Belowground biomass and productivity of a grazed site and a neighbouring ungrazed exclusure in a grassland in central Argentina

PUCHETA, E; BONAMICI, I; CABIDO, M; DÍAZ, S

AUSTRAL ECOLOGY

Blackwell

Año: 2004 vol. 29 p. 201 - 208

1442-9985

We estimated the below-ground net plant productivity (BNPP) of different biomass components in an  intensively and continuously 45-ha grazed site and in a neighbouring exclosure ungrazed for 16 years for a natural  mountain grassland in central Argentina. We measured approximately twice as much dead below-ground biomass in  the grazed site as in the ungrazed site, with a strong concentration of total below-ground biomass towards the upper  10 cm of the soil layer in both sites. The main contribution to total live biomass was accounted for by very fine  (<0.5 mm) and fine roots (0.5–1.0 mm) both at the grazed (79%) and at the ungrazed (81%) sites. We measured  more dead biomass for almost all root components, more live biomass of rhizomes, tap roots and bulbs, and less live  biomass of thicker roots (>1 mm) in the grazed site. The seasonal variation of total live below-ground biomass mainly  reflected climate, with the growing season being limited to the warmer and wetter portion of the year, but such  variation was higher in the grazed site. Using different methods of estimation of BNPP, we estimated maximum  values of 1241 and 723 g m  –2  year  –1  for the grazed and ungrazed sites, respectively. We estimated that very fine root  productivity was almost twice as high at the grazed site as at the ungrazed one, despite the fact that both sites had  similar total live biomass, and root turnover rate was twofold at the grazed site.