Increases and fluctuations in nutrient availability do not promote dominance of alien plants in synthetic communities of common natives

Abstract

1.It is frequently thought that global environmental changes, and especially the concomitant changes in environmental variability, could further increase the success of invasive species in native resident communities. However, very few studies explicitly tested this, and it remains unknown whether invasive and non‐invasive alien species respond differently to resource fluctuations in resident communities.2.We grew ten invasive and ten non‐invasive species as target species in pot‐mesocosms with four different synthetic native resident communities under six nutrient treatments differing in overall nutrient availability and temporal fluctuations in nutrient supply (constant low, constant high, gradual increasing, gradual decreasing, single large pulse, multiple smaller pulses). With the exception of plants in the constant low treatment, the plants were supplied the same total amount of nutrients during the experiment. We tested whether high nutrient availability and fluctuations in nutrient supply increased performance of both invasive and non‐invasive alien plants within native resident communities, and whether invasive ones benefited more than non‐invasive ones.3.We found that the increase in biomass in response to nutrient addition was stronger for invasive than for non‐invasive alien species. However, as the native competitors benefited even more from nutrient addition, the relative biomass of the alien target plant species, particularly the non‐invasive ones, decreased. When the nutrient supply gradually increased, biomass of alien targets as well as native competitors decreased compared to the plants in the constant nutrient supply treatment. Surprisingly, when nutrients were supplied as a single large pulse, the absolute and relative biomass of the alien target plants decreased. The reduction in relative biomass was even stronger for invasive than for non‐invasive alien species, and a similar pattern was found when nutrients were supplied as multiple smaller pulses.4.Our results confirm previous findings that invasive alien species benefit more from nutrient addition than non‐invasive alien species. However, in contrast to previous findings, our results suggest that nutrient fluctuations can suppress biomass of alien plants relative to that of natives, at least when the natives are themselves very successful, common species.