Effects of saline root environment (NaCl) on nitrate and potassium uptake kinetics for rose plants: a Michaelis–Menten modelling approach

Abstract

Greenhouse-grown cut flower roses are often irrigated with moderately saline irrigation water. The salt/ballast ions are either present initially in poor quality raw water or reclaimed municipal water, or accumulated in greenhouse irrigation water that is captured and reused. Such ions can inhibit root absorption of essential nutrients. The objective of this work was to quantify the influence of NaCl concentration on the uptake of nitrate and potassium by roses and develop a predictive model of uptake inhibition based on NaCl, NO3 −, and K+ concentration. One year-old rose plants (Rosa spp. ‘Kardinal’ on ‘Natal Briar’ rootstock) were moved into growth chambers where nitrogen and potassium depletion were monitored during 6 days. Eight different initial NaCl treatments varying from zero to 65 mol m−3 were used and within these there were two initial NO3 − and K+ concentrations: high concentration (HC, 7.0 mol m−3 and 2.6 mol m−3 NO3 − and K+ respectively) or low concentration (LC, 3.5 mol m−3 and 1.3 mol m−3 NO3 − and K+ respectively). Plant NO3 − uptake was negatively affected by NaCl concentration. NO3 − maximum influx (Imax) declined from 5.1 µmol to 2.5 µmol per gram of plant dry weight per hour as NaCl concentration increased from zero to 65 mol m−3. A modified Michaelis–Menten (M–M) equation taking into account inhibition by NaCl provided the best fit for NO3 − uptake in response to varying NaCl concentration. K+ uptake was unaffected by NaCl concentration. A M–M equation that did not include inhibition was suitable for describing K+ uptake at varying NaCl concentration. The resulting empirical models could assist with decision making, such as: adjustment of NO3 − fertilization based on NaCl concentration, necessity of water desalinization, or determination of the desired leaching fraction.