Abstract
Parasitic plants have been shown to affect soil-organic-matter (SOM)
decomposition, but the mechanism is unknown. As arbuscular mycorrhizal
fungi (AMF) can affect decomposition and compete with parasitic plants
for carbon, we hypothesized that parasitic plants can indirectly
regulate decomposition by suppressing AMF. We conducted two experiments
in which Bidens pilosa was inoculated with AMF or not, and parasitized
with Cuscuta australis or not. In hyphae-in-growth bags, we provided SOM
in one experiment as 13C-/15N-labelled maize leaves and in the other as
phytate P. In the presence of AMF, Parasitization increased the 13C but
decreased the organic P remaining in the bags. In the absence of the
parasite, AMF decreased the 13C and increased the organic P remaining in
the bags. Our results demonstrate that parasitic plants can indirectly
regulate the decomposition of organic materials by suppressing the
effect of the extraradical AMF hyphae on decomposition.