干旱区生态环境知识资源中心

Plant facilitation studies commonly test the nurse-plant hypothesis wherein an adult shrub species enhances the establishment of associated herbaceous species under its canopy. Using field and glasshouse experiments, this hypothesis is extended by testing the following four predictions: (1) nurse-plant effects can occur between species with similar life-forms and phenologies (2) positive effects are species specific, (3) the outcome of interactions is life-stage dependent, and (4) facilitative interactions among annuals are primarily commensal. In the Negev Desert in Israel, the response of an annual plant community to removal of relatively larger annuals, Erodium laciniatum, Erucaria pinnata and Trifolium tomentosum, was tested in the field and in the glasshouse. Removal of these dominants was applied early in the growing season, immediately after germination but before establishment of seedlings, and again mid-season following establishment and growth to adults. In both the field and glasshouse, the presence of E. laciniatum increased establishment and survival to reproduction of neighbouring plants. These positive effects were life-stage dependent with more positive effects occurring early in the season, and there was no cost of facilitation to E. laciniatum. This positive effect was species specific in that neither E. pinnata nor T. tomentosum had an effect on the plant community. There was also a cost of association with the nurse E. laciniatum in that biomass of neighbours was reduced. These experiments demonstrate that the positive effects typically detected at larger scales between species of different life-forms are also occurring at finer spatial scales amongst annuals. This study clearly supports the predictions made in the facilitation literature that effects are species-specific and highly life-stage dependent.