Gas Exchange Characteristics of the Invasive Species Mikania Micrantha and its Indigenous Congener M. Cordata (Asteraceae) in South China

Abstract

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(subscript cmax) and J(subscript max), which lead to its higher maximum assimilation rate A(subscript max) values. Similar light compensation point, apparent quantum yield (α), and dark respiration (R(subscript d)), suggested a similar shade-tolerance. Higher A(subscript max), light saturating point, and CO2 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 δ^13C 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.