Study On Growth Characteristics And Nutrient Competition Of Phoebe Bournei-schima Superba Mixed Forest

In order to reveal the competition relationship between Phoebe bournei and Schima superba in growth and nutrient absorption,and to explore the feasibility of the mixed model of P.bournei and S.superba,the 14 years old P.bournei and S.superba pure forest and P.bournei-S.superba mixed forest in Jindong national forest farm were studied.The growth regularity and biomass distribution feature of P.bournei-S.superba mixed forest was studied by stem analysis method and layered cutting method.The spatial distribution feature and seasonal dynamics of carbon(C),nitrogen(N),phosphorus(P),potassium(K),C:N,C:P and N:P were studied by collecting samples and analyzing nutrient element contents.The results showed that:(1)The diameter at breast height(DBH),tree height and volume of P.bournei and S.superba in mixed forest both increased with age.In the 14th year,the DBH,tree height and volume of P.bournei were 12.02cm,15.53m and 0.0636m3 respectively,while those of S.superba were 12.92cm,15.93m and 0.0844m3 respectively.The fast-growing period of DBH and tree height of P.bournei and S.superba were 8-12 years.During the period of 0-8 years,the growth speed values of volume of P.bournei and 5.superba were slow,and they increased after the 8th year.The DBH and volume annual growth curve and average growth curve of P.bournei and S.superba didn’t meet in the 14 years,while The tree height annual growth curve and average growth curve intersected in around the 13th year.Overall,the DBH,tree height and volume growth rate of S.superba in mixed forest were faster than that of P.bournei.(2)The total biomass per plant of P.bournei and S.superba were 64.69kg and 81.15kg respectively.The above ground biomass(accounting for the whole plant)of P.bournei and S.superba were 55.58kg(85.93%)and 68.66kg(84.63%)respectively,while the under ground biomass of them were 9.11kg(14.07%)and 12.49kg(15.37%)respectively.the order of biomass of organs from big to small was:trunk>root>branch>leaf>bark.Except for coarse root and medium root,the biomass of various organs of S.superba was greater than that of P.bournei.Overall,the total biomass,the above ground biomass and the under ground biomass of P.bournei were both significantly lower than those of S.superba.(3)The total biomass per unit area of P.bournei-S.superba mixed forest was 132.19 t·hm-2.The biomass of arbor layer was 123.30 t·hm-2,accounting for 93.27%of total biomass,while that of herb layer and litter layer were 0.25 t·hm-2(0.19%)and 8.64 t·hm-2(6.54%).The order of biomass per unit area from large to small was as follows:arbor layer>semi-decomposed litter layer>undecomposed litter layer>herb layer.There were no significant differences in BNI,BNR,STR,FC and CRR between the two species.(4)The contents of C,N,P and K in different organs of P.bournei and S.superba showed different changes in different stands and seasons.The content of nutrient elements of mixed forest was generally higher than that of pure forest.N:P was at a lower level during the rapid growth period of organs,while C:N and C:P were at a higher level.The N:P of four types of leaves was more than 16,which indicated that their growth was mainly restricted by P.(5)The contents of C,N,P and K in different forests decreased with the increase of soil depth,and P was evenly distributed throughout the space.The seasonal variation of nutrient elements in various layers of soil showed a regular pattern of decreasing first and then increasing.The soil nutrient content of mixed forest was higher than that of pure forest.C:N decreased with the increase of soil depth,while C:P and N:P were opposite.Month had little effect on stoichiometric ratio of soil,and the annual variation range of stoichiometric ratio basically remained within a certain range.(6)P.bournei-S.superba mixed forest could promote the competition between P.bournei and S.superba for nutrients,and effectively improve the utilization ability of P.bournei for nutrients.There were different degrees of competition in the utilization of nutrients in different organs between P.bournei and S.superba.S.superba absorbed more nutrients than P.bournei.In order to the future,when managing P.bournei-S.superba mixed forest,the proportion of mixing should be properly controlled and fertilizer should be supplied according to the phenological rules of P.bournei and S.superba to promote better growth of stands.