Variability of stomatal conductance in a small and isolated population of Silver fir (Abies alba Mill.)

We analyzed the response to drought of 420 individuals from eight half-sib families from a small and isolated population of silver fir (Abies alba Mill.): 105 of them were kept in well-watered conditions as control while the remaining 315 were exposed to drought for 27 days. A model describing stomatal behavior derived from Monteith and developed in beech by Leonardi et al. was fitted to experimental transpiration data obtained simply from the difference between two daily pot weighings. The estimated parameters were maximum stomatal conductance, maximum transpiration in well-watered conditions and sensitivity to soil water deficit. The model worked well: convergence for all but four individuals and concordance between experimental and fitted data were good (R 2 = 0.86). Inter-individual variability for all three estimated parameters was high and two of them (maximum stomatal conductance and sensitivity to soil water deficit) were significantly different among families, suggesting genetic control. Our results validate the simplified method used to evaluate individual stomatal parameters. We also show that in the small and isolated population of our study substantial adaptive variability remains, a crucial prerequisite to endure environmental conditions determined by climatic change foreseen for the next decades.