Elements & energy : modelling nutrient and population dynamics under global change

Global change is affecting biomass production and the functioning of biological systems, which are both essential for the provision of ecosystem services. Global warming and changing nutrient cycles are two major global change drivers that have a strong influence on plant growth, and therefore on biomass production of the whole ecosystem. To improve our understanding of the pathways through which these drivers influence plant growth, I investigated the temperature-dependency of plant nutrient uptake and developed a nutrient-explicit model. To broaden our knowledge on the importance of flexibility in the response of populations to global change, I developed models that included realistic flexibility in the stoichiometry (elemental balance) of the plant and gave the herbivore the ability to react to changing food quality by adjusting their feeding rate. I found that with rising temperature, the maximum amount of nutrients that plants can take increases. At low nutrient supply, however, their uptake efficiency decreases. With my population dynamics model, I show that including temperature-dependent nutrient uptake by the plant results in decreased community biomass with temperature. Allowing plants to vary their carbon uptake dependent on the nitrogen supply results in an increase in community biomass. The herbivore benefits from the higher quantity of plant tissue available. This increase fully compensates for the decrease in food quality for the herbivore. Compensatory feeding as a reaction to decreased food quality does not appear to be a beneficial strategy for the herbivore as it causes depletion of their resource through ‘overfeeding’. Through these studies, I show how important it is to consider the interaction of several global change drivers. Furthermore, to avoid over- or underestimation, it is crucial to consider adaptive strategies available to the different organisms, as they can modulate the impact of global change on ecosystem functioning.