Interaction between Waterlogging Injury and Irradiance Level in Alfalfa

This study investigates the interaction between irradiance and waterlogging injury in alfalfa (Medicago saliva L.) at various plant developmental stages. Alfalfa was subjected to flooding for 8 to10 d under high or low irradiance levels in controlled environmental chambers. Treatments were imposed on alfalfa 8 and 21 d after planting (DAP) and during regrowth following clipping at 31 DAP. Hooding significantly reduced dry matter accumulation regardless of growth stage, although damage was most severe when flooding was imposed on plants during regrowth after clipping. Irradiance levels primarily affected shoot and root dry matter in 21- and 31-DAP treatments. Much greater shoot dry matter accumulation in nonflooded high irradiance plants was observed relative to low irradiance plants. A flooding × irradiance interaction was found at every growth stage except for root dry weight in the regrowth stage after clipping. The flooding interaction was due to greater injury of flooded high-irradiance plants relative to flooded low-irradiance plants when injury was expressed as a percentage of the unflooded control. Results indicate that the irradiance level during flooding can influence damage rating when expressed as a percentage of control. Assimilate supply to roots was sharply reduced by low irradiance as evidenced by reduced root growth and carbohydrate concentration in unflooded controls. Flooding damage, however, was not enhanced under low irradiance, lending support to the hypothesis that carbohydrate (i.e., energy supply) is not a limiting factor in survival of alfalfa roots during short-duration flooding stress.

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