Keele Research Repository

Genders of dioecious species often show secondary sexual dimorphisms (not directly related to the sex organs), which may be related to reproductive demand for resources during the year. Our working hypothesis stated that phenology influences yearly sex-specific pattern of foliar nitrogen concentration in dioecious species. The concentration of carbon (C) and nitrogen (N) of last year’s needles (on part of twigs where strobili are bearing) was measured in 1-month intervals from March to November in Taxus baccata L. and Juniperus communis L. separately for males and females. Seasonal C concentration of needles was unrelated to gender, probably due to storage elsewhere in the plants. Needles of J. communis females had higher N concentration in March and April but this dropped to the same level as males after flowering and vegetative growth began. This suggests that females of J. communis, a species of N-poor habitats, have a long-term strategy of N storage. Nitrogen concentration was not different between the sexes during the rest of the growing season. In T. baccata, N concentration was higher in males throughout the analysed period, but the highest differences were in the period of intensive shoot elongation and radial growth. The high demand for N in the period of intensive growth and female cone maturation may result in restrictions in the vegetative growth of females. The results indicate that the time (phenology) and species-specific strategy significantly affect the concentration of N in females and males.