土壤碳库积累与分配对热带森林恢复的响应

Responses of soil carbon component accumulation and allocation to tropical forest restoration

为探明土壤有机碳沉积对热带森林恢复的响应过程与机理,选取西双版纳处于不同恢复阶段的热带森林类型(前期的白背桐群落、中期的崖豆藤群落、后期的高檐蒲桃群落)为研究对象,探讨土壤有机碳库各组分积累与分配(微生物量碳储量/总有机碳储量、易氧化有机碳储量/总有机碳储量、惰性有机碳储量/总有机碳储量)的时空变化规律,分析乔木与林下物种的丰富度和多样性、土壤温湿度、容重、pH及氮库(全氮、水解氮、铵氮、硝氮)对土壤有机碳库组分积累与分配的影响。结果表明:(1)热带森林恢复显著促进土壤碳库各组分的蓄积(P<0.05),相较于恢复前期,恢复中后期土壤总有机碳、微生物量碳、易氧化有机碳、惰性有机碳储量增幅达9.25%—50.84%;恢复促进了土壤微生物量碳和易氧化有机碳的分配(8.98%—25.36%)(P<0.05),但对惰性有机碳分配无显著影响;(2)不同恢复阶段热带森林土壤碳组分积累与分配的时空变化存在一定的差异。其中上述4种碳组分积累最大值均出现在6月、垂直变化均沿土层递减;土壤易氧化有机碳和微生物量碳分配最大值出现在6月、惰性有机碳分配则在12月最大,易氧化有机碳和微生物量碳分配沿土层递减、惰性有机碳分配无显著垂直变化;(3)土壤微生物量碳、易氧化有机碳、惰性有机碳的储量在土壤碳库储量的分配占比分别维持在2.40%—5.00%、18.22%—39.34%、18.50%—26.55%,土壤有机碳组分对总有机碳储量变化的解释率表现为:微生物量碳(83.71%)>惰性有机碳(82.17%)>易氧化有机碳(78.54%);(4)相较于恢复初期,恢复后期乔木与林下物种丰富度和Shannon多样性提升了42.78%—490.82%,氮库(全氮、水解氮、铵氮、硝氮)含量仅提升了12.73%—25.51%;(5)冗余分析表明,林下物种丰富度、温湿度、水解氮是影响土壤有机碳组分积累的主要驱动因子,而乔木香农多样性、湿度、容重则是影响土壤有机碳库组分分配的主控因子。因此,西双版纳热带森林恢复进程显著促进了土壤有机碳库组分积累与分配,影响程度取决于样地林下物种丰富度、乔木香农多样性、土壤温湿度、容重与水解氮的状况。

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.