Evolution of stomatal closure to optimize water?use efficiency in response to dehydration in ferns and seed plants

Plants control water-use efficiency (WUE) by regulating water loss and CO2 diffusion through stomata. Variation in stomatal has been reported among lineages of vascular plants, thus giving rise to the possibility that different may show distinct WUE dynamics response stress. Here, we compared gas exchange decreasing leaf potential four ferns nine seed plant species exposed a gradually intensifying deficit. The data collected were combined with those from 339 phylogenetically diverse obtained previous studies. In well-watered angiosperms, maximum conductance was high greater than required for WUE, but drought stress caused rapid reduction an increase elevated concentrations abscisic acid. However, ferns, stomata did not open beyond optimum point corresponding actually exhibited steady dehydration. Thus, plants showed improved photosynthetic under ability could provide them advantage over conditions, thereby presumably increasing their fitness selection pressure drought.