高寒草甸土壤异养呼吸对气候变化和氮沉降响应的模拟

Simulating of the response of soil heterotrophic respiration to climate change and nitrogen deposition in alpine meadows

利用研究区植被、土壤和气候观测资料,借助CENTURY模型研究了高寒草甸土壤异养呼吸CO2通量动态变化。结果表明,1）CENTURY模型较好地反映了高寒草甸土壤异养呼吸季节变化。模拟结果与试验点观测结果相吻合,风匣口和干柴滩2个试验点观测值与模拟值的线性回归方程分别为y=0.7776x＋23.796（R^2=0.6885,n=31）和y=0.9487x-8.6994（R^2=0.6062,n=30）。2）过去46年（1960-2005年）研究区年平均气温趋于暖化,平均线性增温率为0.35℃/10a。降水量变化不明显,呈振幅较为稳定的波动变化。同期CENTURY模型模拟的高寒草甸土壤异养呼吸CO2通量呈波动性缓慢上升的趋势,通量变化范围在479.22～624.89g C/（m^2·a）之间,平均值为（539.56±34.32）g C/（m^2·a）,通量增加率为16.5g C/（m^2·10a）。对模拟结果与气温、降水量之间进行的相关性分析结果显示,土壤异养呼吸CO2通量与气温呈显著正相关（r=0.70,P〈0.05）,与降水量相关性不显著。3）氮沉降增加显著促进了高寒草甸土壤异养呼吸CO2通量。中氮（MN）和高氮（HN）与对照（CK）处理间差异极显著（P〈0.01）,但中氮（MN）与高氮（HN）处理间差异不显著。说明,长期受低温和土壤有效氮限制的高寒草甸对气候变化响应敏感,高原气候的暖化和氮沉降的增加均能引起土壤异养呼吸作用的小幅上升,但可能由于异养呼吸作用对氮沉降存在着一定的“氮饱和”现象,随着大气氮沉降的倍增,其促进效应降低。

Vegetation,soil and climate data in the study area was used to simulate the CO2 flux from soil heter-otrophic respiration in alpine meadows using the CENTURY model.The results showed that the CENTURY model was able to predict seasonal changes in soil heterotrophic respiration which closely matched observed changes.The linear regression equation between observed and simulation values at Fengxiakou and Ganchaitan were y =0.7776x ＋23.796 （R^2 =0.6885,n=31）and y =0.9487x -8.6994 （R^2 =0.6062,n=30）,respectively.In the past 46 years （1960 -2005 ）,annual average temperature in the study area increased at a rate of 0.35℃/decade.Precipitation has remained with relatively stable.Simulation of soil heterotrophic respiration CO2 flux in alpine meadows using CENTURY over this period revealed a slowly rising trend （16.5 g C/m^2 · decade）ranging between 479.2 -624.9 g C/（m^2 ·a）.Correlation analysis between temperature and rainfall showed that soil heterotrophic respiration CO2 flux had a significant positive correlation with temperature （r=0.70,P 〈0.05）but was not correlated with precipitation.Nitrogen application significantly promoted soil heterotrophic respiration CO2 flux.Medium nitrogen （MN）and high nitrogen （HN）showed highly significant increases compared to the control （zero nitrogen）（P 〈0.01）,but there was no difference between MN and HN. The results suggest that alpine meadow limited by low temperature and nitrogen was sensitive to climate change.