Abstract: The effect of three P level:0.1 mmol·L^-1 NaH₂PO₄(low P,LP),1.0 mmol·L^-1 NaH₂PO₄ (normal P,NP) and 2 mmol·L^-1 NaH₂PO₄ (high P,HP) on the root growth of alfalfa under waterlogging stress were investigated in sand culture. The results showed that NP promoted the shoot and root growth,but LP and HP inhibited the growth of alfalfa plants under well-watered conditions. The growth rate,shoot dry weight,total root length and root surface area in NP and LP were significantly lower in waterlogged conditions than in well-watered conditions,whereas the shoot growth rate and shoot dry weight in LP were significantly higher in waterlogged conditions than in well-watered conditions. The total root length,root surface area,root volume and number of root tips were higher in short-term waterlogged conditions and lower in long-term waterlogged conditions for LP when compared to the well-watered conditions. In summary,waterlogging alleviated the detrimental effect of low P on the growth of alfalfa and the alleviating effects could attribute to the root growth maintenance,whereas the waterlogging has damaging effect on the alfalfa growth under high P. Less phosphorus fertilizing in those areas of heavy rainfall,poor soil drainage as well as high water table fluctuations in southern China will not only reduce P loss,but also improve the waterlogging tolerance for alfalfa plants.

Key words: Waterlogging stress, Phosphorus, Alfalfa, Root

摘要： 为明确渍水胁迫对不同磷水平下紫花苜蓿生长的影响，本试验通过沙培研究了渍水对低磷（LP，0.1 mmol·L^-1 NaH₂PO₄）、中磷（NP，1.0 mmol·L^-1 NaH₂PO₄）和高磷（HP，2 mmol·L^-1 NaH₂PO₄）下紫花苜蓿根系生长的影响。结果表明：在正常水分下，与NP水平相比LP和HP均抑制了苜蓿的生长；在渍水胁迫下，NP和HP水平下苜蓿的生长速率、地上部干重、总根长、根系表面积、根系体积和根尖数等指标显著低于正常供水，而LP水平下苜蓿的生长速率和地上部干重则高于正常供水，总根长、根系表面积、根系体积和根尖数等指标在短期渍水（2 d）时高于正常供水，在长期渍水（11 d）时则显著低于正常供水。综上所述，渍水能缓解LP对苜蓿的伤害，主要是通过维持根系的生长，而渍水则对HP下苜蓿的生长不利。因此，在我国南方多雨和地下水位高的土壤中栽培苜蓿，适当少施磷肥既可减少磷的流失，又有利于提高苜蓿的耐渍性。

关键词: 渍水胁迫, 磷, 紫花苜蓿, 根系