Earthworms negate the adverse effect of arbuscular mycorrhizae on living bacterial biomass and bacterial necromass accumulation in a subtropical soil

Abstract

Earthworms and arbuscular mycorrhizal fungi (AMF) have substantial individual effects on the supply and absorption of soil nutrients in terrestrial ecosystems. How their interactions regulate the soil living microbial community and microbial necromass accumulation remains unknown. We hypothesized that the effect of their interaction on the microbial community and necromass accumulation may relate to their controls on status of soil N and P. We conducted a greenhouse experiment manipulating the AMF Rhizophagus intraradices and the earthworm Pontoscolex corethrurus in microcosms planted with a fern Dicranopteris dichotoma. Phospholipid fatty acids and amino sugars were used to indicate the living microbial community and necromass accumulation, respectively. The AMF consistently reduced the biomass of bacterial groups and the concentration of total amino sugars, glucosamine and muramic acid, in the absence of earthworms, but had no effect in their presence. The earthworms increased the concentration of soil total dissolved N, water-soluble N and water-soluble P, and the activity of β–1,4–N-acetylglucosaminidase and phosphatase, and the amount of P in total plant biomass. Redundancy analysis showed that the bacterial biomass was positively correlated with most soil labile N indices and negatively correlated with the amount of N in total plant biomass. Pearson correlation revealed that the bacterial nutritional stress indicator Sat/Mono was negatively correlated with soil NH4+ concentration and positively correlated with the amount of N in total plant biomass. The results suggested that earthworms might negate the suppression effect of AMF on bacterial abundance and necromass accumulation by alleviating AMF-induced N deficiency.