PRODUCTION AND NITROGEN CYCLING IN AN ECOSYSTEM OF ERAGROSTIS-CURVULAIN SEMIARID ARGENTINA .1. PLANT BIOMASS AND PRODUCTIVITY

The seasonal changes in aboveground and belowground biomass and produc tivity were studied in Eragrostis curvula (Schrad.) Nees, an important perennial tussock grass in semiarid Argentina. Aboveground material w as separated into live and dead shoots or inflorescences, and litter. Roots were taken up to 1 m soil depth using 25 cm increments, and clas sified as dead or alive. Live shoots contributed most (>50%) to the to tal aboveground biomass from early spring to early autumn, and represe nted 10% of foliage during winter. Inflorescences were a small fractio n (less than or equal to 2%) of total aboveground production which rea ched a maximum of 6418 kg ha(-1). This value was 7% lower than total a boveground annual net productivity (6908 kg ha(-1) yr(-1)). Live and d ead roots had similar biomasses at each soil depth, and values ranged from 4480 (0-25 cm) to 270 (75-100 cm) kg ha(-1) Maximum total belowgr ound biomass (11200 kg ha(-1)) was 15.3% lower than total belowground annual net productivity (13226 kg ha(-1) yr(-1)). Biomasses of live or dead roots, and belowground net productivity decreased with increases in soil depth. Ratios of total belowground to aboveground biomasses w ere >1. This may represent a survival strategy for E. curvula when gro wing under arid and semiarid conditions.