Influence of photosynthetic irradiance on nitrate reductase activity, nutrient uptake and partitioning in tomato plants

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Abstract
The objective of the present work was to study the nutritional behavior of tomato plants (Lvcopersicon esculentum Mill.) subjected to high pressure sodium (HPS) supplementary lighting in relation to nitrate reductase activity (NRA). Tomato plants were grown with or without HPS supplementary lighting at 2 different root‐zone temperatures (RZT). Supplementary lighting combined with low RZT promoted NRA and cation uptake. Magnesium uptake appeared particularly related to the NRA daily pattern. Effects of photosynthetic irradiance (PI) at two growth stages on partitioning of 45Ca and 86Rb were also investigated. Low light level stimulated 45Ca uptake in fruiting plants but depressed 86Rb uptake. A hypothetical mechanism involving the influence of NRA and K cycling on HCO3‐ excretion by root is proposed to explain the effects of treatments on mineral uptake.