Gas exchange characteristics of the invasive species Mikania micrantha and its indigenous congener M. cordata (Asteraceae) in South China

In South China, the photosynthetic characteristics of an invasive exotic weed Mikania micrantha H.B. Kunth and its indigenous close congener Mikania cordata (Burm. f.) B.L. Robinson were studied. Mikania micrantha exhibited a greater biochemical capacity for photosynthesis than M. cordata, as the former had higher V cmax and J max , which lead to its higher maximum assimilation rate (A max ) values. Similar light compensation point, apparent quantum yield (α), and dark respiration (R d ), suggested a similar shade-tolerance. Higher A max , light saturating point, and CO 2 saturating point give M. micrantha greater potential to acclimate to brighter environments and a larger pool of available carbon. These differences in photosynthetic characteristics could be a basis for their niche partitioning. The leaf traits of the native and invasive Mikania species were as follows: higher construction cost (CC), lower specific leaf area (SLA), as well as lower mass-based leaf N and photosynthetic nitrogen-use efficiency (PNUE) for the native species, but M. micrantha had lower area-based leaf N. The higher water use efficiency (WUE) and δC observed in M. micrantha was probably due to its high photosynthetic capacity and not to reduced stomatal conductance, explaining the absence of any trade-off between WUE and PNUE.