Seasonal and daily pattern, temporal and spatial variability of ecosystem CO2-exchange in a temperate Pannonian loess grassland

Abstract

In the photosynthetically most active spring, summer and autumn vege­ tation period the investigated grassland did maintain a relatively strong daytime carbon gain. During winter the grassland displayed a slight daytime carbon loss. These data suggest that the grassland was a weak sink for carbon in the investigated period. CO2 exchange variability during the day seemed to be independent from that of the daily photosynthetic radiation. Thus other factors like soil respiration, soil moisture content and temperature and their interactions could be responsible for the high daily variabil­ ity of grassland CO2-exchange. The considerable temporal (daily and seasonal) vari­ ability of the grassland CO2-exchange can be considered as a characteristic feature of the grassland CO2-exchange. In the investigated loess grassland vegetation the variabil­ ity of CO2-exchange showed clear dependence on measuring area, which is obvious in the CV of NEE. We hypothetised that the spatial scale with the lowest variability is the characteristic area of the grassland ecosystem's CO2-exchange (CO2-exchange physi­ ological unit). In general decreased variability indicates a more regulated state.