Use of chlorophyll fluorescence for the evaluation of crops nitrogen status. A review

Introduction. Optimizing the nitrogen (N) fertilization of crops requires the use of methods that quickly and accurately assess the N status of aboveground biomass during the growing season. Optical measurements on plants allow the achievement of this goal and, among these approaches, the leaf chlorophyll fluorescence based method (ChlF) appears promising. The potential of ChlF has been studied for many years. The value of this method for detecting and quantifying various biotic and abiotic plant stresses has been assessed as well as its potential for the evaluation of crop N status (CNS). For this last application, ChlF could offer solutions to the limitations of the usual methods for evaluating CNS, which are based on light transmittance or reflectance and are related to leaf chlorophyll content. Literature. In this report, two ChlF based approaches are reviewed. The first approach is variable ChlF, or Kautsky kinetics, which represents the approach taken in the majority of the published work examined in the field of ChlF. The second approach is based on ChlF sensing methods for the estimation of the concentration of leaf metabolite compounds in plants, particularly that of leaf chlorophyll and phenolic compounds (mainly flavonoids). The characteristics and the applications of these two fluorescence approaches are studied for their potential use for the in-season monitoring of CNS. Conclusions. Of these two approaches, the use of the ratio of fluorescence combining the estimation of concentrations of leaf chlorophyll and flavonoid content appears to be a relevant potential method to assess CNS, as both concentrations are in close relationship with leaf N concentration.