短期放牧对半干旱草地生态系统CO_2和N_2O排放的影响

Short-term Effects of Different Grazing Intensities on Greenhouse Gas Fluxes in Semi-arid Grassland

通过在北方农牧带半干旱草地生态系统(山西右玉)设置不放牧、轻度放牧、中度放牧和重度放牧4个不同强度的放牧实验,运用静态-暗箱法测定放牧第一年生长季的温室气体通量,研究不同放牧强度对该地区温室气体通量的影响.结果表明:(1) CO_2和N_2O在生长季表现出随着温度和水分变化的明显季节动态变化,但是与不放牧相比,第一年不同放牧强度对CO_2和N_2O排放速率没有显著影响;(2)放牧显著降低了土壤含水量(P <0. 05),中度放牧降低了土壤微生物生物量碳(MBC,P <0. 05),中度和重度放牧降低了土壤微生物生物量氮(MBN,P <0. 05);(3) CO_2排放速率和土壤温度、土壤水分之间呈显著正相关关系,土壤温度、可溶性氮、微生物生物量氮以及CO_2排放速率之间呈显著正相关关系.放牧增加了温度与CO_2排放的相关性,但对N_2O排放相反.(4)虽然放牧降低了土壤含水量,但是没有发现不同放牧强度间CO_2和N_2O排放的差异,说明短期内不同的放牧强度尚未对土壤微生物结构与功能造成显著影响,需要继续进行长期深入地研究,揭示放牧强度对温室气体通量的影响机制.

Grazing is one of the most important ways for managing grassland in northern China. Different studies have focused on the effects of grazing on the structure and function of ecosystems. Grazing affects the structure and function of soil via biological and physical processes,such as animal trampling,feeding,and excretion,which further affects N2 O emissions. However,there is less research on greenhouse gases（ GHGs） emissions by grazing intensities in semi-arid grassland ecosystems in northern China. In this study,four different grazing intensities were considered in the semi-arid grassland ecosystem of the typical agro-pastoral ecotone in northern China（ Youyu,Shanxi）. The influence of different grazing intensities on GHG fluxes was studied by measuring GHGs fluxes in the growing season with an opaque static chamber. The results showed that（1） Grazing had no effect on CO2 and N2 O fluxes during the first year of grazing treatment.（2） However,grazing decreased soil water content（ P 0. 05）,moderate grazing intensity decreased microbial biomass carbon（ P 0. 05）,and moderate and heavy grazing intensities reduced microbial biomass nitrogen（ P 0. 05）.（3） Significant positive correlations between CO2 flux and soil temperature and soil moisture were observed. The correlation between temperature and CO2 emissions was increased by grazing.（4） There was a significant positive correlation between soil temperature,soluble nitrogen,soil microbial biomass nitrogen,CO2 flux,and N2 O flux. Our results indicated that GHG,regulated by soil microorganisms,was affected by soil temperature and moisture.