421.2 Variety of organisms involved in decomposition Decomposition is the breakdown of chemical bonds formed during the construction of plant and animal tissues.Processes: leaching, fragmentation, changes in physical and chemical structure, ingestion and excretion of waste products.Bacteria are dominant decomposer (animal)Fungi (plant)Aided by detritivores4 major groupsMicrofauna(flora), mesofauna, macrofauna, and megafaunaProtozans and nematodes to earthwork and millipeds
521.3 Decomposition rate measurement Litterbag methodMesh bagMass of remaining in the bag includes both original plant matter as well as bacteria and fungi that have colonized and grown on the plant litter.Figure 21.3Carbon is lost to the atmosphere as CO2 in the process of respiration
6Based on the data, the decomposition rate can be calculated Figure 21.4
7Decomposition rate calculated as k=0. 0097 wk-1 and 0 Decomposition rate calculated as k= wk-1 and wk-1 for two tree species
821.4 Rates of Decomposition and influencing factors Rate at which nutrients are made available to primary producers is determined largely by rate of decomposition.influenced by:temperature,moisture,chemical compositions of leaves
9Influencing factors Quality of litter And (Physical environments) Proteins and soluble C are decomposed very fast, then the cellulose and hemicellulose, lignin is very difficult to decomposeFigure 21.5
10Lignin contents influence litter decomposition Figure 21.6, each point represents one speciesTerrestrial environment Aquatic environment
11Physical conditions influence litter decomposition O2 concentrationDecomposition of Spartina litter is more efficient in aerobic than anaerobic conditionsLack of fungi, which require oxygen for respiration, hinders the decomposition of lignin component, slow the decomposition rate.Spartina was introduced in China (sediments purpose) and become an invasive species now.Litter bags on the marsh surface
12Changes in climate influence litter decomposition 7.2oC, 621 mm12.2oC, 720 mm14.4oC, 806 mmFigure 21.8Decomposition of red maple litter at three sites (litter quality similar for three sites). Warm and wet conditions, decompose fast
13Temperature influence on decomposition Figure 21.9Diurnal changes in air temperature and decomposition in a temperature deciduous forest
1421.5 Nutrients in organic matter are mineralized during decomposition Dead organic matter serve as energy source for microbial decomposer.Quality of dead OM varies greatly.Dead leaf N varies from 0.5% to 1.5%High N content means higher nutrient value for microbes and fungi that feed on the leaf.Decomposition is a process that xxxxxx and nutrient in OM released, inorganic form, available for plant to uptake. At the same time, decomposers also need nutrient to grow, the final nutrient depends on litter quality, environemntal conditins and two processes.
15Mineralization, immobilization and net mineralization rate Mineralization: a process that microbial decomposers –bacterial and fungi- transform nitrogen and other elements contained in organic matter compounds into inorganic (or mineral) forms.Organic N ammonia (waste product of microbial metabolism)Immobilization: uptake and assimilation of mineral nitrogen by microbial decomposer.N used by microbes to growNet mineralization rate: different between the rate of mineralization and immobilization
16Nitrogen remaining in the litter during decomposition Initial phase (A) leaching soluble N, then immobilized by microbes, then net N release from litter.Figure 21.10
17Chemical compositions of leaves in response to nutrients C:N ratiolow C:N ratio – high protein levelHigh C:N ration – low in proteins, high in lignin and secondary metabolitesLeaf C:N ration is influenced by nutrients availability in the environmentLeaf C:N ration influences decomposition rate and interactions with herbivoresNutrient requirements for compensatory growthNeed to mention herbivores or not? Grazer can sense the quality of leaf (C:N ratio).
18Litter bag result (winter rye in agricultural field) C:N decreases during decomposition (nitrogen is immobilized and carbon is released back to atmosphere as CO2)Figure 21.11
19N content influence the decomposition Under high N, the initial N can exceed the rate of immobilization from onset of experiment, N concentration will not increaseFigure when leaf N content is high, N mineralization rate is high. If the rate is higher than immobilization rate, then no net N accumulation observed.
20Five year litterbag experiment Figure 21.13Patterns of immobilization and mineralization of sulfur (S), calcium (Ca), and manganese (Mn) in decomposing needles of Scots pineFive year litterbag experiment
2121.7 Key ecosystem processes influence the rate of nutrient cycling Primary productivity determines rate of nutrient transform from inorganic form to organic form (nutrient uptake)Decomposition determines the rate of transformation of organic to inorganic form (N mineralization)Rate of these two determine the internal cycling
22Feedback between nutrient availability, NPP and N release Figure 21.15
23Litter quality and N mineralization rate RR: red pine, RO, red oak, WO white oak, SM sugar maple, WP white pine, Hem hemlock.Figure 21.16
2421.6 Decomposition in aquatic environment Similar to terrestrial ecosystem, with major influence by water environmentPermanently submerged plant litters decompose more rapidly, because of there are more accessible to detritivores and stable physical environment is more favorable to microbial decomposerFigure 21.14
2521.8 Nutrient cycling differs between terrestrial and open-water aquatic ecosystems Figure 21.17ShallowPlantsDeepPhysical separationNeed for a transport systemIn terrestrial ecosystem (shallow water), plants bridge the physical separation between the zones. In deep ocean, there is no direct link. Need a transport system.
26Turnover of water and nutrient link two zones together Figure 21.18Turnover of water and nutrient link two zones togetherTurnover of water and nutrient link two zones together
27Change in T, light and nutrient influence NPP, and photosynthesis also influences nutrient availabilityFigure 21.19
2821.9 Water flow influences nutrient cycling in streams and rivers Nutrient spiralingJack Webster (Virginia Tech?)Because nutrients are continuously being transported downstream, a spiral rather than a cycle better represents the cycling of nutrients.One cycle in the spiral: uptake of one nutrient atom, its passage through food chain, and its return to water, where it is available for re-use.The longer the distance required, the more open the spiral.Figure 21.17
32Outline (Chapter 21) Decomposition and Nutrient Cycling 21.1 Most essential nutrients are recycled within the ecosystem21.2 Decomposition is a complex process involving a variety of organisms
33Static deep water forms three layers Surface warm oxygen rich layerDeep cold oxygen poor layerNarrow transition zone or thermoclineMixing from weather does not affect hypolimnionHowever in winter, thermocline disappearsMixing verticallyThus winter replenishes the Epilimnion’s nutrientsWhile summer depletes the Epilimnion’s nutrients
34Flowing systems are different Inputs from terrestrial systems are significantLeaves, seepage, etcSpiralingVaries with speed of waterVaries with biological system holding nutrientsRetention of detritus can results in tighter spiralWoodland streamP moves 10.4 m/dP cycles once every 18.4 dOne spiral was 190 m
35Where terrestrial and open water system join Influenced by both systemsMeeting of fresh and salt waterCreates nutrient trapLimits release of nutrients into seaCoastal areasUpwellingEquatorialCoriolis force causes by counter currents at equatorUpwelling betweenCoastalCoriiolis force wind causes offshore currents and upwelling at continental edgeBottom chart has been mentioned before, in Aquatic environment chapter