Effects Of Nitrogen Application On Biomass And Carbon Storage Of Pure Eucalyptus Plantations And Eucalyptus×Castanopsis Hystrix Mixed Plantations

Eucalyptus is one of the world's three fast-growing species.In the operation of eucalyptus plantation,fertilization and mixed plantations can significantly increase the biomass and carbon stocks of plantation ecosystems,and we still have limited knowledge of them.In this paper,we investigated the effects of nitrogen application on biomass and carbon storage of pure Eucalyptus plantations and Eucalyptus×Castanopsis hystrix mixed plantations in January 2014 and January 2016.Our results should provide the theoretical basis for the cultivation and transformation of large area artificial pure forest and the construction of mixed forest.The conclusions are as follows:(1)Compared with the control(CK),nitrogen application significantly increased the biomass and net primary productivity of pure Eucalyptus plantations.The biomass of Eucalyptus trees was 1.22 times and 1.17 times of that in 2014 and 2016,respectively.Nitrogen application(15.91 ± 0.08 t/hm2.a)increased by 22.29%compared with the control(13.01 ± 0.82 t/hm2·a),and the productivity of the Eucalyptus trees was 17.14±0.19t/hm2·a,it was 16.60%higher than that of the control(14.70±0.82 t/hm2·a).(2)Compared with the control(CK),nitrogen application significantly increased the carbon storage of pure Eucalyptus plantations.Nitrogen application(80.94 t C/hm2)was 9.07 t C/hm2 higher than that of the control(71.87 t C/hm2),and increased by 12.62%.In the middle of 2016,the carbon storage of pureEucalyptus plantations(110.02 t C/hm2)was 8.14%higher than that of the control(101.74 t C/hm2).(3)Compared with the control(CK),nitrogen application could significantly increase the biomass and productivity of Eucalyptus×Castanopsis hystrix mixed plantations.The biomass of Eucalyptus in mixed plantations was 17.73%and 13.61%higher than that in CK in 2014 and 2016,respectively.The productivity of Eucalyptus in mixed plantations was 17.72%and 13.67%higher than that in control in 2014 and 2016 respectively.The productivity of the mixed plantations was 0.06 t/hm2·a higher than that of the control.(4)Compared with the control(CK),nitrogen application significantly increased the ecosystem carbon storage of Eucalyptus×Castanopsis hystrix mixed plantations(89.62 t C/hm2,121.63 t C/hm2)compared with the control(80.70 t C/hm2,111.35 t C/hm2)in 2014 and 2016.(5)Compared with the pure Eucalyptus plantations,the forest pattern of the Eucalyptus x Castanopsis hystrix mixed plantations significantly increased the biomass and ecosystem carbon storage.The order of the ecosystem biomass of each plantation in 2014 was:EU×CH-N(46.28 t/hm2)>EU×CH-CK(39.94 t/hm2)>EU-N(38.33 t/hm2)>EU-CK(31.52 t/hm2).The biomass of the nitrogen application treatments was higher than that of the control plantations.The biomass of the two stands in the middle of 2016 was:EU×CH-N(92.53 t/hm2)>EU-N(81.95 t/hm2)>EU×CH-CK(81.71 t/hm2)>EU-CK(69.85 t/hm2).The biomass of the nitrogen application treatments was higher than that of the control plantations..The order of the ecosystem carbon storage of each plantation in 2014 was:EUxCH-N(89.62 tC/hm2)>EU-N(80.94 tC/hm2)>EUxCH-CK(80.70tC/hm2)>EU-CK(71.87 tC/hm2).nitrogen application treatments was higher than that of the control plantations The order of the total carbon storage in the forest in 2016 was:EUxCH-N(122.16tC/hm2)>EU×CH-CK(111.84 tC/hm2)>EU-N(110.02 tC/hm2)>EU-CK(101.74 tC/hm2).Mixed forest carbon storage is also higher than the corresponding treatment of pure forest.