Document: FRA-3-38-27

Changes in plant interactions along a gradient of environmental stress.

PUGNAIRE, F.I.* and M.T.LUQUE

Estacion Experimental de Zonas Aridas, CSIC, Almeria, Spain ¹

Abstract:
A combination of competition and facilitation operating simultaneously among plant species appears to be the rule in nature, where these effects change along productivity gradients often in a non-proportional manner. We investigated changes in competition and facilitation between a leguminous shrub, Retama sphaerocarpa, and its associated understory species along a gradient of resource availability in semi-arid Southeast Spain. Our results showed a change in the net balance of the interaction between the shrub and several of its associated species, from clearly positive in the water-stressed, infertile environment to neutral or even negative in the more fertile habitat. There was a weakening of facilitation along the fertility gradient as a consequence of improved abiotic conditions. Competition was intense for belowground resources in the less fertile environment while aboveground competition increased towards the more productive end of the gradient. Changes in the balance of the interaction between and among different plant species along the gradient of stress were caused by a decline in facilitation rather than by a change in competition. As both competition intensity and facilitation change along gradients of resource availability, plant interactions are best viewed as dynamic relationships the outcome of which depends on abiotic conditions.

Keywords: Competition, Environmental stress, Facilitation, Semi-arid environments

This abstract is being presented at: 9:45 AM in session:
Oral Session #72: Plant Competition.