To study the effects of simulated acid rain (SAR) on forest soil C:N:P stoichiometry is of significance in understanding the responses of ecosystem biogeochemical cycling to elevated acid rain.In this study, a field experiment of SAR was conducted in a monsoon evergreen broad-leaved forest at 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 experiments were initiated in June 2009. Responses of soil pH value, soil C, N, and P content,and soil C:N:P stoichiometry to SAR were studied from December 2009 to December 2017. The results showed that during the study period, mean values of soil pH value, soil C, N, P concentration of 0~10 cm soil layer in the CK plots were (3.89±0.01), (31.99±0.37), (2.25±0.05) and (0.23±0.01) g·kg-1, respectively. SAR significantly reduced soil pH value (0.22 lower in maximum, P<0.05), indicated that soil acidification was aggravated under SAR. The soil C concentration increased significantly (14.69% higher in maximum, P<0.05) and the soil P concentration tended to decrease (18.79% lower in maximum) under SAR. However, the soil N concentration did not change obviously under SAR. Mean values of C:N, C:P, and N:P of 0~10 cm soil layer in the CK plots were (14.24±0.23), (141.38±3.35) and (9.91±0.26), respectively. Due to the different responses of soil C, N, and P concentration to SAR, C:P and N:P increase significantly under SAR (41.31% and 27.16% higher in maximum, respectively, P<0.05). In addition, we found that these treatment effects had been strengthened over time with significant difference among treatments occurred only in the later period of the experiment. Furthermore, these effects were only evident in the 0-10cm soil layer (P<0.05), but not in the 10~20 cm soil layer. Our results indicated that long-term acid rain and soil acidification changed the coupling relationship among soil C, N, and P, aggravated the limiting effect of P on forest soil, and thus reduced the stability of the structure and function of lower subtropical forest ecosystem.%研究模拟酸雨对森林土壤C、N、P生态化学计量特征的影响,对于认识森林生态系统生物地球化学循环如何响应酸雨加剧具有重要意义.以鼎湖山季风常绿阔叶林为研究对象,2009年6月开始进行人工模拟酸雨的野外实验,共设置4个不同处理水平,即CK(喷洒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—2017年12月(8年实验周期)对模拟酸雨下土壤pH值和土壤C、N、P质量分数及其生态化学计量特征进行了5次测定.结果显示:对照样地表层(0~10 cm)土壤pH值,土壤C、N、P质量分数分别为(3.89±0.01),(31.99±0.37)、(2.25±0.05)和(0.23±0.01) g·kg-1.长期模拟酸雨处理导致表层土壤pH值显著下降(最大降幅达0.22,P<0.05),土壤酸化加剧;同时,表层土壤C质量分数显著增加(最大增幅达14.69%,P<0.05),P质量分数呈一定程度的下降趋势(最大降幅达18.79%),但N质量分数没有显著变化.对照样地表层土壤C:N、C:P和N:P分别为(14.24±0.23)、(141.38±3.35)和(9.91±0.26),由于土壤C、N、P质量分数对酸雨响应的差异导致土壤C:P和N:P显著增加(最大增幅分别达41.31%和27.16%,P<0.05),从而改变了土壤C:N:P生态化学计量特征.模拟酸雨对上述指标的处理效应随着处理时间的延长而逐渐显现,处理间的差异在试验后期才逐渐达到显著水平(P<0.05),且上述各指标在次层(10~20 cm)土壤在不同处理间不存在显著差异.根据研究结果可推测,长期酸雨引起的土壤酸化会改变南亚热带森林土壤C、N、P耦合关系,加剧该区域森林土壤P限制的趋势,降低森林生态系统结构与功能的稳定性.
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