| Dalbergia oorifera is an endemic tree species in Hainan,and listed as the second class rare and endangered species by the state.With the increase of D.Odorifera plantation scale in Hainan province,the disease problems of D.Odorifera has become increasingly prominent,of which mainly occur on foliage.Phyllachora dalbergiicola Henn is one of the most harmful pathogens.In order to investigate the occurrence mechanism of the P.dalbergiicola in D.Odorifera and provide a theoretical basis,this research studies the correlation between community structure,individual-tree competition,and stand spatial structure and P.dalbergiicola from multiple spatial scales during the year of 2013?2015.Stepwise regression,Redundancy analysis(RDA),structural equation modeling and other methods were used to further analyze the relationships between significant factors and P.dalbergiicola.The main conclusions are as follows:(1)At the regional level,this paper study on impact of Community Structure of Dalbergia odorifera plantations on P.dalbergiicola occurrence.Results from regression analysis showed that there were six dominant factors affecting the diseases(R22013=0.823?R2 2014 =0.861;P<0.01).They were stand density,stand age,canopy cover,and stand crown,stand herb cover,species richness.Stand density affected the disease incidence(DI)and disease severity index(DIS)significantly(P<0.01).DI(r2013=0.814,r2014=0.801)and DIS(r2013=0.815,r2014=0.832)of P.dalbergiicola were positively correlated with stand density.The stand age significantly affected DIand DIS(P<0.01),and DI(r2013=-0.713,r2014=-0.734)and DIS(r2013=-0.676,r2014=-0.706)were negatively correlated with stand age.Stand canopy cover affected DI and DIS of P.dalbergiicola significantly(P<0.05),and DI(r2013=0.424,r2014=0.412)and DIS(r2013=0.446,r2014=0.434)was positively correlated with different stand canopy cover.Stand crown affected DI and DIS of P.dalbergiicola significantly,DI(r2013 =-0.416,r2014=-0.444)and DIS(r2013=-0.483,r2014=-0.421)was negatively correlated with different stand crown.Stand herb cover affected DI and DIS of P.dalbergiicola significantly(P<0.05).DI(r2013 =0.368,r2014=0.312)and DIS(r2013=0.383,r2014=0.332)was positively correlated with different Stand herb cover.Species richness affected DI and DIS of P.dalbergiicola significantly(P<0.05),DI(r2013=-0.337,r2014=-0.322)and DIS(r2013=-0.318,r2014=-0.305)of P.dalbergiicola was negatively correlated with Species richness.Therefore,regulating stand density and stand age oriented,afforesting in a rational close,and taking other four stand factors into consideration simultaneously may be an effective way to reduce the occurrence of the diseases of P.dalbergiicola.(2)At the regional level,In order to explore the correlation between soil variables and Dalbergia odorifera foliage disease,there were 13 sample plots to investigate diseases and determine soil factors.Redundancy analysis(RDA)was used to select dominant factors affecting P.dalbergiicola occurrence on D.Odorifera plantations.RDA results indicated PH,available N,total P and available K were three dominant factors affecting the disease.The three dominant factors explained 87.2%and 79.8%of all information,only less than 8.5%and 16.7%by 15 soil variables.The importance of soil variables be arranged as PH>total P>available K.DI and DIS of P.dalbergiicola were negatively correlated with PH,available K and positively correlated with total P.(3)At the stand level,the 13 individual-tree competition indexes(ITCI)were selected to analysis the relationship between ITCI and thediseases P.dalbergiicola occurrence and we built the structural equation model.The two structral equation model both showed that the importance of tree competition variables be arranged as rown competition indexes>relative state competion indexes>nutrient space competition indexes>tree distance competition indexes.The total effect of Crown competition index affecting the occurrence of P.dalbergiicola is maximum.crown competition indexes had a negative impact on disease,the total effect was-0.758 and-0.779,the direct was-0.613 and-0.638,indirect effect-0.135 and-0.141 respectively in 2014 and 2015.We suggest that D.odorifera ecological regulation give priority to crown competition index.(4)At the individual level,the correlation between occurrence of P.dalbergiicola and neighborhood comparison of height,DBH and crown size under different stand age was analyzed.The two data both showed In 3 and 4 year stand age sample plot,there was no obvious relationship between disease of P.dalbergiicola and neighborhood comparisons.It showed that the occurrence of disease would not be impacted by individual dominance in 3 and 4 year stand age.In 5 and 6 year stand age sample plot,those three neighborhood comparison affected the disease of P.dalbergiicola significantly(P<0.05).The relationship between disease of P.dalbergiicola and neighborhood comparisons increased with the increasing of stand age.(5)At the individual level,the correlation between occurrence of foliage diseases and neighborhood comparison of height,DBH and crown size under different stand density was analyzed.In planting space the of 1 m × 1 m sample plot,those three factors affected the disease of P.dalbergiicola and C.gloeosporioides significantly(P<0.01).Neighborhood comparisonss were negatively correlated with DI and DIS.The relationship declined with the decreasing of stand density.When planting space reaches to 2.5 m × 2.5 m,the occurrence of disease would not be impacted by individual dominance.There was an obvious relationship between DI of D.Odorifera and neighborhood comparison under high stand density mode,and no relationship between them under low stand density mode. |
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