Soil Carbon Pools Research Articles

Warming promotes accumulation of microbial- and plant-derived carbon in terrestrial ecosystems

The impact of global warming on soil carbon pools has been extensively investigated, however, there is still a lack of understanding regarding the specific response of microbial- and plant-derived carbon to warming. To address this knowledge gap, we conducted a comprehensive meta-analysis of 142 studies and evaluated 986 observations comparisons of different carbon source responses to warming. Our results revealed several key insights. Firstly, climate warming resulted in an average increase of 5.46 % in the terrestrial soil carbon pool. Specifically, microbial-derived carbon showed an average increase of 6.32 %, while plant-derived carbon exhibited an average increase of 3.70 %. Secondly, while warming duration and magnitude do not significantly affect the response of microbial-derived carbon to warming, they did impact the response of plant-derived carbon. Lastly, we observed that the response of different carbon sources to warming was affected by the specific environmental backgrounds:ecosystem and climatic zone types affect the response of warming to microbial-derived carbon, while differences in climatic region affect response of warming to plant-derived carbon. The variations in the response of different soil carbon sources to warming can be attributed to the nature of the carbon source themselves, as well as the complex transformations that occur between them through microbial metabolic processes and their interactions with soil mineral particles. We suggest that interactions at the soil-plant-microbe interface should be considered more carefully, and the response of ecosystems to warming should be observed from the perspective of soil organic carbon sources, so as to better understand the response of terrestrial ecosystems carbon cycle to global warming.

Soil carbon pools and fluxes following the regreening of a mining and smelting degraded landscape

Increasing forest cover by regreening mining and smelting degraded landscapes provides an opportunity for global carbon (C) sequestration, however, the reported effects of regreening on soil C processes are mixed. One of the world's largest regreening programs is in the City of Greater Sudbury, Canada and has been ongoing since 1978. Prior to regreening, soils in the City of Greater Sudbury area were highly eroded, acidic, rich in metals, and poor in nutrients. This study used a chronosequence approach to investigate how forest soil C pools and fluxes have changed with stand age in highly “eroded” sites with minimal soil cover (n = 6) and “stable” sites covered by soil (n = 6). Encouragingly, the relationship between stand age and soil C processes (litterfall, litter decomposition, soil respiration, fine root growth) at both stable and eroded sites were comparable to observations reported for jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Ait.) plantations that have not been subject to over a century of industrial impacts. There was a strong “home-field advantage” for local decomposers, where litter decomposition rates were higher using a site-specific pine litter compared with a common pine litter. Higher soil respiration at eroded sites was linked to higher soil temperature, likely because of a more open tree canopy. Forest floor C pools increased with stand age while mineral soil C and aggregate C concentrations decreased with stand age. This loss of soil C is small relative to the substantial increases in aboveground tree and forest floor C pools, leading to a sizeable increase in total ecosystem C pools following regreening.

Biochemical Investigations of Five Recombinantly Expressed Tyrosinases Reveal Two Novel Mechanisms Impacting Carbon Storage in Wetland Ecosystems.

Wetlands are globally distributed ecosystems characterized by predominantly anoxic soils, resulting from water-logging. Over the past millennia, low decomposition rates of organic matter led to the accumulation of 20-30% of the world's soil carbon pool in wetlands. Phenolic compounds are critically involved in stabilizing wetland carbon stores as they act as broad-scale inhibitors of hydrolytic enzymes. Tyrosinases are oxidoreductases capable of removing phenolic compounds in the presence of O2 by oxidizing them to the corresponding o-quinones. Herein, kinetic investigations (kcat and Km values) reveal that low-molecular-weight phenolic compounds naturally present within wetland ecosystems (including monophenols, diphenols, triphenols, and flavonoids) are accepted by five recombinantly expressed wetland tyrosinases (TYRs) as substrates. Investigations of the interactions between TYRs and wetland phenolics reveal two novel mechanisms that describe the global impact of TYRs on the wetland carbon cycle. First, it is shown that o-quinones (produced by TYRs from low-molecular-weight phenolic substrates) are capable of directly inactivating hydrolytic enzymes. Second, it is reported that o-quinones can interact with high-molecular-weight phenolic polymers (which inhibit hydrolytic enzymes) and remove them through precipitation. The balance between these two mechanisms will profoundly affect the fate of wetland carbon stocks, particularly in the wake of climate change.

Microbial pathways driving stable soil organic carbon change in abandoned Moso bamboo forests in southeast China

Mineral-associated organic carbon (MOC) is a stable component of the soil carbon (C) pool, critical to realize carbon sequestration and coping with climate change. Many Moso bamboo (Phyllostachys edulis) forests in subtropical and tropical areas that used to be intensively managed have been left unmanaged. Still, studies on MOC changes occurring during the transition from intensive management to unmanagement are lacking. Besides, the understanding of the role of microorganisms in MOC accumulation is far from satisfactory. Based on the combination of field investigation and laboratory analysis of 40 Moso bamboo forest sampling plots with different unmanaged chronosequence's in southeast China, we observed the MOC content in Moso bamboo forests left unmanaged for 2–5 years had decreased, whereas that in forests left unmanaged for 11–14 years had increased compared with that in intensively managed forests. Specifically, the MOC contents in forests left unmanaged for 11–14 years were significantly higher than in those under intensive management or unmanaged for 2–5 years. Moreover, we found that microorganisms drove MOC change through two different pathways: (i) more microorganisms led to more soil nutrients, which led to more amino sugars, ultimately resulting in the accumulation of MOC, and (ii) microorganisms promoted the accumulation of MOC by influencing the content of metal oxides (poorly crystalline aluminum oxides and free aluminum oxides). We believe that ignoring the interaction between microorganisms and metal oxides may lead to uncertainty in evaluating the relative contribution of microbial residues to MOC.

Global patterns and controls of soil greenhouse gas fluxes and crop yield under biochar application

AbstractBiochar application has been proven to be a viable technique in mitigating soil greenhouse gas (GHG) emissions and improving crop yield; however, the global patterns and responses of soil GHG fluxes, global warming potential (GWP), crop yield, and greenhouse gas intensity (GHGI) to biochar application, as well as the key drivers of biochar‐induced changes, are not fully synthesized. Hence, we conducted a meta‐analysis of 3883 paired observations from 220 studies. Overall, biochar application significantly increased carbon dioxide (CO2) emissions (7.4%) and yield (9.4%) and decreased soil methane (CH4, −13.0%) and nitrous oxide (N2O, −26.8%) emissions, as well as GWP (−7.7%) and GHGI (−14.3%). CH4 uptake was, however, not observed to change. The responses of soil GHG fluxes to the biochar application were more sensitive in the incubation and pot experiments compared to the field studies. In addition, increased CO2 emissions were mainly derived from incubation and pot experiments, whereas the biochar application did not significantly change CO2 emissions in the field studies. The climate, soil, and experimental conditions also affected the responses of soil GHG fluxes to biochar application, and the biochar‐induced change in soil pH was the most essential factor associated with the variations in soil GHG fluxes. Globally, biochar application boosted the soil carbon (C) pool (38.1% in upland and 33.4% in paddy) and decreased soil GHGI (−18.7% in upland and −14.5% in paddy). Our study highlights the role of the reduced CH4 and N2O emissions in the biochar‐induced mitigation of soil GHG emissions while exploring the relative importance of the influencing factors and providing crucial insights for the development of individualized biochar management measures.

Variations in Microbial Residue and Its Contribution to SOC between Organic and Mineral Soil Layers along an Altitude Gradient in the Wuyi Mountains

Microbes are crucial components of soil, and their residue carbon plays a significant role in the formation and stabilization of soil carbon pools. However, current research on microbial residue carbon has predominantly focused on surface soils, with limited studies on deep soils. The patterns of variation along soil profiles and their controlling factors remain unclear. Therefore, this study aimed to investigate the soils from different elevations in the Wuyi Mountains, specifically focusing on the organic layers (0–10 cm) and mineral layers (30–40 cm). Amino sugars were utilized as biomarkers for the microbial residue, and the RDA (redundancy analysis) method was employed to analyze the patterns of microbial residue carbon in different soil layers and to identify the factors that control them. The results indicate that there are significant differences in the microbial residue carbon content and its contribution to soil organic carbon (SOC) between the different soil layers. Specifically, between the organic layer and the mineral layer, the microbial residue carbon content exhibited an increasing trend, whereas its contribution to SOC decreased. This finding suggests that soil layer type has a notable impact on microbial residue carbon content and its contribution to SOC. Moreover, fungal residue carbon content was found to be higher than bacterial residue carbon content in both soil layers. However, the ratio of fungal residue carbon to bacterial residue carbon gradually decreased between the organic layer and the mineral layer. This implies that although fungal residue carbon remains dominant, the contribution of bacterial residue carbon to the soil carbon pool increases as the soil transitions to the mineral layer. The total soil carbon content, elevation, and C/N ratio exhibited positive correlations with fungal and bacterial residue carbon, indicating their significant roles in the accumulation of microbial residue carbon in soils. Notably, elevation emerged as a key regulating factor in the accumulation of microbial residue carbon, explaining 85.8% and 67.9% of the variations observed in the organic layer and the mineral layer respectively. These research findings contribute to a better understanding of the soil carbon cycling process and its mechanisms, providing a scientific basis for developing strategies to enhance soil carbon sequestration by manipulating micro-organisms.

Assessment of carbon loss related to Soil loss in the tropical watershed of Maharashtra, India

Soil carbon pools have a significant impact on the global carbon cycle and soil erosion caused by natural or human activities is one of the main drivers of changes in soil carbon sequestration. The present study aimed to estimate the carbon loss associated with soil loss in the watershed using remote sensing and GIS techniques. The study was carried out at the Central MPKV Campus Watershed, Rahuri, located in the rain shadow region of the Maharashtra state, India. The soil loss from the watershed was estimated using USLE model. The soil loss and carbon loss from the watershed were estimated before the implementation of conservation measures and after the implementation of conservation measures. It was found that the average annual soil loss from the watershed before and after conservation measures was 18.68 t/ha/yr and 9.41 t/ha/yr, respectively. Carbon loss was determined by soil loss rate, organic carbon content and the carbon enrichment ratio. The carbon loss from the watershed before and after conservation measures was 348.71 kgC/ha/yr and 205.52 kgC/ha/yr. The findings revealed that soil and carbon erosion was very severe on steep slopes without conservation measures and with limited vegetation cover. It was found that by reducing the carbon loss associated with soil loss, soil conservation measures not only aid in the conservation of natural resources but also serve as a climate change mitigation measure.

Greater mineral and aggregate protection for organic carbon in the soil amended by weathered coal than by biochar: Based on a 3-year field experiment

Soil carbon pool stability plays an important role in reaching carbon neutrality and mitigating global warming. Applying soil amendments is a practical strategy in agricultural production to improve soil environment. Weathered coal (WC) is an organic amendment that can be used to improve soil quality. However, the effects of WC application on soil organic carbon pool stability, and its differences from the effects of biochar (BC, a common amendment) application remains unclear. In this study, BC was selected as a comparison to further evaluate the potential of WC based on a 3-year field experiment, in which WC and BC were individually applied into a loamy clay soil at 0%, 1%, and 3% (w/w) rates. Soil organic carbon and its fractions (including particulate organic carbon and mineral-bound organic carbon), soil aggregate fractions and its stability, and the organic carbon content in aggregates were examined. The results showed that both WC and BC significantly increased soil total organic carbon, particulate and mineral-bound organic carbon (P < 0.05). The mineral-bound organic carbon content in WC treatment was significantly higher than that in BC treatment (by 32% under the 3% rate) (P < 0.05), whereas, there were no significant differences in soil total organic carbon content. Both WC and BC increased the soil organic carbon content in all aggregate fractions. While only the WC improved the soil aggregate stability, and which was 15% (under 1% rate) and 28% (under 3% rate) higher in WC treatments than in BC treatments (P < 0.05). The proportion of mineral-bound organic carbon to soil total organic carbon content and the soil aggregate stability were obviously related the soil C/N, and the WC treatments had a higher proportion of mineral-bound organic carbon and soil aggregate stability than BC treatments under the same soil C/N. The results indicated that the application of WC may be more effective than BC in increasing mineral and aggregate protection for soil organic carbon and thus improving soil carbon pool stability. Additionally, the purchase cost of WC was clearly lower than that of BC. Combined with the low cost and the benefits in soil structure and carbon pool stability, the application of WC appeared to have advantages over BC. Our findings provide robust evidence that WC is more effective than BC in improving soil carbon pool stability.

Improving food security and farmland carbon sequestration in China through enhanced rock weathering: Field evidence and potential assessment in different humid regions

Enhanced rock weathering (ERW) in farmland is an emerging carbon dioxide removal technology with crushed silicate rocks for soil improvement. However, due to climatic variability and field data limitations, uncertainties remain regarding the influence of ERW on food security and soil carbon pools in temperate regions. This study focused to evaluate the crop productivity and carbon sequestration potential of farmland ERW in China by conducting field monitoring in different humid regions and ERW performance model. Additionally, the contribution of climate, soil, and management factors to ERW-mediated yield and carbon sequestration changes was explored using random forest and correlation networks. Field monitoring indicated that farmland ERW significantly improved crop yield in humid region (13.5 ± 5.2 %), along with notable improvements in soil pH and available nutrients. Precipitation (10.4–16.7 %) and soil pH (9.7–16.8 %) had the highest contribution on ERW mediated yield and carbon sequestration changes, but the contribution of management factors (24–26.2 %), especially N input (2.7–7.0 %), should not be disregarded. The model evaluation demonstrated that the carbon sequestration rate of farmland ERW in China can reach 0.28–0.40 Gt yr−1, thereby presenting an opportunity to expand and accelerate the nationally determined contributions of China. The mean sequestration cost of farmland ERW was 633 ± 161 CNY ¥ t-CO2−1, which was an attractive sequestration price considering the positive benefits of rock powder on soil pH and nutrients. Deploying ERW in acidified and mineral nutrient deficient regions was able to serve as an alternative to lime and part chemical fertilizers to improve yield and maximize agricultural sustainability and resource co-benefits. Farmland ERW also has the potential to resource silicate waste to assist traditional, difficult-to-decarbonize industries to reduce carbon emissions. As a result, a comprehensive assessment of existing artificial silicate waste materials could further expand the application of farmland ERW.

Soil Carbon Stock and Carbon Pool Indices under Major Land Use Systems of Mayiladuthurai District, Cauvery Delta Zone, India

Background- Soil organic carbon serves as potential indicator of the soil quality which is influenced by the changes in management practices. The conversion of natural ecosystem by anthropogenic activities resulted in decline of SOC. So, this study was conducted to assess the carbon indices and understand the dynamics to develop the management strategies for enhancing the C pool in the soil. Methods- The present study was conducted in major land use systems of Mayiladuthurai district of Cauvery delta zone in Tamil Nadu. Soil samples were collected by stratified random sampling at two different depths and estimated for soil carbon indices. Result- The SOC, C stock, bulk density, microbial biomass carbon, dehydrogenase, carbon management index of the study area varied with the mean value of 12.51 Mg ha-1, 10.57 t ha-1, 1.26 Mgm-3, 302.52 µg kg-1, 38.21 µg TPF g-1 day-1and 126.91 % respectively. C stock were in the order of forestry greater than rice-pulses greater than rice-cotton greater than sugarcane greater than uncultivated among the different land uses of the study area. The difference in vegetation, litterfall, soil chemistry, microbial activity, substrate, root exudate, root biomass and root turnover influenced the variation in carbon pool under different land uses of the study area.

Response of active layer thickening to wildfire in the pan-Arctic region: Permafrost type and vegetation type influences

Northern high-latitude permafrost holds the largest soil carbon pool in the world. Understanding the responses of permafrost to wildfire is crucial for improving our ability to predict permafrost degradation and further carbon emissions. Recently, studies have demonstrated that wildfires in the pan-Arctic region induced the thickening of the active layer based on site or fire event observations. However, how this induced thickening is influenced by vegetation and permafrost types remains not fully understood due to the lack of wall-to-wall analysis. Therefore, this study employed remotely sensed fire data and modelled active layer thickness (ALT) to identify the fire-induced ALT change (ΔALT) for the pan-Arctic region, and the contributions of vegetation and permafrost were quantified using the random forest (RF) model. Our results showed that the average ΔALT and the sensitivity of ΔALT to burn severity both increased with decreasing ground ice content in permafrost. The largest values were detected in thick permafrost with low ground ice content. Regarding vegetation, the average and sensitivity of ΔALT in tundra were highest, followed by those in forest and shrub. When the individual environmental factors were all taken into account, the results showed that the contribution of vegetation types was much higher than that of permafrost types (20.2 % vs. 3.5 %). Our findings highlighted the importance of environmental factors in regulating the responses of permafrost to fire.

Thirty years of increased precipitation modifies soil organic matter fractions but not bulk soil carbon and nitrogen in a mesic grassland

Grassland ecosystems, which are known to be sensitive to climate change, have shown minimal responses of soil carbon (C) and nitrogen (N) pools to increased moisture availability, despite moisture-induced changes in plants and soil microbes (e.g., expected drivers of soil C and N). However, it is not clear if this apparent limited response is due to an unresponsive belowground system or because alterations in multiple soil organic matter (SOM) component pools and fluxes offset each other. To investigate potential responses of C and N in SOM to decadal increases in precipitation, we sampled soils from a 30-year precipitation augmentation experiment in an annually burned mesic grassland. We measured C and N in three SOM fractions which vary in their plant and microbial controls 1) free particulate OM (fPOM), 2) occluded POM plus heavy, coarse OM (oPOM + hcOM), and 3) mineral-associated OM (MAOM), as well as amino sugars, pyrogenic C and N, and root quality metrics. We found no changes in bulk C or N under increased precipitation, but SOM fractions were modified. Altered plant inputs and soil N availability appeared to drive the responses of fPOM N and oPOM + hcOM C:N, which were increased and decreased, respectively, by increased precipitation. In contrast, the observed increase in MAOM C and N under increased precipitation could not be connected to a specific driver, suggesting additional plant, microbial, or mineral measurements may be required. Regardless, our results indicate that investigating SOM fractions may more directly connect soil C and N pools and their drivers, compared to measuring only bulk SOM. Further, our finding of greater stable OM (MAOM) under increased precipitation suggests soil C storage could provide a negative feedback to climate change with increased moisture availability, but the lack of bulk SOM response suggests that this feedback is not strong in mesic grasslands.

Forest management practices change topsoil carbon pools and their stability

Forest management may lead to changes in soil carbon and its stability, and the effects are variable owing to the differences in management methods. Our study aimed to determine the impacts of different forest management practices on soil carbon pools and their stability. We chose a natural oak forest, where different forest-management strategies have been practiced. Forest management strategies included cultivating target trees by removing interference trees (CNFM), optimizing the forest spatial structure by the structural parameters (SBFM), reducing the stand density by harvesting timber (SFCS), and using unmanaged forests as controls (NT). Topsoil (depth of 0–10 cm) was collected after eight years of forest management. Soil organic carbon (SOC), labile organic carbon components and the microbial community were determined, and SOC chemical compositions were assessed by nuclear magnetic resonance. The CNFM and SFCS strategies had smaller dissolved organic carbon contents than the NT and SBFM strategies, and the CNFM strategy increased the ratio of alkyl C and o-alkyl C, indicating that the SOC was more stable. Forest management strategies changed the SOC and its labile C pool by adjusting the soil total nitrogen,β-glucosidase, cellobiohydrolase, fine-root carbon and fungal operational taxonomic units, and the SOC chemical compositions were influenced by the number of fungal species. These findings suggest that the soil organic carbon decreased, but its stability increased in the natural forest under the practice of cultivating target trees by removing interference trees. The SOC pools could be regulated by soil nitrogen, enzyme activity, fine roots, and fungi, while soil fungi could affect SOC stability.

Effects of gravel on the evaluation of soil organic carbon density in Pinus massoniana plantations.

Gravel (>2 mm) is one of the main parameters for estimating soil carbon pool. To assess the effects of gravel on soil bulk density (BD) and organic carbon density (SOCD) in Pinus massoniana plantations, we estimated the BD and SOCD at the 0-10, 10-20 and 20-40 cm soil depths of 131 plots under two different conditions, with and without removing gravel. The BD of each soil layer after removing gravel was 0.58-1.57, 0.60-1.67, and 0.59-1.75 g·cm-3, respectively, which was significantly lower than that before removing gravel. Gravel increased the BD by 6.5%-6.8%. The SOCD of each soil layer before removing gravel was 8.93-65.97, 7.63-59.08, and 8.79-94.53 t·hm-2, respectively, which was higher than that after removing gravel. Overall, by neglecting the effect of gravel, SOCD was overestimated by 4.9%-11.8%. As gravel content increased, the relative deviation in the estimated BD and SOCD among different methods increased. When the gravel content was higher than 20%, the estimated SOCD at soil layer of 0-40 cm showed a significant difference between neglecting gravel and removing gravel, with the former being 29.7%-47.4% higher than the latter. In conclusion, gravel markedly affected the estimations of BD and SOCD. It was recommended that SOCD should be estimated by the method that not only uses the BD after removing gravel but also considers gravel as a correction factor (especially when gravel content is above 20.0%) to avoid overestimation of soil carbon pool.

Forest productivity recovery or collapse? Model-data integration insights on drought-induced tipping points.

More frequent and severe droughts are driving increased forest mortality around the globe. We urgently need to describe and predict how drought affects forest carbon cycling and identify thresholds of environmental stress that trigger ecosystem collapse. Quantifying the effects of drought at an ecosystem level is complex because dynamic climate-plant relationships can cause rapid and/or prolonged shifts in carbon balance. We employ the CARbon DAta MOdel fraMework (CARDAMOM) to investigate legacy effects of drought on forest carbon pools and fluxes. Our Bayesian model-data fusion approach uses tower observed meteorological forcing and carbon fluxes to determine the response and sensitivity of aboveground and belowground ecological processes associated with the 2012-2015 California drought. Our study area is a mid-montane mixed conifer forest in the Southern Sierras. CARDAMOM constrained with gross primary productivity (GPP) estimates covering 2011-2017 show a ~75% reduction in GPP, compared to negligible GPP change when constrained with 2011 only. Precipitation across 2012-2015 was 45% (474 mm) lower than the historical average and drove a cascading depletion in soil moisture and carbon pools (foliar, labile, roots, and litter). Adding 157 mm during an especially stressful year (2014, annual rainfall = 293 mm) led to a smaller depletion of water and carbon pools, steering the ecosystem away from a state of GPP tipping-point collapse to recovery. We present novel process-driven insights that demonstrate the sensitivity of GPP collapse to ecosystem foliar carbon and soil moisture states-showing that the full extent of GPP response takes several years to arise. Thus, long-term changes in soil moisture and carbon pools can provide a mechanistic link between drought and forest mortality. Our study provides an example for how key precipitation threshold ranges can influence forest productivity, making them useful for monitoring and predicting forest mortality events.

Mangrove carbon budgets suggest the estimation of net production and carbon burial by quantifying litterfall

Soil carbon burial is the major process enabling mangroves to function as carbon sinks. However, the amount of deposited materials derived from allochthonous or autochthonous inputs in the soil carbon pool of mangroves remains uncertain. Mangrove-derived carbon burial is often laboriously estimated by monitoring the production and decomposition. In this study, ten carbon budgets covering different habitat features were constructed in situ for two mangrove species (Kandelia obovata and Avicennia marina) with distinct root structures. The mangrove-derived carbon burial rate was 0.25–1.55 Mg C ha−1 yr−1 for K. obovata and 0.36–1.00 Mg C ha−1 yr−1 for A. marina. Combined with other studies, there were positive and linear correlations between the carbon burial rate and litterfall production for the two mangroves, which suggests that the carbon burial rate for K. obovata and A. marina can be estimated using 14.8 % and 10.9 % of the litterfall production rate, respectively. The results of dbRDA with DistLM models further showed that wind speed and precipitation were the main factors affecting carbon burial in K. obovata and A. marina mangroves.

Nutrient management impacts on organic carbon pool in soils under different cropping systems in the Indo-Gangetic Plains in South Asia

Nutrient management impacts on organic carbon pool in soils under different cropping systems in the Indo-Gangetic Plains in South Asia

Biochar-based fertilizer under drip irrigation: More conducive to improving soil carbon pool and promoting nitrogen utilization

In order to explore a resource-saving and environmentally friendly approach to reduce nitrogen fertilizer and increase soil carbon pool in crop production. There are 5 treatments in the experiment namely CK: conventional fertilization and irrigation methods (pure nitrogen 30 kg/hm2); T1: drip irrigation fertilization method (pure nitrogen 15 kg/hm2); T2: drip irrigation fertilization method (pure nitrogen 15 kg /hm2), biochar-based fertilizer 600 kg/hm2; T3: drip irrigation method (pure nitrogen 15 kg/hm2), biochar-based fertilizer 1200 kg/hm2; T4: drip irrigation method (pure nitrogen 15 kg/hm2), biochar-based fertilizer is 1800 kg/hm2. The results showed that the microbial carbon content of the biochar-based fertilizer treatment under the condition of drip irrigation to reduce nitrogen was increased by 39.9%-68.4% as compared with the control. All treatments of the biochar-based fertilizer can significantly increase the soil easily oxidizable carbon in the early and mid-term growth. The content of solid carbon and soluble organic carbon increased by 31.3%-148.31% and 12.2%-63.92%, respectively. The application of biochar-based fertilizers significantly increased the net photosynthetic rate and stomatal conductance in the early and mid-transplanting period, as well as the transpiration rate and intercellular CO2 concentration throughout the growth period, and the SPAD, NDVI value, and dry matter accumulation. Under the condition of reducing nitrogen by 50%, drip irrigation combined with biochar-based fertilizer can significantly increase the soil microbial biomass carbon content, oxidizable carbon and soluble carbon content, promote the photosynthetic effect and dry matter accumulation of tobacco plants, and it is beneficial to promote crop planting.

Depth-dependent effects of ericoid mycorrhizal shrubs on soil carbon and nitrogen pools are accentuated under arbuscular mycorrhizal trees.

Plant mycorrhizal associations influence the accumulation and persistence of soil organic matter and could therefore shape ecosystem biogeochemical responses to global changes that are altering forest composition. For instance, arbuscular mycorrhizal (AM) tree dominance is increasing in temperate forests, and ericoid mycorrhizal (ErM) shrubs can respond positively to canopy disturbances. Yet how shifts in the co-occurrence of trees and shrubs with different mycorrhizal associations will affect soil organic matter pools remains largely unknown. We examine the effects of ErM shrubs on soil carbon and nitrogen stocks and indicators of microbial activity at different depths across gradients of AM versus ectomycorrhizal (EcM) tree dominance in three temperate forest sites. We find that ErM shrubs strongly modulate tree mycorrhizal dominance effects. In surface soils, ErM shrubs increase particulate organic matter accumulation and weaken the positive relationship between soil organic matter stocks and indicators of microbial activity. These effects are strongest under AM trees that lack fungal symbionts that can degrade organic matter. In subsurface soil organic matter pools, by contrast, tree mycorrhizal dominance effects are stronger than those of ErM shrubs. Ectomycorrhizal tree dominance has a negative influence on particulate and mineral-associated soil organic matter pools, and these effects are stronger for nitrogen than for carbon stocks. Our findings suggest that increasing co-occurrence of ErM shrubs and AM trees will enhance particulate organic matter accumulation in surface soils by suppressing microbial activity while having little influence on mineral-associated organic matter in subsurface soils. Our study highlights the importance of considering interactions between co-occurring plant mycorrhizal types, as well as their depth-dependent effects, for projecting changes in soil carbon and nitrogen stocks in response to compositional shifts in temperate forests driven by disturbances and global change.

Networks of mineral-associated organic matter fractions in forest ecosystems

Mineral-associated organic matter (MAOM), the largest soil carbon pool, is formed through a series of organo-mineral interaction mechanisms. However, different organo-mineral fractions relevant to specific stabilization mechanisms and their response to environmental variables are poorly understood, which hinders accurate prediction of MAOM preservation under climate change. We applied sequential chemical extraction to separate MAOM into different organo-mineral fractions. To assess of response of different organo-mineral fractions to climate change, alpine forest soils with high environmental sensitivity along a controlled environmental gradient were selected. Residual OM and weakly adsorbed OM were the primary organo-mineral fractions, accounting for approximately 45.1–67.7 % and 16.4–30.6 %, respectively, of the total organic carbon (TOC). Climate exerted considerable indirect effects on the preservation of organo-mineral fractions through weathering and edaphic and biotic variables. Moreover, organo-mineral fractions were closely associated with metal cations (mainly Fe3+/Al3+) and secondary minerals, forming complex networks. Water-soluble OM (WSOM), weakly adsorbed OM and Fe/Al oxyhydroxides-stabilized OM were tightly linked, occupying the central position of the networks, and were closely related to soil pH, moisture and prokaryotic composition, indicating that edaphic and biotic factors might play important roles in maintaining the network structure and topology. In addition, Fe/Al-OM complexes, oxyhydroxides-stabilized OM and residual OM in the network were greatly impacted by climate and weathering factors, including precipitation, temperature and the plagioclase index of alteration (PIA). The complex network among organo-mineral fractions sheds light on MAOM dynamic stabilization for better predicting MAOM preservation under climate change.