BIOMASS STUCTURE OF GRASSLANDS IN SIERRA DE LA VENTANA (BUENOS AIRES, ARGENTINA).

Abstract

This paper deals with the distribution of different plant compartments (aerial green, standing dead, litter and roots) during winter and spring (peak biomass) in six grasslands. The biomass structure relations with the altitudinal gradient, aspect and other environmental conditions, as well as grasslands biomass structure are discussed. In sunny conditions aerial dryweigh t d1minishedexponentially from 400 to 1,100 m a.s.!: 1,625.3 - 2,798.8 g/m in winter and 345.5 - 174.6 g/m in spring. Belowground biomass increased lineallywith altitude: 247.3 - 852.6 g/m and 311.6 - 1,349.3 g/m, along the same gradient and seasons. Tussock-type communities (Sttpa caudata, Paspalum quadrifartum, and Festuca pampeana grasslands) had a 10wer percentage oí underground related to total biomass, than do short grasslands from greater altitudes (Brlza subarlstata, B. brlzotdes and Aira caryophyllea, Sorghastrum pellttum - Sttpafiliculmis, and Piptochaetium hackelli + P. napostaense and Brlza subaristata). However, tussock grasslands, typically of the mountain slopes (F. pampeana type) had a greater percentage of roots and a lower green/root ratio than those from lower altttudes (S.caudata and P. quadrifartum). Grasslands in the less sunny situations (F.pampeana), from the sou thern steeper slopes, had greater total biomass and lower roots/total biomass ratio, than those exposed habitats at similar altitude. These relations are showing different adaptative community tactics according to the energy signature of the diverse mountain habitats. Vegetation alIocatesdífferent proportions ofphotosyntates to underground structures according to the varying combinations of altitude, slope, aspect and soil types, affecting availabllity and balance of water in plants. The more unfavourable the conditions are, the greater root/total or green biomass ratios are. Grasslands adjust biomass structure biomass structure independently to the dominant grass Ufe form (tussock or not). The characteristic proportions root/ total or root/ green biomass of a particular grassland are related to its dominant life form.