Land use affects the net ecosystem CO₂ exchange and its components in mountain grasslands

Abstract

Abstract. Land-use change has been strongly affecting mountain grasslands, however, its controls on the net ecosystem exchange of CO2 (NEE) and its components have not yet been well documented. We analyzed chamber-based estimates of NEE, gross primary productivity (GPP), ecosystem respiration (R) and light use efficiency (LUE) of six mountain grasslands differing in land use, as measured during the growing seasons from 2002 to 2008. The main findings of the study are that: (1) land use affected seasonal NEE, GPP, R and LUE, which all decreased from managed to unmanaged grasslands; (2) these changes were explained by altered leaf area index (LAI), biomass and physiology; (3) diurnal variations of NEE were primarily controlled by photosynthetically active photon flux density (GPP) and soil and air temperature (R), seasonal variations were associated with changes in LAI; (4) parameters of light response curves were generally closely coupled, and the ratio R/GPP was nearly constant across the sites; (5) similarly to our study, GPP and R for other grasslands on the globe decreased with land-use intensity, while their ratio remained largely unchanged. We conclude that land use exerts a major influence on the net ecosystem CO2 exchange and its components in mountain grasslands.