亚热带常绿阔叶林降雨中可溶性碳氮动态及其对模拟氮沉降的响应

Dynamics of dissolved carbon and nitrogen in rainfalls and its response to simulated nitrogen deposition in a subtropical evergreen broad-leaved forest

通过模拟大气氮沉降,对安徽祁门查湾自然保护区亚热带常绿阔叶林大气降雨及穿透雨进行持续监测,探讨森林降雨中可溶性有机碳、氮动态对大气氮沉降的响应。本试验设置了2个处理即高氮处理和无添加对照。结果表明,降雨中水溶性有机碳(TOC)年平均含量为3.204 mg·L-1,NH4+-N为0.243 mg·L-1,NO3--N为0.408 mg·L-1,可溶性有机氮(DON)为0.754 mg·L-1。经过森林林冠淋洗后,穿透雨中TOC年平均浓度达5.623 mg·L-1,对照林分(5.923 mg·L-1)>高氮处理(5.322 mg·L-1);NH4+-N年平均浓度为0.285 mg·L-1,对照(0.273 mg·L-1)<高氮处理(0.297 mg·L-1);NO3--N年平均浓度为0.509 mg·L-1,对照(0.523 mg·L-1)>高氮处理(0.494 mg·L-1);DON年平均浓度为0.691 mg·L-1,对照(0.665 mg·L-1)<高氮处理(0.716 mg·L-1)。降雨经过林冠层后,TOC、NH4+-N、NO3--N含量均有明显提高,但DON的含量有所下降;短期的模拟氮沉降对穿透雨可溶性碳和氮没有显著影响。大气降雨中TOC、NH4+-N、NO3--N、DON含量的季节变化明显,主要受控于降雨强度、降雨量,穿透雨的变化可能和树木的生理需求程度有关。

An experiment including a high-nitrogen（N） treatment（100 kg N·hm^-2·a^-1） and a nitrogen-free control was conducted to investigate the seasonal dynamic patterns of dissolved organic carbon（DOC） and dissolved organic nitrogen（DON） in a subtropical evergreen broad-leaved forest for one and a half years in Zhawan Natural Reserve, Anhui Province. The results showed that an average concentration of DOC, NH4^＋-N, NO3^--N or DON in annual precipitation was 3.204, 0.243, 0.408, and 0.754 mg·L^-1, respectively. After passing through the forest canopy, the concentrations of aforementioned components in annual rainfalls were significantly changed. The concentration of DOC in rainfalls increased to 5.623 mg·L^-1, which was greater than that in the high-nitrogen treatment（5.322 mg·L^-1）（the nitrogen-free control was 5.923 mg·L^-1）. In annual rainfalls that passed through the forest canopy, other compounds were also changed. For examples, annual average concentration of NH4＋-N increased to 0.285 mg·L^-1, which was higher than that of the control（0.273 mg·L^-1）, but lower than that of the high-nitrogen treatment（0.297 mg·L^-1）. The concentration of NO3--N increased to 0.509 mg·L^-1, which was lower than the control（0.523 mg·L^-1） and higher than in the high-nitrogen treatment（0.494 mg·L^-1）. However, the concentration of DON decreased to 0.691 mg·L^-1, while DON concentrations in the high-nitrogen treatment and the nitrogen-free control were 0.716 mg·L^-1 and 0.665 mg·L^-1, respectively. The results demonstrated that short-term simulated N deposition had no significant effect on DOC and DON in the rainfalls that were passing through the forest canopy at the experimental site. The seasonal changes of chemical components in rainfalls were mainly controlled by the amount and intensity of rainfalls; however, such changes in the passing-through rainfalls were likely related to physiological nutrient acquisition of trees.