Effect Of Soil Moisture On The Root Growth And Water Use Efficency In The Seeding Stage Of Alfalfa

Alfalfa(Medicago sativa L.)is a forage crop with characteristics of high yield and quality,well-grown in the warm and semi-arid regions,where annual rainfall 300?800 mm.It is now a major forage planted in northern China.However,the cultivation of alfalfa in southern China is limited due to the humid climate,large amount of annual precipitation,high underground water level and clay soil texture.In order to investigate the effects of soil moisture conditions on root growth and water use efficiency(WUE)of alfalfa in south China,a pot experiment was conducted with varieties of Icon and Sadie 7.Three water treatments i.e.30%?70%and 100%soil moisture were set.And the root growth under the different soil moisture conditions and it's relation to WUE were investigated.The results were as follows.Taproot growth was promoted under low moisture condition.Taproot length was higher than CK.However,the taproot diameter thinning,root volume becomes smaller,a lateral and apical number is less than the number of CK.Waterlogging inhibited the elongation of the root length growth,while also making the main root diameter,root volume and root surface area becomes small,a number of lateral roots and root tips were significantly lower than CK.Stem and leaf dry weight and root dry weight under low moisture condition have no significant difference with CK(P>0.05),but a significant increase in root to shoot ratio of plant.Stem and leaf dry weight and root dry weight significantly reduced under waterlogging condition,but root to shoot ratio have no significant difference to CK(P>0.05).After removing water stress,the plant under 70%soil moisture condition,the root growth which have been under low moisture condition and waterlogging condition have recover,the recovery rate of primary lateral number and root tips is faster,stem and leaf dry weight and root dry weight have grown over time.In addition,plant which have been under low moisture condition and waterlogging condition all becomes smaller different with CK over time.After removing water stress,net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),intercellular CO2 concentration(Ci)and water use efficiency(WUE)all becomes smaller different with CK over time.Water use efficiency(WUE)of low moisture pretreatment was improved due to net photosynthetic rate(Pn)reduce less than transpiration rate(Tr).Water use efficiency(WUE)of waterlogging pretreatment was improved through net photosynthetic rate(Pn)increased and transpiration rate(Tr)reduced to achieve.In summary,the root growth was affected and the structures were changed in different soil water condition.After removing water stress,differences in root growth in the treatments becomes smaller,while the photosynthetic physiology indicators differences are smaller,but the recovery of the root growth is slowly than the photosynthetic physiology.