Uptaking Preference Of Main Subtropical Afforestation Tree Species For Nitrogen Forms And Its Regulatory Factors

Our study is divided into two parts:a global data analysis and experiments.Data were collected articles published until 2017 about the nitrogen absorption preference of tree species for the global data analysis,extracting data from the articles to analyse the effect of characteristics of tree species—types of family,leaf shape and mycorrhizal—on nitrogen absor:ption preference.The experiments first select the Nanping city of Fujian province Fujian Agriculture And Forestry University Xiqin Teaching Forest Farm(26°40'N,118°10'E),Dahe State-owned Forest Farm in Fujian city of Changle province protection(25°57'N,119°24')'and Chishan Forest Farm of Fujian Dongshan country(23°40'N,117°18'E)as experimental sites.Our study seted 10 types of tree species as research objects.In Xiqin forest farm 7 species at the age of 40 were selected,which were Michelia macclurei,Phoebe bournei,Schima superba,Castanopsiskawakamii,Fokienia hodginsin,Cunninghamialanceolata,Pinus massoniana,examining effects of functional properties of tree species on nitrogen absorption preference.3 species in Changle and Dongshan forest farms with great difference in soil nutrient content were selected respectively at each site,which were pinus elliottii(33 a),Eucalyptus robusta(14a)and Casuarina equisetifolia(21a),examining effects of soil nutrient content on nitrogen absorption preference of tree species.Complete randomized block design method was adopted,4 standard trees were selected for each species.Fine roots were unearthed by starting at the base of a tree and following individual roots outward.Measurements were made on four replicate trees per species,with duplicate measurements per tree and form of N.Measurements from the two roots per form of N were averaged after analysis.Nitrogen uptake was determined from uptake of labeled substrate(99.9 atom%15NO3-,99.9 atom%15NH4+,99 atom%15N-13C glycine;Isotec Inc.,Miamisburg,OH).The main conclusions are as follows.(1)The results of global data analysis show that types of leaf functional(needles,broad-leaved)and mycorrhizal infection have no significant influence on the nitrogen absorption preference of tree species.But there is significant difference in the preference of nitrogen absorption among some families.(2)In this study,types of different leaf(coniferous-leaved and broad-leaved forest species,Xiqin site)had no significant difference between total nitrogen absorption rate,but there was significant difference in the nitrogen absorption preference between the broad-leaved tree species.The absorption preference of coniferous tree species is organic nitrogen(glycine)>ammonium nitrogen>nitrate nitrogen,while the absorption preference of broad-leaved tree species is ammonium nitrogen>organic nitrogen(glycine)>nitrate nitrogen.The results of the study showed that there is significant difference between different leaf functional types on the preference of fine root nitrogen absorption.(3)Species characteristics significantly affect the nitrogen uptake rate(Xiqin site).Fine root of glycine and total nitrogen absorption rate were positively correlated to specific root length and surface area.The diameter of fine root had a negative correlation with the absorption of glycine by fine root.The absorption rate of ammonium nitrogen by fine root is positively correlated with the content of fine root carbon.The absorption rate of nitrate nitrogen in tree species was significantly positively correlated with soil bacterial biomass.The absorption rate of glycine was significantly correlated with ratio of gram positive bacteria to gram-negative bacteria.Different nutrient gradient experiments in this study(Changle and Dongshan sites)showed that nitrogen uptake rates of trees were promoted by higher soil nutrients,rapid growth and non-nitrogen-fixing tree species of Eucalyptus urophylla have higher ability to absorp inorganic nitrogen and.