lecture+16+Ecosystems

Insoluble residue with few plant nutrients except a

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insoluble residue with few plant nutrients (except a lot of phosphorus remains because of its low mobility). Much later (millions of years later) even most of the relatively immobile phosphorus has been washed out of the soil. Element Source Mobility Abundance in the Ocean Nitrogen Atmosphere High Low Phosphorus Rocks Low Low Cations Rocks High High
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Bounded and Defined Systems Lakes are a good example of “bounded and defined” ecosystems; so are islands in the ocean. They share the features that their edges are clearly delineated and the influence of internal dynamics (within the lake or island) versus outside influences are relatively clear and constrained. They have been used as ‘model systems’ for ecosystem study, in a way similar to model systems in molecular biology.
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Organisms that Shape Ecosystems Some organisms can influence their geophysical environment: By changing its physical structure creating ponds or stabilizing dunes Through changing disturbance regimes Through altering resource supply Biological invasions are a good way to evaluate these influences. For example, the introduced tree Myrica faya in Hawaii colonizes young volcanic sites, where it grows rapidly in nitrogen poor soil. It can do this because it is a biological N fixer. The nitrogen Myrica fixes can be used by other organisms as well, so it alters how the whole ecosystem works.
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Control N Fert. Diameter Increment (mm/yr) 1 2 3 No Myrica Myrica N Inputs (kg ha -1 yr -1 ) 10 20 30 No Myrica Myrica N Avail. (mg m -2 14d -1 ) 0 1 2 3 No Myrica Myrica Earthworm Biomass (g/m 2 ) 10 20 30
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