Abstract:

【Objective】 To clarify the correlations of drought-induced non-hydraulic root signals (nHRS) with plant growth and grain yield formation could provide a mechanism basis for water-saving agriculture. 【Method】 Pot experiments were conducted with two soybean cultivars, i.e, Jinda 74 and Jin 24. nHRS were traced during manipulative progressive soil drying period at branching, early flowering and grain-filling stages. The effect of water deficit on plant biomass and grain yields of the cultivars were investigated under good soil conditions, high water (H) treatment in 2007 and well-watered (WW) in 2008 experiment, and drought conditions, low water (L) treatment in 2007 as well as light drought (LD) and severe drought (SD) in 2008. 【Result】 In response to soil drying, nHRS appeared earlier in Jinda 74 at branching stage, and later at early flowering and grain-filling stages than in Jin 24, while it disappeared earlier for Jinda 74 than Jin 24 at all the three growth stages. Jin 24 exhibited a wider average soil water content threshold range of nHRS (TR). Drought stress (both LD and SD treatments) significantly decreased the above-ground dry mass, root dry mass and grain yield (P＜0.05), more dramatically for Jinda 74 than Jin 24 which showed a higher maintenance rate of grain yield than the former. The root/shoot ratio was significantly promoted (P＜0.05) under severe drought conditions, i.e., L and SD treatment, more extensively for Jin 24 than Jinda 74. Water use efficiency (WUE) was notably higher (P＜0.05) in Jin 24 than Jinda 74 under drought conditions in both experiments in 2007 and 2008. 【Conclusion】 Soybean cultivar of wider soil water content threshold range for nHRS yielded more, and exhibited lower root/shoot ratio but higher WUE and maintenance rate of grain yield under mild water deficit in pot-cultured condition.

Key words: soybean, drought tolerance, non-hydraulic root-sourced signal, water use efficiency, yield stability