Depth‐dependent mechanisms regulate accumulation of plant‐ and microbial‐derived residues under long‐term nitrogen addition in a semiarid grassland

Microbial- and plant-derived carbons are critical sources of soil organic carbon (SOC), but the specific responses of soil amino sugars and lignin phenols to global change remain unclear. In this study, we conducted 3193 observations across 553 experiments aimed at investigating the potential role of amino sugars and lignin phenols in maintaining SOC accumulation in response to land-use change, nutrient additions, elevated C dioxide (eCO2), warming, and drought. The results showed that land restoration increased amino sugars (35.1%), glucosamine (53.8%), galactosamine (68.6%), muramic acid (33%), lignin phenols (79.3%), and vanillyl phenols (68%), whereas land degradation reduced these compounds, including syringyl. Nitrogen (N) and phosphorus (P) additions enhanced amino sugar, glucosamine, and muramic acid contents, whereas P addition selectively increased glucosamine content. N, P, and potassium additions increased glucosamine (16.8%), galactosamine (17.3%), muramic acid (21.6%), and lignin phenol (4.8%) contents, while eCO2 only increased amino sugar content by 14.6%. Warming increased glucosamine and muramic acid contents, whereas drought had no effect on amino sugar and lignin phenol contents. Soil amino sugars played a more critical role than lignin phenols in SOC accumulation, and their dynamics were influenced by soil nutrient availability and microbial communities under global change. These findings advanced our understanding of the dominant role of microbial residues in SOC accumulation mediated by the nutrient stoichiometry and microbial communities.

Plant-derived lipids play a crucial role in forest soil carbon accumulation

Microbial and plant residues are the primary sources of soil organic carbon (SOC) in forest ecosystems. However, the relative contributions of microbial and plant residues to SOC in Moso bamboo (Phyllostachys edulis) forests remain poorly understood, despite Moso bamboo’s unique growth pattern distinct from that of tree species. In this study, we analyzed amino sugars and lignin phenols as biomarkers for microbial and plant residues, respectively, in the topsoil (0–10 cm) and subsoil (20–40 cm) of a Moso bamboo forest and investigated their regulatory factors. The results showed that microbial-derived amino sugars contributed 1.6% and 1.0% to SOC in the topsoil and subsoil, respectively, comparable to the contributions of plant-derived lignin phenols (1.6% and 0.8%). Both amino sugars and lignin phenols exhibited higher contributions to SOC in the topsoil than in the subsoil. Fine root biomass and microbial phosphorus (P) limitation regulated the contribution of amino sugars to SOC, while fine root biomass and the ratio of gram-positive to gram-negative bacteria controlled the contribution of lignin phenols. These findings highlight that microbial and plant residues contribute equally to SOC sequestration in Moso bamboo forests, with soil carbon and P availability playing critical roles in regulating their contributions. These findings may contribute to SOC management in Moso bamboo forests.

Divergent accumulation of microbial necromass and plant lignin phenol induced by adding maize straw to fertilized soils

Grassland degraded patchiness reduces microbial necromass content but increases contribution to soil organic carbon accumulation

Coastal blue carbon ecosystems, particularly mangroves, are becoming increasingly recognised for their importance in mitigating climate change. Still, the specific patterns and drivers of plant lignin components and microbial necromass accumulation in these ecosystems are unclear. In response, we carried out a study along a 40‐year mangrove restoration chronosequence, measuring lignin phenol and amino sugar concentrations in soil profiles (0–100 cm) as indicators of plant‐based and microbial‐derived residues, respectively. Our results showed that restoration significantly increased plant lignin phenol and amino sugar concentrations, with mature mangroves having much higher concentrations than tidal flats. During restoration, the fungal necromass was greater than the bacterial necromass. The factors influencing the lignin phenols were tree biomass, total nitrogen, pH and salinity, while those influencing the formation of amino sugars were total biomass, soil C: N ratio and pH. While the amino sugars decreased, the lignin phenols increased with the content of SOC, providing evidence of the important role lignin phenol components play in the formation of SOC in mangrove. Synthesis: By separating soil carbon into plant‐based and microbial‐derived components, our results demonstrate that the carbon stock in mangrove sediments is vulnerable to disturbances and that changes from anaerobic to aerobic conditions cause significant carbon mineralisation. The precise identification of soil carbon sources in blue carbon ecosystems could aid in elucidating the mechanisms of soil carbon sequestration and their responses to environmental changes. Read the free Plain Language Summary for this article on the Journal blog.

Plantation is an economical and effective method of ecological restoration, which is also a common means to increase soil organic carbon (SOC) content. However, the effects of vegetation types on SOC accumulation and δ13C distribution during ecological restoration are still not clear. Therefore, we evaluated the soils under four types of restoration measures: plantation (PL, dominated by Olea europaea ‘Leccino’), grasslands [GLs, Setaria viridis], croplands [CLs, Zea mays] and shrublands (SLs, Lycium chinense Mill), after 11-year restoration. SOC and the natural stable carbon isotope abundance in four recovery modes were determined, while amino sugars (ASs) and lignin phenols (LPs) were used as biomarkers to identify microbial- and plant-derived carbon, respectively. The results showed that SOC, AS, and LP decreased with the increasing of soil depth, and SOC and LP showed the same trend in topsoil (0–20 cm). ASs in subsoil (40–50 cm) were significantly higher in GLs than that in CLs and the PL, while fungi residue carbon in GLs was significantly higher in subsoil. The δ13C in topsoil was mainly affected by plant factors, especially by litter. With the increasing soil depth, the effect of plants on δ13C decreased, and the effect of microorganisms increased. Vegetation types could affect SOC and δ13C by influencing plant inputs in topsoil. In the subsoil, differences in microbial compositions under different vegetation types could affect δ13C enrichment. The study revealed the effects of vegetation types on SOC accumulation and δ13C distribution during ecological restoration, emphasized that vegetation types can affect SOC accumulation by influencing the plant input of topsoil and the microbial compositions in subsoil, and provided a reference for the development of management policies in restoration areas.

Microbial residue carbon (MRC) is an important source of soil organic carbon (SOC) formation and plays a vital role in the accumulation and retention of SOC. Vegetation restoration is an effective strategy to restore degraded lands. However, there are no studies on how MRC in the profile changes with vegetation restoration. We evaluated MRC (using amino sugars) accumulation and its contribution to SOC in different soil depths (0-20, 20-50, and 50-100 cm) during vegetation restoration in a severely eroded forest (CK), a restored forest (as ecological restoration management), an orchard (as development management model), and a secondary forest (as ideal control). Microbial biomarkers were extracted from soil profiles and used to measure microbial diversity and microbial community composition (using 16S rRNA). Vegetation restoration, soil depth, and their interaction with each other significantly affected MRC, fungal residue carbon (FRC), and bacterial residue carbon (BRC) contents. The MRC content showed an increasing trend for the four vegetation restoration models in the following order: CK < orchard < restored forest < secondary forest. Furthermore, the contribution of MRC to SOC increased with the increasing soil depth for the restored forest. The rapid accumulation of MRC was substantially influenced by SOC, total nitrogen content, soil pH, bacterial and fungal diversity, bacterial phylum, and fungal phylum. In conclusion, the model of vegetation restoration and soil depth play important roles in the accumulation of soil microbial residue carbon in a red soil erosion area. These findings are pivotal for improving our mechanistic understanding of microbial regulation of SOC preservation during vegetation restoration of a degraded ecosystem.

ABSTRACTMicrobial residue carbon (MRC) is an important source of soil organic carbon (SOC) and plays a vital role in the accumulation and retention of SOC. Vegetation restoration is an effective strategy for restoring degraded lands. However, there are no studies on how the MRC in a profile changes with vegetation restoration. We evaluated MRC (using amino sugars) accumulation and its contribution to SOC at different soil depths (0–20, 20–50, and 50–100 cm) during vegetation restoration in a severely eroded forest (CK), a restored forest (ecological restoration management), an orchard (development management pattern), and a secondary forest (ideal control). Microbial biomarkers were extracted from the soil profiles and used to measure microbial diversity and microbial community composition (using 16S rRNA). Vegetation restoration, soil depth, and their interaction with each other significantly affected the MRC, fungal residue carbon (FRC), and bacterial residue carbon (BRC) contents. The MRC content tended to increase across the four vegetation restoration patterns in the following order: CK (323.25 mg kg−1) < orchard (1035.67 mg kg−1) < restored forest (2919.01 mg kg−1) < secondary forest (6556.72 mg kg−1). Furthermore, the contribution of MRC to SOC increased with increasing soil depth in the restored forest. The contributions of total MRC to the SOC content varied from 13.12% to 71.88%. The rapid accumulation of MRC was substantially influenced by the SOC content, total nitrogen content, soil pH, bacterial and fungal diversity, and bacterial and fungal phyla. In conclusion, the patterns of vegetation restoration and soil depth play important roles in the accumulation of soil MRC in red soil erosion areas. These findings are pivotal for improving our mechanistic understanding of the microbial regulation of SOC preservation during vegetation restoration of a degraded ecosystem.

Effect of 9-year water and nitrogen additions on microbial necromass carbon content at different soil depths and its main influencing factors

ABSTRACTSoil organic carbon (SOC) stabilization is vital for the mitigation of global climate change and retention of soil carbon stocks. The Loess Plateau is a crucial ecological zone in China and even worldwide for major ecosystem protection. However, in the Loess Plateau, there are knowledge gaps about the response of SOC sources and stabilization to different ecological transitions of jujube economic forests. Therefore, our study used clean‐cultivated jujube orchards as a control (CK) and selected five main ecosystem transformation models of abandoned jujube orchards on Lvliang Mountain: abandoned farmland (AF), replanted with Astragalus‐Bupleurum (AB), replanted with alfalfa (AL), replanted with Chinese pine (CP), and replanted with Chinese arborvitae (PO). The soil properties, sources and physical fractions of organic carbon and their correlations in the 0‐ to 20‐cm soil layer at each sample site were analyzed. The results show that the ecosystem transformation significantly increased the SOC by affecting plant‐ and microbe‐derived carbon and altering its components. Different treatments have varying impacts on the SOC content. The lignin phenol (VSC) content in the soils in the five ecosystem transformation models was greater than that in the CK and had the following ranking: CP > AL > PO > AF > AB (p < 0.05). The ecosystem transformation also significantly increased the soil total amino sugar (TAS) content, microbial residue carbon (MRC), and its contribution to organic carbon. Additionally, it promoted the accumulation of particulate organic carbon (POC) and mineral‐associated organic carbon (MAOC) and positively impacted the carbon stability. Among the five ecosystem transformation models, CP had the greatest impact on lignin phenols, amino sugars, SOC content, and stability, whereas AF and AB contributed the least to SOC. The results of this study provide a scientific basis to assess and select optimal transformation modes for the ecosystem transformation of commercial jujube forests.

Divergent accumulation of microbial and plant necromass along paddy soil development in a millennium scale

Plant‐ and microbial‐derived carbon (C) are the two major sources of soil organic carbon (SOC) pools that make important contributions to stable and labile SOC. Although the hypothesis of an increase in SOC during natural vegetation restoration has been broadly verified, the contributions of plant‐ and microbial‐derived C to SOC accumulation remain uncertain. In this study, we used biomarker approaches to assess the contribution and allocation of plant‐ and microbial‐derived C in long‐term vegetation succession sequences. We found a unimodal distribution of total lignin phenols along vegetation succession, with the maximum occurring at 100 years of succession (293 ± 22.7 mg kg−1). Vegetation succession significantly increased microbial‐derived C, including microbial necromass C (MNC) and glomalin‐related soil proteins (GRSP). The contribution of MNC to SOC was high (26%–49%) and increased significantly with vegetation succession, whereas the proportion of plant‐derived C and GRSP in SOC consistently decreased. The results indicated that the distribution of lignin phenols is determined by the quality and abundance of plant litter input to the soil, and the increase in microbial‐derived C is closely associated with microbial metabolism mediated by environmental factors. However, the C turnover pathway from microbial necromass to persistent SOC formation, as inferred from the nonlinear response of the MNC accumulation coefficient, requires 90–100 years to achieve a stable contribution to soil C sequestration. Synthesis and applications. Our findings further highlight the critical role of the microbial C pump in SOC formation and accumulation. We argue that prioritizing native pioneer species and their mixed communities with climax species during revegetation of extensive fragile ecosystems contributes to sustainable soil C sequestration practices.

Abstract. Microbial necromass carbon (MNC) is a significant source of soil organic carbon (SOC). However, the contribution of microbial necromass to different organic carbon fractions and their influencing factors in various soil layers under different grassland types remains unclear. This study was conducted through a comprehensive investigation of soil profiles (0–20, 20–40, and 40–100 cm) across four grassland types in Ningxia, China, encompassing meadow steppe, typical steppe, desert steppe, and steppe desert. We quantified mineral-associated organic carbon (MAOC), particulate organic carbon (POC), and their respective microbial necromass components, including total microbial necromass carbon (TNC), fungal necromass carbon (FNC), and bacterial necromass carbon (BNC), and analyzed the contributions to SOC fractions and influencing factors. Our findings reveal three key insights. First, the contents of MAOC and POC in the 0–100 cm soil layer were in the following order of magnitude: Meadow steppe > Typical steppe > Desert steppe > Steppe desert, with the average content of POC being 9.3 g kg−1, which was higher than the average content of MAOC (8.73 g kg−1). Second, the content of microbial TNC in MAOC and POC decreased with soil depth, the average content of FNC was 3.02 and 3.85 g kg−1, which were higher than the average content of BNC (1.64 and 2.08 g kg−1). FNC dominated both MAOC and POC, and its contribution was higher than the contribution of BNC. Third, through regression analysis and random forest modeling, we identified key environmental drivers of MNC dynamics: mean annual rainfall, electrical conductance, and soil total nitrogen emerged as primary regulators in surface soils (0–20 cm), while available potassium, SOC, and mean annual temperature dominated deeper soil layers (20–100 cm). This research contributes by: (1) establishing the vertical distribution patterns of MNC and SOC fractions in soil profiles; (2) quantifying the relative contributions of MNC to SOC fractions across different grassland ecosystems soil profiles and elucidating their environmental controls, offers a deeper understanding of the mechanisms driving MNC accumulation in SOC fractions in diverse grassland ecosystems, and providing data support for further research on the microbiological mechanisms of soil organic carbon formation and accumulation in arid and semi-arid regions.

Latitudinal patterns and drivers of plant lignin and microbial necromass accumulation in forest soils: Disentangling microbial and abiotic controls