Gas exchange analysis is an important technique, as the reduction in yield may be related to the decreased photosynthetic activity, due to adverse climatic factors in the growing site. The hypothesis of this study was that contrasting soil water conditions result in different photosynthetic performance in soybean genotypes. Thus, our objective was to analyse the physiological capacity in soybean genotypes under field conditions with optimal soil moisture and under water deficit. The experimental design was random blocks with 10 genotypes (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10) and three replicates. Individual analysis of variance was performed in both environments (irrigated and rainfed), and a correlation network between the traits was generated. We measured the traits net photosynthesis, stomatal conductance, internal CO₂ concentration, instant water‐use efficiency, instant carboxylation efficiency and grain yield. Stressed plants reduce stomatal conductance and transpiration, but increase the instant water‐use efficiency as a defence mechanism in sub‐optimal soil moisture conditions. The P6 genotype obtained better physiological capacity under irrigated conditions, while the P10 genotype showed the better performance under rainfed conditions, which makes it tolerant to water stress. Our findings can contribute to the genotype formation and parental choice steps in breeding programs aimed at obtaining both irrigation‐responsive and drought‐tolerant genotypes.

中文翻译：

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灌溉和雨育条件下种植的大豆基因型的生理性能

气体交换分析是一项重要的技术，因为产量的下降可能与光合活性的下降有关，这归因于生长地点的不利气候因素。这项研究的假设是，不同的土壤水分条件导致大豆基因型的光合作用性能不同。因此，我们的目的是分析在最佳土壤水分和缺水条件下田间条件下大豆基因型的生理能力。实验设计是具有10个基因型（P1，P2，P3，P4，P5，P6，P7，P8，P9和P10）的随机区组和三个重复。在两种环境（灌溉和雨养）下均进行了方差的单独分析，并生成了性状之间的相关网络。我们测量了净光合作用，气孔导度，内部CO₂浓度，即时用水效率，即时羧化效率和谷物产量。受胁迫的植物减少了气孔导度和蒸腾作用，但提高了即时水分利用效率，将其作为次佳土壤水分条件下的防御机制。在灌溉条件下，P6基因型获得了较好的生理能力，而在雨水条件下，P10基因型表现出了更好的性能，因此可以耐受水分胁迫。我们的发现可有助于育种计划中基因型的形成和父母选择的步骤，旨在获得灌溉响应型和耐旱型。