Mechanism of nitrous oxide emission from fast-growing tree plantations of tropical legumes and a search for the process to suppress the emission

近年来，亚洲热带地区豆科速生树种人工林规模不断扩大，马占相思等豆科速生树种已被广泛引种。然而，根据前人的研究表明，豆科树种人工林下的土壤比其他树种林下的土壤排放更多的一氧化二氮(N2O)，这是由于共生固氮导致土壤-植物系统中更多的氮素循环。在本研究项目中，我们在印度尼西亚南苏门答腊岛的大型工业人工林中进行了以下两个主题的研究，以提出可能的减缓N2O排放的方案：1)施磷对相思林N2O排放的影响；2)施磷相思人工林的全球缓解效果。(1)施磷促进了无根条件下土壤N2O的排放，同时通过促进植物对氮素的吸收，减少了相思根系存在时的排放和养分吸收。(2)新植相思人工林施磷可抑制土壤N2O排放，促进人工林地生物量增加，从而增强了对全球变暖的缓解作用，但土壤有机碳分解高于不施磷林分。

In the Asian tropics tree plantation with leguminous fast growing species is expanding recently, and leguminous fast-growing tree species like Acacia mangium have been widely introduced. However, based on the our precedent study it was indicated the soil under leguminous tree plantation emit more nitrous oxide (N2O) than those under other species forests because of larger amount of nitrogen cycling in a soil-plant system due to symbiotic nitrogen fixation. In this research project we investigated the following two topics in large-scale industrial plantation in South Sumatra, Indonesia in order to propose possible options to mitigate the N2O emission; 1) effect of phosphorous application to N2O emission from Acacia stand, and 2) evaluation of global mitigation effect of Acacia plantation forest with phosphorous application.The results obtained were as follows. (1) Phosphorous application stimulated N2O emission from soil under the condition without plant roots, meanwhile it reduced the emission wh en Acacia mangium roots exist and uptake nutrients through accelerating nitrogen uptake by the plant. (2) Application of phosphorous to newly planted Acacia plantation strengthened the global warming mitigation function by suppressing N2O emission from soi l and promoting biomass production of planted trees, while decomposition of soils organic carbon was higher than in the stand without phosphorous application.