| Pinus massoniana and Castanopsis hystrix are one kind important native or precious tree species southwest Guangxi,has a broad development prospects.The experimental site is located at state owned Paiyangshan forest farm,Ningming County,Guangxi Province,by selecting three types of young(8-year-old)plantations as research objects of the same age forest?similar site conditions and geographically adjacent,by the research method of location monitoring and laboratory analysis,systematic research on the growth characteristics?biological productivity and C and N characteristics of ecosystems in different forest stands,Expected to provide a scientific basis for the selection of tree species of plantation and reasonable forest management mode in Southwest Guangxi.The main results are as follows:(1)There are differences in mass growth among young plantations of P.massoniana,C.hystrix and their mixture.The average tree height,DBH and individual volume of 8-year-old pure P.massoniana Stand were as follows:9.70 m?14.07 cm and 0.07714 m3,The average tree height,DBH and individual volume of 8-year-old pure C.hystrix Stand were as follows:8.80 m,9.10 cm and 0.03024 m3.The average tree height,DBH and individual volume of P.massoniana in the mixed forest of P massoniana x C hystrix were as follows:10.03 m,14.40 cm and 0.08848 m3.The average tree height,DBH and individual volume of C.hystrix in the mixed forest of P.massoniana x C.hystrix were as follows:10.37 m,11.20 cm and 0.05276 m3.(2)The total biomass of young plantations of P.massoniana,C.hystrix and their mixture were as follows:95.22 t·hm-2 42.91 t·hm-2 and 86.23 t·hm-2.Biomass distribution at different structural levels of young pure plantations of P massoniana are as follows:tree layer>litters>herbs>shrubs.The same Biomass distribution at different structural levels of young pure plantations of C.hystrix and their mixture are as follows:tree layer>litters>shrubs>herbs.Among the proportion of biomass allocation in different structure levels of tree layer,stems was the greatest(51.83%-58.66%),next is the roots(18.11%-19.39%),the branches(10.42%-18.90%)and the bark(5.91%-7.02%),the leaves are least,only 4.53%-5.25%.(3)There are differences in different organs of P.massoniana and C.hystrix carbon nitrogen content and order.Carbon contents in different organs of P.massoniana showed as follows:leaves>trunks>bark>branches>roots,nitrogen contents were leaves>roots>bark>branches>trunks.Carbon contents in different organs of C.hystrix showed as follows:trunks>leaves>bark>roots>branches,nitrogen contents were leaves>bark>branches>roots>trunks.Carbon content of plants in all layers of three young plantations showed arbor layer>shrub layer>herb layer,carbon contents in soil(0-80 cm)decrease with the increase of soil depth.nitrogen contents of plants in all layers showed that herbaceous layer>shrub layer>tree layer,the carbon contents in 0-80 cm soil layer decrease with the increase of soil depth,nitrogen contents in soil showed the same trend as carbon content,what's that,it decreased gradually with the increase of soil depth.(4)The carbon storage of ecosystem of young pure plantations of P.massoniana,C.hystrix and their mixture were as follows:123.74 t·hm-2,101.44 t·hm-2 and 125.29 t·hm-2,the nitrogen storage were 5.73 t·hm-2,5.77 t·hm-2 and 6.08 t·hm-2.Spatial distribution of carbon and nitrogen storage in three young plantation ecosystems at different structural levels basic agreement,most carbon and nitrogen reserves stored in the 0-80 cm soil layer,they accounted for 62.97%-84.28%and 94.59%-97.05%of the total carbon and nitrogen reserves of the ecosystem,respectively.Secondly,the arbor layer accounted for 16.34%-33.60%and 1.91%-4.19%,respectively.The shrub-grass layer and litter layer accounted for 1.15%-1.98%,0.35%-0.87%and 1.45%-2.20%,0.35%-0.69%,respectively.Carbon and nitrogen in soils of young pure plantations of P.massoniana?C.hystrix and their mixture were mainly concentrated in 0-20 cm soil layer,they accounted for 42.31%-43.17%and 34.11%-36.23%of soil carbon and nitrogen storage respectively.Therefore,the above-ground and underground carbon and nitrogen allocation ratios of young pure plantations of P.massoniana,C.hystrix and their mixture ecosystems were relatively low,indicating that the three young plantations still have strong carbon and nitrogen retention potential.(5)The annual net productivity of tree layer in young pure plantations of P.massoniana,C.hystrix and their mixture were 10.69t/(hm2·a),4.41t/(hm2·a)and 9.59t/(hm2·a),respectively,the annual net carbon sequestration was 5.20 t/(hm2·a),2.06t/(hm2·a)and 4.61 t/hm2·a),and the annual net nitrogen accumulation was 0.0297t/(hm2·a),0.0137t/(hm2·a)and 0.0275 t/(hm2·a),respectively. |
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