Carnivorous plant responses to resource availability: environmental interactions, morphology and biochemistry

Understanding how organisms respond to resources available in the environment is a fundamental goal of ecology. Resource availability controls ecological processes at all levels of organisation, from molecular characteristics of individuals to community and biosphere. Climate change and other anthropogenically driven factors are altering environmental resource availability, and likely affects ecology at all levels of organisation. It is critical, therefore, to understand the ecological impact of environmental variation at a range of spatial and temporal scales. Consequently, I bring physiological, ecological, biochemical and evolutionary research together to determine how plants respond to resource availability.

In this thesis I have measured the effects of resource availability on phenotypic plasticity, intraspecific trait variation and metabolic responses of carnivorous sundew plants. Carnivorous plants are interesting model systems for a range of evolutionary and ecological questions because of their specific adaptations to attaining nutrients. They can, therefore, provide interesting perspectives on existing questions, in this case trait-environment interactions, plant strategies and plant responses to predicted future environmental scenarios.

In a manipulative experiment, I measured the phenotypic plasticity of naturally shaded Drosera rotundifolia in response to disturbance mediated changes in light availability over successive growing seasons. Following selective disturbance, D. rotundifolia became more carnivorous by increasing the number of trichomes and trichome density. These plants derived more N from prey and flowered earlier. This suggests that D. rotundifolia extend their fundamental niche in part due to phenotypic plasticity into environments that are shaded and are, for non-carnivorous plants, high in stress and disturbance—untenable environments according to universal adaptive theory.

In an observational study on peatlands across Europe, I investigated how habitat heterogeneity and climate-driven changes in nutrient availability impact on D. rotundifolia trait variability. I found that patterns of hydrology and light are consistent across peatlands. But, climate driven N accumulation alters the expression of carnivory which can reverse expected patterns of trait expression. These findings have implications for predicting the ecological impacts of climate change, as patterns of precipitation and evaporation may have different consequences depending on specific local topology and climate norms and can have significant impacts at small spatial scales, to the extent that entire habitats may be lost.

I conducted a research review to determine the role of secondary plant metabolites in carnivory. This identified similar patterns of metabolite production among closely- and distantly-related carnivorous taxa, which suggests that secondary metabolites are important for plants to facilitate carnivory. The review supports the hypothesis that secondary plant metabolites are drivers of plant diversification and evolution of plants into new environments.

In a laboratory experiment using Drosera capensis, I measured the metabolic response of trap tissue to simulated prey capture, using an omics approach. There was a substantial response to simulated prey capture. More compounds were up-regulated following prey capture than expected (over 30 times more than currently identified across all carnivorous species). In addition, changes in several metabolites suggested that their function is different to that previously reported.

The findings of this thesis highlight substantial phenotypic plasticity and intraspecific trait variation as a means for plants to cope with environmental resource availability and variability. Furthermore, it is clear that climate interacts with processes of nutrient availability, hydrology, and subsequent vegetation patterns which means that accurate predictions of species responses to climate change must be highly contextualised to local environments. The findings of this thesis also suggest that secondary metabolites may hold a significant role in the response and survival of plants to changing environments as they have the propensity for plants to adapt at a rate faster than mutation.