Watling, J. R. | bioRxiv Science

bioRxiv2022

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

There is increasing evidence that native parasitic plants are showing potential as biocontrols for plant invasions which are a major global threat to biodiversity. However, for this potential to be realised, the range of invasive hosts that can be controlled needs to be identified while also evaluating any potential off-target effects the parasite may pose. To address this, we investigated the impact of the Australian native shoot hemiparasitic plant, Cassytha pubescens on the major invasive species Rubus anglocandicans and two native shrubs, Acacia pycnantha and Bursaria spinosa in naturally occurring populations in southern Australia. We measured foliar predawn and midday quantum yield, electron transport rate (ETR), stomatal conductance (gs), carbon isotope composition and foliar nitrogen concentration [N] of uninfected and infected plants and, apart from gs, also for C. pubescens. Infection significantly decreased predawn and midday quantum yield, ETR and gs of invasive R. anglocandicans. In contrast, infection had no effect on predawn and midday quantum yield, ETR or carbon isotope composition of the native hosts. However, C. pubescens had a significant negative effect on native host gs, and a positive effect on host [N]. Parasite stem [N] was significantly higher when infecting A. pycnantha than B. spinosa. These results strengthen evidence for native parasitic plants having greater impact on invasive hosts while having mild off-target effects on native hosts and thus, show potential to mitigate plant invasions and help protect biodiversity.

plant biology↗

bioRxiv2022

Impact of a native hemiparasite and mowing on performance of a major invasive weed, European blackberry

O_LIPlant invasions are a major global threat to biodiversity. Traditional methods of weed control are falling short, and novel and environmentally friendly control tools are needed. Native parasitic plants are showing promise as effective biocontrols for some of the worst weeds, however, their application is in its infancy. C_LIO_LIFirst, we established the native parasitic plant, Cassytha pubescens on unmown invasive European blackberry (Rubus anglocandicans), at three field sites (Belair, Horsnell and Blackwood) in South Australia to measure the impact of infection host performance. Concurrently, we established the parasite on hosts that were mown at two of these sites (Horsnell and Blackwood), to determine the impact of mowing, a commonly used control method, in conjunction with infection by C. pubescens. C_LIO_LIFruit production, midday quantum yield and electron transport rates of infected R. anglocandidans were significantly lower than uninfected plants at only one site, Blackwood. Predawn quantum yield, and foliar nitrogen and phosphorus concentrations of infected plants were significantly lower than uninfected ones across all three sites. Stomatal conductance was negatively affected by infection at one site (Belair). Mowing enhanced parasite impact on host nitrogen concentration at one site (Horsnell), and infection negatively affected host stomatal conductance at the same site, irrespective of whether plants were mown or not. C_LIO_LIWe have demonstrated that this native biocontrol can be artificially established on invasive European blackberry in the field, with negative consequences for its performance. Our results demonstrate the feasibility of implementing native parasitic plants as weed biocontrols to protect biodiversity, and are aligned with the Biotic Resistance hypothesis that invasive species are susceptible and sensitive to enemies native to their newly invaded habitat. C_LI

plant biology↗