黄土高原刺槐林恢复中土壤微生物代谢对团聚体固碳的影响机制

Artificial vegetation establishment is an effective measure to improve soil quality. Particularly, artificial Robinia pseudoacacia is widely planted on the Loess Plateau and its significant carbon sink has been widely recognized. At present, several achievements have been made in the evolution characteristics of soil carbon pool under different restoration stages. However, the research regarding the microbial key metabolism that controls the soil carbon sequestration of artificial Robinia pseudoacacia is relatively insufficient, especially at aggregate levels, the mechanism of microbial carbon sequestration is still unclear. Therefore, this project intends to select different restoration stages of Robinia pseudoacacia, to take different aggregate sizes as the research object, and to use soil carbon decomposition model and 13C isotope tracer technology to highlight: the characteristics of aggregate-associated carbon pool that are dominated by soil active microbial biomass carbon and dead microbial residues (field observation trend); the effects of soil active microbial community and microbial carbon-degrading enzymes on aggregate-associated organic carbon decomposition (indoor mechanism verification); the distribution ratios of soil dead microbial residue carbon in different aggregate sizes and their relative contributions to aggregate-associated organic carbon accumulation (indoor mechanism verification). On this basis, the influence mechanism of soil microbial key metabolism on the aggregate-associated carbon sequestration under artificial Robinia pseudoacacia restoration are explored, which provide a scientific basis for assessing the carbon sequestration potential of artificial vegetation establishment in China.

人工林建设是改善土壤质量的有效措施，特别是人工刺槐林，在黄土高原地区被广泛栽植，其显著的碳汇效应得到了普遍的认可。目前就不同恢复阶段土壤碳库演变特征已经取得了不少研究成果，但是对微生物关键代谢主导的人工刺槐林固碳效应研究相对不足，尤其基于团聚体水平上的固碳机理仍不清楚。因此，本项目拟选择不同恢复阶段刺槐林，以土壤不同粒级团聚体为研究对象，利用有机碳分解模型和13C同位素示踪技术，在人工刺槐林不同恢复阶段重点阐明：土壤活性微生物量碳和死亡微生物残体碳主控的团聚体碳库演变特征（野外观测趋势）；土壤活性微生物群落和微生物碳降解酶对团聚体有机碳分解的影响特征（室内机理验证）；土壤死亡微生物残体碳在不同粒级团聚体中的分配比例及其对团聚体有机碳累积的相对贡献（室内机理验证）等科学问题。据此，探索人工刺槐林恢复中土壤微生物关键代谢对团聚体固碳的影响机制，为评估我国人工林固碳潜力提供科学依据。

在人工刺槐林恢复过程中，从不同粒级土壤团聚体单元角度研究微生物代谢与土壤固碳机制可以进一步完善土壤碳库变化机制。鉴于此，本项目以“植被-土壤-微生物”为研究对象，通过野外调查和室内试验等系统的研究土壤微生物源碳与团聚体碳之间的关系，以及通过室内培养实验和13C标记等探究土壤微生物群落和碳降解酶对有机碳激发的影响,并探索化学计量失衡条件下微生物介导的 C 动态的潜在机制。取得如下结果：.(1) 明确了刺槐林恢复中土壤源碳的变化特征，全土微生物量碳以及全土和团聚体的残体碳含量增加，且真菌残体碳占主导，微团聚体中残体碳含量均高于其他粒级。.(2) 阐明了土壤微生物群落和碳降解酶对有机碳激发的影响，刺槐林恢复中有机碳激发效应均为正向且与团聚体有机碳矿化都表现为先增后降趋势，土壤水解酶活性随刺槐林龄增加而递增，而氧化酶活性随林龄增加呈现先增加后降低的趋势。团聚体纤维二糖水解酶活性也随林龄增加呈现先增加后降低的趋势。不同造林阶段森林土壤微生物分类组成差异显著，土壤稳定碳分解基因的丰度，从而促进了土壤有机碳的激发。.(3) 阐明了刺槐林恢复中土壤植物和死亡微生物残体有机碳及转化的影响，所有主导性的酶家族基因均在造林后均高于农田，且在造林 20 年达到峰值。随着林分年龄的增加，降解植物和微生物衍生成分的土壤微生物CAZyme家族显著增加。变形菌，催化木质素和脂质降解的功能基因也显着增加。相反，催化单糖降解的基因的相对丰度显著降低。.(4) 揭示了土壤微生物对化学计量失衡的适应性调节驱动演变，酶促化学计量学和微生物群落特性均未直接影响土壤微生物呼吸，而是通过改变TERs间接影响了土壤微生物呼吸。.以上研究成果从人工刺槐林恢复时间序列上，研究土壤微生物代谢对团聚体固碳的影响机制，以期阐明土壤微生物代谢在团聚体固碳中的作用机理以及更准确评估人工植被的碳汇价值提供科学依据。.