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

Abstract

Summary Stem hemiparasites are dependent on their hosts for water and nitrogen. Most studies, however, have assessed 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 a host (Ulex europaeus) and its 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 did not 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 δ13C was significantly higher than that of the host. Our results suggested that stem hemiparasites can better extract resources from hosts when water availability is high, resulting in a greater impact on the host under these conditions. When hemiparasitic plants are being investigated as a biocontrol for invasive weeds, they may be more effective in wetter habitats than in drier ones.

Does phosphorus influence performance of a native hemiparasite and its impact on a native legume?

“…Cirocco et al . (2016b, 2020, 2021) also found that C. pubescens significantly decreased nodule biomass of U. europaeus . Similarly, Gao et al .…”

“…Our previous work has also found that C. pubescens has a consistent negative impact on growth of the invasive U. europaeus (Cirocco et al . 2016a, 2016b, 2017, 2020, 2021). Our atypical finding of C. pubescens negatively affecting growth of a native host may be due to parasites (including Cassytha ) having a greater effect on smaller hosts (Cirocco et al .…”

“…We found that hemiparasite δ 13 C was significantly higher than its host, particularly in the low P treatment, as similarly found for the C. pubescens – U. europaeus association (Cirocco et al . 2016b, 2018, 2020, 2021). Holoparasites also tend to have significantly higher δ 13 C than their hosts, which may be due to heterotrophy (Bolin et al .…”

“…Cassytha , on the other hand, may be more conservative in its water‐use than infected plants because it is a thin vine and thus likely more prone to desiccation (see Cirocco et al . 2021).…”

Impact of a native hemiparasitic plant on invasive and native hosts in the field

“…In Australia, the native parasitic vine Cassytha pubescens has been shown to have a strong negative impact on the physiology and growth of the major invasive shrubs, Ulex europaeus and Cytisus scoparius (Prider et al 2009; Shen et al 2010; Cirocco et al 2016a, b, 2017, 2018, 2020, 2021a). Moreover, C. pubescens has little effect on physiology and growth of the native hosts Leptospermum myrsinoides and Acacia paradoxa (Prider et al 2009; Cirocco et al 2016a, 2017; but see Cirocco et al 2021b).…”