Evolutionary Responses of A Dominant Plant Along a Successional Gradient in A Salt-Marsh System

Abstract

\n The ecological responses of plant populations along the successional gradient have been intensively examined; however, the evolutionary responses remain to be elucidated. Here, I explored genetic changes of key phenotypic traits of a dominant plant along a successional gradient, and whether these changes were induced by abiotic and biotic variables. I measured key abiotic (e.g. clay thickness) and biotic variables (e.g. herbivore density) along the successional gradient in the high and low marsh in a Wadden Sea saltmarsh. Also, I collected samples of Elytrigia atherica, grew them in the greenhouse, and measured key functional traits. I found that clay thickness (a proxy of total nitrogen) increased along the successional gradient both in the high and low marsh; herbivore density from hares (the most important herbivores) decreased along the successional gradient in the high marsh. Also, I found that growth in number of leaves and ramets decreased, while rhizome length increased, along the successional gradient for E. atherica collected from the high marsh. Opposite trends were found for E. atherica collected from the low marsh. Results suggest that, in the high marsh, herbivores may overrule nutrients to drive trait changes. That is, at early successional stages, E. atherica had higher growth in number of leaves and ramets to compensate for high-density grazing. In the low marsh, nutrients were the dominant driver for trait changes. These results suggest that ecologically important abiotic and biotic variables such as nutrients and herbivores may also have a substantial evolutionary impact on plant populations.