Light availability experienced in the field affects ability of following generations to respond to shading in an annual grassland plant

Summary For plants competing for light, grasslands represent complex environments. Grassland microhabitats vary in the amount of available light and in the spatial distribution of patches with full sunlight, light shade and deep shade. Plant populations have been shown to adapt to specific competitors and shading conditions, but it is an open question how tightly the responses of populations to different shading situations are linked to the light availability previously experienced in the field. Using maternal families collected in grasslands ranging from open to closed canopies, I tested the effects of no shading, homogeneous and heterogeneous shade created in the glasshouse on trait expression in the annual Erodium cicutarium . Heterogeneous shading was simulated by a patchwork of single and double layers of light filters lowering the R:FR ratio of transmitted light and clear filters simulating gaps. Heterogeneous shading induced a stronger shade avoidance response than homogeneous shading, with larger leaf length, greater vegetative height and larger specific leaf area. Time to first flowering was longer under heterogeneous shading, and plants produced less fruits. Populations differed in their time to first flowering under the shading treatments, and these differences could be traced back to light availability measured in the field. Plants from populations with lower light availability showed a postponed date of first flowering even if they were not shaded. These differences were attributable to plasticity of the maternal families. Across shading treatments, plants from low‐light environments produced more above‐ground biomass. Synthesis . This study indicates that there is a close linkage between the light availability experienced in the field and the ability of following generations to respond to shading. Low average light availability experienced in the past seems to induce a trade‐off of vegetative growth against early flowering, providing the following generations with the capacity to overtop neighbours. This capacity is utilized especially if plants experience a mixture of gaps and deep shade.