| Rapid development of human society economy makes the excessive use of natural forest timber resources.The natural forest area decreases continuously,while plantation development rapidly in the global.Pure forest management pattern of pinus massoniana plantation have caused reduced biodiversity and soil fertility decline ecological problems.In order to solve these problems,people took a variety of ways to remould it,canopy density is one of the transformation ways.Forest canopy density affects the degree of light reach the understorey,which is the key of undergrowth growth and development.Thespecies andquantitative characterof the undergrowthaffectslitterdecomposition and nutrient returned.So,canopy density has important influence on forest ecosystems nutrient circulation.At present,the research about plantation transformation wayseffects on ecological functions including density,forest age,forest gap has reported,while about canopy density is very rare.Therefore,11 years of pinus massoniana plantation in the town of gao xian in sichuan province as a research object in this study.In October 2013,by uniformly thinning,pruning,formed five canopy densities of Pinus massoniana plantations about 0.9,0.8,0.7,0.6,0.5,Have studied the C,N,P content and C:N:P of soil,needles,litter and nutrient absorption in different canopy density of pinus massoniana plantation.And have analyzed the relationship between them and environmental factors.The results showed that:(1)With the decreasing of canopy density,there were significant differences inthe soil carbon content in each season;the nitrogen phosphorus content of soil,the carbonnitrogen phosphorus content of needle,the carboncontent of litterin Autumn;the nitrogencontent of litter in Spring,Summer;the phosphoruscontent of litter in Summer,Autumn and Winter.In each season,the soil carbon content had the minimum value in 0.8?0.6 canopy density;thecarbonnitrogencontent of needlehad the maximum value in 0.7?0.6 canopy density;both the maximum value of litter's carboncontent and the minimum value of litter's nitrogen phosphorus content appeared in 0.8?0.6 canopy density.In eachcanopy density,the soil carbon content,the carbonnitrogen phosphorus content of needle,the phosphorus content of litter;and the carboncontent of litter in 0.6,0.5canopy density had significant seasonal differences.The soil carbon contenthad the maximum value in Spring,the phosphorus content of litterhad the maximum value inAutumn.(2)With the decreasing of canopy density,there were significant differences inthe C:N of soil in Summer and Winter,the C:P soil inSpring Summer and Autumn,the N:P of soil in Autumn and Winter;the C:N and N:P of needles in Autumn;the C:N oflitter in Spring and Summer and the C:P,N:P oflitter in Summer and Winter.In each season,the minimum value of soilC:N,C:P appeared in 0.8?0.6 canopy density;the minimum value of needlesC:N and the maximum value of needlesC:P appeared in 0.7?0.6 canopy density;the maximum value of litterC:N,C:P appeared in 0.8?0.6 canopy density.In eachcanopy density,the C:N,C:P of soil;the C:P,N:P of needles and litter had significant seasonal differences.The C:N,C:P of soilhad the maximum value in Spring;the C:P of needleshad the maximum value inSummer.The N:Pof needles were in 11.76?18.40.(3)With the decreasing of canopy density,there were significant differences intheN nutrient absorption of needles in Summer,Autumn;theP nutrient absorption of needles in Summer Autumn,Winter;theN,P nutrient absorption rate of needles in Spring,Summer.In each season,bothN nutrient absorption andP nutrient absorption had the maximum value in 0.8?0.6 canopy density.In eachcanopy density,there were significant seasonal differences in theN nutrient absorption;P nutrient absorption;and N,P nutrient absorption ratebasically.The N nutrient absorption were in 15.50%?40.91%,the P nutrient absorption were in 34.93%?81.90%.The P nutrient absorption was higher than N nutrient absorption.(4)The correlation analysisresults showed that:the soil carbon nitrogen phosphoruscontent were the main factor that influenced the carbon nitrogen phosphoruscontent of needles in Spring,Autumn.In each season,the carbon nitrogen phosphoruscontent of litter were the main factor that influenced the N nutrient absorption andP nutrient absorption.The C:P,N:P of siol were mainly influenced by the C:N,N:P of needles and the N:P of litter in Autumn;while were mainly influenced by the C:N,N:P of litter in Spring,Summer,Winter.TheN,P nutrient absorption rate of needles were mainly influenced by the C:N,N:P of needles,the nitrogencontent and C:N:P of litter in Spring;were mainly influenced by the nitrogencontent of litter in Summer;were mainly influenced by the C:N,N:P of needles in Autumn;and were mainly influenced by the phosphoruscontent,C:N:P of litter in Winter.In Autumn,the carbon nitrogen phosphoruscontent of siol,litter were the main factor that influenced the C:N:P of needles.The carboncontent of siol were the main factor that influenced the C:P,N:P of litter in Summer,Winter.The C:N:P of soil were mainly influenced by the phosphoruscontent of needles in Spring;were mainly influenced by the nitrogencontent of needles and the carbon nitrogen phosphoruscontent of litter in Summer,Autumn,Winter.The N nutrient absorption andP nutrient absorption were mainly influenced by the C:N:P of litter in Spring;were mainly influenced by the C:N:P of soil and litter in Summer;were mainly influenced by the the C:N:P of soil,the C:N,N:P of neddles,the C:P,N:P of litter in Autumn;and were mainly influenced by the C:N:P of soil and litter in Winter.In Spring,thewater content and pH of soil were greatly influenced the carbon nitrogenC:P and N:P of soil.In conclusion,canopy density control have affected the C:N:P stoichiometric characteristics of soil,needles,litter and nutrient reabsorption in Pinus massonianaplantation.The nutrient reabsorption higher and nutrient return greater in 0.8?0.6canopy density,which promotethePinus massonianaplantation rapid growth and development. |
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