Interaction between foliar-feeding insects, mycorrhizal fungi, and rhizosphere protozoa on pea plants

Pea plants (Pisum sativum) were grown in pots with and without the arbuscular mycorrhizal fungus (AMF) Glomus intraradices. Plants in each AM treatment were subjected to adult weevils (Sitona lineatus) during the periods 15-25 d or 23-39 d and were harvested at day 25 or day 39. Herbivory stimulated AMF root colonisation of mycorrhizal plants at the first harvest and stimulated rhizosphere protozoa in the absence of AMF At the second harvest, herbivory decreased AMF colonization and had no effect on rhizosphere protozoa. The presence of AMF had no effect on herbivory at the first harvest but decreased herbivory at the second harvest. Below-ground respiration was stimulated by herbivory and this effect was most pronounced during vegetative growth. The results therefore suggest, that herbivory stimulated below-ground carbon transfer in young plants in the nutrient acquisition phase as opposed to the reproductive phase where herbivory had no such effect. This herbivory-induced carbon transfer will benefit the AMF symbiont when present and the free-living rhizosphere micro-organisms - here represented by the bacterivorous protozoa - in the absence of AMF.