Plant chlorophyll fluorescence: active and passive measurements at canopy and leaf scales with different nitrogen treatments.

M Pilar Cendrero-Mateo,U Rascher,K R Thorp,G Ponce-Campos,L Alonso,M Susan Moran,G Wang,J Moreno,Shirley A Papuga

doi:10.1093/jxb/erv456

Abstract

Most studies assessing chlorophyll fluorescence (ChlF) have examined leaf responses to environmental stress conditions using active techniques. Alternatively, passive techniques are able to measure ChlF at both leaf and canopy scales. However, the measurement principles of both techniques are different, and only a few datasets concerning the relationships between them are reported in the literature. In this study, we investigated the potential for interchanging ChlF measurements using active techniques with passive measurements at different temporal and spatial scales. The ultimate objective was to determine the limits within which active and passive techniques are comparable. The results presented in this study showed that active and passive measurements were highly correlated over the growing season across nitrogen treatments at both canopy and leaf-average scale. At the single-leaf scale, the seasonal relation between techniques was weaker, but still significant. The variability within single-leaf measurements was largely related to leaf heterogeneity associated with variations in CO2 assimilation and stomatal conductance, and less so to variations in leaf chlorophyll content, leaf size or measurement inputs (e.g. light reflected and emitted by the leaf and illumination conditions and leaf spectrum). This uncertainty was exacerbated when single-leaf analysis was limited to a particular day rather than the entire season. We concluded that daily measurements of active and passive ChlF at the single-leaf scale are not comparable. However, canopy and leaf-average active measurements can be used to better understand the daily and seasonal behaviour of passive ChlF measurements. In turn, this can be used to better estimate plant photosynthetic capacity and therefore to provide improved information for crop management.

Highlights

One promising approach for obtaining global estimates of plant photosynthesis is the use of chlorophyll fluorescence (ChlF)
Previous studies have shown that the decrease in photosynthesis modulated chlorophyll fluorescence via different mechanisms depending on the treatment: through the action of NPQ in response to water stress, or through the action of changes in leaf chlorophyll concentration in response to nitrogen deficiency (Cendrero-Mateo et al, 2015)
The red edge index provided the best approach to discriminate between nitrogen treatments (See Supplementary Table S1 at JBX online); and chlorophyll fluorescence changes were driven by variations in leaf chlorophyll content in response to nitrogen deficit (See Supplementary Fig. S1 at JBX online)

Summary

Introduction

One promising approach for obtaining global estimates of plant photosynthesis is the use of chlorophyll fluorescence (ChlF). ChlF are photons of red and far-red light (Fig. 1A) that are emitted by chlorophyll a pigments nanoseconds after light absorption (Porcar-Castell et al, 2014). Absorbed light energy excites chlorophyll molecules and de-excitation of this energy is mainly attained through three competing processes: photosynthesis, radiative loss of photons or ChlF, and nonradiative thermal energy dissipation (NPQ). As these three energy dissipation processes compete for excitation energy, changes in one process (e.g. photosynthesis) will affect the other two. By measuring ChlF, we can derive information on NPQ and photosynthesis. (Maxwell and Johnson, 2000; Porcar-Castell et al, 2014)

Methods

Results

Conclusion