Data from: A generalist nematode destabilizes plant competition: no evidence for direct effects, but strong evidence for indirect effects on rhizobia abundance

1. Difficulties quantifying pathogen load and mutualist abundance limit
our ability to connect disease dynamics to host community ecology. For
example, specific predictions about how differential pathogen load is
hypothesized to drive host competitive outcomes are rarely tested.
Additionally, although infection is known to affect mutualists, we rarely
measure the magnitude of pathogen effects on mutualist abundance across
host competitive contexts. We tested for both mechanisms in a
plant-rhizobia-nematode system. 2. We paired the legume Medicago lupulina
with intra- and interspecific plant competitors, with and without a
generalist nematode parasite Meloidogyne sp. Relative change in plant
biomass was used to determine how nematode inoculation affected plant
competitive outcomes. We counted nematode galls to test for direct effects
of parasitism on plant competition, and rhizobia nodules to test for
indirect effects of nematode presence on rhizobia abundance. 3. Parasites
were destabilizing despite similar nematode load across competition
treatments. During inter- compared to intraspecific competition, nematode
inoculation decreased nodulation on M. lupulina, increased nodulation on
Trifolium repens, and had no effect on nodulation on Chamaecrista
fasciculata. 4. We found no support for hypothesized direct effects of
nematode load on competitive outcomes, and strong but idiosyncratic
indirect effects of nematode inoculation on rhizobia abundance.