Soil respiration and human effects on global grasslands

Grasslands comprise approximately 40% of the earth's land area (excluding areas of permanent ice cover) and play a critical role in the global carbon cycle. In this paper, by reviewing literature, we quantify annual soil CO2 efflux, contribution of root respiration to total soil respiration, apparent temperature sensitivity of soil respiration (indicated by Q(10)), and turnover rates of soil organic carbon (SOC). We discuss effects of human activities (grazing, land-use changes, and fertilization) on soil respiration rates of global natural grasslands. The Soil CO2 efflux from temperate and tropical natural grasslands is 389.8 +/- 45.5 g C m(-2) yr(-1) and 601.3 +/- 45.6 g C m(-2) yr(-1) (mean +/- S.E.), respectively. The contribution of root respiration to total soil respiration averages 36%, ranging from 8% to 64%. Annual Soil CO2 efflux increases with temperature and precipitation, but increased precipitation can cause a decrease in soil respiration rate in rainy regions. Mean turnover rates of SOC are 71 years in temperate grasslands and 15 years in tropical grasslands. The average Q(10) value is 2.13, with 2.23 for temperate grasslands and 1.94 for tropical grasslands. Human activities significantly affect soil respiration but the extent varies among sites. (C) 2008 Elsevier B.V. All rights reserved.