Alternanthera philoxeroides haplotypes growth response to N and P

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.