Presence of N-fixing neighbors increases leaf N and \u03b413C in Castilleja applegatei, a root hemiparasite

Abstract

Parasitic plants are known for their high transpiration rates and low water use efficiency (WUE), which the N-parasitism hypothesis posits is driven by N limitation. Thus, availability of N-fixing hosts may affect parasite’s WUE and in turn impact the surrounding plant community. Here, I investigate how the availability of an N-fixing host affects the root hemiparasite, Castilleja applegatei, and examines host-mediated effects on community structure and soil moisture. I surveyed plant diversity and percent cover and measured soil moisture in 120 1 × 1 m plots within Sagehen Experimental Forest, CA. Fifty percent of the plots included C. applegatei. In a subset of plots, I measured leaf N, C/N, δ13C, and δ15N in C. applegatei and in one N-fixer (Ceanothus prostratus) and two non-N-fixing plants (Artemisia tridentata and Wyethia mollis). In C. applegatei availability of N-fixing hosts corresponded to a significant increase in leaf %N, a distinct δ15N signature, and an increase in δ13C (which typically signifies an increased WUE). The presence of parasites was associated with a marginally significant decrease in WUE in N-fixing neighbors, but had no effect on the two non-N-fixing species. The presence of parasites did not impact diversity, percent cover, or soil moisture. These results broadly support the N-parasitism hypothesis and indicate that host type can affect parasite’s physiology and therefore have the potential to mediate parasite’s effects in the community; however, community-level impacts were not found here.