Alpine ecosystems are extremely vulnerable to climate change. To address the potential variability of the responses of alpine ecosystems to climate change, we examined daily CO exchange in relation to major environmental variables. A dataset was obtained from an alpine meadow on the Qinghai-Tibetan Plateau from eddy covariance measurements taken over 3 years (2002-2004). Path analysis showed that soil temperature at 5 cm depth (Ts) had the greatest effect on daily variation in ecosystem CO exchangeall year around, whereas photosynthetic photon flux density (PPFD) had a high direct effect on daily variation in CO flux during the growing season. The combined effects of temperature and light regimes on net ecosystem CO exchange (NEE) could be clearly categorized into three areas depending on the change in Ts: (1) almost no NEE change irrespective of variations in light and temperature when Ts was below 0 pC; (2) an NEE increase (i.e. CO released from the ecosystem) with increasing Ts, but little response to variation in light regime when 0 pC[less-than or equal to]Ts[less-than or equal to]8 pC; and (3) an NEE decrease with increase in Ts and PPFD when Ts was approximately >8 pC. The highest daily net ecosystem CO uptake was observed under the conditions of daily mean Ts of about 15 pC and daily mean PPFD of about 50 mol mpo dayp#. The results suggested that temperature is the most critical determinant of CO exchange in this alpine meadow ecosystem and may play an important role in the ecosystem carbon budget under future global warming conditions.
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