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种植园不断扩大，马占相思等豆科速生树种已被广泛引进。然而，根据我们的前期研究，它表明豆科植物人工林下的土壤排放更多的一氧化二氮（N2 O）比其他物种的森林，因为大量的氮循环在土壤-植物系统中，由于共生固氮。在本研究项目中，我们调查了以下两个主题，在大规模的工业种植园在南苏门答腊，印度尼西亚，以提出可能的选择，以减少N2 O排放：1）磷的应用对相思林N2 O排放的影响，2）评估全球减缓效果的相思种植园林与磷的应用。(1)无根系条件下施磷促进了土壤N2 O的释放，而有根系条件下施磷则通过促进马占相思对氮素的吸收而减少了土壤N2 O的释放。(2)施磷可抑制相思树N2 O排放，促进相思树生物量的增加，从而增强相思树减缓全球变暖的功能，但土壤有机碳的分解量高于不施磷的相思树。

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.