Effects of light intensity on morphology and physiology of exotic invasive Bidens pilosa L. and non-invasive congener Bidens bipinnata L.

We compared the ability of physiological and morphological adaptations of the invasive Bidens pilosa L. and the native Bidens bipinnata L. under different light intensities (LI). The morphological and physiological characteristics of the invasive B. pilosa were compared with B. bipinnata at 3-Light intensities (Control (100% full sunlight), 40% full sunlight and 10% full sunlight) for 64 days. Decreased LI significantly decreased the germination and root and shoot biomasses but significantly increased the leaf biomass of both plant species. Under the same LI the invasive species B. pilosa higher leaf mass ratio (LMR), total leaf area (LA), relative growth rate (RGR), maximum net photosynthesis rate (P-max), light saturation point (LSP), light compensation point (LCP) and dark respiration (R-d) and lower root mass ratio (RMR), stem mass ratio (SMR) and root mass/crown mass (R/C) than in B. bipinnata. Decrease in LI significantly reduced the photosynthesis efficiency of the non-invasive B. bipinnata compared with the invasive B. pilosa. The higher photosynthetic response of B. pilosa to variable lighting conditions also indicated its better competitive ability. Our results provide key information concerning the effects of light intensity on the growth and photosynthetic characteristics of B. pilosa and B. bipinnata and indicated that former exhibits greater physiological and morphological adaptation to different light intensities, which facilitates its further invasion.