Combined seasonal and longitudinal variations of element concentrations in two aquatic mosses (Fontinalis antipyretica and F. squamosa)
Martínez-Abaigar, Javier; García-Álvaro, M. Angélica Beaucourt
The seasonal and longitudinal variations in the concentrations of seven elements (N, P, K, Ca, Mg, Fe, and Na) were jointly analysed in two species of aquatic bryophytes (Fontinalis antipyretica and F. squamosa) from a mountain stream in Spain. The analyses were conducted monthly during one annual cycle in three consecutive 1.5-cm segments of the main axis of the moss shoots. The questions under consideration were whether the element concentrations changed seasonally and, if so, whether those changes depended on internal (for instance, the part of the plant considered) or environmental factors. Both species showed similar elemental compositions, in line with their same original stream, except for the higher N concentration found in F. antipyretica (probably due to a higher physiological activity) and the greater accumulation of Fe in F.squamosa. In both species, the concentrations of Ca, Mg, and Fe increased significantly from the apical segments to the basal ones, whereas those of N, P, and K showed the reverse pattern. This variation was similar in the annual means and in the monthly values of the element concentrations, and maybe explained by the higher physiological activity of the apical segments and the higher mobility of the second group of elements within the bryophyte tissues. The longitudinal changes in Na concentration were not significant. In every species and segment, the concentrations of K, Fe, P, and N increased through summer and autumn and decreased through winter and spring. While only scattered correlations were found between the element concentrations in the bryophytes and the physical and chemical variables of the water, these annual cycles presumably depended on the growth cycle of aquatic bryophytes. The concentration of Na in the apical segment of both species was higher in December-April than in the rest of the year, probably because of a higher Na absorption in those periods of the year in which deicing salt was added to a road near the stream. The concentrations of Ca and Mg showed random temporal patterns in all segments and species. Globally, the 4.5-cm apical portion of the shoots of the species studied behaved as a unity when seasonal changes were assessed, with the particular exception of Ca.