Influence of drought and leaf age on photosynthetic utilization of fluctuating light in barley

Diffused light and sunflecks within the crop canopy cause rapid changes in light intensity, which decrease photosynthetic productivity. Under water deficit conditions, the negative effect of light variability on photosynthetic performance can be further aggravated. The differentiation in the response of the youngest fully developed and older leaves of barley varieties to simulated drought was evaluated under fluctuating light. A plastic response of barley to FL was evident in young leaves through quicker induction and relaxation of regulated nonphotochemical quenching in response to FL. Plants were only temporarily capable of utilizing the high light phase of FL for photochemistry, with this effect differing between the studied varieties and being less pronounced in old and dehydrated leaves. The capacity of spring barley to efficiently utilize light of variable intensity for photochemistry and photoprotection strongly depends on leaf age and water status.