The combined effects of water and nitrogen on the relationship between a native hemiparasite and its invasive host

Cirocco, Robert M, Watling, Jennifer R and Facelli, José M (2021) The combined effects of water and nitrogen on the relationship between a native hemiparasite and its invasive host. New Phytologist, 229 (3). pp. 1728-1739. ISSN 0028-646X

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Abstract

Stem hemiparasites are dependent on their hosts for water and nitrogen. Most studies, however, assess the influence of one factor on parasite:host associations, thus limiting our mechanistic understanding of their performance in nature. We investigated the combined effects of water and nitrogen (N) availability on both host (Ulex europaeus) and parasite (Cassytha pubescens). Parasite infection significantly decreased host shoot biomass and shoot:root ratio more severely in high water than low water, irrespective of N supply. Parasite stem [N] was significantly higher in high water than low water treatments, regardless of N supply, but parasite biomass didn't vary among treatments. Irrespective of water and N supply, infected plants had significantly lower total, root and nodule biomass, predawn and midday quantum yields, maximum electron transport rates, water potentials and nitrogen concentration [N]. Parasite δ13 C was significantly higher than that of the host. Our results suggest that stem hemiparasites can better extract resources from hosts when water availability is high, resulting in greater impact on the host in these conditions. Where hemiparasitic plants are being investigated as biocontrol for invasive weeds, they may be more effective in wetter habitats than in dry ones.