Grassland biomass dynamics along an altitudinal gradient in the Pampa

Above and below-ground biomass and necromass dynamics were assessed for 3 g rassland sites located at 550, 850, and 1,025 m elevation in Sierra de la V entana range (38 degrees1'S 62 degrees2'W) in Argentina. The objective was to determine if differences existed in dry matter structure, mycorrhizae in fection, net primary productivity (NPP) partitioning to aboveground and bel owground tissues, senescence and litter fail, and seasonal patterns of dry matter fluxes with altitude, Soil properties, water budgets and temperature at the sites were also assessed. Biomass plus necromass (without litter) w as 1,184 +/- 41, 1,208 +/- 70, and 1,507 +/- 63 gDM m(-2) for the lower, in termediate and upper sites, respectively. The below:aboveground biomass rat io increased with elevation. Total NPP was 1,131, 1,280, and 1,157 gDM m(-2 ) year(-1), respectively, for the 3 grassland sites. belowground allocation of net productivity increased with altitude. Both mass and proportion of t hin roots increased with elevation, and so did mycorrhizae infection. The a boveground and belowground turnover rates decreased with altitude, but rate s were faster for aboveground tissues. We found different temporal patterns in productivity, senescence and disappearance among grassland sites despit e similar total NPP. Water holding capacity of soils and temperature were i mportant factors related to several of the observed trends in structure and function. Differences in grassland structure and fluxes are discussed as r elated to soils and local climate at each site.