[Effects of drought stress at different growth stages on photosynthetic efficiency and water consumption characteristics in sweet potato]

To investigate the effects of drought stress on the growth of sweet potato, photosynthesis, yield, and water consumption characteristics were investigated in field-grown sweet potato plants (Jishu 21, a drought-tolerant cultivar) at different growth stages in 2014-2015. There were five drought treatments, including the whole growth period (DS), the early stage of growth (rooting and branching period, DS₁), the middle stage of growth (storage root initiation period, DS₂), and the late stage of growth (storage root bulking period, DS₃), and a normal irrigation treatment (WW) as control. The results showed that sweet potato plants in DS significantly decreased in dry mass, biomass, and harvest index during two years. The biomass of sweet potato under DS, DS₁, DS₂ and DS₃ was decreased by 31.3%, 21.2%, 19.6% and 7.7%; the harvest index was decreased by 19.9%, 14.5%, 14.1% and 6.5%, and the dry mass was decreased by 45.3%, 33.1%, 31.3% and 14.2%, respectively. The leaf area index in DS, DS₁, DS₂ and DS₃ was decreased by 77.1%, 60.1%, 39.2% and 17.1% at 100 days after transplanting (DAT), and the net photosynthesis was decreased by 56.7%, 26.6%, 18.7% and 9.5% at 90 DAT, respectively. Plants under drought stress reduced diurnal evaporation, transpiration rate, water consumption, daily water consumption, and soil water use efficiency, but increased irrigation water use efficiency. Drought stress decreased leaf area index, P_n, biomass and the allocation of biomass to storage root, resulting in a significant reduction of yield. The early drought and the long stress duration had significant impacts on leaf area index, P_n, biomass and harvest index, leading to a greater reduction in yield and water use efficiency. Therefore, drought stress at the early growth stages of sweet potato should be avoided during cultivation.