Abstract:In order to explore the response process and mechanism of soil organic carbon sequestration to tropical forest restoration, three forest types, i.e, Mallotus paniculatus community (early restoration stage), Mellettia leptobotrya community (middle restoration stage), and Syzygium oblatum community (late restoration stage), were selected to identify the spatio-temporal variations in soil organic carbon component accumulation and allocation (i.e., microbial biomass carbon/total organic carbon, easily oxidizable organic carbon/total organic carbon, and resistant organic carbonin/total organic carbon) in Xishuangbanna tropical forests. We also analyzed the effects of species richness and diversity of tree and understory pants, soil temperature and humidity, bulk density, pH and nitrogen pool (i.e., total, hydrolyzable, ammonium, and nitrate nitrogen) on component accumulation and allocation of soil organic carbon in the tropical forests. The results were as follows. (1) The tropical forest restoration significantly accelerated the accumulation of soil organic carbon components (P<0.05). The stocks of total, microbial, easily oxidizable, and resistant organic carbon at the middle and late restoration stages increased by 9.25%-50.84%, compared with early restoration stage. The forest restoration promoted the allocation of soil microbial and oxidizable organic carbon stocks by 8.98%-25.36%, but it had no significant effect on the allocation of resistant organic carbon (P<0.05). (2) Soil carbon component accumulation and allocation had spatiotemporal changes in the three restoration stages of tropical forests. The maximum accumulation of the above four carbon components was in June and they decreased along the soil layer. The maximum allocation of soil easily oxidized and microbial biomass carbon occurred in June, while that of resistant organic carbon was in December. The allocation of microbial and easily oxidized organic carbon decreased along the soil layer, while that of resistant organic carbon had no significant vertical change. (3) The component allocation of soil organic carbon stocks was ranked as microbial biomass carbon stock (83.71%)>resistant organic carbon (82.17%)>easily oxidized organic carbon stock (78.54%) (P <0.05). The explanation percentages of microbial, easily oxidizable, and resistant organic carbon to total organic carbon in the three restoration stages were 2.40%-5.00%, 18.22%-39.34%, and 18.50-26.55%, respectively. (4) In contrast to early restoration stage, species richness and Shannon diversity of tree and understory plants increased by 42.78%-490.82%, and nitrogen pool (i.e., total, hydrolyzed, ammonium, and nitrate nitrogen) only increased by 12.73%-25.51% at the late restoration stage. (5) Redundancy analysis showed that understory species richness, temperature, humidity, hydrolyzed were the main driving factors affecting carbon component accumulation, while tree Shannon diversity, humidity, and bulk density were the main controlling factors of carbon component allocation. Therefore, Xishuangbanna tropical forests restoration significantly promoted the component accumulation and allocation of soil organic carbon, which was determined by understory species richness and tree Shannon diversity, as well as soil temperature, humidity, bulk density, and hydrolyzed nitrogen.