丛枝菌根真菌调控土壤氧化亚氮排放的机制

氮素是陆地生态系统初级生产力的主要限制因子,自Haber-Bosch反应以来,氮肥的生产和施用极大地提高了粮食产量。然而过量施用氮肥导致氮肥利用率低,并造成了严重的环境污染,包括氮沉降、硝态氮淋洗以及N₂O排放等。微生物直接参与土壤氮素循环,固氮微生物、氨氧化和反硝化微生物分别在土壤固氮、铵态氮转化和硝态氮转化过程中起着重要作用。作为一类共生微生物,丛枝菌根真菌(Arbuscular Mycorrhizal Fungi,AMF)在土壤氮素循环中的作用日益引起人们的重视。最新的研究表明,AMF显著影响土壤硝化、反硝化过程以及N₂O排放过程。本文重点阐述了菌根真菌对N₂O排放的影响并对其作用机制进行了总结。菌根真菌主要通过三个途径实现N₂O减排:(I)影响氨氧化微生物活性,降低了氨氧化过程中产生的N₂O;(II)菌丝分泌物缓解了N2O还原酶在电子竞争中的劣势,促进完全反硝化过程(N₂O→N₂);(III)促进宿主植物吸收土壤氮素,降低氮素有效性,并减少N₂O排放。在农业生产中可以通过强化土著菌根真菌实现N₂O减排,为应用菌根真菌提高氮素利用效率、调控土壤N2O排放和氮循环过程提供科学依据。

Mechanisms Underlying the Regulation of Soil Nitrous Oxide Emissions by Arbuscular Mycorrhizal Fungi

Nitrogen, the major limiting factor of primary production in terrestrial ecosystem, contributes greatly to crop production since the invention of Haber-Bosch process. However, a substantial of nitrogen is lost to the surrounding environment, leading to low nitrogen use efficiency, nitrogen deposition, nitrate runoff and N₂O emission. The microbial groups of nitrogen fixers, nitrifier and denitrifier carry out nitrogen fixation, nitrification and denitrification, respectively. Another group of symbiotic fungi, Arbuscular mycorrhizal fungi (AMF), is also found to be important for nitrogen cycling. Recent studies reported that AMF could significantly affect soil nitrification, denitrification and N₂O emission. This review summarized the advance in the mechanisms by which AMF reduce N₂O emission:(I) AMF inhibit nitrifier activities and reduce N₂O production; (II) AMF exude labile carbon compounds to alleviate the competence between N₂OR and other Nr reductase, which promotes N₂O reduction to a greater extent; (III) AMF take up soil nitrogen and deliver them to host-plant and thus decrease nitrogen availability, lowering N₂O production. Finally, we envisaged future studies in strengthening the role of indigenous AMF in reducing N₂O emission. This review provides scientific evidence for future application of AMF in regulating N₂O emission and N cycling.