Divergent contribution of particulate and mineral-associated organic matter to soil carbon in grassland.

Sequestration of soil organic carbon (SOC) is an effective means to draw atmospheric CO2. Grassland restoration is one of the fastest methods to increase soil C stocks, and particulate-associated C and mineral-associated C play critical roles in soil C stocks during restoration. Herein, we developed a conceptual mechanistic frame regarding the contributions made by mineral-associated organic matter to soil C during the restoration of temperate grasslands. Compared to 1-year grassland restoration, 30-year restoration increased mineral-associated organic C (MAOC) by 41% and particulate organic C (POC) by 47%. The SOC changed from microbial MAOC predominance to plant-derived POC predominance, as the POC was more sensitive to grassland restoration. The POC increased with plant biomass (mainly litter and root biomass), while the increase in MAOC was mainly caused by the combined effects of increasing microbial necromass and leaching of the base cations (Ca-bound C). Plant biomass accounted for 75% of the increase in POC, whereas bacterial and fungal necromass contributed to 58% of the variance in MAOC. POC and MAOC contributed to 54% and 46% of the increase in SOC, respectively. Consequently, the accumulation of the fast (POC) and slow (MAOC) pools of organic matter are important for the sequestration of SOC during grassland restoration. Overall, simultaneous tracing of POC and MAOC helps further understand the mechanisms and predict soil C dynamics combined with the input of plant C, microbial properties, and availability of soil nutrients during grassland restoration.

Liao J ，Yang X ，Dou Y ，Wang B ，Xue Z ，Sun H ，Yang Y ，An S ... -  《-》

Changes of soil nutrients and organic carbon fractions in Caragana korshinskii forests with different restoration years in mountainous areas of southern Ningxia, China.

Zhang YH ，Li Y ，Zhou Y ，Chen YJ ，An SS ... -  《-》

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

Plant and microbially derived carbon (C) are the two major sources of soil organic carbon (SOC), and their ratio impacts SOC composition, accumulation, stability, and turnover. The contributions of and the key factors defining the plant and microbial C in SOC with grassland patches are not well known. Here, we aim to address this issue by analyzing lignin phenols, amino sugars, glomalin-related soil proteins (GRSP), enzyme activities, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC). Shrubby patches showed increased SOC and POC due to higher plant inputs, thereby stimulating plant-derived C (e.g., lignin phenol) accumulation. While degraded and exposed patches exhibited higher microbially derived C due to reduced plant input. After grassland degradation, POC content decreased faster than MAOC, and plant biomarkers (lignin phenols) declined faster than microbial biomarkers (amino sugars). As grassland degradation intensified, microbial necromass C and GRSP (gelling agents) increased their contribution to SOC formation. Grassland degradation stimulated the stabilization of microbially derived C in the form of MAOC. Further analyses revealed that microorganisms have a C and P co-limitation, stimulating the recycling of necromass, resulting in the proportion of microbial necromass C in the SOC remaining essentially stable with grassland degradation. Overall, with the grassland degradation, the relative proportion of the plant component decreases while than of the microbial component increases and existed in the form of MAOC. This is attributed to the physical protection of SOC by GRSP cementation. Therefore, different sources of SOC should be considered in evaluating SOC responses to grassland degradation, which has important implications for predicting dynamics in SOC under climate change and anthropogenic factors.

Ao D ，Wang B ，Wang Y ，Chen Y ，Anum R ，Feng C ，Ji M ，Liang C ，An S ... -  《-》

Divergent accumulation of amino sugars and lignins mediated by soil functional carbon pools under tropical forest conversion.

Tropical primary forests are being destroyed at an alarming rate and converted for other land uses which is expected to greatly influence soil carbon (C) cycling. However, our understanding of how tropical forest conversions affect the accumulation of compounds in soil functional C pools remains unclear. Here, we collected soils from primary forests (PF), secondary forests (SF), oil-palm (OP), and rubber plantations (RP), and assessed the accumulation of plant- and microbial-derived compounds within soil organic carbon (SOC), particulate (POC) and mineral-associated (MAOC) organic C. PF conversion to RP greatly decreased SOC, POC, and MAOC concentrations, whereas conversion to SF increased POC concentrations and decreased MAOC concentrations, and conversion to OP only increased POC concentrations. PF conversion to RP decreased lignin concentrations and increased amino sugar concentrations in SOC pools which increased the stability of SOC, whereas conversion to SF only increased the lignin concentrations in POC, and conversion to OP just increased lignin concentrations in POC and decreased it in MAOC. We observed divergent dynamics of amino sugars (decrease) and lignin (increase) in SOC with increasing SOC. Only lignin concentrations increased in POC with increasing POC and amino sugars concentrations decreased in MAOC with increasing MAOC. Conversion to RP significantly decreased soil enzyme activities and microbial biomasses. Lignin accumulation was associated with microbial properties, whereas amino sugar accumulation was mainly associated with soil nutrients and stoichiometries. These results suggest that the divergent accumulation of plant- and microbial-derived C in SOC was delivered by the distribution and original composition of functional C pools under forest conversions. Forest conversions changed the formation and stabilization processes of SOC in the long run which was associated with converted plantations and management. The important roles of soil nutrients and stoichiometry also provide a natural-based solution to enhance SOC sequestration via nutrient management in tropical forests.

Li T ，Cheng H ，Li Y ，Mou Z ，Zhu X ，Wu W ，Zhang J ，Kuang L ，Wang J ，Hui D ，Lambers H ，Sardans J ，Peñuelas J ，Ren H ，Mohti AB ，Liang N ，Liu Z ... -  《-》

Foraging tunnel disturbances created by small subterranean herbivores enhance soil organic carbon stability but reduce carbon sequestration in different alpine grassland types.

Foraging tunnel disturbances by small subterranean herbivores can alter soil properties and nutrient dynamics in grasslands, potentially altering soil organic carbon (SOC). Examining the impact of foraging tunnel disturbances on mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) is crucial for understanding SOC changes and its stability. However, the effects of these disturbances on POC and MAOC are not well documented. This study uses the plateau zokor (Eospalax baileyi) as a focal subterranean herbivore to investigate the effects of foraging tunnel disturbances on POC and MAOC in alpine steppes, alpine meadows, and alpine meadow steppes. Ninety paired quadrats were used for soil and plant sampling across three alpine grassland types. Results show that foraging tunnel disturbances consistently reduced POC concentrations across all grassland types, with reductions of 44.01 % in alpine steppes, 20.86 % in alpine meadows, and 29.58 % in alpine meadow steppes. MAOC concentrations decreased by 16.49 % in alpine steppes, while no significant changes in MAOC were observed in alpine meadows and alpine meadow steppes. The reduction in the POC to MAOC ratio indicates increased SOC stability. However, despite this increased stability, the change may lead to a decrease in overall carbon sequestration potential, as the total SOC in the soil declines. The main factors influencing POC and MAOC were soil moisture, belowground biomass, and microbial biomass carbon, with their influences varying by grassland type. The findings demonstrate that foraging tunnel disturbances by plateau zokors can lead to substantial modifications in SOC composition, influencing both its stability and sequestration potential. The disturbances necessitate tailored management strategies to mitigate their impacts, considering the unique characteristics of each grassland type to preserve carbon sequestration potential. This study contributes to a deeper understanding of the ecological role of small subterranean herbivores in the carbon cycle of alpine grassland ecosystems.

Yang H ，Duan YY ，Guo ZG ，Pang XP ... -  《-》