黄土高原天然次生林植被演替过程中土壤团聚体有机碳动态变化

土壤团聚体物理保护是促进有机碳积累主要机制之一。以黄土高原子午岭林区天然次生林植被演替群落为对象，研究从农田、草地（白羊草，Bothriochloa ischaemum）、灌木林（沙棘，Hippophae rhamnoides）、先锋林（山杨，Populus davidiana）到顶级林（辽东栎，Quercus liaotungensis）5个植被演替阶段0-20 cm土壤团聚体稳定性和团聚体有机碳的动态变化，并分析团聚体有机碳的影响因素。结果表明：土壤团聚体稳定性随着植被演替显著提高（P<0.05），顶级林的团聚体稳定性最高；土壤有机碳含量和各粒径土壤团聚体（> 2 mm、2-0.25 mm、0.25-0.053 mm、<0.053 mm）有机碳含量均随着植被演替而增加。除草地0.25-0.053 mm团聚体有机碳含量最高外，其他演替阶段均为0.25-2 mm粒径最高。根系生物量、凋落物生物量、微生物生物量碳、团聚体稳定性均与团聚体有机碳含量呈显著正相关关系（P<0.05）。总体而言，长期植被演替有助于团聚体稳定性和团聚体有机碳累积。

Dynamics of soil aggregate-associated organic carbon during secondary forest succession in the Loess Plateau, China

Vegetation restoration plays an important role in soil structure and nutrients. The effects of vegetation restoration on the aggregate stability and soil carbon storage have been widely studied, but the distribution of aggregate associated organic carbon and the effects of plants on aggregate associated organic carbon in the secondary forest succession are still unclear. This paper studied the stability of soil aggregates and the changes of soil aggregate-associated organic carbon under the succession sequence of the secondary forests in Ziwuling forest region of the Loess Plateau, China. We discussed the dynamics of aggregate-associated organic carbon and its influencing factors following the secondary forest succession. In the field investigation, five vegetation succession stages were selected:farmland (CL), grassland (GL), shrub (S), pioneer forest (PF), and climax forest (CF). Soil samples in 0-20 cm were collected and the aggregates were separated by wet sieving. The stability of aggregates was characterized by mean weight diameter (MWD), geometric mean diameter (GMD), and percentage of water stable aggregates (WAS). The organic carbon, root biomass, litter biomass and microbial biomass carbon (MBC) of soil and aggregates were measured. The dynamics of soil aggregate-associated organic carbon and its influencing factors were analyzed. The results showed that soil organic carbon contents increased with vegetation succession, which showed that CF>PF>S>CL, and the organic carbon contents of aggregates increased more significantly from grassland to pioneer arbor stage. The succession of vegetation communities significantly increased the content of soil organic carbon. The stability of soil aggregate increased significantly with vegetation succession (P<0.05). The stability of soil aggregate in climax forest was the highest, and the contents of macroaggregate>0.25 mm in pioneer forest and climax forest were higher than that in farmland. The organic carbon contents of soil aggregates with different particle sizes increased with vegetation succession, and the organic carbon content of 2-0.25 mm was the highest in each succession stage. The stability of aggregates was positively correlated with the soil organic carbon. Root biomass, litter biomass and the MBC were significantly positively correlated with aggregate-associated organic carbon content. The main factors affecting soil organic carbon contents of aggregates were different in different particle sizes. Except the stages of vegetation succession, soil total organic carbon, litter biomass and soil aggregate stability were the main factors affecting the organic carbon content in the macroaggregates (> 0.25 mm), middle aggregates (0.25-0.053 mm), and microaggregates (<0.053 mm). The study suggests that vegetation succession plays an important role in the stability of aggregates and the fixation of organic carbon in aggregates.