Impact of ectomycorrhizal tree dominance and species richness on soil nitrogen turnover in a warm temperate forest
Aims:Ectomycorrhizal(EcM)trees are the dominant tree species in temperate forests and play a vital role in driving ecosystem functions,particularly soil nitrogen turnover.The proportion of EcM tree species within a community is believed to influence the relationship between plant diversity and ecosystem function;however,the underlying mechanisms remain unclear.In this study,we aim to investigate the effects of tree species richness,the proportion of EcM tree species,and various biotic and abiotic factors on nitrogen turnover and availability in soil collected from different habitats and depths within a warm-temperate forest ecosystem.Methods:Soil samples were collected over time from a 20-ha plot in the warm-temperate deciduous broad-leaved forest of Dongling Mountain.Each sample was analyzed to determine the net nitrogen mineralization rate(Rm),nitrification rate(Rn),and concentration of inorganic nitrogen(NH4+-N and NO3-N).Soil nitrogen mineralization and nitrification are crucial ecological processes that indicate soil nitrogen availability.We also assessed the presence of ammonia-oxidizing archaea(AOA)and ammonia-oxidizing bacteria(AOB),which are key drivers of soil nitrogren processes.Result:The proportion of EcM tree species had a stronger,and habitat-dependent effect on soil nitrogen turnover and availability compared to tree species richness.Specifically,Rm,Rn,NH4+-N,and NO3--N significantly decreased with increasing proportions of EcM tree species in low altitude areas with gentle slopes and mid altitude steep slopes.Additionally,while NH4+-N significantly decreased,Rn increased with greater tree species richness in low altitude areas with gentle slopes.Soil inorganic nitrogen was limited by the proportion of EcM tree species in subsoil and deep soil layers than in topsoil,with both NH4-N and NO3-N significantly decreasing as the proportion of EcM tree species increased.Further,Rm,Rn,NH4+-N,and NO3-N showed stong correaltions with the proportion of EcM tree species,tree species richness,soil moisture,and the presence of AOA and AOB.Multivariate linear regression analysis indicated that soil moisture,AOA,and AOB were major contributers to variations in Rm,Rn,NH4+-N,and NO3--N.Conclusion:Our findings demonstrate that the proportion of EcM tree species,rather than overall tree species richness,plays a more critical role in influencing soil nitorgen turnover and availability in the warm-temperate forest ecosystem.This effect is primarily associated with soil moisture,and AOA and AOB.Our findings are significant for developing a theoretical framework that explores the relationships between tree species richness,the proportion of EcM tree species,and ecosystem functions.Moreover,our findings strengthen our capacity for biodiversity conservation and sustainable management in warm-temperate forest ecosystems.
soil inorganic nitrogensoil net nitrogen transformation rateectomycorrhizal tree speciestree species richnesswarm-temperate forest ecosystem
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