毛乌素沙地油蒿灌丛生态系统的土壤呼吸特征

Characterization of Soil Respiration in a Shrubland Ecosystem of Artemisia ordosica in Mu Us Desert

【目的】探究毛乌素沙地半干旱区典型油蒿灌丛生态系统土壤呼吸速率特征,揭示土壤温湿度对土壤呼吸速率的影响,以期为预估半干旱区土壤碳排放提供科学依据。【方法】在宁夏盐池选取典型油蒿群落,采用切根法剖分土壤呼吸组分,于2014年4—10月利用自动气室法对切根处理与对照样地的土壤呼吸速率进行连续观测,采用指数方程拟合土壤呼吸组分对土壤温度的响应,并运用线性回归分析温度响应函数残差(观测值/预测值)与土壤含水率间的关系。【结果】在日尺度、自养呼吸速率最大值出现时间(11:00)早于土壤温度最大值出现时间(15:00),而异养呼吸速率最大值出现时间基本与土壤温度最大值出现时间一致;在生长季中期(6—8月),土壤总呼吸速率,自养呼吸速率和异养呼吸速率的温度敏感性(Q10)分别为1.51,1.40和1.88;自养呼吸速率对温度的响应受水分的影响,当土壤含水率小于8%时,土壤温度仅能解释自养呼吸速率季节变异的36%(Q10=1.10),自养呼吸速率的温度响应函数残差随土壤含水率升高而增加(R2=0.59,P<0.05);当土壤含水率大于8%时,自养呼吸速率随土壤温度升高呈指数增加(R2=0.75,Q10=1.88),自养呼吸速率的温度响应函数残差与土壤含水率无显著关系;与自养呼吸速率不同,异养呼吸速率对温度的响应受水分的影响较小,在不同土壤水分条件下均随土壤温度升高呈指数增加(R2>0.65);自养呼吸贡献率(自养呼吸速率/土壤总呼吸速率)在日尺度上存在中午降低的现象;在季节尺度,RA/RT呈现出明显的季节性波动,在5—8月平均为54%,9—10月平均为69%。【结论】在日尺度,自养呼吸速率受土壤温度的影响较小,而异养呼吸速率主要受土壤温度调节;在季节尺度,异养呼吸速率主要受土壤温度调节,其Q10高于自养呼吸速率;而自养呼吸速率对温度的响应受水分的调节,其Q10随土壤含水率升高而增大;自养呼吸贡献率在日尺度与季节尺度的动态变化很可能来源于呼吸组分对环境因子的差异响应。

【Objective】 We investigated the characteristic of soil respiration rate and its responses to soil temperature and soil moisture in a shrubland ecosystem in Mu Us Desert to provide a scientifics basis for predicting soil carbon emission in semiarid region.【Method】 The trench method has used in a typical Artemisia ordosica community in Yanchi County to separate the components of soil respiration. Using an automated chamber system,soil respiration rate was measured continuously from April to October 2014 in both trenched and control plots. An exponential function was used to fit the relationship between soil respiration rates and soil temperature（ Ts）,and a linear regression was used to test the relationship between soil water content（ SWC） and temperature normalized soil respiration rates（ the ratio of observed values to estimated values）. 【Result 】 At the diurnal scale, autotrophic respiration ratio（ RA） showed a middy depression,and reached the peak value earlier（ 11： 00） than Ts（ 15： 00）,while heterotrophic respiration ratio（ RH）peaked in consistent with Ts. During mid-growing season（ Jun-Aug）,the temperature sensitivity（ Q10） of total soil respiration ratio（ RT）,RAand RHwas 1. 51,1. 40,and 1. 88,respectively. However,the response of RAto Tswas modified by SWC. When SWC 〈 8%,Tsexplained only 36% of the variation in RA（ Q10= 1. 10） and temperaturenormalized RAshowed a significant linear relationship with SWC. When SWC 〉 8%,RAincreased exponentially with increasing Ts（ R^2= 0. 75,Q10= 1. 88）,and there was no significant relationship between temperature normalized RAand SWC. In contrast to RA,SWC had little effect on the relationship between RHand temperature,RHincreased exponentially with increase of Tsunder different water conditions（ R^2〉 0. 65）. The contribution of RAto RT（ RA/RT） showed a middy depression at diurnal scale. At the seasonal scale,RA/RTshowed clear seasonal variation. RA/RTaveraged 54% during May-Aug and was higher（ 69%） during Sep-Oct.【Conclusion】 At the diurnal scale,RAwas decoupled from Ts,while RHwas primarily controlled by Ts. At the seasonal scale,RHwas primarily controlled by Tswith a higher Q10 than that of RA. However,the response of RAto Tswas regulated by SWC. The variations in RA/RTat diurnal and seasonal scales are most likely derived from the different responses of RAand RHto environmental factors. Our result could help understand the dynamics in soil respiration and provided a scientific basis for predicting carbon budget in semiarid regions.