Spatial and temporal heterogeneity of Eragrostis curvula in the downstream flood meadow of a regulated river

Abstract

We studied the spatiotemporal trends of Eragrostis curvula (Schrad.) Nees in a flood meadow of a regulated river. The response variables, including the abundance of colonies, colony sizes, flowering spikes, biomass and root structure were checked against a set of environmental variables. These variables included distance from the river, substrate conditions (stony to sandy), soil nutrients (total nitrogen, phosphorous and calcium) and soil moisture. Relationships were evidenced using redundancy analysis. Response variables were found to be distinctive and based on substrate conditions (i.e. stony or sandy). The variables ‘distance from the river’ and ‘soil phosphorous’ contributed significantly to the overall variance. Stony habitats were observed to have lower soil nutrient levels and were characterised by monospecific stands of E. curvula, while the high nutrient levels of sandy habitats promoted heterogeneous herbaceous vegetation growth. Primary production, especially belowground, was measured to be significantly higher (t-test, P<0.05) in stony habitats. Spatiotemporal trends suggested that, irrespective of the number of colonies, E. curvula demonstrated significant levels of adaptation to micro-environments through biomass allocation and the morphological plasticity of its roots. The study results suggest that river regulation and the subsequent reduction in the frequency of inundation, in addition to the reduction of nutrients and fine sediment supply downstream, give a competitive edge to E. curvula over other herbaceous species.