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Abstract. 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.

Soil depth may affect plant diversity in two apparently opposing manners: on the one hand, deeper soil may increase the available space for below‐ground niche partitioning, on the other hand, soil depth may have a negative effect on plant diversity by increasing productivity and the rate of competitive exclusion. Due to the scarcity of experimental studies that actively manipulate soil depth, the conditions under which each mechanism dominates are still unclear. Here, we studied the interactive effects of soil depth with common land use practices, namely, nutrient addition, trampling by grazers and mowing on plant diversity in grasslands. We manipulated these factors in a full‐factorial manner in grassland mesocosms. Soil depth had a strong positive effect on species richness under mowing, suggesting increased space for niche differentiation in deeper soils. In unmown plots, deep soils harboured a similar diversity of species as shallow soils, and our findings suggest that this effect on diversity is due to larger biomass and lower light availability on deep soils. Fertilization and trampling had no effect on diversity. Overall, our findings indicate that soil depth effects on grassland communities strongly interact with common land use practices. We therefore advocate the inclusion of soil depth effects in manipulative experiments and management plans.