Johanna Pihlblad


PhD Candidate

Thesis title

Mechanisms by which nitrogen availability for plants changes under elevated CO2

Research project

Increasing atmospheric CO2 concentrations are expected to change the rate of net primary productivity of the biosphere. However, Free-Air Carbon dioxide Enrichment (FACE) experiments have resulted in a wide range of observed responses in ecosystem productivity that currently cannot be explained by general climate mechanisms. The dynamic responses reported, and the would-be increase of net primary production, is believed to be constrained by the availability of nutrients in the soil.

While nitrogen is considered the main nutrient limiting productivity there is increasing evidence of the important role of phosphorus to sustain growth under elevated CO2. With elevated atmospheric CO2, plants photosynthesis becomes more effective and additional carbon can be assimilated. However, to sustain the increase in photosynthesis and biomass growth plants have a higher demand and subsequently need to acquire nutrients from the soil. By exuding labile carbon rich compounds, plants interact with the soil microbial community in the rhizosphere by stimulating activity, to release nutrients, with consequences for the decomposition rate of soil organic matter (SOM). The decomposition of SOM under elevated CO2 is of major importance both as a source of nutrients in unmanaged forest ecosystems and as a powerful feedback for soil carbon to the atmosphere with the potential to further force climate change.

Mechanistic drivers of soil nutrient stoichiometry, microbial activity, nutrient availability, plant growth, and carbon feedback to the atmosphere under elevated CO2 are connected, but currently poorly understood and constrained. My aim is to study the soil microbial transformations of nitrogen and carbon in rhizosphere soil under different phosphorus availabilities and elevated CO2. I will use stable isotope techniques to look at gross rates of parallel transformations and dynamic pools of nitrogen and carbon to further the understanding of changing nutrient availability in the context of climate change.


Wild B, Li J, Pihlblad J, Bengtson P, Rutting T, (2019) 'Decoupling of priming and microbial N mining during a short-term soil incubation', Soil Biology and Biochemistry, vol.129, pp 71-79


Dr Yolima Carrillo, Professor David Ellsworth, Dr Catriona Macdonald, and Dr Louise Andresen (UGOT)