Drought responses in two resprouting tree species differ across range-expanding and invasive populations

Abstract Understanding the effects of disturbance on plant species inside and outside of their native ranges can provide insights into traits that lead to successful persistence and spread. Drought is an acute form of disturbance that is widespread. Species living outside of their native ranges may have physiological differences that allow them to spread to new areas and persist through disturbances such as drought. We compared differences in resource allocation and functional traits in native, range-expanding (shifting within a geographic area), and invasive populations (moving outside a country) of two species of nitrogen-fixing resprouting trees, Honey Locust (Gleditsia triacanthos) and Black Locust (Robinia pseudoacacia). Four populations of each species (native, range-expanding, and invasive (European and South African)) were exposed to experimental drought treatments where growth and physiological traits were measured. Native and South African trees of both species differed significantly in growth metrics (biomass, leaf area, specific leaf area, relative growth rate, number of leaves) and aboveground non-structural carbohydrates under drought conditions compared to range-expanding and European trees. Nitrogen-fixing nodule formation in Black Locust seedlings decreased under drought, as did aboveground nitrogen concentration. These results suggest populations living outside of their native ranges may use differences in resource allocation to better survive drought disturbance compared to native populations.