Effects of converting natural grasslands into planted grasslands on ecosystem respiration: a case study in Inner Mongolia, China

With increasingly intensifying degradation of natural grasslands and rapidly increasing demand of high quality forages, natural grasslands in China have been converted into planted grasslands at an unprecedented rate and the magnitude of the conversion in Inner Mongolia is among the national highest where the areal extent of planted grasslands ranks the second in China. Such land-use changes(i.e., converting natural grasslands into planted grasslands) can significantly affect carbon stocks and carbon emissions in grassland ecosystems. In this study, we analyzed the effects of converting natural grasslands into planted grasslands(including Medicago sativa, Elymus cylindricus, and M. sativa+E. cylindricus) on ecosystem respiration(F) in Inner Mongolia of China. Diurnal Fand its components(i.e., total soil respiration(F), soil heterotrophic respiration(F) and vegetation autotrophic respiration(F)) were measured in 2012(27 July to 5 August) and 2013(18 July to 25 July) in the natural and planted grasslands. Meteorological data, aboveground vegetation data and soil data were simultaneously collected to analyze the relationships between respiration fluxes and environmental factors in those grasslands. In 2012, the daily mean Fin the M. sativa grassland was higher than that in the natural grassland, and the daily mean Fwas higher in all planted grasslands(i.e., M. sativa, E. cylindricus, and M. sativa+E. cylindricus) than in the natural grassland. In contrast, the daily mean Fand Fwere lower in all planted grasslands than in the natural grassland. In 2013, the daily mean F, Fand Fin all planted grasslands were higher than those in the natural grassland, and the daily mean Fin the M. sativa+E. cylindricus grassland was higher than that in the natural grassland. The two-year experimental results suggested that the conversion of natural grasslands into planted grasslands can generally increase the Fand the increase in Fis more pronounced when the plantation becomes more mature. The results also indicated that Fcontributed more to Fin the natural grassland whereas Fcontributed more to Fin the planted grasslands. The regression analyses show that climate factors(air temperature and relative humidity) and soil properties(soil organic matter, soil temperature, and soil moisture) strongly affected respiration fluxes in all grasslands. However, our observation period was admittedly too short. To fully understand the effects of such land-use changes(i.e., converting natural grasslands into planted grasslands) on respiration fluxes, longer-term observations are badly needed.