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 H 2 O, 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? 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

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 ***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 CO 2 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. CO2 + H2O-> H2CO3 -> H+ + carbonate ions-> Carb. ions + Ca++ -> CaCO3 (calcium carbonate)

***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered? Figure 5

***Carbon cycle: What are 2 new fluxes due to human activities? What pools are being altered? The missing C sink Figure 6

ORNL FACE experiment Figure 7

Duke FACE experiment 18 year-old forest; 6, 30-m plots; ~100 pine trees/plot; ~50 woody species; 10 years of CO 2

Units: gC m -2 y -1 ; Open bubbles, ambient plots; closed bubbles, fumigated plots. E. DeLucia, unpub. Carbon budget for pine and sweetgum forests exposed to elevated carbon dioxide

G Generate an ‘if-then’ to answer the ?: “Is plant productivity CO2-limited?”

*** What caused the large drop in CO 2 ? Predict what happened to earth’s temperature from the peak to the dip in CO 2. Figure 10

Carboniferous forest: a huge sink for C

Nitrogen cycle: N assumes many oxidation states; microbes play essential roles. NH4 1 3b 2a 2b 3a i Figure 11

Nitrogen fixation using nitrogenase (anaerobic): convert N2 to NH4 Blue-green algae Bacteria e.g. Rhizobium (symbiotic with legumes) lightning; volcanoes Figure 12

Many legumes are N-limited unless infected by Rhizobium.

Phosphorus cycle includes few chemical changes of PO Solubility less with low + high pH. Losses to sediments.***What are consequences? Figure 13

Mycorrhizae: symbiosis (mutualism) of fungi/plant roots

How mycorrhizae work: penetrate large volume of soil secrete enzymes/acids - increase solubility of nutrients, especially P (N?) consume large amount of plant C Figure 14

***What is one basic hypothesis/prediction being tested? Do the data support the prediction? Figure 15

Sulfur cycle: used in 2 amino acids Figure 16.

Sulfur exists in many oxidized and reduced forms; many microbes Figure 17

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. How did S get incorporated into coal?