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

在试验开始时，满江红要么作为双季作物(覆盖)种植，要么作为绿肥+双季种植(这里是AGM+覆盖)与水稻一起种植。与对照(化肥；NPK)相比，NPK+覆盖和AGM+覆盖处理在整个水稻生育期内不影响CH4的累积排放量。然而，与NPK+覆盖处理相比，AGM+覆盖处理对水稻生长前期、中期和后期的显著CH4排放分别影响了141%、25%和33%。这些排放归因于在将满江红作为绿肥加入后，甲烷菌容易获得的碳基质。与NPK相比，NPK+覆盖和AGM+覆盖水稻生育中期N2O排放量分别增加646%和816%。在水稻生育前期和后期，三个处理间的N2O排放差异不显著。水稻生长中期较高的N2O排放归因于较高的夏季气温使死掉的满江红具有较高的底物利用率。AGM+覆盖显著降低水稻产量38%(NPK)和35%(NPK+覆盖)，NPK和NPK+覆盖之间差异不显著。这种减少归因于被结合的满江红在早期阶段对氮素的固定。因此，为了确定红萍在维持产量的同时解决环境安全问题的潜力，有必要强调不同的使用方法和不同的管理措施的相互作用。

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.