Mycorrhizal effects on decomposition and soil CO2 flux depend on changes in nitrogen availability during forest succession

Mycorrhizal fungi play a central role in plant nutrition and nutrient cycling, yet our understanding on their effects on free-living microbes, soil carbon (C) decomposition and soil CO2 fluxes remains limited.

Here we used trenches lined with mesh screens of varying sizes to isolate mycorrhizal hyphal effects on soil C dynamics in subtropical successional forests.

We found that the presence of mycorrhizal hyphae suppressed soil CO2 fluxes by 17% in early-successional forests, but enhanced CO2 losses by 20% and 32% in mid- and late-successional forests, respectively. The inhibitory effects of mycorrhizal fungi on soil CO2 fluxes in the young stands were associated with changes in soil nitrogen (N) mineralization and microbial activities, suggesting that competition between mycorrhizae and saprotrophs for N likely suppressed soil C decomposition. In the mid- and late-successional stands, mycorrhizal enhancement of CO2 release from soil likely resulted from both hyphal respiration an...