大兴安岭兴安落叶松林树木生物量对氮沉降的响应

目的]研究兴安落叶松生物量增长率对氮沉降是否存在响应,年际间是否存在差异;不同径级是否会影响兴安落叶松生物量增长率对氮沉降的响应。方法]通过人工氮添加的方法模拟大气氮沉降变化,探究兴安落叶松林连续3年(2014—2016)树木生物量的变化对氮沉降的响应。从2012年开始,共设置4个氮添加水平,分别为对照(CK,0 g·m-2·a-1)、低氮(TL,2.5 g·m-2·a-1)、中氮(TM,5 g·m-2·a-1)和高氮(TH,7.5 g·m-2·a-1),每年的生长季(5—10月)按月将NH4NO3溶于32 L蒸馏水,利用背喷式喷雾器均匀喷洒于样方内,对照样地喷洒等量纯净水。结果](1)3年间各施氮处理生物量增长率均显著高于对照组(P0.05)、各年份生物量增长率均存在显著差异(P0.05),而且2016年生物量增长率明显高于前两年(P0.05)。(2)2014年各处理间无显著差异;2015年TL处理的生物量增长率显著高于TM和TH处理(P0.05),2016年TL处理的生物量增长率显著高于TH处理(P0.05)。(3)不同处理对年际间不同径级生物量增长率也产生不同影响。TL处理对2014和2016年的10 15cm径级的兴安落叶松生物量增长率有显著促进作用(P0.05);TM处理对所有年份10 15 cm和15 20 cm径级兴安落叶松生物量增长率均有显著促进作用(P0.05);TH处理对所有年份胸径大于10 cm的3个径级(1015、15 20、20 cm)兴安落叶松生物量增长率均有显著促进作用(P0.05)。结论](1)长期氮添加有可能导致树木生长率的增量逐渐减少甚至出现抑制,将改变现有北方森林生态系统碳源汇动态;(2)由于不同径级树木对氮沉降的响应不同,为提高氮沉降对北方森林碳库影响的模型预测精度,应按不同径级分别模拟。

Response of Tree Biomass to Nitrogen Deposition in Larch Forest in Greater Khingan Mountains

Objective] To study whether there is a response of biomass growth rate of Larix gmelinii forest to nitrogen deposition, whether there is difference among years and whether different diameters can affect the response. Method] This study simulated the change of atmospheric nitrogen deposition by artificial nitrogen addition method to investigate the response of biomass growth in three years to nitrogen deposition in L. gmelinii forests during the period of 2014-2016. The nitrogen was added from 2012, 4 nitrogen addition levels were set as control (CK,0 g·m^-2·a^-1), low nitrogen (TL, 2.5 g·m^-2·a^-1), middle nitrogen (TM, 5 g·m^-2·a^-1) and high nitrogen (TH, 7.5 g·m^-2·a^-1). The growth season (May-October) will dissolve NH₄NO₃ in 32 L distilled water monthly, spray evenly on the sample plot with back atomize, and spray the same amount of pure water in the same way on the CK. Result] (1) The biomass growth rate of every treatment was significantly higher in three years (P<0.05). The annual biomass growth rate was significantly different (P<0.05), and the growth rate of 2016 was significantly higher than that of the previous two years (P<0.05). (2) There was no significant difference between the three treatments in 2014 (P<0.05). The growth rate of TL in 2015 was significantly higher than that of TM and TH(P<0.05). The growth rate of TL in 2016 was significantly higher than that of TH (P<0.05). (3) Different treatments had different effects on different diameter class. Between 2014 and 2015, TL significant increased the biomass growth rate of L. gmelinii (P<0.05) in 10 15 cm diameter. TM had a significant effect on the biomass growth rate of L. gmelinii of 10 15 cm and 15 20 cm diameter in all the 3 years (P<0.05). In 2016, the biomass growth rate of L. gmelinii significantly increased (P<0.05) in the 15 20 cm diameter. TH had more significant effect on the biomass growth rate of three diameters class (10 15,15 20, and > 20 cm) than that <10 cm (P<0.05) in all the 3 years. Conclusion] (1) Long-term nitrogen addition will lead to a growth rate gradually reduce or even suppress, which is likely to change the boreal forest carbon source & sink dynamic; (2) Since different diameter trees have different responses to the nitrogen deposition, it should be as the basal factor in simulation in order to increase the prediction accuracy about nitrogen deposition on the boreal forest carbon pool.