Soil respiration patterns for four major land-use types of the agro-pastoral region of northern China

摘要

Land-use types and management practices are critical factors that affect soil CO2 efflux (R-s). In the agropastoral area of northern China, land-use types have changed considerably during the last 60 years due to changes in the social-economic status of the.human population and associated changes in land-use needs. Only a few studies have examined& in this region of China, and these studies have mainly focused on grazing intensity effects on R-s rather than comparisons among land-use types. The aim of this study was to evaluate annual variation of R-s for the dominant land-use types in the agro-pastoral region of northern China, including ungrazed grassland (UG), moderately grazed grassland (MG), perennial pasture (PP), and cropland (CL). Measurements of R, were obtained throughout the year for these four land-use types using a mobile greenhouse gas analyzer. Values of R-s from the four land-use types for the growing season, non-growing season, and across the entire year were in the order PP > CL > UG > MG. Annual values of R, in PP and CL were 1.6- and 1.1-fold greater, respectively, than that for UG, while R-s in MG was 94% of UG. Daily mean soil temperature (Ts) was the main factor that controlled R-s and explained 52-71% of the variability in daily R. Monthly mean temperature and precipitation explained 67-87% of the variability in monthly cumulative R. Annual R-s for all land-use types averaged 1.9 kg C m(-2) yr(-1) (range: 1.6-2.5) with about 94% of annual R-s occurring during the growing season. No pulses of R-s were observed during the autumn and spring freeze-thaw period, probably because of the large snow accumulation, which minimized R-s during these two periods. These results showed that land-use types exhibit different R-s that were associated with differences in temperature and precipitation. Results also suggest that conversion of UG or MG to CL and PP will likely increase R. (C) 2015 Elsevier B.V. All rights reserved.