1. ECOSYSTEM ECOLOGY … the integrated study of biotic and abiotic components of ecosystems and their interactions. To achieve this integration: follow the path of matter and energy. Divides ecosystems into stores and fluxes.

2. Modeling pools and fluxes: X P : quantity of compound x in pool P in units of mass/area or mass/volume kg carbon m -2  mol NO 3 l -1 Q x, P1-P2 : flux density for compound X from pool P1 to pool P2 in units of mass/(area*time) or mass/(volume*time) kg carbon m -2 yr -1  mol NO 3 l -1 s -1 X PjPj Q X, P i -P j Q X, P j -P k

3. Modeling pools and fluxes: X PjPj Q X, P i -P j Q X, P j -P k

4. Fluxes are controlled by different sorts of processes, which determine their mathematical representation: X PjPj Q X, P i -P j Q X, P j -P k Case 1A: Chemostat (mixing of a constant volume):

5. C in = 0.2

6. X PjPj Q X, P i -P j Q X, P j -P k Case 1B: Mixing with volume change: W PjPj Q W, P i -P j Q W, P j -P k

7. C in = 0.2 Concentration C:Amount X:

8. N min Case 2: Biochemical cycles: N plant Plant uptake N litter Plant senescence Microbial mineralization

9. Notes: Michaelis-Menton relationship for nutrient uptake assumes saturation of uptake; Nutrients in a constant relation to total biomass in living organisms; stoichiometric ratios between nutrients maintained. N min N plant Plant uptake Plant senescence

10. Notes: Rates of loss are the same for all plant nutrients, when nutreint concentrations are assumed fixed. N plant N litter Plant senescence Microbial mineralization

11. N min N plant Plant uptake N litter Microbial mineralization

12. N min N plant Plant uptake N litter Plant senescence Microbial mineralization Notes: Total mass should be conserved in closed cycles.