Abstract: Photosynthesis is the powerhouse of the biosphere, and the largest single flux in the global carbon cycle. The photosynthesis-temperature (P-T) response is essential for predicting climate change and its effects on the biosphere. P-T responses are quantified by photosynthetic thermal traits, such as the activation energy, optimal temperature, maximum temperature, and temperature breadth. However, understanding the relationships between photosynthetic thermal traits and other key traits, such as carbon economics traits, has been challenging due to time-intensive methods and methodological inconsistencies. To overcome these challenges, we used a new FAsTeR (Fast Assimilation-Temperature Response) method to quantify photosynthetic thermal traits for 123 species spanning the diversity of vascular plants in a common garden. We also measured prominent carbon economics traits, including leaf mass per area, leaf dry matter content, and maximum photosynthetic rate. We found that photosynthetic thermal traits are strongly coordinated and orthogonal to the carbon economics spectrum. These results highlight the importance of photosynthetic thermal traits for quantifying leaf ecophysiological trait space, and identify a new axis of ecophysiological variation that bears particular relevance for understanding and predicting climate change.
