小麦-玉米-大豆轮作下黑土农田土壤呼吸与碳平衡

农田生态系统是陆地生态系统的重要组成部分,探讨农田生态系统的土壤呼吸与碳平衡对于科学评价陆地生态系统在全球变化下的源汇效应具有重要意义。基于中国科学院海伦农业生态实验站的长期定位试验,对不同施肥处理下黑土小麦-玉米-大豆轮作体系2005—2007年的作物固碳量与土壤CO2排放通量进行了观测,并对该轮作体系下黑土农田生态系统的碳平衡状况进行了估算。结果表明:在小麦-玉米-大豆轮作体系中,作物固碳量的高低表现为:玉米>大豆>小麦,平均值分别为6 513 kg(C).hm-2、4 025 kg(C).hm-2和3 655kg(C).hm-2。从作物生长季土壤CO2排放总量来看,3种作物以大豆农田生态系统的土壤CO2排放总量最高,平均值达4 062 kg(C).hm-2;其次为玉米,为3 813 kg(C).hm-2;而小麦最低,为2 326 kg(C).hm-2。3种作物轮作下NEP(净生态系统生产力)均为正值,表明黑土农田土壤-作物系统为大气CO2的"汇",不同作物系统的碳汇强度表现为玉米>小麦>大豆,三者的平均值分别为3 215 kg(C).hm-2、1 643 kg(C).hm-2和512 kg(C).hm-2。长期均衡施用氮、磷、钾化肥或氮、磷、钾化肥配施有机肥后,小麦、玉米和大豆农田生态系统的固碳量和土壤CO2排放总量均明显增加,并在氮、磷、钾配施有机肥处理下达到最高。不同的施肥管理措施将改变土壤-植物系统作为大气CO2"汇"的程度,总体表现为化肥均衡施用下NEP值较高,而化肥与有机肥配施下农田生态系统的NEP值较低。

Soil respiration and carbon budget in black soils of wheat-maize-soybean rotation system

Farmlands are important terrestrial ecosystems with characteristic soil respiration and carbon budget processes.Data from the long-term experiment at Hailun Agricultural Ecology Station of Chinese Academy of Sciences for 2005-2007 were ana-lyzed for the characteristics of crop carbon fixation,soil cumulative CO2 flux and carbon budget in the black soils of wheat-maize-soybean rotation systems.Results showed that in wheat-maize-soybean rotation system,the amount of carbon fixed by crops decreased in the order of cultivated maize in 2006 > cultivated soybean in 2007 > cultivated wheat in 2005.The averages of fixed carbon by maize,soybean and wheat were 6 513 kg(C)·hm 2,4 025 kg(C)·hm 2 and 3 655 kg(C)·hm 2,respectively.Soil cumu-lative CO2 flux during crop growth seasons was highest for soybean ecosystem [average of 4 062 kg(C)·hm 2],followed by maize ecosystem [average of 3 813 kg(C)·hm 2 ] and then lowest for wheat ecosystem [average of 2 326 kg(C)·hm 2].Rhizosphere derived CO2 flux accounted for about 69%~73%,66%~80% and 46%~63% of soil cumulative CO2 flux for soybean,maize and wheat eco-systems respectively.This indicated that CO2 flux derived from crop rhizosphere was crucial for soil CO2 emission.NEP(net eco-system productivity) was positive in black soil/crop systems of wheat-maize-soybean rotation,where farmlands served as CO2 sink from the atmosphere.NEP in different crop systems decreased in the order of maize > wheat > soybean and with averages of 3 215 kg(C)·hm 2,1 643 kg(C)·hm 2 and 512 kg(C)·hm 2,respectively.Compared with plots without sufficient nutrients,long-term applica-tions of chemical fertilizers(NPK) or organic manure amended chemical fertilizers(NPKOM) increased crop carbon fixation and soil cumulative CO2 flux in all cropping systems.They were highest for plots with organic manure amended chemical fertilizers(NPKOM).NEP in each cropping system was significantly affected by different fertilization treatments.NEP was highest in plots with NPK fertilizers and lowest in plots with organic manure amended chemical fertilizer(NPKOM).The findings of this study were significant for the proper management of black soils as potential carbon pools in Northeast China.