Congruency analysis of species ranking based on leaf traits: which traits are the more reliable?

Nine leaf traits area, fresh weight, dry weight, volume, density, thickness, specific leaf area SLA, dry matter content LDMC, leaf nitrogen content LNC from ten plant species at eight sites in southern mediterranean France were investigated in order to assess their variability along a climatic gradient and their ranking congruency power. After examination of trait correlation patterns, we reduced the nine initial leaf traits to four traits, representative of three correlation groups: allometric traits dry weight, functional traits SLA and dry matter percentage and Leaf Thickness. We analysed the variability of these four leaf traits at species and site level. We observed that between species variation between 64.5 for SLA and 91% for LDMC is higher than within species variation. Allowing a good congruency of species ranking assessed by spearman rank correlation and a good reallocation of individuals to species by discriminant analysis. A site level variability between 0.7% for Dry weight and 6.9% for SLA was identified and environmental parameters altitude, temperature, precipitation, nitrogen, pH were considered as probable control factors. We found significant correlation between SLA, LDMC and the average minimum temperature respectively r0.87 and r-0,9 and no correlation for the other traits or environmental parameters. Furthermore, we conclude that two leaf traits appear to be central in describing species: specific leaf area SLA, percentage of dry matter LDMC. While, SLA and LDMC are strongly correlated, LDMC appears to be less variable than SLA. According to our results the Dry Matter Content or its reversal Leaf Water Content appears the best leaf trait to be quantified for plant functional screening. Leaf thickness appeared to be rather uncorrelated with other leaf traits and show no environmental contingency; its variability could not have been explained in this study. Further studies should focus on this trait.