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Understanding the impact of temperature variations (i.e., maximum, minimum, and diurnal temperature ranges [DTRs]) on ecosystems is now recognized as being of paramount importance in global change ecology; the roles of different aspects of these temperature variations in influencing plant photosynthesis remain under-studied. Here, we investigated the photosynthetic responses of two local dominant wetland plants to two simulated air-warming scenarios (+2 degrees +/- 0.5 degrees C and +3.5 degrees +/- 0.5 degrees C) by using open-top chambers in the northwest Yunnan plateau. During the growing season from 2014 to 2016, we explored photosynthetic parameters and the relationships linking photosynthesis to temperature variations. We found that open-top chambers had increased the daily maximum temperature as well as DTRs. The photosynthetic responses of two plant species to warming were species-specific during the first two years but species-independent in the third year. The two warming scenarios did not significantly alter the linear relationships linking maximum net photosynthetic rate (A(max)) to stomatal conductance (g(s)), intercellular CO2 concentration (C-i), and transpiration rate (T-r), despite changes in slopes and intercepts of the fitted lines. The DTRs between 0 degrees C and 30 degrees C were positively correlated with photosynthesis, while DTRs over 30 degrees C were negatively correlated with photosynthesis. Our results provide experimental evidence that temperature variations play a greater role than increasing average temperature in explaining plant photosynthesis, and more attention should be paid to temperature variations when assessing the impact of climate warming on wetland ecosystem.