Do water and host size interactively affect the impact of a native hemiparasite on a major invasive legume?

Abstract

AbstractIt is unknown how the combined effects of host size and water availability influence parasitic plant:host associations. This is a major gap considering that parasitic plants would frequently encounter hosts of different size growing in different water conditions in nature. In a glasshouse experiment, small or large Ulex europaeus (major invasive host) were provided high or low water supply and infected or not with the Australian native shoot hemiparasitic vine, Cassytha pubescens. Infection significantly decreased host total, shoot and root biomass, in both low water and high water conditions but more severely so in the latter. Infection also significantly decreased total biomass of both large and small plants and more severely so for the latter. Infection significantly decreased host foliar nitrogen and potassium concentrations in well-watered but not in low water conditions. Infection significantly suppressed host predawn and midday quantum yield, midday electron transport rates, foliar phosphorus concentration and nodule biomass, irrespective of water conditions or host size. Parasite biomass (including g-1 host total biomass) was significantly greater on hosts growing in well-watered than in low water conditions. Our results suggest that some native parasitic plants may effectively control major invasive hosts, particularly in wetter habitats and or when the host is small, leading to enhanced biodiversity protection in those settings.