Modelling photodegradation in the global carbon cycle

Photodegradation has been shown to play a role in plant litter degradation in some ecosystems, and therefore potentially in the global carbon cycle. To introduce photodegradation into models of carbon turnover we need an equation that relates mass loss to incident radiation. Based on experimental data from the literature we developed a linear equation for photodegradation as a function of light exposure. We also scaled up the results to global scale, based on global data on incident radiation and shading by plant cover. The results indicate that photodegradation plays a part in semi-arid environments and potentially some arctic and alpine environment. However, the percentage of global plant production decomposed by photodegradation is estimated to be less than 1% (range 0.5–1.6). Photodegradation is therefore important locally, but probably not very important for the global carbon budget.

► Photodegradation can be described as a linear function of cumulative radiation interception.
► Using this model, photodegradation is predicted to be important in semi-arid areas, mountains and potentially arctic areas.
► Photodegradation is not an important carbon flux in the global carbon cycle, because areas where photodegradation is important are not very productive.