BIOL 4120: Principles of Ecology Lecture 17: Community Ecology
BIOL 4120: Principles of Ecology Lecture 19: Decomposition and Nutrient Cycling Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: [email protected] 21.1 Most essential nutrients are recycled within ecosystem
Internal cycling Retranslocation or reabsorption Fast way compared to uptake 21.2 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 detritivores 4 major groups Microfauna(flora), mesofauna, macrofauna, and megafauna 21.3 Decomposition rate measurement Litterbag method Mesh bag Mass 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. Carbon is lost to the atmosphere as CO2 in the process of respiration Based on the
data, the decomposition rate can be calculated Decomposition rate calculated as k=0.0097 wk-1 and 0.0167 wk-1 for two tree species 21.4 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 Influencing 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 decompose Lignin contents influence litter decomposition Terrestrial environment Aquatic environment Physical conditions influence litter decomposition O2 concentration
Decomposition of Spartina litter is more efficient in aerobic than anaerobic conditions Lack of fungi, which require oxygen for respiration, hinders the decomposition of lignin
component, slow the decomposition rate. Litter bags on the marsh surface Changes in climate influence litter decomposition 7.2oC, 621 mm 12.2oC, 720 mm 14.4oC, 806 mm
Decomposition of red maple litter at three sites (litter quality similar for three sites). Warm and wet conditions, decompose fast Temperature influence on decomposition Diurnal changes in air temperature and decomposition in a temperature deciduous forest 21.5 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. Mineralization, immobilization and net mineralization rate Mineralization: a process that microbial decomposers bacterial and fungitransform 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 grow Net mineralization rate: different between the rate of mineralization and immobilization
Nitrogen remaining in the litter during decomposition Initial phase (A) leaching soluble N, then immobilized by microbes, then net N release from
litter. Chemical compositions of leaves in response to nutrients C:N ratio
low C:N ratio high protein level High C:N ration low in proteins, high in lignin and secondary metabolites Leaf C:N ration is influenced by nutrients availability in the environment Leaf C:N ration influences decomposition rate and interactions with herbivores Nutrient requirements for compensatory growth Litter bag result (winter rye in
agricultural field) C:N decreases during decomposition (nitrogen is immobilized and carbon is released back to atmosphere as CO2) N content influence the decomposition Under high N, the initial N can exceed the rate
of immobilization from onset of experiment, N concentration will not increase Patterns of immobilization and mineralization of sulfur (S), calcium (Ca), and manganese (Mn) in decomposing needles of Scots pine Five year litterbag experiment
21.7 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 Feedback between nutrient availability, NPP and N release
Litter quality and N mineralization rate RR: red pine, RO, red oak, WO white oak, SM sugar maple, WP white pine, Hem hemlock. 21.6 Decomposition in aquatic environment Similar to terrestrial
ecosystem, with major influence by water environment Permanently submerged plant litters decompose more rapidly, because of there are more accessible to detritivores and stable physical environment is more favorable to microbial decomposer
21.8 Nutrient cycling differs between terrestrial and open-water aquatic ecosystems In terrestrial ecosystem (shallow water), plants bridge the physical separation between the zones. In deep ocean, there is no direct link. Need a transport system. Turnover of water and nutrient link two zones together
Change in T, light and nutrient influence NPP, and photosynthesis also influences nutrient availability 21.9 Water flow influences nutrient cycling in
streams and rivers Nutrient spiraling Jack 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. End Why NP decrease when PPT is very high? Outline (Chapter 21) Decomposition and Nutrient Cycling 21.1 Most essential nutrients are recycled within the
ecosystem 21.2 Decomposition is a complex process involving a variety of organisms Static deep water forms three layers Surface warm oxygen rich layer Deep cold oxygen poor layer Narrow transition zone or thermocline
Mixing from weather does not affect hypolimnion However in winter, thermocline disappears Mixing vertically
Thus winter replenishes the Epilimnions nutrients While summer depletes the Epilimnions nutrients Flowing systems are different Inputs from terrestrial systems are significant Leaves, seepage, etc
Spiraling Varies with speed of water Varies with biological system holding nutrients Retention of detritus can results in tighter spiral Woodland stream
P moves 10.4 m/d P cycles once every 18.4 d One spiral was 190 m Where terrestrial and open water system join Influenced by both
systems Meeting of fresh and salt water Creates nutrient trap Limits release of nutrients into sea
Coastal areas Upwelling Equatorial Coriolis force causes by counter currents at equator Upwelling between
Coastal Coriiolis force wind causes offshore currents and upwelling at continental edge
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