Study On Ecological Stoichiometric Characteristics Of Plant-Litter-Soil Of Three Forest Types In Subtropical Northern Guangdong

To explore the ecological adaptation characteristics and nutrient utilization strategies of different forest types to the external environment,and the internal nutrient regulation mechanism of the plant-litter-soil continuous.Therefore,this study took coniferous forest,broad-leaved forest and coniferous and broad-leaved mixed forest in subtropical northern Guangdong forest as research objects.Based on the core theory and hypothesis of ecological stoichiometry,using the method of field sampling and laboratory analysis,the study analyzed the organic carbon,total nitrogen,total phosphorus and total potassium(POC,TN,TP,TK)contents and their ecological stoichiometric ratios,Seasonal characteristics,homeostasis,utilization and restriction and reabsorption of plant nutrient in three forest types;and analyzed litter nutrient contents(LOC,TN,TP,TK),soil nutrient contents(SOC,TN,TP,TK)and ecological stoichiometric characteristics of litter layers(AG,OL,OY)and soil layers(0-10,10-20,20-40,40-60,60-100cm);and analyzed the impacts of seasons,forest types,organs,litter decomposition and soil depths on the stoichiometric characteristics in plants-littersoil.In order to provide theoretical data support for revealing the nutrient conversion,distribution and balance mechanism of subtropical forest ecosystem.The main results of this study are as follows:(1)Compared with the global average level,the overall nutrient distribution pattern of plants in this study was"high C,low N,low P and low K".Among them,the ability of C fixation of conifer species was strong,but the ability of N,P and K fixation was weak.To some extent,the mixing of conifer and broadleaf species can alleviate the limiting of P element in subtropical south China.Among different species,Pinus Massoniana’s C content,Castanopsis hystrix’s N content,Liquidambar formosana’s P content,Schima superba’s K content were all higher than those of other tree species.The element stoichiometric ratios in plant organs objectively reflect the limiting elements,that is,N:P>14 indicates that the whole study area is generally strongly restricted by P;In the study,coniferous forest is restricted by N and P elements,broad-leaved forest is only restricted by P,and mixed forest is restricted by N more than P.N:K<2.1,P:K>3.4 indicates that the growth of plants in coniferous forest,broadleaf forest and mixed forest is basically not restricted by K element.(2)Compared with the global average level of soil and litter,On the whole,the soil nutrient distribution pattern in this study was "high C,low N,low P and low K".The litter nutrient in coniferous forest were low N and low P,broad-leaved forest was high N and low P,and mixed forest was low N and low P.With the increase of litters decomposition degree,C and K contents in litters gradually decreased,while the N and P contents gradually increased.Compared with other forest types,the high C:N and low C:P values of broadleaved forest indicated that the decomposition rate of litters in broadleaved forest was faster and the P availability was higher.In this study litters N:P<25,indicating that the decomposition rate of litters is mainly limited by P element at the overall level.The soil nutrient contents between different soil layers were mainly concentrated in the soil surface(0-20cm).Compared with the global average value of soil C:P,the higher C:P of coniferous forest indicates that it is more constrained by P than broad-leaved forest and mixed forest.(3)Plant nutrient reabsorption and nutrient utilization efficiency respectively reflect the relative reabsorption hypothesis and temperature-plant physiology hypothesis.Compared with other elements,P has the highest nutrient utilization efficiency.Compared with summer,C and P nutrient use efficiency was higher in autumn,K nutrient use efficiency was higher in spring,and N nutrient use efficiency had no significant difference between seasons.Besides,POC content in plant organs was an important factor to affect the reabsorption rate of C and P nutrients.Plant roots belong to"no homeostatic",which reflects the element plasticity hypothesis.Plant leaves keep certain stoichiometric homeostasis to soil C,P and C:P,indicating that plant leaves had certain adaptability to the P limitation in the study.K element and its proportion in different plant organs belong to"strictly homeostatic",indicating that K element in plants keep strong stoichiometric homeostasis.(4)The plant stoichiometric characteristics(except N:K,P:K)were influenced by the interaction season-organ,and forest type-organ.Litter TN,TP,TK,C:N,N:P,P:K was affected by forest type and decomposition degree.Soil SOC,TN,C:P,N:P,C:K,N:K was affected by forest type and soil depth(p<0.001,p<0.01,p<0.05).Among them,plant POC is influenced by the interaction of season,forest type and organ.Plant TP is influenced by the interaction between season and forest type.(5)On the whole,the nutrient contents of plant-litter-soil were plant>Litter>soil.The C:N:P ratios were 904:9:1 for plants,1366:27:1 for litter,55:1:1 for soil.For the plant-litter-soil continuum,N element accumulated continuously with the forward succession process of forest community,and coniferous forest was the most restricted by P element.There are significant coupling relations in plant organs-litters,and plant organs-soil continuum,among them,the C,N cycle mainly occured in the plant leaf-branch-litters continuum and the plant root-stem-leaf-soil continuum,P cycle mainly depended on the plant leaf-branch-litters continuum,and K cycle depended on the plant branch-litters continuum,plant root-stem-leaf-soil continuum.