Altered rainfall regimes are predicted to greatly affect the response of plant species to climate change, particularly in water-limited and densely populated regions where plant communities face the risk of extinction. In the past, the interactive effects of biotic interactions and abiotic factors on plant fitness have garnered considerable interest, but only a few empirical studies have addressed the effects of biotic interactions on plant responses to climate change. We tested the effects of plant-plant and plant-soil biota interactions in determining adaptive responses of four Eastern Mediterranean annual plant species to climate change. We applied reciprocal seed sowing and soil transplants, combined with neighbor manipulations, between two sites with Mediterranean and semi-arid climates. Furthermore, to separate the effects of abiotic and biotic soil properties on plant performance we repeated the field experiment in a greenhouse, including soil-biota manipulation treatments. We predicted that if plant ecotypes were adapted to local conditions then they would experience 1) a home-site advantage, 2) home-soil advantage, and 3) higher competitive ability from communities with higher species richness.
Results/Conclusions
Contrary to our expectations, the field experiment showed that the direct effect of site (i.e. climate) on plant performance was negligible, but soil origin had a strong effect on fecundity, most likely due to differential water-holding capacity. Furthermore, competition by neighbors had a similarly negative effect on both (home and away) ecotypes. Results from the greenhouse experiment were mostly consistent with the findings from the field experiment. However, we observed plant species-specific responses to soil biota that suggest differential sensitivity to negative and positive soil-biota effects. Overall, we found that biotic interactions had strong effects on plant fitness, but climate acted as a filter on the importance of plant-soil biota interactions. Thus, integrating biotic interactions in predictions of plant responses to climate change will better inform conservation strategies and our understanding of plant ecosystems.