Influence of light, nutrients, and soil moisture on the growth and resource allocation of Arundo donax

Understanding how invasive species respond to changes in abiotic factors and what influences their ability to colonise newly disturbed areas is necessary to predict species expansion, prioritise management efforts, and develop ecological models. We conducted a fully factorial greenhouse experiment using rhizome fragments to examine the effects of four nutrients levels, three soil moisture levels, and two light levels (with five replicates, n = 120) on the growth and resource allocation patterns of Arundo donax, a large-statured invasive wetland species. We predicted that A. donax's performance-related traits-traits that directly influence the functionality and fitness of an individual-such as aboveground biomass (AGB), belowground biomass (BGB), net photosynthesis, and average stem height, would be highest under high light, high soil moisture and high nutrient conditions due to the ability of aggressive invasive species to capitalise on greater resource availability. Analyses using general linear mixed-effects models revealed significant interactions between soil moisture and light. Plants grown in saturated, high light conditions exhibited the highest values for performance-related traits. However, contrary to predictions, nutrients did not significantly influence these traits. Multivariate analysis of variance demonstrated that nutrients did influence biomass allocation patterns, with plants grown with added nitrogen and phosphorus displaying higher AGB:BGB and stem:leaf ratios. This research highlights A. donax's unique response to nutrient addition and the plasticity of biomass allocation patterns. By understanding how invasive species respond to common abiotic factors, we can better predict their expansion and prioritise management efforts, such as focusing on areas of low overstory shading, while also providing crucial information for ecological model development.