氮添加对华北落叶松树枝CO_(2)通量的影响

Effects of nitrogen addition on the branch CO_(2)efflux of Larix principis-rupprechtii

【目的】枝CO_(2)通量是林分碳释放的重要组成部分之一,研究模拟氮沉降下的华北落叶松枝CO_(2)通量变化,可以为氮沉降背景下的华北落叶松林分固碳增汇管理提供一定的理论依据。【方法】在2021年6-10月,以华北落叶松25年生中龄人工林和32年生近熟人工林为研究对象,设置对照(CK,0 kg/(hm^(2)·a))、低氮(N1,75 kg/(hm^(2)·a))、中氮(N2,150 kg/(hm^(2)·a))、高氮(N3,225 kg/(hm^(2)·a))4个强度的氮添加处理,并使用LI-8100A对枝CO_(2)通量进行原位监测,同时采集枝条样品以测定其氮含量。【结果】(1)华北落叶松枝CO_(2)通量与空气温度基本呈现出“单峰型”月变化,峰值出现在6-8月,空气温度可以分别解释2个林龄枝CO_(2)通量37%~82%、40%~70%的变化。(2)25年和32年生华北落叶松6-10月平均枝CO_(2)通量随氮添加处理强度增加都呈增大的趋势,但只在N3处理下与CK差异显著(P<0.05)。CK、N1、N2处理下,25年生枝CO_(2)通量均显著高于32年生(P<0.05)。除32年生的N1处理外,其余氮添加处理均降低了枝CO_(2)通量的温度敏感性(Q_(10))。(3)氮添加处理显著增加了25年生枝氮含量(P<0.05),32年生枝氮含量没有显著变化(P>0.05)。2个林龄的华北落叶松枝CO_(2)通量与枝氮含量均存在显著的负向线性关系(P<0.01),且氮含量分别可解释25和32年生华北落叶松16%和32%的枝CO_(2)通量变化。【结论】枝CO_(2)通量受空气温度、氮添加和林龄影响,在构建华北落叶松林木碳释放模型时应考虑这3个因素。

[Objective]Branch CO_(2)efflux is one of the important components of stand carbon release.Studying the change of branch CO_(2)efflux of Larix principis-rupprechtii under simulated nitrogen deposition could provide a theoretical basis for the management of carbon sequestration and sink increase of L.principis-rupprechtii forest under the background of nitrogen deposition.[Method]25-year-old and 32-year-old plantations of L.principis-rupprechtii were selected.Four nitrogen addition treatments,i.e.control(CK,0 kg/(ha·year)),low nitrogen(N1,75 kg/(ha·year)),medium nitrogen(N2,150 kg/(ha·year))and high nitrogen(N3,225 kg/(ha·year))were set.From June to October in 2021,the branch CO_(2)efflux was monitored in situ using LI-8100A,and the branch samples were collected to determine the nitrogen content.[Result](1)The CO_(2)efflux and air temperature of L.principis-rupprechtii branches basically showed a“single-peak”monthly change,and the peak appeared from June to August.The air temperature could explain the changes of branch CO_(2)efflux of two stands by 37%−82%and 40%−70%,respectively.(2)The average branch CO_(2)efflux of L.principis-rupprechtii at 25-year-old and 32-year-old from June to October showed an increasing trend with the increase of N addition intensity,but only differed significantly under N3 treatment(P<0.05).The CO_(2)efflux of CK,N1 and N2 treatments at 25-year-old was significantly higher than that at 32-year-old(P<0.05).The temperature sensitivity(Q_(10))of branch CO_(2)efflux was decreased by N addition except for 32-year-old plantations under N1 treatment.(3)Nitrogen addition significantly increased the 25-year-old branch nitrogen content;there was no significant change in shoot nitrogen content in 32-year-old branch nitrogen content(P>0.05).There was a significantly negative linear relationship between the branch CO_(2)efflux of L.principis-rupprechtii and the branch nitrogen content at both ages(P<0.01).The nitrogen content can explain 16%(25-year-old)and 32%(32-year-old)variation of branch CO_(2)efflux.[Conclusion]The branch CO_(2)efflux is affected by air temperature,nitrogen addition and forest age.All three factors should be considered when constructing a tree carbon release model of L.principis-rupprechtii.