Intraspecific trait plasticity to N and P of the wetland invader,
Alternanthera philoxeroides under flooded conditions
Abstract
Interactions between invaders and resource availability may explain
variation in their success or management efficacy. For widespread
invaders, regional variation in plant response to nutrients can reflect
phenotypic plasticity of the invader, genetic structure of invading
populations, or a combination of the two. The wetland weed Alternanthera
philoxeroides (alligatorweed) is established throughout the southeastern
USA and California, and has high genetic diversity despite primarily
spreading clonally. Despite its history in the USA, the role of genetic
variation for invasion and management success is only now being
uncovered. To better understand how nutrients and genotype may influence
A. philoxeroides invasion, we measured the response of plants from 26 A.
philoxeroides populations (three cp haplotypes) to combinations of
nitrogen (4 or 200 mg/L N) and phosphorus (0.4 or 40 mg/L P). We
measured productivity (biomass accumulation and allocation), plant
architecture (stem diameter and thickness, branching intensity) and
foliar traits (toughness, dry matter content, percent N, percent P). A
short-term developmental assay was also conducted by feeding a subset of
plants from the nutrient experiment to the biological control agent
Agasicles hygrophila, to determine whether increased availability of N
or P to its host influenced agent performance, as has been previously
suggested. A. philoxeroides haplotype Ap1 was more plastic than other
haplotypes in response to nutrient amendments, producing more than
double the biomass from low to high N and 50-68% higher shoot:root
ratio than other haplotypes in the high N treatment. A. philoxeroides
haplotypes differed in 7 of 10 variables in response to increased N. We
found no differences in short-term A. hygrophila development between
haplotypes but mass was 23% greater in high than low N treatments. This
study is the first to explore the interplay between nutrient
availability, genetic variation, and phenotypic plasticity in invasive
characteristics of the global invader, A. philoxeroides.