RESPONSE OF WHEAT GROWTH AND CO2 ASSIMILATION TO ALTERING ROOT-ZONE TEMPERATURE

Wheat plants (Triticum aestivum L. var. Chisholm) grown at an air temperature of 23-degrees-C and a root-zone temperature of 3-degrees-C exhibited a significant reduction in shoot and root dry weight and leaf area compared with plants grown at a root-zone temperature of 23-degrees-C. This reduction was correlated with a significantly lower CO2 assimilation rate that was associated with lower leaf conductance, lower internal CO2 concentration, and more negative water potential. Low CO2 assimilation rate was also associated with high starch and total soluble sugar levels in the shoot, less translocation of photosynthate, and possibly less sink demand. Leaf chlorophyll concentration was not affected by altering the root-zone temperature, whereas water use efficiency of plants grown at a root-zone temperature of 3-degrees-C was as much as 1.5 times higher as those grown at 23-degrees-C.