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Ecosystem Carbon Balance. Net Ecosystem Carbon Balance (NECB ) = GPP - R ecosys other C transfers. R ecosys = Resp. of plants, animals, and soil microbes. NECB = NPP F lateral R heterotrophic -F disturb -F leach -F emiss. What types of ecosystems have….
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Ecosystem Carbon Balance Net Ecosystem Carbon Balance (NECB) = GPP - Recosys other C transfers Recosys= Resp. of plants, animals, and soil microbes • NECB = NPP Flateral • Rheterotrophic • -Fdisturb • -Fleach • -Femiss
What types of ecosystems have… • Positive NECB (carbon sinks)? • NECB = 0 (carbon neutral)? • Negative NECB (carbon source)?
Ecosystem Carbon Balance Steady state = NEP near zero Inputs = outputs Ecosystem + 0 - Disturbance NEP (a very long) time Atmosphere
Net Biome Production (NBP) = NECB, integrated over large spatial scales to include removal of C by fire and harvest Sensu Schultze et al. 1997
Ecosystem Carbon Balance NEP = GPP - Recosystem Recosystem = Rplant + Rheterotrophs Recosystem = (50%)Rplant + (50%)Rhet. Rheterotrophs = Rmicrobes + Ranimals Rheterotrophs = (90%)Rmicrobes + (10%)Ranimals
Ecosystem Carbon Balance Rmicrobes = respiration by bacteria, fungi Respiration from microbes occurs in conjunction with decomposition Decomposition is the physical and chemical breakdown of dead organic matter
Plant Litter Decomposition Three phases: 1. Leaching by water. Removes soluble materials (nutrients, simple C compounds) 2. Fragmentation by soil animals. 3. Chemical alteration. Changes chemical composition of detritus.
The role of microbes: phase 3 Chemistry is altered as microbes break down organic matter molecules Compounds are decomposed at different rates, new compounds are synthesized Microbial activity controlled by: Environment: soil T, H2O, soil O2 Substrate: chemical makeup of organic matter
Fungi Accounts for most aerobic decomposition - 60-90% of microbial biomass in forests - About half of microbial biomass in grassland • Broad enzymatic capability • - Cell walls (lignin, cellulose, hemicellulose) • - Cell contents (proteins, sugars, lipids) • Can transport metabolites through hyphae • Surface litter (import nitrogen from soil) • Wood degraders (import nitrogen from soil)
Bacteria • Grow rapidly on labile substrates • Some function anaerobically • Dependent on substrates that diffuse. Diffusion gradient caused by • Production of soluble substrates (enzymes) • Uptake of substrates by bacterium • Spatial specialists • Rhizosphere, macropores, interior of aggregates • form biofilms on particle surfaces • Chemical specialists • Different bacteria produce different enzymes (consortia)
Decomposition measured as mass loss through time using litterbags
dM/dt = -kM Litter bags Litterfall = k x litter pool Mass balance litterfall k = litter pool Litter mass declines exponentially with time Mt = M0 *e-kt At steady state, K calculated from both approaches should be equivalent Turnover time (TT) = 1/k
Plant Litter Decomposition Microbial activity controlled by: Environment: soil T, H2O, soil O2 Substrate: chemical makeup of organic matter Rate of microbial activity determines rate of C loss, nutrient release etc. Rate of activity measured as organic matter mass loss =decomposition
Substrate quality depends on: 1. Size of molecule • 2. Types of chemical bonds. • sugars,proteins,organic acids > cellulose, hemicellulose >lignin, tannins 3. Regularity of structure 4. Toxicity C:N ratio? 5. Nutrient concentrations
Ecosystem Decomposition Environment Substrate Quality Species Composition Allocation (stems, leaves, wood) Species composition > Whole plant allocation > Within-tissue allocation