Abstract Agriculture is an important source of the greenhouse gas nitrous oxide (N2O) due to the over- or non-synchronised application of nitrogen to crops. Symbiotic nitrogen fixation (SNF) by legume-rhizobia symbiosis can be an effective strategy for N2O mitigation, but several environmental factors such as copper (Cu) availability might affect N2O emissions derived from legume crops. The aim of this research was to study how Cu can modulate N2O emissions by soybean root nodules. Soybean plants inoculated with Bradyrhizobium diazoefficiens USDA110 were grown in the presence of 4 mM KNO3 and a battery of Cu2+ concentrations added during growth (0, 5, 10, 20, 40, 60 or 100 μM). N2O emissions were measured by gas chromatography in both, nodulated roots and detached nodules, after root flooding. Also, 15N isotope dilution was assayed for SNF and N2O determinations. Results showed that an excess of added Cu during growth significantly affected plant physiology, nodulation and SNF of the soybean-B.diazoefficiens symbiosis, being 20 μM the threshold that soybean plants can tolerate without suffering Cu stress. Meanwhile, Cu addition reduced statistically N2O emissions by soybean nodules. This reduction was correlated with Cu accumulation in nodules, which affected the denitrifying enzymes activities. Cu excess produced a simultaneous decrease of nitrate and nitrite reductase activities, but an increase of nitrous oxide reductase activity. Finally, the modulation of bacteroidal nitrate reductase activity is proposed as an effective target for the strategies for mitigation of N2O emissions derived from soybean crops, probably more effective than nitrous oxide reductase activity.

中文翻译：

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铜调节大豆根瘤的一氧化二氮排放

摘要 由于氮对作物的过度或非同步施用，农业是温室气体一氧化二氮 (N2O) 的重要来源。通过豆科植物-根瘤菌共生进行的共生固氮 (SNF) 可以成为缓解 N2O 的有效策略，但铜 (Cu) 等多种环境因素可能会影响豆科作物产生的 N2O 排放。本研究的目的是研究铜如何调节大豆根瘤的 N2O 排放。在 4 mM KNO3 和在生长过程中添加的一系列 Cu2+ 浓度（0、5、10、20、40、60 或 100 μM）存在下，接种了重氮缓生菌 USDA110 的大豆植物生长。根浸水后，通过气相色谱法测量根瘤根和脱离根瘤中的 N2O 排放量。还，为 SNF 和 N2O 测定分析了 15N 同位素稀释液。结果表明，生长过程中过量添加的铜显着影响大豆-重氮芽孢杆菌共生的植物生理、结瘤和 SNF，20 μM 是大豆植物在不遭受铜胁迫的情况下可以耐受的阈值。同时，Cu 添加减少了大豆根瘤的 N2O 排放统计。这种减少与结核中铜的积累有关，后者影响了反硝化酶的活性。Cu过量导致硝酸盐和亚硝酸盐还原酶活性同时降低，但一氧化二氮还原酶活性增加。最后，拟杆菌硝酸还原酶活性的调节被提出作为缓解大豆作物产生的 N2O 排放的策略的有效目标，