Ecosystem retrogression and its effect on Betula pubescens : Adaptations and responses to nutrient availability and its implications for plant palatability | Degradering av ekosystem och dess påverkan på Betula pubsecens : Växtanpassningar till -, och gensvar på näringstillgång och dess betydelse för betespreferenser

Plants adapt genetically and phenotypically to abiotic and biotic environmental conditions, and associated changes in their traits and investment strategies may affect their palatability to herbivores. This study aims to investigate if ecosystem retrogression results in heritable adaptation of Betula pubescens and how this impacts seedling growth, response to fertilizer, and palatability to the herbivore Spodoptera littoralis. Seeds were collected from a retrogressive island chronosequence for which nutrient availability increased with island size. Seeds were grown in a common garden and a fertilizer experiment was carried out to analyze genetic and phenotypic adaptations to nutrient availability. A bioassay using S. littoralis larvae was conducted to reveal the effect of adaptations to nutrient availability and herbivory on plant palatability. Only the root-to-shoot ratio indicated any heritable adaptation, being higher for seedlings originating from small islands. Seedlings showed highly plastic responses to fertilizer, indicative of an increased acquisition of resources. The palatability of B. pubescens was mainly determined by a tradeoff between leaf dry matter content and specific leaf area and was reduced by induced defenses. The acquisition of resources, growth, and reproduction of B. pubescens appears to be driven largely by phenotypic plasticity rather than prior genetic adaptation. Since all treatment responses were independent of island size, the whole population may be resilient to future changes in environmental conditions. The study revealed that ecosystem retrogression does not have to result in heritable plant adaptations, even if changes in ecosystem conditions can be substantial. It is of great importance to gain more knowledge on how species may adapt to future changes in environmental conditions over different timescales, both to naturally and anthropogenically induced changes.