Tiller dynamic and production on a SW Atlantic Spartina alterniflora marsh

We used non-destructive methods to study the bi-monthly changes in standing stock, turnover, and net aerial primary productivity (NAPP) of Spartina alterniflora in the Bahía Blanca Estuary, Argentina, from 2005 to 2007. Tillers were tagged and counted bimonthly and a weight:height relationship developed for the live and dead stems in a regularly flooded zone (low marsh, LM) and an irregularly flooded one (high marsh, HM). The annual tiller natality in year one compared to year two decreased from 440 ± 68 to 220 ± 58 new individuals m–2 yr–1 in the HM and from 500 ± 103 to 280 ± 97 new individuals m−2 yr−1 in the LM (μ ± 1 SE). Tiller mortality averaged 670 ± 70 individuals m−2 yr−1.Living biomass was present throughout the year in both the sites, but flowering occurred only at the HM where it began in December. The live biomass in the LM was significantly greater than in the HM in the first year, but decreased in the second year from 455 ± 66 to 266 ± 31 g m−2 in the HM and from 572 ± 76 to 277 ± 78 g m−2 in the LM (μ ± 1 SE). The highest levels of standing dead material were in the HM (55%) and the lowest in the LM (24%). The average total (live + dead) aboveground biomass in the HM was significantly greater than in the LM in the first year, but decreased in the second year from 1033 ± 120 to 556 ± 33 g m−2, and in the LM from 679 ± 57 to 355 ± 61 g m−2 (μ ± 1 SE). The annual NAPP, calculated as the sum of positive growth in individual tillers between intervals, showed no significant differences between years and sites, and averaged 628 ± 94 g m−2 yr−1 (μ ± 1 SE). The dead biomass output (DBO), calculated as the sum of negative increments in NAPP between sampling intervals, was 956 ± 121 g−2 yr−1, and was not statistically different between sites. The productivity at this site is not different from that estimated for other marshes, when similar methods are used. The production at this site, however, may be limited by high salinity levels, and the differences observed between years related to climate changes between years, e.g., the 2006–2007 was an ENSO period.