Data from: The litter C/N ratio governs the dual role of Ectomycorrhizal fungi in decomposition and plant nutrition absorption

Ectomycorrhizal fungi (EcMF) modulate litter decomposition in a manner
dependent on litter chemistry and facilitate nutrient acquisition through
the soil–mycorrhiza–plant pathway. However, how litter carbon/nitrogen
(C/N) ratio regulates EcMF-induced decomposition and subsequent plant
growth remains unclear. Using a microcosm experiment with five litter
types, we assessed decomposition rates, C and N loss, microbial biomass,
enzyme activities, and plant growth under ectomycorrhizal and
non-ectomycorrhizal seedlings. Results indicated that effects of EcMF on
litter decomposition were litter-specific and time-dependent. After 120
days, EcMF enhanced decomposition of low C/N litters (Carex breviculmis,
Lindera glauca, and Liquidambar formosana) by 13–28%, but suppressed that
of high C/N litters (Quercus acutissima and Pinus massoniana) by 19–20%.
Initially (30 days), EcMF inhibited low C/N litter decomposition, later
shifting to promotion, whereas high C/N litter decomposition was
consistently suppressed. Correlation analysis revealed that the hyphal
effects correlated negatively with litter stage C/N ratio. EcMF
significantly increased plant N content and biomass under low C/N litters
(biomass increased by 20–30%), but only marginally enhanced biomass under
high C/N litters (14–16%) without improving N content. Partial Least
Squares Path Modeling revealed that EcMF promoted C and N release from low
C/N litter, thereby increasing N availability and plant growth. Even under
high C/N conditions, EcMF directly supported plant growth despite
suppressed decomposition. These findings underscore
the dual roles of EcMF, which are regulated by litter
C/N ratio, in mediating decomposition and plant nutrient
acquisition, highlighting the importance of litter–microbe interactions in
forest nutrient cycling and productivity.