College of Grassland Agriculture, Northwest A&F University, Yangling 712100, China.
College of forestry, Northwest A&F University, Yangling 712100i, China.
Sci Total Environ. 2024 Dec 15;956:177058. doi: 10.1016/j.scitotenv.2024.177058. Epub 2024 Nov 9.
Grassland fencing is acknowledged as a crucial initiative to enhance biodiversity and to increase soil organic carbon (SOC) content in ecologically fragile regions or barren systems. Theoretical perspectives propose that fencing induced an increase in root biomass, and its penetration into the soil profile introduced organic matter that facilitated SOC formation through microbial necromass and root residues. It is hypothesized that long-term grassland fencing increases root biomass, thereby enhancing SOC formation within the soil profile through microbial residues in badland ecosystems. To test this hypothesis, we selected grasslands subjected to varying durations of fencing post-grazing (i.e., 10, 15, 20, 30, and 40 y). Our investigation aimed to clarify microbial necromass dynamics in 0-100 cm soil profiles after fencing and to identify the influencing factors. Long-term grassland fencing (i.e., >30 y) increased root biomass by 160 %, SOC by 69 %, and necromass by 41 % compared to grazed grassland within the 0-40 cm horizon; in contrast, increased root biomass by 870 %, SOC by 111 %, and necromass by 46 % in the 40-100 cm horizon. Necromass in deep soil (40-100 cm) accounted for about 50 % of total residues in the 0-100 cm profile. Increased root and living microbial biomass stimulated the necromass accumulation, with a more pronounced increase in fungal residues compared with bacterial residues. Nonetheless, microbial nutrient limitation increases C or N-acquisition enzyme coefficients, which subsequently reduced fungal and bacterial residues and stimulated their recycling. Despite substantial increases in root biomass within the soil profile after fencing, limitation of microbial N and depth reduced the effectiveness of enhancing SOC and necromass. In conclusion, although microbial residues were the important source of SOC in grasslands of the Loess Plateau, microbial N limitation impeded necromass accumulation, and the interplay of root biomass, soil depth, and nutrient limitation regulated the dynamics of necromass following grassland fencing.
草原围栏被认为是提高生物多样性和增加生态脆弱地区或贫瘠系统土壤有机碳 (SOC) 含量的重要措施。理论观点认为，围栏导致根系生物量增加，其根系穿透土壤剖面，引入的有机物质通过微生物残体和根系残体促进 SOC 的形成。有人假设，长期的草原围栏会增加根系生物量，从而通过荒地生态系统中的微生物残体增强土壤剖面中的 SOC 形成。为了检验这一假设，我们选择了经历不同放牧后围栏时间（即 10、15、20、30 和 40 年）的草地。我们的研究旨在阐明围栏后 0-100cm 土壤剖面中微生物残体的动态，并确定影响因素。与放牧草地相比，长期的草原围栏（即>30 年）使 0-40cm 土壤剖面中的根系生物量增加了 160%，SOC 增加了 69%，微生物残体增加了 41%；而在 40-100cm 土壤剖面中，根系生物量增加了 870%，SOC 增加了 111%，微生物残体增加了 46%。深层土壤（40-100cm）中的微生物残体约占 0-100cm 土壤剖面中总残体的 50%。增加的根系和活微生物生物量刺激了微生物残体的积累，真菌残体的增加比细菌残体更为明显。尽管围栏后土壤剖面中的根系生物量显著增加，但微生物氮素限制增加了 C 或 N 获得酶系数，从而减少了真菌和细菌残体，并刺激了它们的再循环。尽管在围栏后土壤剖面中的根系生物量大幅增加，但微生物氮素限制和土壤深度降低了增强 SOC 和微生物残体的效果。总之，尽管微生物残体是黄土高原草地 SOC 的重要来源，但微生物氮素限制阻碍了微生物残体的积累，而根系生物量、土壤深度和养分限制之间的相互作用调节了围栏后微生物残体的动态。
