Inbreeding limits responses to environmental stress in Silene vulgaris

Phenotypic plasticity enables plants to respond to different environmental conditions by changing morphological and physiological traits and patterns of biomass allocation. However, it is not well understood how these responses are influenced by inbreeding. We grew clones of self- and cross-pollinated offspring of Silene vulgaris (Caryophyllaceae) and measured a number of functional traits involved in stress responses under eight different treatments, including a control, drought, copper addition, simulated herbivory, and two levels of nutrient deficiency and shade. Inbreeding influenced phenotypic plasticity in some functional traits. In particular, the environmental sensitivity of four traits - stem length, leaf area, leaf chlorophyll content and specific leaf area - was lower in offspring from self-than from cross-pollination. Biomass allocation patterns changed in response to the environment in agreement with optimal partitioning theory, but were not influenced by inbreeding. Two traits potentially involved in general stress response - leaf senescence and anthocyanin production - were increased under copper stress and nutrient deficiency but reduced in the herbivory and shade treatments. Inbreeding did not increase these general stress responses, but reduced anthocyanin production in all stress treatments. Our findings suggest that by reducing phenotypic plasticity, inbreeding may limit the ability of plants to cope with changing environmental conditions.