College of Nature Resources and Environment, Northwest A&F University, Yangling 712100, China.
College of Grassland Agriculture, Northwest A&F University, Yangling 712100, China.
Sci Total Environ. 2024 Nov 15;951:175717. doi: 10.1016/j.scitotenv.2024.175717. Epub 2024 Aug 26.
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.
植物和微生物衍生碳（C）是土壤有机碳（SOC）的两个主要来源，它们的比例影响 SOC 的组成、积累、稳定性和周转。草原斑块中 SOC 中植物和微生物 C 的贡献及其定义的关键因素尚不清楚。在这里，我们通过分析木质素酚类、氨基糖、胶结相关土壤蛋白（GRSP）、酶活性、颗粒有机碳（POC）和矿物结合有机碳（MAOC）来解决这个问题。灌木斑块由于植物输入增加而表现出较高的 SOC 和 POC，从而刺激植物衍生 C（例如木质素酚）的积累。而退化和暴露的斑块由于植物输入减少，微生物衍生 C 较高。在草原退化后，POC 含量的下降速度快于 MAOC，而植物生物标志物（木质素酚）的下降速度快于微生物生物标志物（氨基糖）。随着草原退化的加剧，微生物残体 C 和 GRSP（胶结剂）增加了它们对 SOC 形成的贡献。草原退化刺激了 MAOC 形式的微生物衍生 C 的稳定化。进一步的分析表明，微生物存在 C 和 P 的共同限制，刺激了残体的再循环，导致 SOC 中微生物残体 C 的比例随着草原退化基本保持稳定。总的来说，随着草原的退化，植物成分的相对比例减少，而微生物成分的比例增加，并以 MAOC 的形式存在。这归因于 GRSP 胶结对 SOC 的物理保护。因此，在评估 SOC 对草原退化的响应时，应该考虑 SOC 的不同来源，这对于预测气候变化和人为因素下 SOC 的动态具有重要意义。
