Variations in the temperature dependence of photosynthesis among nine common tree species planted in Singapore

Tree planting is regarded as one of the most cost-effective ways to mitigate climate change impacts. As a part of the global tree planting movement, the tropical city-state of Singapore initiated a project to plant one million trees in 10 years. However, the environmental impacts (e.g., carbon sequestration, urban cooling) of this reforestation effort are challenging to assess as historically we lack understanding of key plant traits (i.e. photosynthetic capacity, or Vcmax) for species in tropical Asia. Here, we conducted a comprehensive survey of key photosynthetic traits of the nine most popular tree species planted in Singapore and their short-term temperature dependence. We found a three-fold inter-species variation in their photosynthetic capacities (e.g., Vcmax ranges from 20 to 60 mol m-2 s-1) as well as a large discrepancy in their temperature dependence. The photosynthesis of some species (e.g., Tembusu) is more sensitive to rising temperature than others (e.g., Mangroves) while a commonly-used photosynthesis model consistently overestimates photosynthesis but underestimates many species temperature sensitivities. The species with smaller temperature sensitivity of photosynthesis is likely related to their stronger ability to adjust leaf temperature via transpiration. Our study provides critical information on the temperature-dependence of photosynthesis of tree species in tropical Asia, which can be used to guide reforestation in Singapore and broadly in Southeast Asia.