西双版纳热带森林碳循环中土壤呼吸对次生演替的响应

【目的】探明热带森林次生演替过程中土壤呼吸速率的季节变化及其主要调控因素,分析土壤微生物生物量碳及理化性质对土壤呼吸速率时间动态的影响,为精确评估热带森林恢复对土壤碳库变化的影响提供参考。【方法】采用LI-6400-09便携式土壤呼吸测定仪对西双版纳热带森林演替前期的白背桐(Mallotus paniculatus)群落与演替后期的高檐蒲桃(Syzygium oblatum)群落土壤呼吸速率进行连续定位观测,结合相关分析和主成分分析,探讨热带森林演替过程中土壤微生物生物量碳、容重、pH及碳氮库各组分含量变化对土壤呼吸速率的影响。【结果】研究区白背桐与高檐蒲桃群落土壤呼吸具有明显的单峰型季节变化特征,最大值出现在湿季(6月),其中高檐蒲桃群落土壤呼吸速率3.80~6.19 μmol/(m²·s)]显著高于白背桐群落2.40~4.35 μmol/(m²·s)],但恢复前期土壤呼吸变幅(1.81倍)显著高于恢复后期(1.63倍);土壤呼吸速率随土壤温度和水分季节变化呈非线性显著或极显著增加的趋势(P<0.01或P<0.05),其中,高檐蒲桃群落温度、水分对土壤呼吸的解释率分别为49.00%~65.30%、2.96%~53.00%,显著高于白背桐群落的6.40%~49.10%、2.48%~43.70%;两群落土壤呼吸速率均与碳库(总碳、土壤微生物生物量碳)及氮库(硝态氮、全氮、铵态氮)含量显著或极显著正相关(P<0.01或0.05),并与pH呈极显著负相关 (P<0.01);土壤易氧化碳、硝态氮、含水量对土壤呼吸变化的贡献最大,而土壤温度、土壤微生物生物量碳、全氮、铵态氮及水解氮的影响次之。【结论】西双版纳热带森林次生演替显著促进了土壤呼吸,土壤呼吸时间动态主要受土壤微气候(如含水量)及土壤碳库(如易氧化碳)、氮库(如硝态氮)组分含量所调控。

Responses of soil respiration to tropical forest secondary succession in Xishuangbanna

【Objective】This study aimed to examine seasonal variations in soil respiration rates during secondary tropical forest succession, which could provide a reference basis for an accurate assessment of the effects of tropical forest restoration on soil carbon and nitrogen pool changes.【Method】The LI-6400-09 respiration chamber connected to a portable infrared gas analyzer was employed for continuous observation of soil respiration rates in Mallotus paniculatus and Syzygium oblatum communities. We also assessed the effects of changes in soil microbial biomass carbon, bulk density, pH, and concentrations of carbon and nitrogen pools on soil respiration rates using the statistical methods of correlation and principal component analyses. 【Result】There were significant seasonal variations in respiration rates in the two secondary forests. Soil respiration exhibited a similar fluctuation pattern, with a single peak occurring during the wet season (June). Soil respiration rates were significantly higher in the S. oblatum community3.80~6.19 μmol/(m²·s)]than in the M. paniculatus community2.40~4.35 μmol/(m²·s)]. However, the variations in soil respiration rates were significantly higher in the early restoration stage (1.81 times) than in the late restoration stage(1.63 times). Soil respiration rates increased nonlinearly with seasonal variations in soil temperature and water values (P<0.01, or P<0.05). The contributions of soil temperature (49.00%~65.30%) and water content (2.96%~53.00%) to soil respiration variations were higher in the S. oblatum community than in the M. paniculatus community (6.40%~49.10%, 2.48%~43.70%). Soil respiration rates in the M. paniculatus and S. oblatum communities were positively correlated with the concentrations of the carbon pool (e.g., total organic carbon and microbial biomass carbon) and nitrogen pool (e.g., total nitrate and ammonium nitrogen)(P<0.01, or P<0.05). In contrast, there was a negative correlation with soil pH (P<0.01). Furthermore, the values of easily oxidized carbon, nitrate nitrogen, and water content contributed the most to variations in soil respiration rates, whereas the contributions of soil temperature, microbial carbon, total nitrogen, ammonium nitrogen, and hydrolyzable nitrogen to soil respiration dynamics ranked second. 【Conclusion】The secondary succession of Xishuangbanna tropical forests significantly promoted the soil respiration rates. The temporal variations in soil respiration rates were mainly controlled by the soil microclimate (e.g., water content), the concentrations of the carbon (e.g., easily oxidized carbon)and nitrogen (e.g., nitrate nitrogen) pools.