Effect of light intensity at varied potassium supply on CO2assimilation and yield formation of spring wheat.1The effect of a varied K+supply on CO2assimilation rates and yield formation has been studied at two different light intensities with wheat (Triticum aestivumL.) grown in solution culture. Light intensity was reduced in one treatment by shading the plants with a cloth, which caused a reduction of about 50 of the light intensity. This shading was applied from the heading stage until grain maturation.2Reduced light intensity resulted in remarkably decreased rates of dry matter increments in both K treatments. In the beginning this growth depression, however, was small in the treatment with the higher K supply. At the stage of transition from the vegetative to the reproductive stage the better K+nutrition obviously could compensate the lacking light to some degree. This favourable K+effect, however, decreased with the advance of the reproductive phase. Thus at maturation in both K treatments equal quantities of dry matter were harvested. In the treatments with full light the higher K supply resulted in a yield increase at maturation.3The CO2assimilation rates measured at flowering, milk stage and dough stage indicated that rather the K supply than the light intensities influenced the CO2assimilation. The treatments with the higher K supply showed almost twice as high assimilation rates compared with the treatments with the lower K supply.4The reduced light intensity caused a substantial depression in grain yield in both K treatments. The poor grain yield was mainly due to a reduced thousand grain weight and to a less extent to a reduction in the number of ears.5As the better K supply resulted in increased CO2assimilation rates without having an influence on the grain filling of the plants exposed to a lower light intensity, it is concluded that at low light intensities the grain filling is not limited by the supply of grains with photosynthates but probably is affected by other processes..
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