Will root-associated fungi affect enzyme activity in the root-detritusphere?

Abstract

Root-associated fungal groups play a key role in plant productivity and belowground processes. However, how root-associated fungi will affect rhizosphere processes after the death of root still remain unknown. We applied soil zymography to visualize the spatio-temporal distributions of enzyme activities involved in root decomposition processes of European Spruce (Picea abies) between rhizosphere (living root) and detritusphere (7, 14, and 28 days after shoot cutting), and evaluated the effects of different root associated functional fungal groups (ectomycorrhizal fungi: EcMF; non-mycorrhizal rhizosphere fungi: NMRF; a mixture of EcMF and NMRF: Mix) on microbial growth rate and enzyme functions. In the root-detritusphere, the amount of available substrate released by dead root was increased, which stimulated microbial growth and enzyme activity. This was supported by larger hotspots area and broader extension of C-, N-, and P-enzyme activity (1.3–12.8 times) compared to rhizosphere (at day 0 after shoot cutting). This further shifted microorganisms from K-strategies in the rhizosphere to r-strategies in the detritusphere. Since NMRF benefited from the newly available resources as well as from the decreased competition with EcMF after root dead, enzyme activities were higher under a mixture of EcMF and NMRF than that under bare root or individual fungi alone. Furthermore, plants inoculated with EcMF increased the secretion of enzymes after shooting cutting, which may be explained by that the C and nutrients remaining in the root support the growth of EcMF to searching for new nutrients in the short-term. Overall, turnover of fungal biomass in detritusphere and soil represents an important process in the environment.