What to Choose for Estimating Leaf Water Status - Spectral Reflectance or In Vivo Chlorophyll Fluorescence?

Summary

In the context of global climate change and the increasing need to study plant response to drought, there is
a demand for easily, rapidly, and remotely measurable parameters that sensitively reflect leaf water status.
Parameters with this potential include those derived from leaf spectral reflectance (R) and chlorophyll
fluorescence. As each of these methods probes completely different leaf characteristics, their sensitivity
to water loss may differ in different plant species and/or under different circumstances, making it difficult
to choose the most appropriate method for estimating water status in a given situation. Here, we present
a simple comparative analysis to facilitate this choice for leaf-level measurements. Using desiccation of
tobacco (Nicotiana tabacum L. cv. Samsun) and barley (Hordeum vulgare L. cv. Bojos) leaves as a model
case, we measured parameters of spectral R and chlorophyll fluorescence and then evaluated and compared
their applicability by means of introduced coefficients (coefficient of reliability, sensitivity, and inaccuracy).
This comparison showed that, in our case, chlorophyll fluorescence was more reliable and universal than
spectral R. Nevertheless, it is most appropriate to use both methods simultaneously, as the specific ranking
of their parameters according to the coefficient of reliability may indicate a specific scenario of changes
in desiccating leaves.