Phylogenetic relatedness may mediate the effects of increases and temporal pulses in nutrient supply on plant invasion in wetland mesocosms

The fluctuating resource hypothesis posits that temporal variation in resource availability can facilitate plant invasion. However, invasion success under resource fluctuation is further constrained by the biotic resistance of resident communities, yet how native community attributes—particularly invader–native phylogenetic relatedness and native community diversity—mediate the effects of resource fluctuation remains unclear. We experimentally tested the effects of nutrient availability (constant and temporally pulsed), native species richness (1, 2, or 4 species), and invasive–native phylogenetic relatedness on plant invasion in wetland mesocosms. Five invasive species were introduced into 18 native species assemblages under four nutrient regimes: constant low, constant high, a single large pulse, and multiple small pulses. Constant high nutrient supply significantly increased relative invasive biomass compared to constant low supply. A single large nutrient pulse produced effects similar to constant high nutrients, whereas multiple small pulses reduced invader relative biomass. Native species richness and its interaction with nutrient regimes had no significant effects on invasion. Importantly, nutrient effects depended on invasive–native phylogenetic relatedness: nutrient enrichment most strongly promoted invasion, and multiple small pulses most strongly suppressed invasion, when invaders were closely related to native species. These results demonstrate that phylogenetic relatedness mediates invasion responses to resource variability.