GROWTH AND WATER-USE EFFICIENCY OF 10 TRITICUM-AESTIVUM CULTIVARS AT DIFFERENT WATER AVAILABILITY IN RELATION TO ALLOCATION OF BIOMASS

In environments where the amount of water is limiting growth, water-us e efficiency (biomass production per unit water use) is an important t rait. We studied the relationships of plant growth and water use effic iency with the pattern of biomass allocation, using 10 wheat cultivars , grown at two soil moisture levels in a growth chamber. Allocation pa ttern and relative growth rate were not correlated, whereas allocation pattern and water use efficiency were. Variation in transpiration per plant resulted from variation in the rate of transpiration per unit l eaf area or root a eight, rather than from differences in leaf area or root weight per plant. Transpiration per unit leaf area or root weigh t was lower when the leaf area or root weight per unit plant weight wa s larger. Also, the efficiency of water use at the plant and leaf leve ls was higher for plants with a higher leaf area per unit plant weight , and it was not correlated with the plant's growth rate. Differences in water-use efficiency at the leaf level were related to variation in stomatal conductance, rather than in the rate of photosynthesis. A hi gh photosynthetic water-use efficiency was associated with a low effic iency of nitrogen use for photosynthesis.