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OUR Ecological Footprint - 13 1. 13. Pathways of Elements in the Ecosystem: Bio-geo-chemical (Nutrient) Cycles Objectives: • Elements and their uses • Spatial and temporal scales of ecosystems • General model of cycles in ecosystems • H2O, C, N, P, S cycles • Sources, sinks, pools • Chemical changes • Microbes involved • Human changes ***Elements and their uses in organisms • • • • • CHO: N, P, S: Ca, P: Fe, Mg: K, Na: • Green: focus on these cycles for macronutrients. Nutrients and their uses in organisms • • • • CHO - organic compounds and water N, P, S - proteins, nucleic acids Ca, P - bones, exoskeletons, cell membranes Fe, Mg - pigments, enzymes - hemoglobin, chlorophyll • K, Na - ionic balance, neural transmission • Physiological ecology and ecosystem ecology linked The fate of matter in ecosystems: Energy flows through the system once. Chemicals (nutrients) cycle = reused. Figure 1 Ecosystems can be large or small. Ecosystem boundaries can be arbitrary, but must be defined. Can be large spatial and temporal scales. ***What are the four compartments of the global ecosystem? For C, identify 4 natural processes that contribute to flux. • • • • Atmosphere (air) Biosphere (all organisms) Lithosphere (soil, rock, minerals) Hydrosphere (water) • Hence: bio-geo-chemical cycles Ecosystems modeled as linked compartments (box = pool; arrow = flux). Figure 2 What is measured in a nutrient cycle? • Pool: compartment (box); • (storage reservoir) gaseous (C, N, O) sedimentary (P, S, C) • Flux: amount / time / area or volume of movement between compartments (arrow) • Sink: pool with input/output increasing • Source: pool with input/output decreasing • Residence time = pool size/flux Human alterations affect cycles: • • • • • • size of pools, sources and sinks rates of flux residence time disturbances cause nutrients loss from one ecosystem pool and gain in another introduced species, e.g. N-fixing species Global BGC cycles: Water cycle: a physical model * Figure 3 How did sulfur get incorporated into coal? Of what consequence is its presence? ***Start at * and trace the water cycle. How do the numbers add up? Figure 3 Carbon cycle • closely tied to global energy flux • solar-powered • principal classes of C-cycling processes: 1) assimilation/dissimilation processes in plants/decomposers 2) exchange of CO2 between air and oceans 3) sedimentation of carbonates Classes of chemical transformations: • Assimilation processes: inorganic to organic, • uses energy (reduction) • Reducer = electron donor • Dissimilation processes: organic to inorganic, • gets energy (oxidation) • Oxidizer = electron acceptor Redox reactions Transformations of compounds in the carbon cycle. (GH gas) Microbes (GH gas) Figure 4 Most of the earth’s C is in sedimentary rock as precipitated calcium carbonate. ***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered? Figure 5 Figure 6 ***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered? The missing C sink ORNL FACE experiment Figure 7 Duke FACE experiment 18 year-old forest; 6, 30-m plots; ~100 pine trees/plot; ~50 woody species; 8 years of CO2 Carbon budget for pine and sweetgum forests exposed to elevated carbon dioxide Units: gC m-2 y-1; Open bubbles, ambient plots; closed bubbles, fumigated plots. E. DeLucia, unpub. G • Generate an ‘if-then’ to answer the ?: • “Is plant productivity CO2-limited?” The C-cycle in a semi-arid grassland. How will rising CO2 affect its productivity? Why are there 3, not 2, treatments? What is the conclusion? Figure 8 Do all species respond similarly to elevated CO2? Qualify the earlier results. Figure 9 Additional mechanisms that arise with elevated CO2… • Needle grass under elevated CO2 was less digestible by grazers than under ambient CO2. • What’s the ‘take-home’ message about future plant productivity and food available to cattle and other grazers? • Needle grass had greater productivity. Why? • Plots with elevated CO2 had more soil water. • Create a scenario that accounts for the increase in soil moisture. • Include: acclerated CO2 assimilation, stomates, transpiration, WUE, withdrawal of water from soil *** What caused the large drop in CO2? Predict what happened to earth’s temperature from the peak to the dip in CO2. Figure 10 Carboniferous forest: a huge sink for C Fossil soils reveal changes in the biosphere. Nitrogen cycle: N assumes many oxidation states; microbes play essential roles. 4 -3 NH4 3a 1 3b 2a 2b i 5 +3 Figure 11 Nitrogen fixation using nitrogenase (anaerobic): convert N2 to NH4 • • • • Figure 12 Blue-green algae Bacteria e.g. Rhizobium (symbiotic with legumes) lightning; volcanoes Many legumes are N-limited unless infected by Rhizobium. Phosphorus cycle includes few chemical changes of PO4-3. Solubility less with low + high pH. Losses to sediments.***What are consequences? Figure 13 Mycorrhizae: symbiosis (mutualism) of fungi/plant roots How mycorrhizae work: Figure 14 • penetrate large volume of soil • secrete enzymes/acids - increase • solubility of nutrients, especially P • consume large amount of plant C ***What is one basic hypothesis/prediction being tested? Do the data support the prediction? Figure 15 Sulfur cycle: used in 2 amino acids Sulfur exists in many oxidized and reduced forms; many microbes. -2 2 5 4 3 1 +6 Figure 17 How did S get incorporated into coal? • When non-decomposed plants got buried in swamps, allowing these anaerobic processes to proceed. Of what consequence is its presence? • strip-mine - sulfuric acid into streams. • burn high-S coal, increase acid rain --> both lower Ca in soils, lower forest productivity. Also lower pH in lakes disrupts aquatic community.