Stoichiometric And Hydro Climatic Controls On Soil And Litter Mineralization

The cycling of carbon, nitrogen, and other nutrients through vegetation and soils has major effects on global-scale climate, agricultural productivity, and natural ecosystem dynamics. The release of carbon dioxide from soil organic matter mineralization actively contributes to global climate change, while the availability of nutrients (nitrogen and phosphorus in particular) in the soil constrains vegetation growth. A proper management of soil carbon and nutrient dynamics may allow reducing carbon emissions to the atmosphere, and optimizing agricultural production. For soil management to be successful there is a need for a quantitative understanding of soil carbon and nutrient processes. Mathematical models have thus been developed to describe soil processes at spatial scales ranging from few microns to thousands of kilometers and temporal scales spanning seconds to centuries. In this dissertation, the theory behind these mathematical models is critically revisited and extended to explore the mathematical and practical limitations of some model formulations and to unify different theoretical approaches. The main focus is on the effects of climatic variables and stoichiometric constraints on soil and plant residue decomposers, which are the predominant drivers of carbon and macro-nutrient mineralization from plant residues and soil organic matter. More specifically, the results suggest that nonlinear decomposition models are best suited to quantify carbon dynamics at short time scales where the interactions between the decomposers and their substrate is stronger, while linear models can be used at longer scales. Linear stability analysis of the nonlinear models also demonstrated that the climatic factors control the dynamic behavior of the soil system. Nutrient dynamics are tightly coupled to carbon evolution in soils and decomposing plant residues. Such coupling is primarily regulated by the stoichiometric requirements of the decomposers, which are shown to be more important than climatic variables in shaping the global scale patterns of accumulation and release of nitrogen and phosphorus in decomposing plant residues. A major consequence of these stoichiometric constraints is that decomposer respiration rates tends to increase in response to low nutrient content of the residues, suggesting that mechanisms of carbon overflow may be more important than currently thought.