Alter Soil Carbon Research Articles

Grazing disturbance reduces biocrust-related cyanobacteria and N-fixer abundance but increases bacterial diversity: Implications for biocrust restoration in degraded drylands

Overgrazing is a major driver of dryland degradation, however, so far, there is limited understanding on how this process affects biocrust-related microbial community, and especially how the key groups respond to grazing disturbance. In this study, quantitative polymerase chain reaction (qPCR) and high throughout sequencing technologies were used to investigate the bacterial community abundance and diversity in the Horqin Sandland (China) experiencing different livestock grazing disturbances, in order to examine whether a shift in bacterial community (in particular the key biocrust components, cyanobacteria) was involved, and how this was related to biocrust development and altered soil carbon and nitrogen level. Our results revealed that a clear heterogeneous soil bacterial community was associated with grazing disturbance, which inhibited biocrust development. The decreased photosynthetic cyanobacterial abundance (81.81 % in relative abundance and 98.83 % in absolute abundance) and nitrogen-fixing genes (87.72 %), associated with the lower total carbon and nitrogen content (P<0.05), illustrated a low soil carbon and nitrogen-fixing capability and nutrient level in the grazing-disturbed soils. In particular, a switch of nitrogen-fixing dominance from cyanobacteria to proteobacteria was induced by the grazing disturbance. Compared to the grazing-disturbed soils, higher dominant cyanobacterial operational taxonomic units (OTUs) (especially the species of Nostoc and Scytonema) and lower bacterial diversity (e.g., Shannon, Ace, and Chao index) were observed in the undisturbed biocrust soils, highlighting that the dominants rather than diversity played more important roles in biocrust development. Collectively, our results demonstrate that cyanobacteria are very sensitive (even more than others, e.g., proteobacteria and actinobacteria) to grazing disturbance, therefore, we propose that cyanobacterial inoculation is likely an effective approach to supplement soil cyanobacterial abundance, which is expected to induce biocrust development and increase carbon and nitrogen level in the disturbed drylands.

Invasion of Prosopis trees into arid ecosystem alters soil carbon and nitrogen processes and soil trace gases emissions

The invasion of drylands by leguminous mesquite (Prosopis spp.) is frequently associated with increases in the soil organic carbon (C) and nitrogen (N) pools. These increases stimulate soil microbial activity and accelerate soil C and N cycling. However, the impact of mesquite invasion on soil biogeochemistry, especially the emission of trace gases, in an ecosystem with an already established population of N-fixing plants is not well studied. To fill this knowledge gap, we quantified the in-situ soil trace gas emissions and the potential microbial activity in soils under invasive mesquite (Prosopis juliflora) trees (Prosopis), native acacia (Acacia tortilis) trees (Acacia), and in unvegetated soil between trees (Bare soil) on the western shore of the Dead Sea. To account for contributions of spatial and weather variabilities to the emission processes we conducted measurements across two geographic sites, 45 km apart, over two years, both under naturally dry soil conditions and after soil wetting. Before wetting, soil emissions of carbon dioxide (CO2) and nitric oxide (NOx) followed the order: Acacia > Prosopis ≥ Bare soil, while soil nitrous oxide (N2O) emissions were low and uniform across the three habitats. The soil inorganic N concentration, microbial biomass, and water-extractable organic C were significantly higher under the A. tortilis canopies compared with P. juliflora and Bare soil. After wetting, soil trace gases emissions increased up to 66, 1534, and 42 times, for CO2, N2O, and NOx, respectively, and remained higher under the native A. tortilis than under P. juliflora and Bare soil (Acacia > Prosopis > Bare soil). The potential soil microbial activity, however, was similar between the soils under the tree canopies. Our results show that the establishment of invasive leguminous trees increase soil CO2 and gaseous N emissions relative to the Bare soils, but not relative to native leguminous trees.

Maize Straw and Nitrogen Fertilizer Alter Soil Carbon and Nitrogen Mineralization during the Fallow Period in the Oasis Farmland area

Maize Straw and Nitrogen Fertilizer Alter Soil Carbon and Nitrogen Mineralization during the Fallow Period in the Oasis Farmland area

Nitrogen-fixing cyanobacteria enhance microbial carbon utilization by modulating the microbial community composition in paddy soils of the Mollisols region

Nitrogen-fixing cyanobacteria (NFC) are photosynthetic prokaryotic microorganisms capable of nitrogen fixation. They can be used as biofertilizers in paddy fields, thereby improving the rice tillering capacity and yield. To reveal the microbiological mechanisms by which nitrogen-fixing cyanobacteria alter soil carbon storage, we conducted a field experiment using NFC as a partial substitute for nitrogen fertilizer in paddy fields in the Sanjiang Plain of Northeast China's Mollisols region. Using metagenomic sequencing technology and Biolog Ecoplate™ carbon matrix metabolism measurements, we explored the changes in the soil microbial community structure and carbon utilization in paddy fields. The results indicated that the replacement of nitrogen fertilizer with NFC predisposed the soil microbial community to host a great number of copiotrophic bacterial taxa, and Proteobacteria and Actinobacteria were closely associated with the metabolism of soil carbon sources. Moreover, through co-occurrence network analysis, we found that copiotrophic bacteria clustered in modules that were positively correlated with the metabolic level of carbon sources. The addition of NFC promoted the growth of copiotrophic bacteria, which increased the carbon utilization level of soil microorganisms, improved the diversity of the microbial communities, and had a potential impact on the soil carbon stock. The findings of this study are helpful for assessing the impact of NFC on the ecological function of soil microbial communities in paddy fields in the black soil area of Northeast China, which is highly important for promoting sustainable agricultural development and providing scientific reference for promoting the use of algal-derived nitrogen fertilizers.

Warming and increased precipitation alter soil carbon cycling in a temperate desert steppe of Inner Mongolia

Abstract Warming and precipitation are key global change factors driving soil carbon (C) dynamics in terrestrial ecosystems. However, the effects of warming and altered precipitation on soil microbial diversity and functional genes involved in soil C cycling remain largely unknown. We investigated the effects of warming and increased precipitation on soil C cycling in a temperate desert steppe of Inner Mongolia using metagenomic sequencing. We found that warming reduced plant richness, Shannon–Wiener and Simpson index. In contrast, increased precipitation significantly influenced Shannon–Wiener and Simpson index. Warming reduced soil microbial species by 5.4% while increased precipitation and warming combined with increased precipitation led to increases in soil microbial species by 23.3% and 2.7%, respectively. The relative abundance of Proteobacteria, which involve C cycling genes, was significantly increased by warming and increased precipitation. Warming significantly reduced the abundance of GAPDH (Calvin cycle) and celF (cellulose degradation) while it enhanced the abundance of glxR (lignin degradation). Increased precipitation significantly enhanced the abundance of pgk (Calvin cycle), coxL (carbon monoxide oxidation), malZ (starch degradation), and mttB (methane production). Moreover, a wide range of correlations among soil properties and C cycling functional genes was detected, suggesting the synergistic and/or antagonistic relationships under scenario of global change. These results may suggest that warming is beneficial to soil C storage while increased precipitation negatively affects soil C sequestration. These findings provide a new perspective for understanding the response of microbial communities to warming and increased precipitation in the temperate desert steppe.

Thinning enhances forest soil C storage by shifting the soil toward an oligotrophic condition

Forests are significant carbon reservoirs, with approximately one-third of this carbon stored in the soil. Forest thinning, a prevalent management technique, is designed to enhance timber production, preserve biodiversity, and maintain ecosystem functions. Through its influence on biotic and abiotic factors, thinning can profoundly alter soil carbon storage. Yet, the full implications of thinning on forest soil carbon reservoirs and the mechanisms underpinning these changes remain elusive. In this study, we undertook a two-year monitoring initiative, tracking changes in soil extracellular enzyme activities (EEAs), microbial communities, and other abiotic parameters across four thinning intensities within a temperate pine forest. Our results show a marked increase in soil carbon stock following thinning. However, thinning also led to decreased dissolved organic carbon (DOC) content and a reduced DOC to soil organic carbon (SOC) ratio, pointing toward a decline in soil carbon lability. Additionally, fourier transform infrared spectroscopy (FTIR) analysis revealed an augmented relative abundance of aromatic compounds after thinning. There was also a pronounced increase in absolute EEAs (per gram of dry soil) post-thinning, implying nutrient limitations for soil microbes. Concurrently, the composition of bacterial and fungal communities shifted toward oligotrophic dominance post thinning. Specific EEAs (per gram of soil organic matter) exhibit a significant reduction following thinning, indicating a deceleration in organic matter decomposition rates. In essence, our findings reveal that thinning transitions soil toward an oligotrophic state, dampening organic matter decomposition, and thus bolstering the soil carbon storage potential of forest. This study provides enhanced insights into the nuanced relationship between thinning practices and forest soil carbon dynamics, serving as a robust foundation for enlightened forest management strategies.

Reconciling carbon quality with availability predicts temperature sensitivity of global soil carbon mineralization

Soil organic carbon (SOC) mineralization is a key component of the global carbon cycle. Its temperature sensitivity Q10 (which is defined as the factor of change in mineralization with a 10 °C temperature increase) is crucial for understanding the carbon cycle-climate change feedback but remains uncertain. Here, we demonstrate the universal control of carbon quality-availability tradeoffs on Q10. When carbon availability is not limited, Q10 is controlled by carbon quality; otherwise, substrate availability controls Q10. A model driven by such quality-availability tradeoffs explains 97% of the spatiotemporal variability of Q10 in incubations of soils across the globe and predicts a global Q10 of 2.1 ± 0.4 (mean ± one SD) with higher Q10 in northern high-latitude regions. We further reveal that global Q10 is predominantly governed by the mineralization of high-quality carbon. The work provides a foundation for predicting SOC dynamics under climate and land use changes which may alter soil carbon quality and availability.

Microplastics alter soil carbon cycling: Effects on carbon storage, CO2 and CH4 emission and microbial community

Abstract Microplastics (MPs) are carbon-rich polymers that are ubiquitous in the environment. With the increase of plastic production, microplastic pollution may be exacerbated and result in significant changes in microbial communities and biogeochemical processes such as carbon cycling, eventually impacting greenhouse gas emission and carbon storage in terrestrial ecosystems. However, current research on the effect of MPs on soil carbon cycling is still limited, and there is a lack of systematic review of the scattered information obtained from previous studies. Accordingly, this review provides a systematic overview of the current knowledge on the effects of MPs on soil carbon cycling and gives future research suggestions. Emerging evidence indicates that MPs could affect soil carbon stability and CO2 and CH4 emission by modifying soil physicochemical and microbiological properties; though biodegradable MPs often exhibit a greater effect than nonbiodegradable ones, the specific effects are highly dependent on plastic type, size and concentration. The specific mechanisms of MPs’ impact on soil carbon cycles remain elusive, which are discussed mainly from the perspective of microbial changes, including microbial biomass, microbial community composition, and key enzymes and functional genes associated with carbon metabolism. Further research is needed to elucidate whether MPs have a positive priming effect on soil carbon decomposition and the biotic and abiotic mechanisms involved. This review paper helps researchers gain a clearer picture of how and through which way MPs impact carbon cycling in soil ecosystems.

Enhanced Nitrogen Fertilizer Input Alters Soil Carbon Dynamics in Moso Bamboo Forests, Impacting Particulate Organic and Mineral-Associated Carbon Pools

The application of nitrogen fertilizer is crucial in the cultivation of bamboo forests, and comprehending the alterations in soil organic carbon (SOC) due to nitrogen application is essential for monitoring soil quality. Predicting the dynamics of soil carbon stock involves analyzing two components: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). This study aimed to investigate the impact of high nitrogen inputs on SOC stock in Moso bamboo forests located in southwestern China. The research focused on analyzing changes in soil chemical properties, SOC content, and its components (POC and MAOC), as well as microbial biomass in the surface layer (0–10 cm) under different nitrogen applications (0, 242, 484, and 726 kg N ha−1 yr−1). The results indicate that nitrogen application significantly reduced the SOC content, while concurrently causing a significant increase in POC content and a decrease in MAOC content within the Moso bamboo forest (p &lt; 0.05). The HM treatment notably increased the NO3−-N content to 2.15 mg/kg and decreased the NH4+-N content to 11.29 mg/kg, although it did not significantly influence the microbial biomass carbon (MBC) and nitrogen (MBN). The LN and MN treatments significantly reduced the MBC and MBN contents (71.6% and 70.8%, 62.5% and 56.8%). Nitrogen application significantly increased the Na+ concentration, with a peak observed under the LN treatment (135.94 mg/kg, p &lt; 0.05). The MN treatment significantly increased the concentrations of Fe3+ and Al3+ (p &lt; 0.05), whereas nitrogen application did not significantly affect Ca2+, Mg2+ concentration, and cation exchange capacity (p &gt; 0.05). Correlation and redundancy analyses (RDAs) revealed that the increase in annual litterfall did not significantly correlate with the rise in POC, and changes in extractable cations were not significantly correlated with the decrease in MAOC. Soil nitrogen availability, MBC, and MBN were identified as the primary factors affecting POC and MAOC content. In conclusion, the application of nitrogen has a detrimental impact on the soil organic carbon (SOC) of Moso bamboo forests. Consequently, it is imperative to regulate fertilization levels in order to preserve soil quality when managing these forests. Our research offers a theoretical foundation for comprehending and forecasting alterations in soil carbon stocks within bamboo forest ecosystems, thereby bolstering the sustainable management of Moso bamboo forests.

Soil environment and annual rainfall co-regulate the response of soil respiration to different grazing intensities in saline-alkaline grassland

Grazing is a prevalent management strategy in grassland ecosystems that has profound effects on plants and soil microorganisms, consequently altering soil carbon (C) fluxes. However, the difference responses and regulatory mechanisms of soil autotrophic respiration (SRa) and heterotrophic respiration (SRh) to different grazing intensities remain unclear, especially in saline-alkaline grasslands. A six–year (2017–2022) field experiment involving four grazing intensities (no grazing, light grazing, moderate grazing, and heavy grazing) was conducted in a saline-alkaline grassland located in the agro-pastoral ecotone of northern China. Soil total respiration (SRtot) and its components (SRa and SRh), and the related biotic and abiotic factors (plants, soil microorganisms, and soil environment) were measured. The results showed that light grazing significantly decreased the mean SRh by 17.7% across six measuring years. The effects size of grazing on soil respiration fluctuated consistently with soil water content during the growing seasons (May–September), resulting in a neutral effect of grazing on the seasonal mean SRa. The cumulative soil C emissions of the current year varied with the seasonal precipitation in the previous year, whereas the changes in cumulative soil C emissions induced by grazing showed the same trends as annual precipitation. In addition, the key control factors for SRh and SRa differed and varied with grazing intensity and the soil environment played a critical role in regulating soil C fluxes. In conclusion, light grazing reduces soil microbial-driven C emissions and the soil environment and precipitation co-regulate the response of soil C fluxes to different grazing intensities in saline-alkaline grasslands.

Emergent Climatic Controls on Soil Carbon Turnover and Its Variability in Warm Climates

AbstractClimate plays a critical role in altering soil carbon (C) turnover and long‐term soil C storage by regulating water availability and temperature, and in turn biological activity. However, a systematic analysis of how key climatic factors shape the global patterns of soil C turnover is still lacking. Using global observation‐based data sets and a transit time theory, here we show that—excluding croplands and cold regions—soil C turnover time (τTO) and its variability are strongly related to ecosystem aridity through a power law scaling. According to such a relation, soil C turnover is faster but also more variable in wetter regions, suggesting more complex C cycling processes. The observed scaling of τTO and its coefficient of variation with aridity underlines the fundamental controls of climate on soil C turnover and may help reconcile soil C models with empirical observations for improved projection of soil C dynamics under climate change.

Distinct dynamics of plant- and microbial-derived soil organic matter in relation to varying climate and soil properties in temperate agroecosystems

Global environmental change can substantively alter soil carbon storage and dynamics in agroecosystems. However, investigations of soil organic matter (OM) composition associated with various environmental factors are still limited, and this hinders the understanding of soil carbon biogeochemistry in agricultural settings. Soil samples were collected at two times (time 0 and 8 or 10 years) from 10 agricultural sites across Canada and New Zealand with varying soil properties (i.e., soil texture, pH) and climates (MAT, mean annual temperature; MAP, mean annual precipitation). The soils were analyzed for organic carbon, nitrogen and soil OM composition using molecular-level techniques that included targeted compound-specific and solid-state 13C nuclear magnetic resonance analyses. Soil carbon contents were similar over time and were not correlated with environmental factors. Molecular-level characterization of soils found that the preservation and degradation of specific soil OM components differed. Simple sugars and microbial-derived compounds (i.e., fungi-derived ergosterol and microbial-derived lipids) persist less with time in soils compared to other OM components. However, the increased cutin- and suberin-derived compounds at most sites and similar alkyl carbon contents with time suggested that cutin- and suberin-derived compounds were longer-lived compared to other soil OM compounds. Correlation analyses indicated that temporal differences in fungal-derived ergosterol were positively correlated with silt content (r = 0.78). An inverse correlation was observed between lignin degradation and silt content (r = −0.75). Cutin- and suberin-derived compounds were negatively correlated with MAT (r = −0.69); when the analysis was restricted to only Canadian sites, cutin- and suberin-derived compounds and their degradation were correlated with MAP and MAT (climate variables). Further, partial correlation analysis revealed that the correlations between soil texture and the temporal shifts in soil OM composition were indirectly regulated by MAP but not MAT. Overall, distinct environmental constraints were observed for specific OM components in agroecosystems, suggesting that the preservation mechanisms are not uniform across a wide range of soils under different climates and soil properties.

Plant invasion strengthens the linkages between dissolved organic matter composition and the microbial community in coastal wetland soils

Exotic plant invasion dramatically alters soil carbon transformation and shapes the structure and diversity of the microbial community in coastal wetlands. However, it remains unclear how the dissolved organic matter (DOM) optical components and chemical composition and their linkages with soil microorganisms change with increasing time since invasion. Here, we explored the impacts of Spartina alterniflora (S. alterniflora) invasion on DOM compositions and relationships with microbial communities along a short-term chronosequence (i.e., 3-, 5-,10-, and 15-year) in the Yellow River Delta. The results showed an increase in the soil water content, soil organic carbon, dissolved organic carbon, and C/N ratio along the invasion chronosequence, whereas bulk density showed the opposite trend. Moreover, invaded wetland soils had a higher abundance of total phospholipid fatty acids, gram-positive bacteria (G + ), gram-negative bacteria (G-), and fungi than tidal flat soils. The DOM in invaded wetland soils was mainly composed of endogenous protein-like components, and the proportion of autochthonous DOM increased over invasion time. The DOM was characterized by low molecular weight, low aromatic content, and low hydrophobic compounds in S. alterniflora wetland soils, whereas in tidal flat soils, the humification degree and DOM molecular weight were higher. The soil microbial communities exhibited stronger linkages with various environmental variables and DOM fluorescence components in invaded wetlands based on redundancy analysis (RDA) and correlation analysis using Mantel tests. Structural Equation Model (SEM) revealed that the soil microbial abundance and community structure induced by increasing S. alterniflora invasion time were the most important drivers of DOM content and chemical composition. The findings of this work provide a better understanding of labile carbon pool turnover in coastal wetlands invaded by S. alterniflora.

Drought re-routes soil microbial carbon metabolism towards emission of volatile metabolites in an artificial tropical rainforest

Drought impacts on microbial activity can alter soil carbon fate and lead to the loss of stored carbon to the atmosphere as CO2 and volatile organic compounds (VOCs). Here we examined drought impacts on carbon allocation by soil microbes in the Biosphere 2 artificial tropical rainforest by tracking 13C from position-specific 13C-pyruvate into CO2 and VOCs in parallel with multi-omics. During drought, efflux of 13C-enriched acetate, acetone and C4H6O2 (diacetyl) increased. These changes represent increased production and buildup of intermediate metabolites driven by decreased carbon cycling efficiency. Simultaneously,13C-CO2 efflux decreased, driven by a decrease in microbial activity. However, the microbial carbon allocation to energy gain relative to biosynthesis was unchanged, signifying maintained energy demand for biosynthesis of VOCs and other drought-stress-induced pathways. Overall, while carbon loss to the atmosphere via CO2 decreased during drought, carbon loss via efflux of VOCs increased, indicating microbially induced shifts in soil carbon fate.

Chemical Fertilization Alters Soil Carbon in Paddy Soil through the Interaction of Labile Organic Carbon and Phosphorus Fractions

The influence of long-term chemical fertilization in paddy soils is based on the interaction between labile carbon and phosphorus fractions and the manner in which this influences soil organic carbon (SOC). Four soil depths (0–30 cm) were analyzed in this study. Easily oxidized organic carbon components, such as permanganate oxidized carbon (POXC) and dissolved organic carbon (DOC), and other physicochemical soil factors were evaluated. The correlation and principal component analyses were used to examine the relationship between soil depth and the parameter dataset. The results showed that Fe-P concentrations were greater in the 0–5 cm soil layer. DOC, inorganic phosphate fraction, and other soil physiochemical characteristics interacted more strongly with SOC in the 0–5 cm soil layer, compared to interactions in the 10–15 cm layer, influencing soil acidity. An increase in DOC in the 0–5 cm soil layer had a considerable effect on lowering SOC, consistent with P being positively correlated with POXC, but negatively with SOC and water-soluble carbon (WSC). The changes in SOC could be attributed to the relationship between DOC and inorganic phosphate fractions (such as Fe-P) under specific soil pH conditions. An increase in soil DOC could be caused by changes in the P fraction and pH. The DOC:Avai. P ratio could serve as a compromise for the C and P dynamic indicators. The soil depth interval is a critical element that influences these interactions. Agricultural policy and decision-making may be influenced by the P from chemical fertilization practices, considering the yields and environmental effects.

Frequent defoliation of perennial legume-grass bicultures alters soil carbon dynamics

Frequent defoliation of perennial legume-grass bicultures alters soil carbon dynamics

Flooding lowers the emissions of CO2 and CH4 during the freeze-thaw process in a lacustrine wetland

The frequency and strength of soil freeze–thaw alternation have been increasing with the aggravation of climate change, which will affect soil physicochemical properties and biological characteristics and in turn alter soil carbon (C) emissions. The emissions of carbon dioxide (CO2) and methane (CH4) are often influenced by the water level in wetland ecosystems. However, the effects of soil freeze–thaw alternation under different water levels on soil C emissions in wetland ecosystems are still not clear. We examined the impacts of soil freeze–thaw alternation under different water levels on the emission of CO2 and CH4 in a wetland dominated by Phragmites australis, and the soil microbial community structure and enzymatic activities were studied. The results showed that freeze–thaw treatments promoted soil carbon emissions, and flooding significantly lowered soil CO2 and CH4 emissions under freeze–thaw treatments. The soil water content (SWC), dissolved organic carbon (DOC), and the activities of β-N-acetyl-glucosaminidase (NAG), polyphenol oxidase (PPO), and peroxidase (PER) were the main predictors of soil carbon emissions under freeze–thaw treatments. Flooding played a direct role in carbon emissions during the freeze–thaw processes, and the interpretation rates of soil CO2 and CH4 emissions were 65% and 37%, respectively. The high-water level indicated fewer carbon emissions during the freeze–thaw period. Therefore, appropriately raising the water level is conducive to reducing carbon emissions from wetlands in areas of seasonal frost.

Investigating the response of soil nitrogen cycling to grass invasion

In heathlands, high mineral N input causes replacement of Calluna vulgaris, the dominant plant, by fast-growing grasses such as Molinia caerulea. The vegetation shift signifies altered litter quality from low- to high-quality litter due to differences in lignin content. Litter quality usually affects decomposition processes, which can, in turn, alter nutrient cycling. Therefore, the change in plant dominance in this ecosystem possibly alters soil carbon and nutrient cycles, and consequently, ecosystem services (e.g. biodiversity conservation, groundwater recharge, …). We hypothesise that, because of its higher litter quality, nutrient turnover becomes faster with grass encroachment. We tested this hypothesis in a field set-up consisting of 14 plots presenting a gradient of increasing grass dominance (from 0% to 100%). We measured nine soil parameters and assessed possible associations between grass dominance and the soil parameters using multivariate analysis and linear mixed models. We found that grass dominance significantly impacted net N mineralisation and the root biomass. Our results showed very low net N mineralisation rates (0.09 ± 0.04 mg N (kg soil)−1 day−1) and relative nitrification rates (1.99 ± 0.62%). At high grass levels, acid phosphatase activity was significantly lower than at lower grass percentages. These results show that grass encroachment has a minimal impact on heathland soil biochemistry at this point. Still, we consider that it may take many years to translate a change in litter quality and dynamics into a change in soil functioning.

Constraints on the spatial variations of soil carbon fractions in a mangrove forest in Southeast China

Mangroves, carbon-rich ecosystems, store significant amounts of carbon in the soil to mitigate climate change. For better mangrove carbon management, the spatial distributions and driving factors of distinct soil carbon fractions, notably soil inorganic carbon (IC) and labile carbon, require clarification. Here, we quantified variations in the soil carbon fractions (total organic carbon (TOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), permanganate-oxidizable carbon (POC), and IC) with landward distance and soil depth, and identified the means by which edaphic and biotic factors affect soil carbon fractions in a mangrove forest in Southeast China. Average TOC, IC, POC, DOC, and MBC densities were 15.22 kg/m3, 1.39 kg/m3, 4.23 kg/m3, 43.49 g/m3, and 63.25 g/m3, respectively. Soil total nitrogen was the most important factor affecting TOC, POC, and MBC. Soil IC was found to be controlled by pH, and plant biomass was the main factor explaining soil DOC variation. Except for MBC, landward distance was negatively correlated with organic carbon fractions and positively correlated with IC via soil nutrients, pH, bulk density, and plant biomass. Soil depth directly or indirectly altered soil carbon fractions via soil nutrients, pH, clay, and salinity, resulting in negative relationships with TOC, POC, and MBC and a positive relationship with IC. Collectively, our results indicate that future changes in soil total nitrogen content and pH are likely to impact carbon storage in mangroves, and that the conservation of landward mangroves is important with respect to their high labile carbon contents.

Keeping thinning-derived deadwood logs on forest floor improves soil organic carbon, microbial biomass, and enzyme activity in a temperate spruce forest

Deadwood is a key component of forest ecosystems, but there is limited information on how it influences forest soils. Moreover, studies on the effect of thinning-derived deadwood logs on forest soil properties are lacking. This study aimed to investigate the impact of thinning-derived deadwood logs on the soil chemical and microbial properties of a managed spruce forest on a loamy sand Podzol in Bavaria, Germany, after about 15 years. Deadwood increased the soil organic carbon contents by 59% and 56% at 0–4 cm and 8–12 cm depths, respectively. Under deadwood, the soil dissolved organic carbon and carbon to nitrogen ratio increased by 66% and 15% at 0–4 cm depth and by 55% and 28% at 8–12 cm depth, respectively. Deadwood also induced 71% and 92% higher microbial biomass carbon, 106% and 125% higher microbial biomass nitrogen, and 136% and 44% higher β-glucosidase activity in the soil at 0–4 cm and 8–12 cm depths, respectively. Many of the measured variables significantly correlated with soil organic carbon suggesting that deadwood modified the soil biochemical processes by altering soil carbon storage. Our results indicate the potential of thinned spruce deadwood logs to sequester carbon and improve the fertility of Podzol soils. This could be associated with the slow decay rate of spruce deadwood logs and low biological activity of Podzols that promote the accumulation of soil carbon. We propose that leaving thinning-derived deadwood on the forest floor can support soil and forest sustainability as well as carbon sequestration.