Production and decomposition in floating soils of the Iberá wetlands (Argentina)

Floating soils grow due to the deposition of dead material onto their surface as well as the increment in belowground biomass. The imbalance between biomass production and decomposition is the source of organic matter accumulation. The Esteros del Iberá wetland (Argentina) features extensive areas of floating soils, locally known as “embalsados”. The annual aboveground biomass production, decomposition rate, and changes in nitrogen content in Thalia multiflora, a common species of Iberá, were determined in order to assess the organic matter addition and the nitrogen dynamics in the floating soils dominated by this species. The aboveground net primary production was estimated by measuring the standing crop at the peak registered during the sampling period. The decomposition rates of leaves and stems were determined by the litterbag method. The litter-bags were collected periodically during a year. The annual organic matter addition was estimated from the relation between aboveground production and the amount of mass lost in a year. The maximum aboveground biomass was 1368 g/m2 ( ± 271 SD), 71 % stems and 29 % leaves. The loss of weight in the sampling period (399 days) corresponds to 78 % of the initial mass: the total biomass exponential decay coefficient was significantly (ANCOVA; p<0.001) lower in stems (k = 0.0036) than in leaves (k = 0.0040). Both the decomposition rate value as well as the P/D ratio = 1.37, indicate that in T. multiflora stands the organic matter incorporated to the floating soil’s surface is small when compared to other peatlands. Initial nitrogen con-centration in leaves and stems was 1.07 % and 0.32 %, respectively, this value increased to 1.76 % and 1.25 % in both substra