Resource limitation and the role of a hemiparasite on a restored prairie

Abstract

Hemiparasitic plants tend to thrive in and significantly affect plant communities in low-nutrient, high-light environments. Hemiparasites are assumed to be weak competitors for light but strong parasites, leading to the prediction that effects on hosts and communities should be a function of resource supply. We investigated the effects of light and mineral nutrients on hemiparasite-host relations in two experiments. Removal of the hemiparasite, addition of fertilizer, and full sun significantly increased total aboveground dry mass in small plots on a restored tallgrass prairie. After 3 years, removal of Pedicularis canadensis almost doubled the mass of grasses and had smaller effects on forb species, but the impact of the parasite was independent of resource level. Fertilizer increased grass growth only in full sun, increased non-legume forb growth only when shade was applied, and tended to depress legume growth when shaded. Light manipulation did not affect the hemiparasite across 4 years of manipulation but fertilizer increased P. canadensis shoot mass. A complementary greenhouse experiment with Andropogon gerardii as host produced qualitatively similar effects and showed that shade reduced root growth of both the host and the parasite. These results do not support common assumptions regarding hemiparasite-host relations under field conditions but indicate that a small hemiparasite can significantly affect prairie productivity regardless of resource supply.

The role of hemiparasitic plants: influencing tallgrass prairie quality, diversity, and structure

“…Although MRSW and the remnant have identical soil, Drummer silty clay loam (Soil Survey Staff Natural Resources Conservation Service, United States Department of Agriculture 2008), hemiparasite frequency is considerably lower in MRSW than WCP (30 vs. 92%), and hemiparasites have a more patchy distribution. This may allow better detection of differences along a hemiparasite abundance gradient, consistent with previous studies (Hedberg et al 2005;Borowicz & Armstrong 2012;Bao et al 2015), than in the remnant where hemiparasites are almost ubiquitous and effects may be more homogenous. That is, hemiparasites could have increased richness uniformly across the remnant, making it difficult to detect a hemiparasite effect in the absence of a frequency gradient.…”

“…In greenhouse experiments with P. canadensis , Hedberg et al () had 25% P. canadensis mortality, and Borowicz and Armstrong () also reported high mortality. It was suggested that the greenhouse environment favored host species growth over P. canadensis growth (Hedberg et al ).…”

“…There was no relationship between combined cover of the four C 4 species present ( Andropogon gerardii , Sorghastrum nutans , Panicum virgatum , and Sporabolus heterolepis ) and hemiparasite cover at our sites, and no relationship at another site in the region (Hedberg et al ). Grass responses to parasitism might be better determined from dry biomass data rather than by percent cover (Borowicz & Armstrong ), so future field studies should determine shoot biomass responses of grasses rather than cover data alone, especially given the unexpected positive growth response of A. gerardii in the mesocosm study described here.…”

“…Two previous studies investigated the effect of wood betony, Orobanchaceae ( Pedicularis canadensis ) on a tallgrass prairie plant community. Pedicularis canadensis abundance was significantly correlated with species richness (SR) (Hedberg et al ), and forb biomass was reduced in plots with P. canadensis compared to areas where the hemiparasite had been removed three years earlier (Borowicz & Armstrong ). The presence of P. canadensis also reduced grass biomass by 80% and total biomass by 32%, demonstrating that this hemiparasite can exert a similar pattern on community structure as the annual R. minor in European meadows (Cameron et al ).…”

Host shoot clipping depresses the growth of weedy hemiparasitic Pedicularis kansuensis

“…Parasitism by a root hemiparasite often leads to significant biomass reduction in the host plant, which in most cases cannot be compensated by the increase in biomass of the hemiparasite (Matthies 1995;Niemelä et al 2008). Consequently, presence of root hemiparasitic plants often results in significant reduction in plant community productivity (Borowicz and Armstrong 2012;Decleer et al 2013), which is particularly the case in agricultural ecosystems where root hemiparasitic weeds occur in great abundance (Parker 2009;Rodenburg et al 2011).…”