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1 Dafeng Hui Room: Harned Hall 320 Phone: 963-5777
BIOL 4120: Principles of Ecology Lecture 19: Decomposition and Nutrient Cycling Dafeng Hui Room: Harned Hall 320 Phone:

2 21.1 Most essential nutrients are recycled within ecosystem
Internal cycling Retranslocation or reabsorption Figure 21.1

3 Fast way compared to uptake
Table 21.1

4 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 Protozans and nematodes to earthwork and millipeds

5 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. Figure 21.3 Carbon is lost to the atmosphere as CO2 in the process of respiration

6 Based on the data, the decomposition rate can be calculated
Figure 21.4

7 Decomposition rate calculated as k=0. 0097 wk-1 and 0
Decomposition rate calculated as k= wk-1 and wk-1 for two tree species

8 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

9 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 Figure 21.5

10 Lignin contents influence litter decomposition
Figure 21.6, each point represents one species Terrestrial environment Aquatic environment

11 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. Spartina was introduced in China (sediments purpose) and become an invasive species now. Litter bags on the marsh surface

12 Changes in climate influence litter decomposition
7.2oC, 621 mm 12.2oC, 720 mm 14.4oC, 806 mm Figure 21.8 Decomposition of red maple litter at three sites (litter quality similar for three sites). Warm and wet conditions, decompose fast

13 Temperature influence on decomposition
Figure 21.9 Diurnal changes in air temperature and decomposition in a temperature deciduous forest

14 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. 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.

15 Mineralization, 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 grow Net mineralization rate: different between the rate of mineralization and immobilization

16 Nitrogen 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

17 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 Need to mention herbivores or not? Grazer can sense the quality of leaf (C:N ratio).

18 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) Figure 21.11

19 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 Figure 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.

20 Five year litterbag experiment
Figure 21.13 Patterns of immobilization and mineralization of sulfur (S), calcium (Ca), and manganese (Mn) in decomposing needles of Scots pine Five year litterbag experiment

21 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

22 Feedback between nutrient availability, NPP and N release
Figure 21.15

23 Litter 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

24 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 Figure 21.14

25 21.8 Nutrient cycling differs between terrestrial and open-water aquatic ecosystems
Figure 21.17 Shallow Plants Deep Physical separation Need for a transport system 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.

26 Turnover of water and nutrient link two zones together
Figure 21.18 Turnover of water and nutrient link two zones together Turnover of water and nutrient link two zones together

27 Change in T, light and nutrient influence NPP, and photosynthesis also influences nutrient availability Figure 21.19

28 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. Figure 21.17

29 End


31 Why NP decrease when PPT is very high?

32 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

33 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 Epilimnion’s nutrients While summer depletes the Epilimnion’s nutrients

34 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

35 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 Bottom chart has been mentioned before, in Aquatic environment chapter

36 Figure 21.21

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