凋落物处理对森林地表CO2通量的影响及其调控机理

全球变化和森林演替可以导致森林地表凋落物数量和质量的变化，从而对森林地表 CO2通量产生影响。本实验对亚热带不同演替阶段的3种，即马尾松林（前期）、混交林（中期）和季风林（后期）进行地表凋落物去除、加倍与置换处理，利用静态箱气相色谱法测定地表CO2通量，并同步测定气温、土壤温度和湿度，分析凋落物质量和数量变化对森林地表CO2通量的影响及其调控机理。结果表明，（1）去除凋落物处理显著降低了不同演替阶段的3种森林地表CO2通量，而加倍凋落物处理可以增加森林地表CO2通量，但不同演替阶段增加的幅度不同，依次为：季风林＞马尾松林＞混交林。（2）置换凋落物对不同演替阶段的森林地表 CO2通量的影响不同，在演替后期的季风林中，置换混交林和马尾松林凋落物处理均增加地表CO2通量；在演替中期的混交林中，置换季风林和马尾松林凋落物均降低地表CO2通量。在演替前期的马尾松林中，置换季风林凋落物增加地表CO2通量，而置换混交林凋落物降低了地表CO2通量（3）结合测定的土壤温度和水分数据分析得出，凋落物处理引起森林地表 CO2通量的变化是通过处理凋落物质量和数量后改变森林地表水热条件来实现的。（4）3个林型的各种处理，地表 CO2通量与土壤温度均呈显著的指数相关关系，但不同处理不同地改变了森林地表土壤 CO2通量对温度的敏感性，即Q10值。

Effects of litter treatments on CO2 emission at forest floor

Global change and forest succession are likely to change litter input to forest soils, including litter quality and litter amount, but the effects of such changes on CO2 emission at forest floor still remain largely unknown. We initiated a manipulated experiment of litter in three successional subtropical forest （Masson pine forest （early stage）, mixed forest （interim stage） and monsoon forest （advanced stage） in Dinghushan Nature Reserve. 5 replicates of litter remove, litter double, litter replacement （e.g., litter from mixed forest and monsoon forest take the place of original litter in Masson pine forest）, and control treatments were established in each forest type. CO2 emission at forest floor was measured using static chamber and gas chromatography techniques and air temperature, soil temperature and moisture were determined during the study period. We found that：（1） Litter remove decreased CO2 emission at forest floor in each of three successional forests, while litter double increased CO2 emission at forest floor in each of three successional forests. （2）The response of CO2 emission at forest floor to litter replacement was very different in the three forests. Litter replacement from Masson pine forest or mixed forest in monsoon forest increased CO2 emission at forest floor. Litter replacement from Masson pine forest or monsoon forest in mixed forest decreased CO2 emission at forest floor. Litter replacement from monsoon forest in Masson pine forest increased CO2 emission at forest floor. Litter replacement from mixed forest in Masson pine forest decreased CO2 emission at forest floor. （e）Both litter quality and amount affected CO2 emission at forest floor through the changes of soil temperature and moisture. （4） CO2 emission at forest floor increase exponentially with soil temperature under all treatments in each forest. Different treatments can alter differently the sensitivity of CO2 emission at forest floor to soil temperature.