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When plant populations show local adaptation along climatic gradients, climate change may displace them from their current fitness optima. Unclear is whether foreign genotypes originating from sites that approximate future climatic conditions can attain higher fitness and support existing populations, because foreign genotypes may lack important adaptations to other local conditions besides climate. We conducted a fully reciprocal transplant experiment with the winter annual Biscutella didyma across four sites along a steep natural rainfall gradient in Israel. It experienced an exceptional drought event that approximated future climatic conditions. This unique opportunity allowed to test whether genotypes transplanted from drier sites outperform local genotypes under a drier climate. The four population origins showed consistent clines in germination fraction, phenology, and vegetative biomass that suggest local adaptation along the rainfall gradient. In terms of fitness (survival, seed number), however, local origins were outperformed by genotypes originating from the next‐drier site along the gradient. Our results suggest that the experienced drought conditions favored origins from drier conditions over local origins despite local biotic interactions. Genotypes originating from drier sites may thus support existing populations and reduce their vulnerability to climate change. Moreover, we conceptualize under which conditions foreign genotypes may benefit local populations in general, which adds to clarify the importance of local adaptation to climatic and nonclimatic factors for populations under climate change. [ABSTRACT FROM AUTHOR]

Altered rainfall regimes will greatly affect the response of plant species to climate change. However, little is known about how direct effects of changing precipitation on plant performance may depend on other abiotic factors and biotic interactions. We used reciprocal transplants between climatically very different sites with simultaneous manipulation of soil, plant population origin, and neighbor conditions to evaluate local adaptation and possible adaptive response of four Eastern Mediterranean annual plant species to climate change. The effect of site on plant performance was negligible, but soil origin had a strong effect on fecundity, most likely due to differential water retaining ability. Competition by neighbors strongly reduced fitness. We separated the effects of the abiotic and biotic soil properties on plant performance by repeating the field experiment in a greenhouse under homogenous environmental conditions and including a soil biota manipulation treatment. As in the field, plant performance differed among soil origins and neighbor treatments. Moreover, we found plant species-specific responses to soil biota that may be best explained by the differential sensitivity to negative and positive soil biota effects. Overall, under the conditions of our experiment with two contrasting sites, biotic interactions had a strong effect on plant fitness that interacted with and eventually overrode climate. Because climate and biotic interactions covary, reciprocal transplants and climate gradient studies should consider soil biotic interactions and abiotic conditions when evaluating climate change effects on plant performance. [ABSTRACT FROM AUTHOR]

Abstract Climate warming enables plant species to migrate to higher latitudes and altitudes. Within Europe, the Mediterranean harbours many species that might expand their ranges towards Western Europe. Small seed size may facilitate dispersal, however, it may impair establishment of the range-expanding plant species in the novel vegetation. In a greenhouse experiment, we examined effects of average seed size of Mediterranean plant species on their establishment in a mixed community of Western European plant species. Applying two levels of densities of the natives and a herbivory treatment, we tested how seed size is linked to response in plant growth and fitness in novel vegetation. While all non-native plant species showed a negative response to increased planting density, species with small seeds showed a less negative response. This effect persisted under herbivory. Our data suggest that small-seeded non-native plant species may tolerate competitive pressure from novel plant communities better than large-seeded species, so that small seed size may confer a higher probability of establishment of non-native species in novel communities. Highlights • Native plant communities can have a large role in the success of non-native plants. • Competition arising from high plant densities was more important than herbivory. • All non-native plant species showed a negative response to increased planting density. • Small-seeded species coped better than large-seeded species with high densities. [ABSTRACT FROM AUTHOR]

Predicting responses of plant communities to environmental changes is a key challenge in ecology. Here we examined climate-related mechanisms regulating seedling dynamics of a common Mediterranean shrub. Our objective was to analyze effects of water availability on seedling survival and to determine whether geographical gradients can serve as proxy for predicting local climate change effects. We conducted a field experiment along a natural rainfall gradient with additional long-term rainfall manipulations at a Mediterranean site, enabling the investigation of the relative importance of biotic and abiotic factors on seedling dynamics. Along the natural and artificial rainfall gradient seedling survival increased with increasing soil water availability. However, seedling survival at the Mediterranean site yielded a clear trend of decreasing seedling survival with artificially increasing aridity whereas at the dry end of the geographical gradient seedling survival was relatively high. We attribute this pattern to biotic interactions, which appeared less negative at the dry end. These findings indicate that ignoring biotic interactions is misleading when predicting shifts in the distribution of species under climate change and that because of the complex interplay between abiotic and biotic factors, environmental gradients can be poor proxies for predicting the response of plant species to climate change. [ABSTRACT FROM AUTHOR]