放牧对呼伦贝尔草甸草原土壤呼吸温度敏感性的影响

放牧是影响草地生态系统碳循环过程的重要人类活动因素,定量研究放牧对土壤呼吸温度敏感性(Q10)的影响,对于准确评估草地碳收支和碳平衡至关重要.本研究依托呼伦贝尔草甸草原放牧梯度试验平台,利用动态密闭气室法(Li 6400-09)测量草地不同放牧梯度下的土壤呼吸作用.结果表明,不同放牧梯度下土壤呼吸具有明显的季节变化,且主要受温度因子主导,7月土壤呼吸速率达最大;2011年生长季5~9月不同放牧强度的平均土壤呼吸速率大小顺序为:G1(0.23Au·hm-2)>G0(未放牧)>G2(0.34 Au·hm-2)>G3(0.46 Au·hm-2)>G4(0.69 Au·hm-2)>G5(0.92 Au·hm-2).与不放牧相比,重度放牧(0.92 Au·hm-2)条件下Q10值减少了约10%,而轻度放牧(0.23 Au·hm-2)条件下Q10值略有升高.总体上,土壤呼吸温度敏感性(Q10)与放牧强度显著负相关(r=0.944,P<0.05),放牧不同程度地降低了土壤呼吸的温度敏感性.不同放牧梯度下Q10值与地上、地下生物量、土壤有机碳和土壤含水量之间存在显著的正相关线性回归关系,可以解释不同放牧梯度下Q10值71.0%~85.2%的变异性.放牧条件下Q10值发生变化本质上是生物因素和环境因子共同作用的结果.

Effect of Grazing on the Temperature Sensitivity of Soil Respiration in Hulunber Meadow Steppe

Grazing is one of the major human activities which lead to disturbance on grassland ecosystem. Quantifying the effect of grazing on the temperature sensitivity of soil respiration (Q10) is essential for accurate assessment of carbon budget in grassland ecosystem. This study was conducted on the grazing gradients experiment platform in Hulunber meadow steppe. Soil respiration was measured by a dynamic closed chamber method (equipped with Li 6400-09, Lincoln, NE, USA) during the growing season in 2011. The results showed that soil respiration had significant seasonal variation and the maximum occurred in July, which was mainly dominated by temperature. The order of average soil respiration during the period from May to September in different treatments was G1>G0>G2>G3>G4>G5. Comparing with non-grazing treatment, Q₁₀ under heavy grazing conditions (0.92Au·hm^-2) was reduced by about 10%, and was increased a little under light grazing conditions (0.23 Au·hm^-2). There was a significant negative correlation between Q₁₀ and grazing intensities (r=0.944, P<0.05). Grazing could decrease the temperature sensitivity of soil respiration to different degrees. The Q₁₀ under different grazing gradients had positive linear regression relationships with aboveground biomass, belowground biomass, soil organic carbon and soil moisture. They could explain 71.0%-85.2% variations of Q₁₀. It was suggested that the variation of Q₁₀ was mainly determined by the change of biotic and environmental factors due to grazing.