Carbon Isotope Constraints on Plant Water Use Efficiency in a Tropical Invaded Ecosystem

Abstract Exotic plant invasions have caused substantial changes in plant diversity and the functioning of terrestrial ecosystems. One of the key determinants of plant invasion success is its resource utilization strategy, such as water utilization strategies. However, how iWUE differs between exotic and native plants, and between natives under invasion and non‐invasion, remains unclear, limiting our understanding of the role of water use strategies in plant invasion and coexistence. In this study, leaf δ 13 C was measured to quantify the iWUE of 19 native C 3 and nine native C 4 species under no invasion, two exotic C 3 species ( Ageratina adenophora and Chromolaena odorata ), and 16 C 3 and 10 C 4 co‐occurring natives in a tropical ecosystem of southwestern China. The significantly higher iWUE of invading plants compared with co‐occurring C 3 species was associated with their invasion success and spread. Under invasion, the iWUE of coexisting native C 3 plants decreased by 42 ± 30% possibly due to enhanced water losses associated with nitrogen acquisition. Oppositely, native C 4 plants increased their iWUE by 65 ± 140%, along with enhanced photosynthetic N and NH 4 + assimilations, which supported greater productivity. These results highlight the critical role of water use and its coupling with other resource use strategies in facilitating exotic plant invasion and promoting native plant coexistence. This work is of great significance for advancing the understanding of mechanisms shaping plant community composition and for informing the management of water and nutrient resources to control exotic plant invasion and sustain plant diversity in tropical ecosystems.