Production and nutrient dynamics of plant communities on a sub-Antarctic Island

Summary Studies of plant standing crop and nutrient concentrations have enabled an assessment of the seasonal changes in nutrient standing stocks (the mass of nutrients per m²) in a fjaeldmark and two fernbrake communities on Marion Island (46°54S, 37°45E). These communities are an important component of the island's vegetation on rocky plateaux and slopes. For most species the aboveground accumulations of N, P and K early in the season were more rapid than increases in the aerial biomass. Rates of Ca, Mg or Na accrual were either similar to, or lower than, rates of aboveground growth. Nutrient (N+P+K+Ca+Mg+Na) standing stocks at the three communities were high; 71 g m^-2 at fjaeldmark, 116 g m^-2 at open fernbrake and 154 g m^-2 at closed fernbrake. The aboveground component accounted for 47% to 65% of these values. N was the most abundant element in the vegetation, followed by K (closed fernbrake) or Ca (open fernbrake and fjaeldmark). Nutrient standing stocks at the two fernbrakes were mostly higher than for most sub-Arctic and alpine dwarf-shrub tundras. Nutrient pool sizes (i.e. the total quantities of nutrients contained in the soil/plant system to a depth of 25 cm) were lower than those reported for arctic tundra meadows but were similar to, and often greater than, those found at heath communities, sub-Arctic dry meadows and dwarf-shrub tundras and some boreal forests. Annual net primary productions of the fernbrake vegetations were high and substantial quantities of nutrients are aquired annually from the soils by the vegetations. Depending on plant species, either N or K was the element taken up in the largest quantity, whereas P was mostly taken up in the lowest amount. A large proportion (mostly all) of the Ca and Mg and a substantial proportion of the N taken up aboveground was lost in the litterfall but little of K taken up was lost in this way.