Plant endophytes and arbuscular mycorrhizal fungi alter the decomposition of Achnatherum sibiricum litter

Symbiotic infection with endophytic fungi has been shown to affect the decomposition rate of host plant leaf litter, but whether this effect is influenced by the presence of arbuscular mycorrhizal fungi (AMF) remains unclear. In this study, we placed litterbags with endophyte-infected (E+) and endophyte-free (E-) Achnatherum sibiricum leaf litter in experimental microcosms in which three AMF inoculation treatments (Funneliformis mosseae, FM; Claroideoglomus etunicatum, CE; and no AMF, NM) were conducted. We then studied the dynamics of mass and nutrient losses and the soil microbial community during a 300-day decomposition period. The presence of endophytes inhibited A. sibiricum litter decomposition, while AMF significantly enhanced the rate of litter decomposition. The degree of inhibition of endophytes was dependent on the AMF species identity. The presence of endophytes significantly decreased the decomposition rate at later decomposition stages under FM inoculation, while the inhibitory effect of endophytes on litter decomposition was eliminated under CE inoculation. In the presence of endophytes, the ratio of carbon to nitrogen in litter increased, which is usually associated with lower decomposition rates. The effect of endophytes on nitrogen accumulation was also influenced by the host plant AMF status, i.e., endophytes reduced nitrogen loss from litter during decomposition only in the FM inoculation treatment. Endophytes had significant negative effects on the biomass of the soil fungal, bacterial and total microbial communities. Our findings suggest that the presence of endophytes can decrease the decomposition rate of A. sibiricum leaf litter directly by altering litter quality and indirectly by inhibiting soil microbial community development during decomposition. Moreover, this inhibitory effect changes depending on the AMF species present. These results may further our understanding of the interactive effects of these two symbionts on nutrient cycling and carbon sequestration in natural communities.