Resarch Of Crop Hydraulic Lift

Hydraulic lift is the process of water movement from relatively moist to dry soil layers using plant root systems as a conduit during periods when transpiration ceases (usually at night). Little information is currently available on the extent and magnitude of hydraulic lift in crop plants. In this field study, we separately investigated hydraulic lift of two drought-tolerant corn hybrids (drought-tolerant 8407 and zhongdan 2) and a drought-susceptible hybrid (sweet corn) at the jointing stage, the large horn stage, and the flowering stage. At the same time, we also investigated the wheat (dingxi 24, dingxi 33, dingxi 35 and longchun 16) separately at the jointing stage, the heading stage, and the filling stage. Root systems were grown in two soil compartments drier upper and a wetter deep soil. Soil weight water content (s,) in the upper pots was measured with neutron probe separately at night 21:00 and the following day 5:00. Meanwhile, the plants were shaded for 3 h during daytime. Soil o. was monitored before and after shading. An increase in O~ in the upper pot was detected with neutron probe only in the three corn hybrids at the following day 5:00 of the flowering stage, but not at the other stage. Furthermore, water exuded from roots in the top soil layers was greater in drought-tolerant 8407 than in zhongdan 2 and sweet corn (202.5g vs. 140g and 85g) (pKO.008). This suggested hydraulic lift can be a draught-tolerant index in corn hybrid. The average quantity of water was lifted each night each plant in drought-tolerant 8407 was 67.5g, and the largest each night each plant was 88.3g. The time of water reverse flow was from night 21:00 to the following morning 5:00, and the lifted water was quickly used for transpiration. Reverse flow occurred on condition that soil water potential was smaller than ?.03 LMPa or between -0.48MPa and -l .33MPa. Root characteristics may be responsible for difference in hydraulic lift of the three corn hybrids. More primary roots at the deep moist soil in drought tolerant 8407 and zhongdan 2 than in sweet corn may enable these hybrids to absorb and transport water at faster rates; therefor, more water can be exuded into the upper drier soil when transpiration decrease at night. Larger primary roots in the upper soil in drought tolerant 8407 and zhongdan 2 than in sweet corn may contribute to higher root hydraulic conductance and greater magnitude of hydraulic lift. The transpiration rate of daytime was higher in drought tolerant 8407 than in sweet corn (5150 vs. 4033 mg/dm2/h). The transpiration rate of nighttime was the reverse (125 vs. 607 mg/dm2/h). The negligible hydraulic lift in sweet corn may also relate to higher nighttime transpiration of the hybrid. We also found the little hydraulic lift was just detected in three dingxi strain at the flowering stage.