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Nitrogen fixation sensitivity related to water use efficiency at reproductive development in soybean

Soybean [Glycine max (L.) Merr.] nitrogen fixation is sensitive differentially to drought among different genotypes at different growth and development stages, which directly affects soybean yield. Acetylene reduction activity (ARA) response to a gradual drought and rewatering period at late podding (late R3) and late seed fill (late R5) were evaluated in two different water use efficiency (WUE) genotypes. Drought-stressed plants with high WUE (PI 372413) decreased ARA more insensitively than that of low WUE (PI 548534), and drought-stressed plants with low WUE (PI 548534) maintained low ARA level after stress alleviation at late R5. The recovery ability of N2 fixation was a genotypic difference with WUE at late reproductive development (late R5), especially. Analysing relation between fraction of transpirable soil water (FTSW) and relative ARA, it was confirmed that PI 372413 with high WUE was more insensitive to water deficit and had drought tolerance by N2 fixation and recovery ability with a threshold of 0.139–0.147 FTSW than PI 548534 with a threshold of 0.192–0.209 FTSW. The ability to recover N2 fixation following drought during the reproductive developmental stage would be of an important value in the actual planting environment.