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1st Int. Transborder Conf. of the Timor Island: Timor %u2013 Science without borderDili, 7-8 May 202535Physiological Responses of Soybeans During Water Stress Occurring At Pre-Anthesis And Post-Dehydration Mar%u04abal Gusm%u00e3oDepartment of Agronomy and Centre for Climate Change and Biodiversity, National University of Timor Lorosa%u2019e, Dili, Timor-Leste, and Department of Agronomy, IOWA State University of Science and Technology, Ames, USAemail: marcalgusmao@gmail.comAbstractDroughts caused by climate change bring uncertainty for soybean (Glycine max [L.] Merr) growers in the US and around the globe, adversely interrupting the growth and yields of soybeans. The present study aimed to investigate the physiological characteristics of soybean genotypes with different maturity groups in response to water stress before and at flowering during reproduction and rehydration. The growth chamber study was delivered in a greenhouse of the IOWA State University, USA, from August to November 2024 using a completely randomized design (CRD) factorial 3 x 3 with three replications. The soybean genotypes of Bayer-Kansas (A32E33), Pioneer (P18A73E), and Xitavo (var. 03120254) were imposed to severe water stress before (SBF) and at flowering (SF) and rewatered to 90% FC until physiological maturity. Parameters investigated were plant physiology, including leaf relative water content (RWC), stomatal conductance (gsw), photosynthesis (A), leaf temperature, leaf water use efficiency (WUEl), and grain yield. Water stress increased leaf temperature immediately, leading to decrease gsw within two days (SBF, SF) and A within three (SF) or four days (SBF) after stress imposition. Water stress significantly decreased RWC at three (SF) or five (SBF) days after stress imposition. Water stress increased WUEl as gsw decreased reaching the highest WUEl when gsw was at about 1 mol/m2/s. Rewatering improved plant physiology and delayed maturity, compensating for seed yield loss due to water stress. Water stress imposed before (6.26 g/plant) and at flowering (5.49 g/plant) produced similar grain yield, but significantly decreased by 26.07% and 35.13%, respectively, less to control. Bayer-Kansas produced 26.34% and 30.54% less seed yield than Xitavo and Pioneer. This study concludes that soybeans avoid or tolerate dehydration under severe water stress through a rapid decrease in gsw in addition to growth and recovery after rehydration, compensating for seed yield loss due to water stress. The three genotypes did not accelerate seed filling when severe water stress required breeding intervention for better adaptation to terminal drought.Keywords: field capacity, wilting point, plant available water, moderate water stress, severe water stress.