R ecosys = Resp. of plants, animals, and soil microbes

2. 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

3. What types of ecosystems have… • Positive NECB (carbon sinks)? • NECB = 0 (carbon neutral)? • Negative NECB (carbon source)?

4. Ecosystem Carbon Balance Steady state = NEP near zero Inputs = outputs Ecosystem + 0 - Disturbance NEP (a very long) time Atmosphere

5. How does fire affect NEP?

7. Net Biome Production (NBP) = NECB, integrated over large spatial scales to include removal of C by fire and harvest Sensu Schultze et al. 1997

8. Ecosystem Carbon Balance NEP = GPP - Recosystem Recosystem = Rplant + Rheterotrophs Recosystem = (50%)Rplant + (50%)Rhet. Rheterotrophs = Rmicrobes + Ranimals Rheterotrophs = (90%)Rmicrobes + (10%)Ranimals

9. 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

10. Litter Decomposition

11. 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.

12. 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

13. 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)

14. 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)

15. Decomposition measured as mass loss through time using litterbags

16. Plant Litter Decomposition

17. 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

18. 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

19. 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

20. Decomposition rate varies according to substrate

21. Ecosystem Decomposition Environment Substrate Quality Species Composition Allocation (stems, leaves, wood) Species composition > Whole plant allocation > Within-tissue allocation

22. Ecosystem Decomposition