Effect of yttrium on photosynthesis and water relations in young maize plants

Despite an increase in spectrum of industrial applications of yttrium (Y) and the fact that it is widely present in the soils and plants, some of which are agronomically important crops, its effects on plant growth and metabolism are still obscure. Therefore, the aim of this work was to examine the effect of different concentrations of Y on its accumulation and distribution, photosynthetic responses, water relations, free proline concentration and growth of young maize plants. The experiment was done with maize (Zea mays L., hybrid NS-640), in water cultures, under semi-controlled conditions of a greenhouse. Plants were supplied with half-strength complete Hoagland nutrient solution, to which was added either 0 (control), 10−5, 10−4 or 10−3 mol/L Y, in the form of Y(NO)3·5H2O. Each variant was set in thirteen replications, with six plants in each replication. Plants were grown for 21 d and they were at the stage of 3 and 4 leaves when they were analyzed. The presence of Y reduced maize growth and photosynthetic performance. Dimensions of stomata significantly decreased while their density significantly increased on both adaxial and abaxial epidermis. Plant height, root length, total leaf area and dry mass also declined. Concentration of photosynthetic pigments (chl a and b and carotenoids) and free proline decreased. Photosynthesis and transpiration were impaired in the presence of Y – their intensities were also reduced, and the same stands for stomatal conductance of water vapor, photosynthetic water use efficiency (WUE) and water content. Although the highest concentration of Y was found in maize roots in each treatment, Y concentration in the second leaf and shoot also significantly increased with an increase in Y concentration in the nutrient solution. Albeit Y concentration was much higher in roots than in shoots, shoot metabolism and growth were much more disrupted. The results demonstrated that young maize plants accumulated significant amount of Y and that this element, when present in higher concentrations, had unfavorable effect on physiological processes and therefore plant growth.

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