| Cunninghamia lanceolata is one of the most important timber species in southern China.In order to reveal the competition relationship between C.lanceolata and P.massoniana in growth and nutrient absorption,the 11 years old C.lanceolata-P.massoniana mixed forest in Huitong national forest farm were studied.The spatio-temporal distribution characteristics of carbon(C),nitrogen(N),phosphorus(P),potassium(K),Calcium,(Ca),Magnesium(Mg)and C,N,P stoichiometric ratios of C.lanceolata and P.massoniana in the stand were discussed by analyzing the nutrient element contents of roots,branches,stems and leaves of the two species.The main research results showed that:(1)The diameter at breast height(DBH),tree height and volume of 11-year old C.lanceolata and P.massoniana in mixed forest both increased with age.In the 11 th year,the DBH,tree height and volume of C.lanceolata were 10.46cm,9.0m and0.1275m3 respectively,while those of P.massoniana were 9.64cm,7.3m and 0.0990m3 respectively.The DBH annual growth of Cunninghamia lanceolata reached a maximum of 1.12cm at 3 years,which was consistent with the year when the annual growth of tree height reached a maximum of 1.6m.The annual DBH growth of Pinus massoniana reached a maximum of 1.28cm at 4 year,while the annual tree height growth reached a maximum of 1.1m at 2 year.The volume growth of C.lanceolata and P.massoniana were slow during the period from 0 to 6 years.After 6 years,it entered a fast-growing period,but the volume growth rate of P.massoniana was obviously lower than that of C.lanceolata,and the two species were still in a fast-growing period at 11 years.Overall,the total growth rate of C.lanceolata in mixed forest is faster than that of P.massoniana.(2)The average biomass per plant of 11-year-old C.lanceolata and P.massoniana in mixed forest was 23.14kg and 28.78kg respectively.The aboveground biomass of C.lanceolata was 19.3kg,accounting for 83.52%of the individual biomass,while the underground biomass was 3.83kg,accounting for 16.48%.The aboveground biomass and underground biomass of P.massoniana are 25.2kg and 3.58kg respectively,accounting for 87.56%and 12.44%of the total biomass per plant.The order of biomass of each organ of C.lanceolata was:trunk>root>branch>leaf;the order of biomass of each organ of P.massoniana was:trunk>branch>root>leaf Overall,the biomass per plant of C.lanceolata was significantly lower than that of P.massoniana.(3)The biomass in the mixed forest is mainly composed of tree layer,herb layer and litter layer,and the total biomass per unit area of C lanceolata-P.massoniana mixed forest was 73.85t·hm-2.The biomass of tree layer was 64.86t·hm-2,accounting for 87.83%.The herbaceous layer and litter layer were 2.07t·hm-2(2.89%)and 6.92t·hm-2(9.66%)respectively.The order of biomass per unit area from large to small was as follows:arbor layer>litter layer>herb layer.The BNI,BNR,STR,FC and CRR values of C.lanceolata are 0.20,1.82,0.76,0.07 and 5.02 respectively.For P.massoniana,it is 0.34,2.87,0.61,0.09 and 7.04 respectively.(4)The contents of C,N,P,K,Ca and Mg in each organ of C.lanceolata and P.massoniana showed different changes in different seasons.The two tree species had certain competition and complementary relationship in nutrient utilization.In the use of N,P and K,competition is the main factor,while the use of Ca and Mg is more obvious in the complementary relationship.From the utilization strategy,the content of N,P and K nutrient elements in leaves of P.massoniana was higher than that of C.lanceolata,while the content in roots,branches and stems of P.massoniana was lower,which indicates that P.massoniana could better distribute nutrient elements in organs of substance synthesis,which was conducive to improving the utilization efficiency of nutrients.Therefore,P.massoniana could better adapt to relatively poor site conditions(5)In terms of nutrient content per plant of C.lanceolata and P.massoniana,Cunninghamia lanceolata is significantly larger than Pinus massoniana.The nutrient content carried away by thinning the same amount of P.massoniana in the mixed forest of C.lanceolata and P.massoniana is obviously lower than that carried away by C.lanceolata.Cutting off part of P.massoniana during thinning is beneficial to the nutrient balance among the stands.The economic value of C.lanceolata wood is higher than P.massoniana,so the mixed proportion of C.lanceolata and P.massoniana should be maintained when the mixed forest is built.When thinning the stand,thinning P.massoniana is mainly used,which is not only beneficial to the growth of the mixed young forest before thinning,but also can ensure the good economic benefits of the stand and promote the growth of the stand better.(6)In the process of rapid growth of various organs of C.lanceolata and P.massoniana,N:P mostly decreased from a higher level to a lower level.The N:P ratio of the leaves of the two tree species was basically less than 14,indicating that their growth was mainly limited by N;C:N and C:P were both at a higher level in the vigorous growing season. |
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