Justine Bresson, François Vasseur, Myriam Dauzat, Garance Koch, Christine Granier, Denis Vile
We developed a method to quantify the dynamics of spatial heterogeneity of photosynthetic efficiency through the distribution-based analysis of Fv/Fm values. The method was applied to Arabidopsis thaliana grown under well-watered and severe water deficit (survival rate of 40%). First, whole-plant Fv/Fm shifted from unimodal to bimodal distributions during plant development despite a constant mean Fv/Fm under well-watered conditions. The establishment of a bimodal distribution of Fv/Fm reflects the occurrence of two types of leaf regions with contrasted photosynthetic efficiency. The distance between the two modes (called S) quantified the whole-plant photosynthetic heterogeneity. The weighted contribution of the most efficient/healthiest leaf regions to whole-plant performance (called Wmax) quantified the spatial efficiency of a photosynthetically heterogeneous plant. Plant survival to water deficit was associated to high S values, as well as with strong and fast recovery of Wmax following soil rewatering. Hence, during stress surviving plants had higher, but more efficient photosynthetic heterogeneity compared to perishing plants. Importantly, S allowed the discrimination between surviving and perishing plants four days earlier than the mean Fv/Fm. A sensitivity analysis from simulated dynamics of Fv/Fm showed that parameters indicative of plant tolerance and/or stress intensity caused identifiable changes in S and Wmax. Finally, an independent comparison of six Arabidopsis accessions grown under well-watered conditions indicated that S and Wmax are related to the genetic variability of growth.