鼎湖山针阔叶混交林凋落物CO2释放对模拟酸雨的响应

该研究2011年1月开始在鼎湖山针阔叶混交林(混交林)进行模拟酸雨实验,设置4个不同处理水平,即对照(CK)(pH为4.5左右的天然湖水)、T_1(pH=4.0)、T_2(pH=3.25)和T_3(pH=2.5)。2013年1—12月对不同酸雨强度处理下的森林凋落物CO_2释放速率进行为期1 a的连续观测,探讨酸雨对混交林凋落物C排放的影响。结果表明:凋落物CO2释放通量在对照样方为(1 507.41±155.19) g CO_2·m~(-2)·a~(-1),其中湿季和旱季分别占年通量的68.7%和31.3%。模拟酸雨抑制了森林凋落物CO_2释放,与CK相比,T_2和T_3处理下的CO_2释放通量分别显著降低15.4%和42.7%(P0.05);且这种抑制作用具有季节差异性,处理间的显著差异只出现在湿季。凋落物CO_2释放速率与土壤温度和土壤湿度分别呈显著指数相关和显著直线相关,同时,酸雨处理降低了凋落物CO_2释放的温度敏感性。混交林凋落物CO_2释放在模拟酸雨下的抑制效应与土壤累积酸化而导致的土壤微生物活性变化有关,表现为模拟酸雨作用下土壤pH值和微生物量碳显著下降。上述结果说明酸雨是影响混交林土壤碳循环的重要因子之一。

Responses of litter CO2 emission to simulated acid rain in a mixed conifer and broad-leaved forest of Dinghushan Nature Reserve

A field experiment of simulated acid rain(SAR)was conducted in a mixed conifer and broadleaf forest(MF)at Dinghushan Nature Reserve. SAR treatments included CK(the local lake water, pH 4.5), T1(pH 4.0), T2(pH 3.25), and T3(pH 2.5)with four replicates. SAR experiments were initiated in January 2011, and the litter CO₂ emission rate under SAR was measured twice a month over one year from January 2013 to December 2013. The results indicated that litter CO₂ emission followed a clear seasonal pattern in the forest during the study period, with significantly higher rates in the wet season and lower rates in the dry one(P<0.05). The mean annual litter CO₂ emission in the CK plots was(1 507.41±155.19)g CO₂·m^-2·a^-1, to which the wet season and the dry season contributed 68.7% and 31.3%, respectively. SAR significantly reduced litter CO₂ emission in the forest(P<0.05). Compared with CK, mean annual litter CO₂ emission was 15.4% and 42.7% lower in T2 and T3 treatments, respectively. SAR reducing litter CO₂ emission had seasonal differences, and these negative effects were evident in the wet season(P<0.05), but not in the dry one. In all treatments, litter CO₂ emission rate exhibited significantly positive exponential relationships with soil temperature and significantly positive linear relationships with soil moisture. In addition, the mean temperature sensitivity(Q₁₀)values showed a declining trend with the increasing level of SAR. The depression of litter CO₂ emission after SAR in the MF was related to the aggravation of soil acidification and the depression of microbial activity, as we found that soil pH value and soil microbial biomass C significantly decreased under SAR. In conclusion, our results supported an important role of acid rain in regulating soil carbon cycle.