Impacts Of Different Tree Species On Soil Nitrogen Retention And The Functional Microorganisms In Subtropical Forest Ecosystems

This research was carried out in Tingxi Forest Farm?24°49?N,118°07?E?in Xiamen City,Fujian Province.Five plantations of Phoebe bournei?Michelia macclurei?and Schima superba?Cunninghamia lanceolata and Fokienia hodginsii were selected as the research objects.The maximum distance between stands is less than 3 km.Each tree species has three duplicates,each plot area is 20 m*20 m,and a total of 15 plots.By measuring the five different tree species forests soil properties of layer of 0¹0 cm,study on gene abundance of microorganisms related to nitrogen cycle by qPCR,and establishment of cloned library and sequencing for phylogenetic analysis of different AOA TRFs and the community structure of ammonia oxidizing archaea?AOA?using Terminal restriction fragment length polymorphism fingerprints and ¹⁵N tracing study gross nitrogen transformation rates.This paper reveals how different tree species affect the properties of soil through the quantity and quality of litter and fine roots,thereby affecting the gene abundance and community structure of nitrogen cycling microorganisms,and affecting the nitrogen cycling process and nitrogen retention capacity of soil of different tree species.The major findings of this paper are summarized as follows:?1?Soil pH between different tree species was no significant difference,and no significant correlation between soil pH and litter Ca and Mg contents.Soil total carbon content of Fokienia hodginsii was significantly higher than that of Cunninghamia lanceolata;soil NO₃ content of Schima superba and Michelia macclurei was significantly higher than that of Phoebe bournei and Fokienia hodginsii;soil NH₄+NO₃ content of Michelia macclurei was significantly higher than that of Phoebe bournei.It is suggested that planting Phoebe bournei and Fokienia hodginsiimay contribute to the improvement of soil nitrogen retention capacity.There was no significant difference in soil C/N among five tree species in this study,which may be related to the small difference in soil background C/N.?2?Among the five tree species,the MBC of Michelia macclurei and Schima superba was significantly higher than that of Phoebe bournei and Cunninghamia lanceolata,and the MBN of Michelia macclurei,Schima superba and Fokienia hodginsii was significantly higher than that of Phoebe bournei and Cunninghamia lanceolate.Soil microbial biomass of Michelia macclurei and Schima superba were the highest in all five plantations,while that of Phoebe bournei and Cunninghamia lanceolate were the lowest.The content of lignin and cellulose in litter was negatively correlated with soil microbial biomass,MBC was positively correlated with soil NO₃,MBN was positively correlated with soil total N.The characteristics of different tree species change the properties of soil,thus indirectly affecting soil microbial biomass.?3?Quantative PCR showed that there were significant differences in gene abundance of soil ammonia oxidizing microorganisms among different tree species,showing that Schima superba was higher than the other four tree species,and compared with ammonia oxidizing bacteria?AOB?,AOA was dominant in quantity.There was no significant difference in gene abundance?narG,nirK,nosZ?of microorganisms involved in soil denitrification among five tree species.However,there were significant differences in the gene abundance of nirS among five tree species.Schima superba was significantly higher than Michelia macclurei,Cunninghamia lanceolata and Fokienia hodginsii,but there was no significant difference between Schima superba and Phoebe bournei.The gene abundance of AOA and AOB in Schima superba soil were the highest among the five tree species,and the gene abundance of nirS were also significantly higher than those of other tree species.These results suggest that that the nitrogen cycle of soil under Schima superba forest may be more rapid,nitrification and denitrification are more active,and it is facing a high risk of nitrogen loss from forest ecosystem,which is not conducive to nitrogen retention.?4?The gene copies of AOB were positively correlated with soil pH,but not with AOA.Redundancy analysis also found that soil NO₃ content was negatively correlated with AOA,but not with AOB.This indicates that compared with AOB,AOA are more advantage in acid forest soils in the south,and soil nitrification is strong.They face the risk of NO₃ leaching and nitrogen oxides leaving the ecosystem through denitrifying,which is not conducive to nitrogen retention.Soil pH was positively correlated with narG,nosZ.?5?The AOA groups of soil of five tree species belong to Nitrosopumilus cluster and Nitrosophaera cluster.Using RsaI restriction endonuclease to digest the PCR products of AOA can produce four different TRFs,of which TRF-76 and TRF-165 are the two main fragment types.There was no significant difference in community structure of AOA between different tree species.?6?It was found that gross nitrogen mineralization rate under Schima superba forest was higher than that of other four tree species,which may be related to the high litter quality.When exogenous nitrogen was added,the soil of Schima superba showed strong nitrification,which may be related to the high gene abundance of AOA.