Ecophysiological differences between male and female plants of Pistacia lentiscus L.

Previous studies in spatial distribution of male and female shrubs of Pistacia lentiscus have demonstrated that less perturbed areas, older communities with a well developed cover, have male-biased sex ratios, whereas in abandoned old agricultural areas there are no significant differences between the number of male and female plants. In this study, we analyse both sexes in terms of their photosynthetic features that could provide a physiological basis for habitat partitioning between sexes. Rates of light-saturated assimilation and stomatal conductance were studied in male and female plants during summer. Assimilation rates were higher in the morning than in the afternoon and mean daily maximum assimilation rates reached 10.9 and 6.6 mu mol m(-2) s(-1), for male and female plants, respectively. In the absence of drought stress (laboratory conditions), the measured photosynthetic characteristics of leaves of male and female plants, provided by fluorescence studies and light and CO2 response curves, were similar. Under natural stress conditions however, lower CO2 assimilation rates and stomatal conductances were recorded in female plants. The differences in the light response curve of effective quantum yield (Phi (II)) recorded under stress conditions showed also higher quantum yield for male plants under low irradiances. From this study we suggest that the differences observed between male and females are largely due to different degrees of stomatal control rather than to differences in photosynthetic activity, leading to higher water use efficiency (WUE) in female plants. However, despite the higher leaf control of water loss by females, they reduce the water potential to the same values as male plants, probably due to specific characteristics of the root system or of the conducting xylem. These results suggest that the ecological advantage of male plants in older communities is due to a higher competition for water uptake, while in the youngest open areas is the higher WUE in female plants that confer an ecological advantage.