Facilitation of the non-native annual plant Mesembryanthemum crystallinum (Aizoaceae) by the endemic cactus Eulychnia acida (Cactaceae) in the Atacama Desert

Abstract

The Atacama Desert is one of the most stressful environments worldwide and represents a strong barrier for the establishment of native and non-native plants. In this study, we report the establishment of a non-native annual plant through facilitation by a native endemic cactus in a relatively undisturbed coastal area in north-central Chile. Soil collected under Eulychnia acida contained more available nutrients (N, P and K), water, and soluble salts than soils collected away from E. acida. Co-occurrence analyses showed a strong positive spatial association (facilitation) between the native cactus E. acida and the non-native annual, Mesembryanthemum crystallinum. The aboveground biomass of M. crystallinum individuals was 4-fold higher under the influence of E. acida. Native halophytes occasionally shared the cactus understory with the non-native species, but dominant native shrubs and perennial herbs did not co-occur with the cactus at scales of 1 and 4 m2. All these results support facilitation of the native cactus on the non-native herb. The combination of direct and indirect positive effects could explain the assembly of the non-native annual plant in these undisturbed areas of the Atacama Desert and have major implications on M. crystallinum capacity to colonize new areas.