Facilitation: A novel mechanism of adaptive capacity

One of today’s largest concerns is the worldwide rapid degradation of ecosystems due to human-induced environmental change. If these environmental changes occur too fast for species to adapt, biodiversity will further decline, with negative impacts for ecosystem functioning and human wellbeing. Hence, it is of crucial importance to understand which mechanisms allow species to timely adapt. Interspecific plant facilitation (positive species interactions) may be one of these mechanisms. Facilitation plays an important role in upholding plant species diversity, especially in drylands that are particularly vulnerable to climate change. However, the role of interspecific facilitation for the adaptive diversity and eco-evolutionary dynamics in plant communities has so far received little attention. In this project, we hypothesize that interspecific facilitation can act as a mechanism of adaptive capacity: facilitation by nurse plants may conserve genetic variation in beneficiary species that promotes their adaptive capacity to new environmental conditions. To test this novel hypothesis, we propose a combination of reciprocal experiments, greenhouse studies, molecular analyses, and dynamic modelling. As a study system we will use Brachypodium distachyon, a model grass with a sequenced genome that has been intensively studied by the agricultural community. In a field study in southern Spain, we will compare B. distachyon populations with and without facilitating nurse plants (bunch grass Stipa tenacissima) in terms of physiological traits (photosynthesis, gas exchange, water use efficiency, stomatal conductance, transpiration, phenology, growth rate, biomass) and genetic variation using recently developed microsatellites (simple sequence repeat: SSR). In a reciprocal sowing experiment, we will sow seeds from facilitated populations into bare patches, and seeds from unfacilitated populations under the canopy of S. tenacissima, and follow plant performance and ecophysiological traits. In a supplementary greenhouse study, we will grow plants from facilitated and unfacilitated populations, as well as their crossbred line, and subject plants to a combination of drought and temperature treatments for multiple generations. We will select for plants with the highest fitness (e.g. reproductive traits) and test for evolved adaptive capacity and fitness to elevated drought and temperature. In parallel with the empirical studies, we will develop a simulation model to predict how the adaptive diversity and eco-evolutionary dynamics of beneficiary plants evolve over time under different environmental scenarios. Our project will lead to an improved understanding of facilitation for the adaptive diversity and evolutionary dynamics of beneficiary plants, a potential novel mechanism for plant species to cope with ongoing environmental change.