Trait values and not invasive status determine competitive outcomes between native and invasive species under varying soil nutrient availability

Abstract

AbstractInvasion by exotic plants is often associated with nutrient enrichment of soils, particularly on soils of naturally low fertility. As a consequence, it is likely that the outcome of competitive interactions between native and invasive plants may be mediated by soil nutrient availability. We independently investigated competitive effect and response as well as the occurrence of asymmetric competition among native and invasive plants on soils of varying nutrient availability, using a glasshouse experiment. Seedlings of eight co‐occurring pairs of invasive and native species from low fertility Hawkesbury Sandstone‐derived soil were grown under low and high nutrient availability. We tested the hypotheses that native species would be competitively superior at low nutrient availability and have trait values associated with a resource conservation strategy while invasive species would be competitively superior at high nutrient availability and have trait values associated with a resource acquisition strategy. We found that nutrient availability did not mediate competitive interactions between invasive and native species. Instead, two invasive and one native species were always competitively superior irrespective of nutrient availability. Competitively superior species displayed a mixture of both resource conservation and acquisition strategies at low and high nutrient availability. In support of previous studies, we found that the a priori classification of invasive and native species does not predict competitive superiority at varying nutrient levels. Rather, species specific differences in trait values provide a competitive advantage in response to nutrient availability.