Utilization of Azolla in rice cultivation for environmental conservation and adaptation to climate change

在试验开始时，绿肥加两熟（AGM + Cover）与水稻一起种植杜鹃花。与对照（化肥、氮磷钾）相比，氮磷钾+覆盖和AGM +覆盖处理对水稻生育期累积CH4排放没有影响。与氮磷钾+覆盖处理相比，AGM +覆盖处理对水稻生育早期、中期和后期CH4排放的影响分别为141%、25%和33%。这些排放归因于在绿肥中掺入杜鹃花后甲烷菌可利用的碳基质。与NPK相比，NPK + Cover和AGM + Cover在水稻生育中期N2O排放量分别显著增加了646%和816%。在水稻生育前期和后期，3个处理的N2O排放均无显著差异。水稻生育中期N2O排放量增加的主要原因是夏季较高的气温对枯死的杜鹃花产生了较高的基质利用率。AGM + Cover分别使水稻产量降低了38% （NPK）和35% (NPK + Cover)，与NPK + Cover之间差异不显著。这种减少归因于在早期阶段从掺入的杜鹃花氮固定化。因此，为了确定绿萍在水田中的潜力，以解决环境安全问题，同时保持产量，强调不同施用方法与各种管理措施的相互作用是必要的。

Azolla was either grown as a dual crop (Cover) or incorporated as green manure plus dual cropping (herein AGM + Cover) at the beginning of the experiment along with rice. Compared with the control (chemical fertilizer; NPK), NPK + Cover and AGM + Cover treatments did not influence cumulative CH4 emissions throughout the rice growth period. However, AGM + Cover treatment affected significant CH4 emissions at early, middle, and later rice growth stages by 141%, 25%, and 33%, respectively, compared with NPK + Cover treatment. These emissions were attributed to the readily available carbon substrate for methanogens following the incorporation of Azolla as green manure. Compared with NPK, NPK + Cover and AGM + Cover significantly increased N2O emissions by 646% and 816%, respectively, during the middle rice growth stage. No significant N2O emission differences were observed in the three treatments in the early or later rice growth stages. The higher N2O emissions from the middle rice growth stage were ascribed to high substrate availability from the dead Azolla by higher summer air temperature. AGM + Cover significantly decreased rice yield by 38% (NPK) and 35% (NPK + Cover), with no significant differences between NPK and NPK + Cover. This reduction was attributed to nitrogen immobilization from the incorporated Azolla during the early stage. Therefore, to ascertain the potential of Azolla in paddy fields to address environmental safety while sustaining yield, emphasis on the interaction of different application methods with various management practices is necessary.