased soil moisture were also observed in edge environments. Despite elevated soil respiration at the edge, soil carbon storage, litter biomass, and decomposition rates were invariant along edge to interior gradients. The temperature responsiveness of soil respiration was significantly higher in the forest interior (100 m), relative to locations ≤60 m from the edge. Edge effects altering elements of the soil carbon cycle were apparent in the forests of southeastern Pennsylvania, and principally manifest as increased soil respiration rates and decreased temperature responsiveness of soil respiration. Lack of variation in soil carbon pools and decomposition rates from the forest edge to interior suggests that increased soil respiration may be related to changes in root and rhizosphere respiration at the edge. These findings contribute to a growing body of evidence documenting increased soil respiration in the edge environments of temperate broadleaf forests. Discounting the alterations imposed by forest fragmentation on carbon cycling has the potential to produce misleading estimates of land–atmosphere CO2 exchange and terrestrial carbon storage.

Nitrogen and phosphorus addition exerted different influences on litter and soil carbon release in a tropical forest

Terrestrial soils release large amount of carbon dioxide (CO2) each year, which are mainly derived from litter and soil carbon (C) decomposition. Nutrient availability, especially nitrogen (N) and phosphorus (P), plays an important role in both litter and soil C decomposition. Therefore, understanding the underlying mechanism is crucial for mitigating CO2 emission and climate changes. Here, we assessed patterns of litter and soil C decomposition after 11 yrs. in-situ N and P addition in a tropical forest where corn leaves or corn roots were added as litter C. The total CO2 efflux was quantified and partitioned using 13C isotope signatures to determine the sources (litter or soil C) every three months. In addition, Changes in C-degrading enzyme activities: β-1,4-glucosidase (BG), phenol oxidase (PHO) and peroxidase (PER), and microbial biomarkers were assessed to interpret the underlying mechanism. Total C-release was enhanced up to17% by the long-term N addition but inhibited up to 15% by P addition. Precisely, N addition only accelerated the litter decomposition and increased about 42% and 6% of the litter C release at 0–5 cm and 5–10 cm soil depths, respectively; while P addition only impeded the soil C decomposition and decreased about 9% and 11% of the soil C release at 0–5 cm and 5–10 cm, respectively. The enhanced C release under N addition might be attributed to the enhanced microbial biomass, the ratio of fungi to bacteria and C-degrading enzyme activities. However, P addition resulted in the reverse result in microbial properties and C-degrading enzyme activities, associated with a decreased C release. Our study suggests that the long-term N and P addition selectively affected the litter and soil C decomposition because of their different physiochemical properties and this tendency might be more pronounced in tropical forests exposed to increasing atmospheric N deposition in the future. The study indicates that the different patterns of litter and soil C decomposition under climate change should be taken account in the future C management strategies.

Anthropogenic warming reduces the carbon accumulation of Tibetan Plateau peatlands

Peatland carbon accumulation generally increased during past intervals of natural warming. With recent anthropogenically-dominated warming being unprecedented over the past ∼2000 years, however, it is unclear how peatland carbon dynamics may operate compared to those under historical natural warmings. Here we examine the impacts of the recent warming from 1850 CE to present (Recent Warm Period; RWP) and the historical warming during 1000–1300 CE (Medieval Warm Period; MWP) on peatland carbon accumulation of the Tibetan Plateau using two continuous peat core records. We observed major seasonal difference between the two warming periods, with growing season (summer) warming dominating the MWP, while greater non-growing season warming characterizing the RWP. Consequently, we found a high net carbon balance during the MWP, suggesting that warming increased plant production more than decomposition of organic matter. In contrast, a low net carbon balance was observed during the RWP because non-growing season warming greatly enhanced soil carbon decomposition that could have completely offset plant carbon uptake. Therefore, recent anthropogenic warming might have induced a different ecosystem response with lower net carbon balance over the past millennium than that during historical natural warmings. As other regions of the globe have similar growing season versus non-growing season warming patterns, the risk of carbon loss from global peatlands may have been underestimated, implying that there is an even greater challenge for managing ecosystem carbon sinks under future climate change.

Drought impacts on microbial trait distribution and feedback to soil carbon cycling

Abstract Quantifying the impact of drought on microbial processes and its consequences for soil carbon cycling is hindered by the lack of underlying mechanistic understanding. Therefore, there is a need to scale up the physiological response to changing water status from individual soil microbes to collective communities across different ecosystems. Here we propose the use of a framework that incorporates trait‐based ecology to link drought‐impacted microbial processes to rates of soil carbon decomposition and stabilisation. We briefly synthesise existing knowledge on the effects of drought on microbial physiology at the individual to community scale, before integrating this understanding within a framework incorporating life‐history strategy, ecological strategy and biochemistry. This framework highlights a dynamic allocation to high yield (Y), resource acquisition (A) and stress tolerance (S) pathways as environmental conditions change. Y‐A‐S strategies represent sets of traits that tend to correlate due to physiological or evolutionary trade‐offs. This framework enables assessment of microbial processes along two key environmental gradients of water and resource availability, both of which are constrained by drought. The variable chemistry of biomass and necromass produced under different physiological strategies in response to drying–rewetting impacts organic matter decomposition and stabilisation in soils, and should also be considered when quantifying soil carbon balance. We highlight that diversion of resources away from microbial growth can alter soil organic matter chemistry and its persistence depending on the kind of microbial compounds produced. To advance such a framework, we highlight avenues of research that would enable the further identification and quantification of traits linked to Y‐A‐S strategies and the physiological outcomes at the community level under drought and rewetting, and conclude by hypothesising how ecosystem‐level changes might feedback on to the soil carbon cycle. A scalable understanding of microbial drought‐response mechanisms affecting soil carbon cycling will transform the way microbial physiology is represented in ecosystem studies. Read the free Plain Language Summary for this article on the Journal blog.

How Physical Disturbance and Nitrogen Addition Affect the Soil Carbon Decomposition?

The decomposition of soil organic carbon (SOC) plays a critical role in regulating atmospheric CO2 concentrations and climate dynamics. However, the mechanisms and factors controlling SOC decomposition are still not fully understood. Here, we conducted a 60 days incubation experiment to test the effects of physical disturbance and nitrogen (N) addition on SOC decomposition. N addition increased the concentration of NO3- by 51% in the soil, but had little effect on the concentration of NH4+. N addition inhibited SOC decomposition, but such an effect differed between disturbed and undisturbed soils. In disturbed and undisturbed soils, application of N decreased SOC decomposition by 37% and 15%, respectively. One possible explanation is that extra N input suppressed microbial N mining and/or increased the stability of soil organic matter by promoting the formation of soil aggregates and incorporating part of the inorganic N into organic matter, and consequently decreased microbial mineralization of soil organic matter. Physical disturbance intensified the inhibition of N on SOC decomposition, likely because physical disturbance allowed the added N to be better exposed to soil microbes and consequently increased the availability of added N. We conclude that physical disturbance and N play important roles in modulating the stability of SOC.

Highly spatial variation of soil microbial respiration and temperature sensitivity in a subtropical forest

Quantifying the spatial variation and drivers of microbe-driven soil carbon (C) decomposition (also called soil microbial respiration, MR) and its temperature sensitivity (Q10) is crucial for reducing the uncertainty in modelling the terrestrial C cycle under global warming. To this end, most previous studies sampled soils from multiple sites at regional scales and incubated them at the same temperature level in the laboratory. However, this unified incubation temperature is too warm to the cold sites, and too cold to the warm sites, thus causing a large bias in the MR and Q10 estimations. Here, we conducted fine scale intensive sampling (194 soil samples) and measurements within a 4-ha subtropical forest plot to examine the underlying mechanisms driving the spatial pattern of MR and Q10. Our results showed that both MR and Q10 varied spatially within subtropical forests. The fine scale variation of MR was dominated by soil nitrogen concentration and slope position, and Q10 was dominated by soil fungi abundance. Overall, the 35 investigated biotic and abiotic factors explained 38% of the spatial variation of MR and 9% of the spatial variation of Q10 in the subtropical forest. This suggests that the fine scale variation of soil C dynamics is much more complex than that at the regional scale reported in previous studies, which should be considered in the assessments of terrestrial soil C cycles.

High stability and metabolic capacity of bacterial community promote the rapid reduction of easily decomposing carbon in soil

Irreversible climate change alters the decomposition and sequestration of soil carbon (C). However, the stability of C components in soils with different initial organic matter contents and its relationship with the response of major decomposers to climate warming are still unclear. In this study, we translocated Mollisols with a gradient of organic matter (OM) contents (2%–9%) from in situ cold region to five warmer climatic regions to simulate climate change. Soil C in C-rich soils (OM >5%) was more vulnerable to translocation warming than that in C-poor soils (OM ≤ 5%), with a major loss of functional groups like O-alkyl, O-aryl C and carboxyl C. Variations of microbial β diversity with latitude, temperature and precipitation indicated that C-rich soils contained more resistant bacterial communities and more sensitive fungal communities than C-poor soils, which led to strong C metabolism and high utilization ability of the community in C-rich soils in response to translocation warming. Our results suggest that the higher sensitivity of soils with high organic matter content to climate change is related to the stability and metabolic capacity of major bacterial decomposers, which is important for predicting soil-climate feedback.

Trade-off between soil aggregate stability and carbon decomposition under 44 years long-term integrated nutrient management in rice-wheat-jute system

ABSTRACT Soil stability, yield decline and higher carbon decomposition are the key issues in intensive agriculture. Long-term integrated nutrient management (INM) influences carbon (C) dynamics and maintains the soil aggregate stability, which driven by the type of cropping system and climatic zone. Therefore, the specific effects of rice-wheat-jute cropping system on soil aggregate distribution, C-stability, and trade-off between C-storage and decomposition rate were studied of a long-term INM trial in the sub-tropical zone. We investigated the effect of four long-term nutrient management practices that include, control, N (nitrogen (N) and no phosphorus (P), and potassium (K)), NPK (N, P and K) and INM (N, P, K + farmyard manure (FYM)). Results showed that the addition of FYM with NPK improved macro-aggregates by 71%, and associated C-pools by 30%. The INM enhanced C-storage (20%), however, the decomposition rate was also higher (28%) over control at 35 °C at field capacity. A trade-off exists between the soil-aggregate stabilization and C-decomposition rate. The proportion of C-storage was higher than decomposition in INM. Further, the C-sequestration varied (0.17 to 0.26 t ha−1 y−1) under different treatments and were found highest in INM, indicating long-term soil stability and yield sustainability in the rice-wheat-jute system.

Optimization of environmental variable functions of GPP quantitative model based on SCE-UA and minimum loss screening method

Environmental variable functions are of key importance for gross primary productivity (GPP) modeling. This study proposes a method about the optimization of environmental variable function to obtain a more robust and accurate GPP quantitative model. The key idea is to explore the impact of environmental factors on the accuracy of the GPP quantitative model from the following three aspects: the first is using tensor as the alternative environmental factor equation to construct the basis-function set of photosynthetically active radiation (PAR), atmospheric temperature and atmospheric carbon dioxide concentration for the given environmental conditions, and soil moisture functions of new environmental conditions. The second is building 144 candidate model based on a tensor product. The third is finding the best model from the candidates according to the Shuffled Complex Evolution (SCE-UA) algorithm and the Minimum Loss Screening Method. Through the above experiments, we have the following conclusions: First, this paper obtains two new best models from 144 candidate models, and their accuracy is higher than that of the initial model, indicating that this paper proposes a more robust and accurate GPP quantitative model. Then, the model proposed in this paper has common characteristics, that is, PAR and atmospheric temperature can be replaced by more appropriate quantitative functions, named Sigmoid-like function and Q10 equation, and the carbon dioxide equation can use half-saturated equation or Sigmoid function. Finally, the method in this paper can provide new ideas for simulating the fluxes of other ecosystems, including soil carbon decomposition and plant respiration.

Alpine meadow degradation enhances the temperature sensitivity of soil carbon decomposition on the Qinghai–Tibetan plateau

Grassland degradation is widespread globally, yet limited information is available on the effects and mechanisms of grassland degradation regarding the response of soil organic carbon (SOC) to temperature change. This is especially true for alpine regions, which can have high SOC storage and are extreme vulnerability to global warming. Here, we studied the temperature sensitivity of SOC decomposition (Q10, proportional change in decomposition rate for a 10 °C difference in temperature) in both the topsoil (0–10 cm depth) and subsoil (20–30 cm) along an alpine meadow degradation gradient on the Qinghai–Tibetan plateau (QTP). Q10 values were increased in response to alpine meadow degradation (severely degraded (2.42) > moderately degraded (2.20) > non-degraded (2.11)) and were higher in subsoil (2.34) than in topsoil (2.14) as a whole. Soil carbon quantity and quality and extracellular enzyme activities all decreased significantly with increasing degradation levels and soil depths. Among all the factors considered (soil texture; soil pH; carbon quantity, availability, and quality; and enzyme activities), Q10 values were found to be primarily mediated by carbon quality and enzyme activities. This result supported the “carbon-quality temperature” hypothesis in degraded alpine grassland, and that considering soil carbon quality and enzyme activity could improve predictions of the feedbacks between soil carbon and global warming under grassland degradation. Our findings suggest that alpine meadow degradation will further increase the losses of SOC in a warming climate, making the ecosystem more vulnerable to climate change.

Trade-off between microbial carbon use efficiency and microbial phosphorus limitation under salinization in a tidal wetland

Sea level rise–induced salinization is projected to influence the decomposition of soil carbon (C) in tidal wetlands. Despite evidence showing that microbial metabolism can determine the fate of soil C decomposition, the response of microbial metabolism to salinization in tidal wetlands remains largely unknown. Microbial metabolism is impacted by the microbial metabolic limitation and carbon use efficiency (CUE), which can provide mechanistic insights into soil C decomposition. Here, we measured microbial metabolic limitation, microbial CUE, and extracellular enzyme activities along an estuarine salinity gradient ranging from freshwater (0.1 ± 0.1 mg g−1) to oligohaline (2.1 ± 0.5 mg g−1) in a tidal wetland. Overall, microorganisms were limited by phosphorus (P) in the tidal wetlands, where salinization increased microbial P limitation by 34%. The enhanced microbial P limitation was attributed to increases in soil C:P and belowground biomass, as well as decreases in root C:P with increasing salinity. Microbial CUE decreased from 0.38 to 0.33 as salinity increased, while microbial P limitation was negatively correlated with microbial CUE, representing the trade-off between the two. Furthermore, microbial P limitation was positively associated with C-, nitrogen (N)-, and P-acquiring extracellular enzyme activities, while all these enzyme activities were negatively correlated with microbial CUE. These results illustrate that to balance microbial P limitation with salinization, microorganisms transfer more energy from the microbial CUE to extracellular enzyme production, and this was the mechanism underlying the trade-off. Microorganisms were also limited by C in the tidal wetlands. However, as the increasing belowground biomass alleviated microbial C limitation with salinization, no relationship was observed between microbial C limitation and CUE. Future C and nutrient models aimed to simulate tidal wetland ecosystem responses to salinization will benefit from the inclusion of trade-off between microbial CUE and microbial P limitation for more accurate prediction.

Mycorrhizal effects on decomposition and soil CO2 flux depend on changes in nitrogen availability during forest succession

Abstract Mycorrhizal fungi play a central role in plant nutrition and nutrient cycling, yet our understanding on their effects on free‐living microbes, soil carbon (C) decomposition and soil CO2 fluxes remains limited. Here we used trenches lined with mesh screens of varying sizes to isolate mycorrhizal hyphal effects on soil C dynamics in subtropical successional forests. We found that the presence of mycorrhizal hyphae suppressed soil CO2 fluxes by 17% in early‐successional forests, but enhanced CO2 losses by 20% and 32% in mid‐ and late‐successional forests respectively. The inhibitory effects of mycorrhizal fungi on soil CO2 fluxes in the young stands were associated with changes in soil nitrogen (N) mineralization and microbial activities, suggesting that competition between mycorrhizae and saprotrophs for N likely suppressed soil C decomposition. In the mid‐ and late‐successional stands, mycorrhizal enhancement of CO2 release from soil likely resulted from both hyphal respiration and mycorrhizal‐induced acceleration of organic matter decay. Synthesis. Our results highlight the sensitivity of mycorrhizal fungi‐saprotroph interactions to shifts in nutrient availability and demand, with important consequences for soil carbon dynamics particularly in ecosystems with low nutrient conditions. Incorporating such interactions into models should improve the simulations of forest biogeochemical cycles under global change.

Carbon isotopic measurements from coastal zone protected forests in northern China: Soil carbon decomposition assessment and its influencing factors

Panting protected forests to increase soil carbon sequestration is an effective means of reducing carbon emissions. Soil organic carbon (SOC) decomposition is one of the main indicators of soil carbon sequestration. However, SOC decomposition and its influencing factors in protected forests have not been fully characterized, especially in coastal zones. In this paper, coastal zone protected forest stands composed of Quercus acutissima Carruth (QAC), Pinus thunbergii Parl (PTP) and mixed PTP and QAC (MF) were selected as the research objects. The trends of the SOC decomposition rate were characterized by the beta (β) value, and the influencing factors were further explored with structural equation models. The results were as follows: The SOC content decreased from leaf to litter and then to the soil profile at all sites, while the δ13C value increased. The β value ranged from −3.12 to −5.76, with an average of −3.81. The β value was positively correlated with the diversity and richness of soil bacteria, supporting the hypothesis that the increase in δ13C with depth was mainly caused by isotope fractionation in the process of microbial SOC decomposition. The structural equation model showed that nitrogen and the availability of nitrogen have a strong ability to explain the value of β, which indicates that nitrogen-based edaphic variables play an important role in affecting SOC decomposition. The SOC decomposition rate in PTP was higher than that in QAC and MF. The results of this study indicate that the prediction of SOC decomposition based on the β value is suitable for coastal zone protected forests. The incorporation of edaphic variables into global carbon cycle models may enhance the predictions of SOC dynamics in coastal zone protected forests.

Tundra Underlain By Thawing Permafrost Persistently Emits Carbon to the Atmosphere Over 15 Years of Measurements

AbstractWarming of the Arctic can stimulate microbial decomposition and release of permafrost soil carbon (C) as greenhouse gases, and thus has the potential to influence climate change. At the same time, plant growth can be stimulated and offset C release. This study presents a 15‐year time series comprising chamber and eddy covariance measurements of net ecosystem C exchange in a tundra ecosystem in Alaska where permafrost has been degrading due to regional warming. The site was a carbon dioxide source to the atmosphere with a cumulative total loss of 781.6 g C m−2 over the study period. Both gross primary productivity (GPP) and ecosystem respiration (Reco) were already likely higher than historical levels such that increases in Reco losses overwhelmed GPP gains in most years. This shift to a net C source to the atmosphere likely started in the early 1990s when permafrost was observed to warm and thaw at the site. Shifts in the plant community occur more slowly and are likely to constrain future GPP increases as compared to more rapid shifts in the microbial community that contribute to increased Reco. Observed rates suggest that cumulative net soil C loss of 4.18–10.00 kg C m−2—8%–20% of the current active layer soil C pool—could occur from 2020 to the end of the century. This amount of permafrost C loss to the atmosphere represents a significant accelerating feedback to climate change if it were to occur at a similar magnitude across the permafrost region.

A Comparison of Linear Conventional and Nonlinear Microbial Models for Simulating Pulse Dynamics of Soil Heterotrophic Respiration in a Semi‐Arid Grassland

AbstractAs a critical process in regulating terrestrial feedback to climate change, soil heterotrophic respiration is commonly simulated with the first‐order kinetics in current Earth system models. Compared with the first‐order kinetic models, explicit microbial models are expected to better simulate nonlinear carbon (C)‐cycle phenomena, such as the pulse dynamics of soil heterotrophic respiration driven by dry‐rewetting cycles in grasslands. However, these two types of models (i.e., linear conventional and nonlinear microbial models) have never been compared based on in situ observations of soil heterotrophic respiration in the semi‐arid grassland, which is significantly affected by the dry‐rewetting events. Here, based on the field data of soil heterotrophic respiration in a semi‐arid grassland in northern China, we first showed that the shift from a conventional linear model to a nonlinear microbial model did not substantially improve the simulation of soil heterotrophic respiration. Then, we quantified the contributions of different moisture‐response functions to the uncertainty in simulating the soil C dynamics. The results showed that the selection of moisture‐response functions combined with parameterization in the soil C models dominated the modeled uncertainties in soil heterotrophic respiration. These findings suggest that both the conventional linear model and nonlinear microbial model can simulate well the pulse dynamic of soil heterotrophic respiration in grasslands with an improved parameterization of water regulation on soil carbon decomposition. This study also calls for more observations of nonlinear C phenomena for reducing the simulation uncertainty on soil C cycling in Earth system models.

Microbial Activity and Root Carbon Inputs Are More Important than Soil Carbon Diffusion in Simulating Soil Carbon Profiles

AbstractIt is well‐known that soil carbon composition and turnover rate vary with soil depth, and the responses of soil carbon to global change in deeper soil layers may differ from those near the surface. Therefore, vertically resolved soil carbon models are needed for accurately predicting future soil carbon under global warming. In this study, we developed a vertically resolved soil carbon model by including vertical transport of soil carbon and using Michaelis‐Menten kinetics for soil carbon decomposition by microbes. The model was calibrated against six sites with the observed profiles of both soil carbon concentration and 14C measurements, and against 91 forest sites with soil carbon concentrations across a wide range of climate and soil conditions for four forest types in Europe and China. Results of independent model validation at another 93 sites showed that the calibrated model explained 40%–94% of the observed variance of soil carbon concentrations at different depths. Model sensitivity analysis showed that microbial activity and root carbon inputs are more important than soil carbon diffusion in simulating soil carbon profile. Results from our study highlight the need for detailed measurements of soil microbial activities and root carbon input at different soil depths in the field.

Coastal reclamation alters soil microbial communities following different land use patterns in the Eastern coastal zone of China

Coastal reclamation seriously disturbs coastal wetland ecosystems, while its influences on soil microbial communities remain unclear. In this study, we examined the impacts of coastal reclamation on soil microbial communities based on phospholipid fatty acids (PLFA) analysis following the conversion of Phragmites australis wetlands to different land use types. Coastal reclamation enhanced total soil microbial biomass and various species (i.e., gram-positive bacterial, actinomycete, saturated straight-chain, and branched PLFA) following the conversion of P. australis wetland to aquaculture pond, wheat, and oilseed rape fields. In contrast, it greatly decreased total soil microbial biomass and various species following the conversion of P. australis wetland to town construction land. Coastal reclamation reduced fungal:bacterial PLFA, monounsaturated:branched PLFA ratios, whereas increasing gram-positive:gram-negative PLFA ratio following the conversion of P. australis wetland to other land use types. Our study suggested that coastal reclamation shifted soil microbial communities by altering microbial biomass and community composition. These changes were driven primarily by variations in soil nutrient substrates and physiochemical properties. Changes in soil microbial communities following coastal reclamation impacted the decomposition and accumulation of soil carbon and nitrogen, with potential modification of carbon and nitrogen sinks in the ecosystems, with potential feedbacks in response to climate change.

Hydraulic lift: processes, methods, and practical implications for society

Soil water is an essential factor in soil–water–plant studies and larger-scale hydrological investigations. It is considered more critical than other factors that limit plant growth and also affects many fundamental biophysical processes. New strategies are needed to overcome drought and to maintain environmental sustainability. Hydraulic lift (HL) or hydraulic redistribution (HR) processes are one of these strategies found in soil–plant systems, but their effects on crop production and the environment have not been well documented. This article reviews (1) the process of HL, (2) methods showing evidence of HL using soil water potential (Ψs) and sap flow techniques, (3) hydraulically-lifting plants, and (4) practical implications for society. The HL is whereby soil water may be transported upward by deep roots of trees and grasses from the moist region (subsurface) to dry region (surface) at night. Thus, HL provides water to areas planted to shallow rooted plants at the upper soil layers. The HL of water by roots from wet to dry soil layers is a potential approach for better use of water resources for crop/grass growth. Also, increases in soil water by HL improve root growth and function which include soil carbon decomposition or nutrient mineralization rates, and this can probably be associated in nutrient cycling. Another benefit is that mycorrhizal fungi play a relevant role in HL and in the redistribution of this water among plants. Thus, HL provides many soil, agricultural, and environmental benefits.