COMPARATIVE PHYSIOLOGY AND GROWTH OF 2 PERENNIAL TUSSOCK GRASS SPECIES IN A SEMIARID ENVIRONMENT

The physiology and growth of Lygeum spartum and Stipa tenacissima, two perennial tussock grasses which dominate wide areas of semi-arid sout h-eastern Spain, were compared at times of high and low availability o f water, in autumn and summer respectively, to study the adaptation of this growth form to arid environments. The two species differed in mo rphological and physiological trails. Stipa tussocks were larger and h ad opportunistic growth, and Stipa leaves had a smaller specific area and lower diffusive conductance to water vapour. The two grasses were similar in maximum photosynthetic rate, leaf nitrogen concentration, a nd in the response to high light conditions but had different tissue w ater relations. Stipa was better suited to cope with drought and errat ic rainfall, because of its more effective control of water loss and i ts growth patterns. Lygeum seems to be adapted to less dry conditions and more saline soils. The tussock growth form provides an adaptive ad vantage in these infertile environments by reducing radiation absorban ce. (C) 1996 Annals of Botany Company