Field study of the effects of excess copper on wheat photosynthesis and productivity

Abstract

Copper concentration in wheat plants growing in a Cu-contaminated area, was 3.5-times higher than that of the control, while the total chlorophyll (a + b) content of plants growing in an ore site was significantly reduced. The significant decline of the chlorophyll concentration in the Cu-stressed wheat plants in relation to the decrease in the chlorophyll a/b ratio was an indication of the poor condition of those plants and the lack of adaptive adjustment in pigment concentrations to high Cu levels. Plants grown in ore soils displayed a significantly smaller height and length of ear and produced significantly fewer seeds and spikelets per ear, while grain filling and development were negatively affected. The relative decrease in the assimilation rate for stressed plants was 90%. Increased Cu levels in the soil led to a decrease of the stomatal conductance (43%) and of the transpiration rate (10%). The water use efficiency (i.e. the ratio between leaf photosynthesis and transpiration) of the stressed leaves decreased by about 9-times. A positive relationship was found between leaf photosynthesis and grain production under Cu-stress. Changes in the rate of CO2 assimilation were due to the changes in stomatal conductance. Lower CO2 assimilation under Cu-stress was associated with a lower chlorophyll content. The sharp impact of Cu on wheat leaf water use efficiency, suggests a decreasing control over water loss. The results indicate that, in wheat, it may be possible to use measurements of water use efficiency to predict productivity under environmental stress conditions.