Effect of traditional soybean breeding on water use strategy in arid and semi-arid areas

Water is the main factor determining yield performance under drought conditions. Traditional soybean breeding has significantly increased grain yield under drought, but its effect on water use strategies and associated traits are not well understood. Field and pot experiments with new cultivars and landrace soybean genotypes were undertaken to identify the effect of soybean breeding on water use strategies and related leaf and root functional traits under different water regimes. The new cultivars, on average, had 33.9 %, 45.1 % and 169 % higher grain yields and 47.9 %, 98.4 % and 244 % higher water use efficiencies for grain yield (WUE_G) but 8.8 %, 38.1 % and 19.6 % lower water use than the landraces in the field and pot experiments 1 and 2, respectively. Stomatal conductance decreased in the new cultivars at higher soil water contents than the landraces during soil drying. The new cultivars, on average, had a 22.9 % lower root fraction, 21.5 % lower leaf fraction, 20.6 % lower stem fraction and 69.8 % higher pod fraction than landraces, which had 21.7 % and 26.8 % lower root hydraulic conductance at the R2 and R6 stages, respectively, than the landraces. Our results show that (1) traditional soybean breeding has changed the water use strategy from profligate to conservative and improved yield performance and WUE_G, (2) the high sensitivity of stomatal conductance to water stress is coordinated with lower root hydraulic conductance to limit water use, and (3) selecting new cultivars with high grain yield but low water use may a new way to improve yield performance under water-limited conditions.