Effects of ultraviolet‐B irradiance on soybean VII. Biomass and concentration and uptake of nutrients at varying P supply

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Abstract
Glycine max (L.) Merr. cv Essex was grown hydroponically in a greenhouse in a factorial combination of 4 levels of P (6.5, 13, 26 and 52 μM P) ‐2 ‐1 and 2 levels of ultraviolet‐B (0 and 2500 J m day biologically effective UV‐B) radiation. Plants were grown through the full expansion of the 4th trifoliolate leaf. Decreased supply of P decreased plant biomass, and the uptake and concentration of other macronutrients. Decreased P supply also reduced allocation of biomass to leaves and stems but increased allocation to roots. The effect of UV‐B radiation depended upon P supply. At the lowest P supply (6.5 μM) UV‐B radiation did not affect any of the parameters measured, except biomass allocation. UV‐B radiation increased biomass allocation to leaves but decreased allocation to stems and roots. At higher levels of P supply, UV‐B radiation significantly decreased plant bioraass, uptake of Ca and Mg, and increased concentrations of N, P, K, and Mg in plant dry matter. UV‐B radiation did not affect the uptake of N, P, K nor Ca concentration. The effects of P supply and UV‐B on nutrient concentration and uptake was through its indirect effect on dry matter production and allocation, and anion‐cation balancing.