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BIOL 121
Carol Pollock

Biol 121 225 Freeman 1230-42 Jan. 20, 10 Biogeochemical cycle -energy is not the only thing transferred in a food web/chain -ingested matter also contain carbon, nitrogen, phosphorus, calcium, and other elements that act as nutrients -atoms are constantly reused as they cycle through trophic levels and air, water, and soil -path element takes as it moves from abiotic systems through organisms (biotic) and back again is the biogeochemical (“life-Earth-chemical”) cycle -humans disturb biogeochemical cycles on massive scale, so research is exploding What kinds of questions are posed 1) What are the nature and size of the reservoirs, or areas where elements are about biogeochemical cycles? stored for a period of time? (e.g. C is stored in biomass of organisms, also sediments, soils, coal and oil) 2) How fast does the element move between reservoirs, and what factors influence these rates? 3) How does a biogeochemical cycle interact with other cycles? General terrestrial nutrient cycle -cycle starts when nutrients taken up from soil by plants and assimilated into plant tissue -if plant eaten, nutrients pass to animal members of ecosystem’s consumer food web; if plant dies then nutrients enter decomposer food web -once consumed by animal, nutrients excreted and taken up by parasite or predator, or added to the dead biomass reservoir when the animal dies -nutrients in plant litter, animal excretions, dead bodies are used by primary composers like bacteria -the combo of microscopic decomposers and ions/mcules released form the soil organic matter -soil organic matter is a complex mixture of partially and completely decomposed detritus completely decayed organic material is humus b/c it is rich in family of C- containing mcules called humic acids -eventually, nutrients in soil organic matter converted to an inorganic form -e.g. cell resp by bacteria converts nitrogen in AA found in detritus to NH4+ and NO3- ions – nutrients are available for uptake by plants Reuse of nutrients -in the general terrestrial nutrient cycle described above, nutrients are reused -however, reuse is not complete -nutrients leave ecosystem whenever plant/animal biomass leaves -e.g. plant biomass is removed if herbivore enters ecosystem, eats plant, and migrates out of ecosystem before excreting nutrients or dying -also, flowing water or wind removes particles/inorganic ions to deposit somewhere else -soil erosion removes nutrients rapidly and in potentially large quantities What are factors of rate of nutrient -decomposition of detritus most often limits overall rate at which nutrients move cycling? through ecosystem -until decomp occurs, nutrients stay tied up in intact tissues -decomposition rate, in turn, is influenced by two types of factors: abiotic conditions (T, ppt) and quality of the detritus as a nutrient source for the decomposer(s) Biol 121 225 Freeman 1230-42 Jan. 20, 10 How do abiotic conditions affect -abiotic conditions like temp and ppt can affect nutrient cycling nutrient cycling? -e.g. in boreal forest, decomposition rate limited by cold soil temp – organic matter builds up b/c detritus input into soil exceeds decomp rate -the cold and wet conditions in boreal forests limit metabolic rates of decomposers -in contrast, in tropics, conditions are favourable for fungi, bacteria, archaea so decomp keeps pace with detrital inputs -nutrients cycle slowly in boreal forest, quickly in wet tropics How does quality of detritus affect -e.g. decomposers can be inhibited by presence of large compounds in detritus rate of nutrient cycling? hard to digest like lignin -that is why wood takes much longer to decompose than leaves do -growth of decomposers also inhibited if detritus is low in nitrogen What factors influence rate of -human activity like farming, logging, burning, soil erosion accelerate nutrient nutrient loss? loss in ecosystems -devegetation has a huge impact on nutrient export -instead of being held in the ecosystem and recycled, nutrients wash out in the absence of vegetation – nutrients in soil are either dissolved in water or attached to small particles of sand or clay Global biogeochemical cycles -when nutrients leave one ecosystem, they enter another -in this way, movement of ions and mcules among ecosystems links local biogeochemical cycles into one massive global system -local and global cycles interact when water, organisms, or wind move nutrients Global water cycle -evap of water out of ocean and subsequent precipitation of water back into ocean -evaporation exceeds precipitation over the marine area: net gain to atmosphere -when this water vapour moves over continents (wind) then joined by small amount of water that evaporates from lakes and streams and a large volume of water that is transpired by plants -total volume of water in atmosphere over land is balanced by amount of rain and other ppt that occurs on the continents -cycle is completed by water that moves from land to oceans via streams and groundwater (groundwater is water found in soil) How do humans affect the global -asphalt and concrete surfaces reduce amount of ppt to enter deep soil layers water cycle? -conversion of grasslands/forests into agricultural fields increases amount of water running off Earth’s surface into streams instead of penetra
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