Nutrient cycling in ecosystems: Lecture Content. Introduction to nutrient cycles Driving forces for nutrient cycles in ecosystems Water (hydrological) cycle as a physical model of nutrient cycling Case study of N, Ca limitation: Hubbard Brook Experimental Forest, NH
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What dets comm structure, comp, distribution? Big scale, big picture things….. E in system, nutrients, solar radiation, rain…….=productivity.
Means that Sun+nutrients + water = plants
Herbivores eat them, preds eat them…….
E always lost w. each transformation from one trophic level to next…..
(What is missing? (Omnis).
Primary production –Unabsorbed energy given off as heat. Photosynthesis, Respiration
Secondary production – wastage (bones, stems, uneaten material, ie. Production and Consuption efficiencies), heat
Trophic level transfer efficiency is around 10%.
What OTHER very important trophic level receives lots of available energy due to inefficiency of primary producers and secondary producers (consumers)?
What are the limits, determinants of primary production (see biome lecture!)
Secondary productivity- well…. Primary productivity
Atmospheric cycles (e.g., N)
Energy releasing reaction is paired with energy requiring one; oxidation side must release more energy than reduction side requires; rest lost as heat
Assimilatory reactions (e.g., photosynthesis) incorporate inorganic forms of nutrients (e.g., carbon) into organic forms (e.g., carbohydrates); dissimilatory rxns. the reverse
Represents difference between evaporation and precipitation over sea, i.e., 425 - 385
Global hydrological cycle drives other cycles (units g18 = teratons (tt) = 1012 metric tons for pools (dark blue). Fluxes in light blue, units of tt/yr.
Represents difference between precipitation, & evaporation, i.e., 111 - 71
25% of total solar radiation on Earth used to drive hydrological cycle!
97% of global H2O pool in oceans
Which nutrient cycles to study? Those that are most limiting to plants (& thus ecosystems), i.e., N, P, S, sometimes Ca because demands high relative to supply (soils, lakes, oceans)
Nitrogen budget for forested watershed, Hubbard Brook Experimental Forest (values in boxes are pool sizes, kg/ha; arrows give fluxes in kg/ha/yr)
Clean-air Act, 1970
Acknowledgements: Some illustrations for this lecture from R.E. Ricklefs. 2001. The Economy of Nature, 5th Edition. W.H. Freeman and Company, New York.