Interactions between the carbon and nitrogen cycles under elevated CO2

The main topic of my PhD research was on the interactions between the carbon and nitrogen cycles under elevated CO2. We published a review paper synthesizing the ideas I developed during my PhD, describing my own view of the cascading effects of elevated CO2 in a quantitative framework. We review observations from CO2 experiments and suggest potential avenues that most likely explain these dynamics. This framework assumes differentiated effects of CO2 based on the type of mycorrhizal fungi the plant species associate with. The two main types of mycorrhizal fungi (arbuscular mycorrhizae -AM- and ectomycorrhizae -ECM-) have different nutrient economies (transfer different amounts of nutrients to their host plant), which causes differentiated growth and soil responses. Photosynthesis enhancement in response to rising CO2 increases the amount of carbohydrates that the plants can use for different purposes, including trading for nutrients with mycorrhizae, accentuating these dynamics.

Conceptual framework, representing the effects of elevated CO 2 under low nitrogen (N)‐acquisition costs in ectomycorrhizal (ECM ) systems (left) and high costs in arbuscular mycorrhizal (AM ) systems (right). The area within dashed lines represents plant N‐acquisition through N2‐fixation and external N‐fertilization. N inputs through N2‐fixation and N‐fertilization are relevant in ECM systems as well, but not drawn here. Tabulated values represent the inverse of the carbon (C) cost of N‐acquisition (urn:x-wiley:0028646X:media:nph14872:nph14872-math-0028, Eqn 1) and mean CO 2‐effects (%) on N‐acquisition (Nacq), leaf‐level photosynthesis (A sat), aboveground biomass production (ANPP ) and soil organic matter (SOM ) for ECM , AM , AM with N2‐fixing capacity and N‐fertilized systems derived from Figs 24. The CO 2 effect on A sat for AM  + N2‐fixers corresponds to the value reported in the meta‐analysis by Ainsworth & Long (2005) for legumes. Ctransfer, C exported to mycorrhizas, root exudation and symbiotic N2‐fixation; ECMF , ectomycorrhizal fungi; AMF , arbuscular mycorrhizal fungi; FLM , free‐living microbes; DOC , dissolved organic carbon; DON , dissolved organic nitrogen; R s, soil respiration; N2, atmospheric N; NFB , N2‐fixing bacteria; FERT , N‐fertilization. Differences in box‐size between AM and ECM systems represent differentiated changes in pool or flux size by elevated CO 2, and arrows inside boxes represent the sign of the CO 2 effect.

These are some of the main aspects of my research (click below to know more):

CO2 effects on plant biomass – the CO2 fertilization effect –

CO2 effects on soil carbon content – soil carbon storage –

Quantification of the terrestrial CO2 fertilization effect upscaling mycorrhizal effects on CO2 fertilization.