Foliar potassium nitrate application improves the tolerance of Citrus macrophylla L. seedlings to drought conditions.

Scarcity of water is a severe limitation in citrus tree productivity. There are few studies that consider how to manage nitrogen (N) nutrition in crops suffering water deficit. A pot experiment under controlled-environment chambers was conducted to explore if additional N supply via foliar application could improve the drought tolerance of Citrus macrophylla L. seedlings under dry conditions. Two-month-old seedlings were subjected to a completely random design with two water treatments (drought stress and 100% water/field capacity). Plants under drought stress (DS) received three different N supplies via foliar application (DS: 0, DS + NH4NO3: 2% NH4NO3, DS + KNO3: 2% KNO3). KNO3-spraying increased leaf and stem DW as compared with DS + NH4NO3 and DS treatments. Leaf water potential (Ψw) was decreased by drought stress in all the treatments. However, in plants from DS + NH4NO and DS + KNO3, this was due to a decrease in the leaf osmotic potential, whereas the decrease in those from the DS treatment was due to a decrease in the leaf turgor potential. These responses were correlated with the leaf proline and K concentrations. DS + KNO3-treated plants had a higher leaf proline and K concentration than DS-treated plants. In terms of leaf gas exchange parameters, it was observed that net assimilation of CO2 [Formula: see text] was decreased by drought stress, but this reduction was much lower in DS + KNO3-treated plants. Thus, when all results are taken into account, it can be concluded that a 2% foliar-KNO3 application can enhance the tolerance of citrus plants to water stress by increasing the osmotic adjustment process.