黄土高原植被演替中土壤团聚体有机碳迁移过程及其驱动机制

Vegetation succession is one of the key factors affecting the function transformation of soil carbon "source" and "sink". Through the determination of total soil (bulk soil) organic carbon is difficult to accurately and timely reflect the internal changes in soil carbon library during the process of vegetation succession, therefore, clear the distribution of smaller soil organic carbon fractions contents is a key factor to reveal the effects of vegetation succession on soil organic carbon. This study mainly focus on the dynamics of soil aggregate-associated organic carbon following vegetation succession on the loess plateau of China, to clear the litter and root (plant organic matter) input contributions to soil aggregate-associated organic carbon accumulation and influence mechanism, tracer the distribution patterns of new inputs of organic carbon in soil aggregates and quantitative the contributions of "new" carbon and "old" carbon to soil aggregate organic carbon mineralization, to reveal the influence mechanism of soil microbe effects on soil aggregate-associated organic carbon accumulation and transformation during the process of vegetation succession, to explore the correlations among soil aggregate-associated organic carbon, litter and root inputs, as well as soil microbial community and the trends along with vegetation succession, expecting to provide a scientific theory basis for further understanding soil organic carbon stability mechanism and regulation process of ecological restoration and reconstruction on the Loess Plateau.

植被演替是影响土壤碳“源/汇”功能转变的关键因素之一。通过总有机碳的测定很难准确、及时反映植被演替中土壤碳库的内在变化，所以，明确较小的有机碳组分含量的分布特征是揭示植被演替影响土壤有机碳的关键。本研究通过对黄土高原植被演替中土壤团聚体有机碳进行研究，明确植被演替中凋落物和根系输入对土壤团聚体有机碳累积的贡献和影响机制；示踪新输入有机碳组分在土壤团聚体碳库中的分配格局和迁移过程，量化“新碳”与“老碳”对土壤团聚体有机碳矿化的贡献；揭示植被演替中微生物对土壤团聚体有机碳积累和转化的作用机制；探讨土壤团聚体有机碳、凋落物和根系输入以及微生物群落之间的关联性及其随植被演替的演变规律，以期为深入认识黄土高原生态恢复与重建中土壤有机碳库稳定性机制及其调控过程提供科学依据。

植被演替是影响土壤碳“源/汇”功能转变的关键因素之一。通过总有机碳的测定很难准确、及时反映植被演替中土壤碳库的内在变化，所以，明确较小的有机碳组分含量的分布特征是揭示植被演替影响土壤有机碳的关键。本研究通过对黄土高原植被演替中土壤团聚体有机碳进行研究，探讨了植被演替中“新碳”与“老碳”对土壤团聚体有机碳的贡献，分析了土壤团聚体有机碳与植物和微生物群落之间的关联性，揭示了植物和和微生物对土壤团聚体有机碳累积的影响机制。取得如下研究进展：（1）明确了植被演替中土壤团聚体有机碳“新碳”和“老碳”的迁移动态，即从大团聚体向小团聚体迁移。发现不同粒径团聚体有机碳增加速率、分解速率和新碳比例主要发生在植被演替初期，且颗粒态有机碳对总有机碳的影响总效应大于0.8，可作为土壤固碳功能恢复的重要指标；土壤有机碳的稳定性在表层土壤中主要是由凋落物、根系和微生物等生物化学稳定性机制决定，而在下层土壤中主要受土壤团聚体物理保护机制影响。（2）揭示了植被演替中凋落物分解对团聚体有机碳的影响。发现凋落物氮、纤维素、木质素含量以及土壤酶活性是影响凋落物分解的主要因素；植被演替早期土壤有机碳库及其组分主要与凋落物的纤维素、木质素含量相关，而植被演替后期土壤有机碳组分与凋落物碳氮比关系更为密切。（3）阐明了植被演替中土壤微生物动态及其对土壤有机碳周转的影响。发现植被演替中细菌和真菌数量显著增加，但微生物群落组成较稳定，且微生物群落的变化滞后于植被和土壤演替的变化。微生物的养分限制是影响植被演替后期土壤有机碳周转的重要因素。（4）发现了土壤有机碳矿化效率高低是决定土壤碳库累积的关键。发现植被恢复后由于土壤活性碳库的增加显著增加了土壤碳排放，但由于土壤质地的改善、大团聚体的形成以及pH的降低，降低了土壤微生物碳利用效率和有机碳矿化效率，从而促进了土壤有机碳累积。研究结果可为深入认识黄土高原生态恢复与重建中土壤有机碳库稳定性机制及其调控过程提供科学依据。