Seasonal and interannual variations of ecosystem photosynthetic features in an alpine dwarf shrubland on the Qinghai-Tibetan Plateau, China

Ecosystem photosynthetic characteristics are of utmost importance for the estimation of regional carbon budget, but such characteristics are not well understood in alpine regions. We collected CO2 flux data measured by eddy covariance technique over an alpine dwarf shrubland on the Qinghai-Tibetan Plateau during years 2003-2010; and we quantified the temporal patterns of ecosystem apparent quantum yield (a), saturated photosynthetic rate (P max), and ecosystem dark respiration (R De). Results showed that the strong seasonality of a and R De was driven mainly by air temperature (T a), whereas that of P max was much more determined by leaf area index rather than abiotic factors. Diurnal thermal fluctuation inhibited significantly the daytime photosynthetic capacity. Stepwise regression revealed that the seasonal deviations of a, P max, and R De were significantly controlled by T a. The annual a was regulated mainly by annual growing season T a, which indicated that the response of ecosystem a was instant. The annual variations of P max correlated positively with soil temperature 5 cm below ground (T s) of the annual nongrowing season and those of R De related negatively with the annual nongrowing season precipitation. We suggested that a lagged response regulated the annual P max and the annual R De. Annual deviations of a and R De were both significantly controlled by annual T s, and those of P max were marginally determined by annual PPFD. Thus, the future warming scenario, especially significant for nongrowing seasonal warming in the Qinghai-Tibetan Plateau, would favor ecosystem photosynthetic capacity in the alpine dwarf shrubland.