Seasonal variations in carbon isotope discrimination and foliar nitrogen content in males and females of the subdioecious dune plant Honckenya peploides

Background/Question/Methods

Male and female plants of dimorphic species often differ in ecophysiological traits and display spatial segregation. These differences have been interpreted as an evolved response of the sexes to meet the specific resource demands associated with reproduction. Honckenya peploides (L.) Ehrh. is a subdioecious plant that grows on coastal dunes and that has two distinguishable, spatially segregated sexual morphs. Flowering and fruiting patterns change throughout the season, and therefore we expect that sex-specific patterns of water use efficiency will depend on time. The aim of the present study was to investigate whether seasonal variations in the water use efficiency of male and female H. peploides might explain the observed spatial segregation of the sexes. For this, water use efficiency -as inferred from carbon isotope discrimination (Δ¹³C)- and the foliar carbon and nitrogen contents were measured in male and female plants growing at four locations on the coast of Galicia, in April, June and August 2005.

Results/Conclusions

The sexes did not differ in Δ¹³C or foliar nutrient content, but there were some significant intersexual differences in the relationships between Δ¹³C and foliar nitrogen content. Soil water content decreased more sharply throughout the season in male than in female habitats. The observed lack of sex-related differences in integrated water use efficiency and leaf nitrogen content make it difficult to establish a physiological basis for the spatial segregation of the sexes. We suggest that males and females may select different habitats to meet the different demands for reproductive resources, with each sex achieving the best performance in the habitat in which it predominates.