Future nutrient limitations across ecosystems - a dual look at nitrogen and phosphorus
Short description
We develop a fast protocol with isotope techniques to determine if nitrogen (N) or phosphorus (P) limitation is present and possibly shifting in a natural terrestrial ecosystem. This is carried out across sites with widely different geological parent material and long-term weathering history (Sweden, Germany, Rwanda and Australia), e.g. different N or P limitation. Treatment with elevated atmospheric CO2 (EucFACE and GiFACE) will elucidate the response in nutrient limitations to climate change. The experimental work with soils consists of combined laboratory assays for determining gross N and P mineralization rates and N depolymerization rate. At ecosystem level, our method presents an instant assessment of the soil nutrient dynamics and availability.
In order to cover a severe knowledge-gap we need to obtain more empiric knowledge on N and P limitations and shifts between these, in ecosystems at a variety of soil types. As ecosystems age, N accumulates in soil through biological fixation, whereas available P is depleted from the soil through mineral weathering and occlusion during paedogenesis, therefore a shift from N to P limitation is suggested to progress globally at long term. Long-term paedogenic changes drive ecosystem development into ‘retrogression’ by declining nutrient (mainly P) availability, due to leaching and chemical transformation which occlude nutrients or through build-up of deep humus soils. This project includes soil types with a high variety of age and weathering history and a wide variety of assumed N and P limitation. With present and future global change the elevated atmospheric CO2 can ‘push’ ecosystem development towards a ‘younger’ progressive (regenerating) stage or towards a collapsing retrogressive stage. Implicit, the soil N and P availability changes via changes in gross N and P mineralization rates, with consequences for the nutritional value of the plant biomass (food for humans, their life stock and other plant feeders). The here measured gross Nmin and Pmin rates will result in a suggested ranking of the soils, as being richly or weakly supplying N and P, and hereby express the soil status on a relative scale of N and P limitation. This will be a fast alternative and supplement to traditional methods, and enables prediction of potential response (as being positive, negative or non-responding) to global warming and eCO2.
