Effects Of Nitrogen Addition On Fine Roots And Rhizosphere Soils Of Different Functional Natural Plants

Fine roots are an important part of plants and play an important role in soil nutrient cycling,plant growth and development,and even the stability of forest ecosystems.The physicochemical properties of rhizosphere soil directly affect the acquisition and utilization of soil resources by plant roots.In order to explore the effect of nitrogen deposition on fine-root traits and the main physicochemical properties of rhizosphere soils of different functional natural plants,and to reveal the response mechanism of fine roots and rhizosphere soils of different functional types to nitrogen addition,different nitrogen addition treatment tests were set in three natural forests of Evergreen broad-leaved forest,Moso bamboo forest and Bamboo-broad-leaved mixed forest.The DBH?tree height((Moso bamboo is under branch height)?fine root traits and main physicochemical properties of rhizosphere soil of different functional plants(including evergreen broad-leaved tree species,deciduous broad-leaved tree species,and moso bamboo species)were measured after 1 year of nitrogen application.The effects of nitrogen addition on the fine root traits and the main physicochemical properties of rhizosphere soil of different functional natural plants,as well as their relationship were analyzed.The research results can provide a theoretical basis for exploring the management of subtropical natural forests under the background of nitrogen deposition.The main results are as follows:(1)After one year of nitrogen addition,the response characteristics of fine root phenotypic traits of different functional natural plants growing in different forest types to nitrogen addition were different,and the effects of different nitrogen additions on them were different.(1)In Eevergreen broad-leaved forest,LN treatment significantly reduced the RB(fine root biomass),RVD(root volume density),and RTD(root tissue density)of0-1mm fine roots of evergreen broad-leaved tree species,and significantly increased their SRL(specific root length),SRA(specific root area);HN treatment significantly reduced RB and RVD of 1-2mm fine roots of evergreen broad-leaved tree species and SRL and SRA of 1-2mm fine roots of deciduous broad-leaved tree species.(2)In Bamboo-broad-leaved mixed forest,LN treatment significantly reduced the RTD of1-2mm fine roots of evergreen broad-leaved tree species,SRL and SRA of 1-2mm fine roots of deciduous broad-leaved tree species,and RVD of two diameter classes fine roots(0-1mm and 1-2mm)of moso bamboo,and significantly increased the RTD of two-diameter fine roots of moso bamboo;HN treatment will significantly increase the RTD of 0-1mm fine roots of evergreen broad-leaved tree species,and SRL of 0-1mm fine roots and RTD of 0-1mm fine roots of deciduous broad-leaved tree species,but the SRL of 1-2mm fine roots of Moso bamboo was significantly reduced.(3)In Moso bamboo forest,LN treatment significantly increased the RLD and RVD of 0-1mm fine roots of Moso bamboo,and decreased its RTD;HN treatment will significantly increased RLD,SRL and SRA of 1-2mm fine root of Moso bamboo.(2)The response characteristics of fine root nutrient traits of different functional natural plants growing in different forest types to nitrogen addition were different,and the effects of different nitrogen additions on them were different.(1)In Eevergreen broad-leaved forest,LN treatment will significantly increase the N,P,and K content of fine roots of two-diameter grades(0-1 mm and 1-2 mm)of evergreen broad-leaved tree species and deciduous broad-leaved tree species and N of 0-1 mm fine root N/P,N/K,and0-1mm fine root Si content of deciduous broad-leaved tree species,and significantly reduce the C / N of fine roots of evergreen and deciduous broad-leaved forest trees;HN treatment will significantly increase the evergreen and deciduous broad-leaved Ca content of 1-2mm fine roots of forest trees.(2)In Bamboo-broad-leaved mixed forest,LN treatment will significantly increase the C content of 0-1mm fine roots and the Ca content of 1-2mm fine roots of deciduous broad-leaved tree species,and the C,C/N of 1-2mm fine roots of evergreen broad-leaved tree species,and The C content of 0-1mm fine root of Phyllostachys pubescens and its C/N of 1-2mm fine root,but applying N fertilizer(especially LN)significantly reduced the Mg,Fe,Al,Si content and 1-of 0-1mm fine root of Phyllostachys pubescens N,P,K content of 2mm fine roots;HN treatment will significantly increase the K content of evergreen broad-leaved tree species 0-1mm fine roots and C,C / N of 1-2mm fine roots,and is significantly higher than LN treatment,but will Significantly reduce the Fe and Si content of 1-2mm fine roots of Phyllostachys pubescens.(3)In Moso bamboo forest,LN treatment will significantly increase the N content of 1-2mm fine roots of Phyllostachys pubescens,but significantly reduce its C/N;and make the Si content of 0-1mm fine roots of Phyllostachys pubescens significantly higher than HN treatment,while its 1-2mm fine roots are just the opposite.(3)The response characteristics of main physicochemical properties of rhizosphere soil of different functional natural plants growing in different forest types to nitrogen addition were different,and the effects of different nitrogen additions on them were different.(1)In Evergreen broad-leaved forest,LN treatment significantly increased total P and available P content in the rhizosphere soil of evergreen broad-leaved tree species and deciduous broad-leaved tree species;N fertilizer application(especially HN)significantly increased total N and ammonium nitrogen,nitrate nitrogen and available K content in the rhizosphere soil of two forest trees.but significantly reduced the rhizosphere soil p H value of deciduous broad-leaved trees.(2)In Bamboo-broad-leaved mixed forest,LN treatment significantly reduced total C,total N,total P,ammonium nitrogen,nitrate nitrogen,and available K content in rhizosphere soil of evergreen broad-leaved tree species,and total C,total N,total P,total K,available K,available P content in rhizosphere soil of deciduous broad-leaved tree species,and total K content in the rhizosphere soil of Moso bamboo,and significantly increased the total C,total N,total P,available P content in the rhizosphere soil of Moso bamboo;HN treatment significantly increased the ammonium nitrogen and nitrate nitrogen contents in the rhizosphere soils of the three plants and significantly reduced the p H value of the deciduous broad-leaved tree rhizosphere soils.(3)In Moso bamboo forest,N fertilizer application significantly increased the nitrate nitrogen content in rhizosphere soil of Moso bamboo.(4)RDA analysis showed that under the background of nitrogen addition,the relationship between fine-root traits and main physicochemical properties of rhizosphere soils of different functional natural plants growing in different forest types also differed.(1)In Evergreen broad-leaved forests,the main rhizosphere soil factors that affect fine root traits of evergreen broad-leaved tree species were water content(SWC),total iron(STFe),total silicon(STSi),total nitrogen(STN),total phosphorus(STP),nitrate nitrogen(NN),available phosphorus(Sa P)content and p H.Among them,rhizosphere soil STFe was significantly positively correlated with fine-root RB,RVD,C/N,and significantly negatively correlated with fine-root N,P,and K contents;p H was extremely significantly positively correlated with fine root Al content;SWC was significantly positively correlated with fine-root C content;STP was extremely significantly positively correlated with fine-root K content;Sa P and Sa K were positively correlated with fine-root N,P,N/P;NN was significantly positively correlated with fine-root N/K.The main rhizosphere soil factors that affect the fine-root traits of deciduous broad-leaved tree species were total aluminum(STAl),total potassium(STK),STN,ammonium nitrogen(AN),Sa P,STP,and STFe content.Among them,rhizosphere soil Sa P was extremely positively correlated with fine-root Mg content;STFe was significantly positively correlated with fine-root RTD,C/N;p H was extremely significantly positively correlated with fine-root Al content;STK was extremely significantly positively correlated with fine-root Si content;Soil total calcium(STCa)and SWC were extremely significantly positively correlated with fine-root C content.(2)In Bamboo-broad-leaved mixed forest,the main rhizosphere soil factors that affect the fine-root traits of evergreen broad-leaved tree species are STCa,SWC,STP,NN,and Sa P content and p H.Among them,rhizosphere soil STCa was significantly positively correlated with fine-root RTD;p H is extremely significantly positively correlated with fine-root K/P,and and significantly negatively correlated with fine-root N/K;SWC was significantly positively correlated with fine-root Al,Fe,and Si contents,and significantly negatively correlated with fine-root C content;NN,STP was extremely significantly correlated with fine-root N/P.The main rhizosphere soil factors that affect fine-root traits of deciduous broad-leaved tree species were STCa,STK,NN,SWC,STFe,available potassium(Sa K),total magnesium(STMg),AN content and p H.Among them,rhizosphere soil STCa was significantly positively correlated with fine-root Al,Fe,and Si content;STK was significantly positively correlated with fine-root C content;NN was extremely positively correlated with fine-root RTD,N,and Mg contents;p H was significantly negatively correlated with fine-root C content.The main rhizosphere soil factors that affect the fine-root traits of Moso bamboo were AN,STAl,STMg,STCa content and p H.Among them,rhizosphere soil AN was significantly positively correlated with fine-root C content;STMg was extremely significantly negatively correlated with fine-root RTD;p H and STCa were extremely significantly positively correlated with fine-root Ca and Si contents;STAl was significantly positively correlated with fine-root N/K,and significantly negatively correlated with fine-root K/P.(3)In Moso bamboo forest,the main rhizosphere soil factors that affect the fine-root traits of Moso bamboo are STC,STN,STP,STK,and STFe content.Among them,rhizosphere soil STK was extremely significantly positively correlated with fine-root K content,and extremely negatively correlated with fine-root Ca content;STSi and STK had exactly the opposite effect;STP was extremely significantly positively correlated with fine-root K content;Sa P and Sa K were significantly positively correlated with fine-root C and N contents;STFe was extremely significantly positively correlated with fine-root Al and Si contents.