模拟酸雨对鼎湖山季风常绿阔叶林土壤呼吸的初期影响

通过在鼎湖山季风常绿阔叶林(季风林)进行野外模拟酸雨试验,对不同酸雨强度处理下的林地土壤呼吸速率进行原位测定,探讨酸雨对南亚热带森林土壤呼吸的初期影响。结果表明:在两年的测定周期内,4个酸雨水平:CK(pH值4.5左右的天然湖水)、T1(pH值4.0)、T2(pH值3.5)和T3(pH值3.0)处理下的年平均土壤呼吸速率分别为(3.07±0.08)、(3.06±0.17)、(2.78±0.29)和(2.56±0.08)μmol·m~(-2)·s~(-1),其中T3处理显著低于CK和T1处理(P0.05),说明模拟酸雨抑制了季风林土壤呼吸。这种抑制作用大体上随处理时间的延长而逐渐显著,处理间的差异只在测定周期的第二年达到显著水平,且抑制作用的差异显著性只出现在湿季(P0.05)。模拟酸雨对土壤呼吸的抑制作用可能与其胁迫下土壤酸化而导致土壤微生物异养呼吸及凋落物CO_2释放量下降有关。表现为模拟酸雨导致土壤pH值降低,使得土壤酸化加剧;降低了土壤微生物量碳、氮含量,抑制了微生物活性;提高了凋落物质量残留率,抑制了凋落物分解。还与土壤呼吸结果相对应,上述指标对模拟酸雨的响应也大体上随处理时间的延长而逐渐显著。另外,土壤呼吸温度敏感系数Q_(10)值随处理pH值降低有下降的趋势,表明酸雨处理在一定程度上降低了土壤呼吸的温度敏感性。

Effects of simulated acid rain on soil respiration in a monsoon evergreen broad-leaved forest at Dinghushan Nature Reserve

Determining the effects of elevated acid rain on forest soil respiration can provide useful information for under-standing of the process of carbon cycle of forest ecosystem and its response to global change. Therefore, a simulated acid rain ( SAR ) experiment was conducted in a monsoon evergreen broad-leaved forest at the Dinghushan Nature Reserve. SAR treatments included CK ( the local lake water, pH4.5) , T1( pH4.0) , T2( pH3.5) , T3( pH3.0) with three replicates. SAR experiments were initiated in June 2009 and were sprayed twice a month during the study period. Re-sponses of soil respiration to SAR were studied from April 2010 to March 2012 with a LI-8100 soil CO2 efflux system. The results showed that mean annual soil respiration rates for the CK, T1, T2, and T3 treatments were (3.07±0.08), (3.06±0.17), (2.78±0.29), (2.56±0.08) μmol·m-2·s-1, respectively, and the T3 treatment was significant lower than the CK and T1 treatments (P<0.05), indicating that soil respiration was depressed under SAR. These negative effects were evident in the warm-wet seasons ( P<0.05) , but not in the cool-dry ones. In addition, by analyzing the an-nual soil respiration of each year, we found that these negative effects had been strengthened over time with significant difference among treatments occurred only in the second year. The depression of soil respiration may be related to the re-duction of heterotrophic respiration and CO2 production from litter caused by soil acidification under SAR, as we found that soil pH value and soil microbial biomass carbon and nitrogen significantly decreased after exposure to SAR for two years;and litter decomposition rate was also depressed during the study period. Coincide with the situation of soil respi-ration, the negative effects SAR on these index had been strengthened over time with significant differences among treat-ments mostly occurring in the later stage of the study period. Furthermore, we found the effects of SAR on the tempera-ture response of soil respiration, with a decline in Q10 during the study period, suggesting that SAR would decrease the temperature sensitivity of soil respiration. According to the results of this study, soil carbon in forests of subtropical Chi-na would accumulate as the reduction of soil respiration under the continued acid rain in the future.