开展酸雨增加对森林土壤酸化和土壤微生物活性的影响，可以为正确评估森林生态系统碳氮过程及其对全球气候变化的响应提供依据。以鼎湖山处于不同演替阶段的3种森林类型（马尾松Pinus massoniana）针叶林、针阔叶混交林和季风常绿阔叶林）为研究对象，从2009年6月开始，在自然林里喷施4个不同处理水平的模拟酸雨，即CK（pH=4.5左右的天然湖水）、T1（pH=4.0）、T2（pH=3.5）和T3（pH=3.0）；2009年12月─2013年3月对模拟酸雨下土壤pH值和土壤微生物量碳、氮含量进行长期观测研究。重复测量方差分析表明，观测周期内，模拟酸雨没有显著影响松林的土壤pH值和土壤微生物量碳、氮含量，但却显著地降低了阔叶林的这3个指标（P<0.05），而对混交林的降低程度也接近显著。具体表现为：与CK处理相比，松林、混交林和阔叶林表层土壤pH值在T1、T2和T3处理分别下降了0.01、0.01和0.04，0.01、0.06和0.07，0.04、0.09和0.10；相应地，土壤微生物量碳含量分别下降了-1.0%、2.7%和0.4%，4.2%、4.4%和13.6%，12.3%、12.6%和18.4%；土壤微生物量氮含量则分别下降了0.8%、4.2%和9.7%，5.4%、17.4%和15.6%，12.3%、16.2%和25.1%。这表明模拟酸雨加速了土壤酸化，同时降低了土壤微生物活性，而从降低的幅度和差异的显著性可看出，3个林型的响应敏感性随森林的顺行演替而增强，处于演替后期的阔叶林敏感性最强。同时，这种处理效应大体上随着模拟酸雨处理时间的延长而逐渐显著。以阔叶林为例，表现为实验初期，模拟酸雨并没有显著降低其土壤pH值和土壤微生物量碳、氮含量，而在模拟酸雨24、30和36个月后，T3和T2处理的土壤pH值显著低于CK和T1处理（P<0.05）；同样，在模拟酸雨24、36和45个月后，T3处理的土壤微生物量碳、氮含量显著低于 CK 处理（P<0.05）；这表明模拟酸雨对土壤酸化和土壤微生物活性的影响是一个逐渐累积的过程。%Determining the effects of elevated acid rain on forest soil acidification and soil microbial activity can provide useful information for understanding of the process of carbon and nitrogen cycle of forest ecosystem and its response to global change. Therefore, a simulated acid rain (SAR) experiment was conducted in three subtropical forests of different successional stages [i.e. a young pine forest (PF), a transitional mixed conifer and broadleaf forest (MF), and an old-growth broadleaved forest (BF)] at the Dinghushan Nature Reserve. Acid rain treatments included CK (the local lake water, pH 4.5), T1 (pH 4.0), T2 (pH 3.5), and T3 (pH 3.0) with three replicates. SAR experiment was initiated in June 2009. Responses of soil pH value and soil microbial biomass carbon and nitrogen to the SAR were studied from December 2009 to March 2013. The repeated measures ANOVA showed that, during the study period, the SAR did not affect soil pH value and soil microbial biomass carbon and nitrogen in the PF (P>0.05), but it significantly reduced soil pH value and soil microbial biomass carbon and nitrogen in the BF (P<0.05), and the reduction was marginally significant in the MF. Compared with the CK treatment, mean rate of soil pH valuewere 0.01~0.04, 0.01~0.07, and 0.04~0.10 lower in the acid treatment plots in the PF, MF, and BF, respectively; similarly, mean rate of soil microbial biomass carbon were -1.0%~0.4%, 4.2%~13.6%, and 12.3%~18.4% lower, and mean rate of soil microbial biomass nitrogen were 0.8%~9.7%, 5.4%~17.4%, and 12.3%~25.1% lower in the acid treatment plots in the PF, MF, and BF, respectively. These results indicated the aggravation of soil acidification and the inhibition of soil microbial activity under the SAR in our forests, and more over, the sensitivity of the response of soil acidification and soil microbial activity to the SAR showed an increasing trend with the progressive succession of three forests. In addition, by analyzing the responses of soil pH value and soil microbial biomass carbon and nitrogen of each year, we found that these negative effects had been strengthened over time with significant difference among treatments occurred only in the later period of the experiment. Take the BF for example, treatment effects was not evident in the initial stage of this study. However, after exposing to the SAR for 24, 30, and 36 months, soil pH value of the T3 and T2 treatments were significant lower than the CK and T1 treatments; similarly, soil microbial biomass carbon and nitrogen of the T3 treatment were significant lower than the CK treatment after exposing to the SAR for 24, 36, and 45 months. These results indicated that the acidification and the inhibition of soil microbial activity under the SAR was a gradual process in the forests.
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