Aerial Production, Mortality, and Mineral Accumulation‐Export Dynamics in Spartina Alterniflora and Juncus Roemerianus Plant Stands in a Georgia Salt Marsh

Abstract

Biomass and disappearance of dead material were measured in stands of tall creekbank Spartina alterniflora, short high marsh S. alterniflora, and Juncus roemerianus in Georgia, USA at 4—wk intervals for 1 yr and at 8—wk intervals for a 2nd yr. Growth and mortality were calculated from these data. Net primary production estimates, using changes in biomass only, ranged from 10 to 75% lower than estimates which included the disappearance of dead material. Agreement between the methods was closest when the interval between harvest was shortest and the rate of dead material disappearance the slowest. Estimates of mean annual net primary production, computed from changes in biomass and disappearance of dead plant material, were: creekbank S. alterniflora 3700g/m², high marsh S. alterniflora 1300 g/m², and J. roemerianus 2200g/m². The seasonal amplitude in the amount of N, P, K, Ca, and Mg in the living tissue was greatest in the creekbank S. alterniflora. The maximum accumulation of most elements was in late summer. In the tissue of S. alterniflora, N and P were highest in concentration in late winter and early spring. In summer, growth occurred faster than nutrient accumulation therefore, tissue concentrations decreased. Seasonal p patterns of element disappearance from the "dead plant community" showed that maximum export depended on community type and the element under consideration.