Photosynthetic Responses of Invasive Acacia mangium and Co-Existing Native Heath Forest Species to Elevated Temperature and CO₂ Concentrations

Abstract

The impacts of climate change, in particular via elevated temperature and atmospheric CO2 concentrations, cause differential photosynthetic responses between native and invasive alien plants, often resulting in varying magnitudes of plant growth and productivity. This study investigated variations in photosynthetic responses of an invasive alien Acacia species and two successional groups of tropical heath forest species: early secondary (Buchanania arborescens and Dillenia suffruticosa) and secondary (Calophyllum inophyllum and Ploiarium alternifolium) groups at elevated temperature (25 to 30°C) and CO2 levels (400 to 700 ppm). Invasive A.mangium appears better adapted to higher temperature and CO2. High temperature improved CO2 assimilation of A.mangium compared to heath species, which was attributed to increased transpiration rate and stomatal conductance but decreased water-use efficiency. Photosynthetic responses showed no differences in early secondary species at elevated temperature and CO2 but invasive A.mangium and P.alternifolium were stimulated by elevated CO2. The greater maximum net photosynthesis of A.mangium coincided with lower light compensation point and electron transport rate for RuBP regeneration, to a certain extent. Findings provide insights into possible underlying ecophysiological mechanisms contributing to the invasion success of Acacias in degraded tropical heath forests in response to future climate change.