Direct and indirect effects of Tillandsia recurvata on Prosopis laevigata in the Chihuahua desert scrubland of San Luis Potosi, Mexico

摘要

The function of epiphytes within ecosystems remains unclear; the high biomass and nutrient content of epiphytes suggests an indirect beneficial role, while other evidence indicates that epiphytes are directly harmful to their hosts. We studied the direct and indirect (associated with soil properties) effects of Tillandsia recurvata on Prosopis laevigata. Soils located below trees supporting large loads of T. recurvata differed in nutrient content from soils below trees carrying few T. recurvata and from bare soils. Greenhouse experiments showed that soils with added T. recurvata or P. laevigata litter increased seed germination and seedling survival of P. laevigata, but that the seedlings sown in soil with T. recurvata organic matter were shorter and of lower biomass. In vitro experiments showed that dichloromethanic and methanolic extracts of T. recurvata reduced the radicle size of P. laevigata seedlings. P. laevigata branches with ＞50% T. recurvata cover presented more dead and less live shoots than branches with ＜50% T. recurvata cover. Our data suggest that T. recurvata has a direct negative effect on P. laevigata. While T. recurvata does increase the organic matter and nutrient content of the scrubland soil, it also releases allelochemical compounds that act to reduce P. laevigata growth.