High nitrate concentration reduces growth in Zea mays

Resumen

Nitrogen is one of major factors limiting crop yield and its central role on plant growth has longbeen recognized. An adequate supply of N is fundamental to optimize crop yields, but itsmismanagement, such as an excessive application, can result in contamination of groundwater.Although no negative effects of nitrate excess on plant development have been described,preliminary studies in our laboratory have showed lower growth in maize plants watered withhigh nitrate solution. The aim of this work is to find when and where high nitrate supply affectsplant growth by analysing leaves growth.Zea mays plants were grown for 45 days in a fitotron under controlled conditions and wateredthree times a week using modified Hoagland solution, containing 2.5, 5, 10 and 15 mM ofnitrate. Length and width of every new fully expanded leaf was measured through theexperiment. In addition, photochemical efficiency of the PSII (Fv/Fm), CO2 assimilation andchlorophyll content were measured in those leaves.Data showed that plants watered with 10 and 15 mM nitrate had shorter and narrower leaves andshorter internodes than 5 mM nitrate plants. This effect could be noticed firstly in the third trueleaf and persisted in the younger ones. Furthermore, 10 and 15 mM nitrate plants showed lowerchlorophyll content, Fv/Fm values and lower CO2 assimilation rates. Plants treated with 2.5 mMof nitrate couldn’t reach the CO2 assimilation rates found in 5 mM NO3- plants, despite havingsimilar values for both Fv/Fm and chlorophyll content.In conclusion, results showed that 5 mM nitrate is an optimum concentration for maize plantsgrowth, while higher or lower concentrations results in a lower plant growth trough leaf andinternode elongation decrease and photosynthesis reduction.