Differences In Root Exudates Inputs And Associated Soil N Transformation Processes Between Deciduous And Evergreen Tree Species In Southwest Mountainous Regions,China

In order to explore the differences in root exudates and associated soil N transformation process between deciduous and evergreen tree species,in this study,three deciduous tree species(i.e.,Larix kaempferi,Cercidiphyllum japonicum and Betula platyphylla Sukaczev)and three evergreen tree species(i.e.,Pinus armandi,Pinus tabulaeformis and Pinus yunnanensis)in the southwest mountainous region were selected to to perform an insitu collection of root exudates during the growing season(June,August,October)in 2016 and 2017.The net N mineralization rates and associated microbial enzyme activities were measured in rhizosphere and bulk soils to evaluate rhizosphere effects.Moreover,we compiled the dataset related to root exudation and their associated biological traits and the soil chemical properties for 21 tree species from temperate forests.Through this study,we hope to reveal the differences in root exudate C input and the soil N transformation process mediated by different tree growth forms in order to enrich and expand the rhizosphere ecological mechanism of the biogeochemical cycle process of soil key nutrients driven by different tree growth forms in the southwest mountainous regions,China.The main findings are as follows:1.Differences in root exudation rate and annual C flux between deciduous and evergreen trees.Both field experiment monitoring and data integration analysis showed that there is a significant difference of the root exudates C input between the two tree growth forms.In temperate regions,the root exudation rate and annual C flux of deciduous tree species is significantly higher than that of evergreen tree species,and the root exudate C input rate per root biomass is about twice that of evergreen tree species.The root exudation rate between deciduous and evergreen trees has the same seasonal dynamics,which are the highest in the middle(August)of the growing season,but lower in the early(June)and late(October).2.Differences in rhizosphere N transformation between deciduous and evergreen tree species.There were significant differences in the content of dissolved organic nitrogen(DON),total nitrogen(TN),NH4+-N,NO3--N and net Nmineralization rate in the rhizosphere soil of deciduous tree species and evergreen tree species.Specifically,deciduous tree species are significantly higher than evergreen tree species.The soil N content and mineralization rate show a seasonal dynamic of increasing first and then decreasing during the growing season.3.Differences in rhizosphere soil microbial biomass and extracellular enzyme activity between deciduous and evergreen tree species.The MBC and MBN of rhizosphere soil of deciduous tree species were significantly higher than that of evergreen tree species.The soil AP,NAG,BG,and PER enzyme activities of deciduous tree species were significantly higher than those of evergreen trees,while the soil PPO enzyme activities were significantly lower than that of evergreen trees.Throughout the growing season,soil AP,NAG and BG enzyme activities showed a trend of increasing first and then decreasing,soil PPO enzyme activity showed a gradual upward trend,and soil PER enzyme activity changed in the opposite direction.4.Coupling effect of root exudate input between deciduous and evergreen tree species and soil N transformation.The rhizosphere effect of net N mineralization rate and soil microbial processes of deciduous trees were significantly higher than those of evergreen trees,and the rhizosphere effect was significantly positively correlated with the root exudation rate.This implies that the higher rhizosphere exudate input of deciduous tree species induces a greater intensity of soil extracellular enzymes and microbial processes,which is accompanied by accelerated soil N mineralization and increased soil N availability.In summary,compared with evergreen tree species,deciduous tree species greatly stimulated microbial activity and extracellular enzyme production during the growing season by releasing more root exudates C to the rhizosphere,and induced a greater rhizosphere effect of soil N transformation,which effectively promotes the N transformation in rhizosphere soil and improves the soil N availability.The results of this study provide a new understanding of the regulation of soil biochemical cycling processes between different tree growth forms from the perspective of rhizosphere ecology,and also contribute to the improvement and development of terrestrial ecosystem biogeochemical models.