Neutral interactions between native Alternanthera sessilis and exotic Alternanthera philoxeroides along a light gradient under tropical climatic conditions

Abstract

AbstractRiparian ecosystems are under a serious threat of invasion due to the clearance of riparian vegetation, which allows for increased light levels at ground level. This study presents the interactions between native Alternanthera sessilis (L.) R. Br. ex DC and invasive Alternanthera philoxeroides (Mart.) Griseb. during the colonization stage along a light gradient under tropical climate conditions. We conducted a 6 week growth experiment with monocultures of A. philoxeroides and A.sessilis and mixed communities of two species under four light levels (100%, 46%, 26% and 14% of full sunlight). Exposure to full sunlight (nearly 1800 μmol m−2 s−1) resulted in a significantly high biomass accrual in both species. However, biomass accrual did not correlate with the light intensity. At higher shade levels, reduction of lateral spread and shoot/root ratio was observed. Community composition had no influence on biomass accrual or morphological variations. Plasticity index values were approximately same in both species. Total relative yield was approximately two in all shade conditions, indicating that the two species interact neutrally along the light gradient. Therefore, the results of the study indicate that increased light levels will accelerate the proliferation of both species in riparian zones. Nevertheless, increased or decreased shade is unlikely to alter neutral interactions between A. philoxeroides and A. sessilis.