Part Six Ecosystem Ecology Chap.20 Ecosystem Energetics Chap.21 Decomposition and nutrient cycling Chap.22 Biogeochemical cycles Smith & Smith (2015) Elements of ecology. 9th. Ed. Pearson. Part Six Ecosystem Ecology 生態體系 生態學 鄭先祐 (Ayo) 教授 生態科學與技術學系 國立臺南大學 環境與生態學院

Chap.22 Biogeochemical Cycles 生物地理化學循環 Smith & Smith (2015) Elements of ecology. 9th. Ed. Pearson. 鄭先祐 (Ayo) 教授 生態科學與技術學系 國立臺南大學 環境與生態學院

Chapter Opener Impala (Aepyceros melampus) standing in the shade of acacia trees. Their urine and droppings make the impala important contributors to the internal nitrogen cycle of these trees.

Chapter 22 Biogeochemical Cycles http://myweb.nutn.edu.tw/~hycheng/ Many chemical reactions take place in abiotic components of the ecosystem. Atmosphere Water Soil Parent material The biogeochemical cycle is the cyclic flow of nutrients from the nonliving to the living and back to the nonliving components of the ecosystem.

22.1 There Are Two Major Types of Biogeochemical Cycles http://myweb.nutn.edu.tw/~hycheng/ Two types of biogeochemical cycles In gaseous biogeochemical cycles, the main pools of nutrients are the atmosphere and the oceans Global Nitrogen, carbon dioxide, oxygen In sedimentary biogeochemical cycles, the main pool of nutrients is the soil, rocks, and minerals Inorganic sources of minerals are released to living animals through weathering and erosion Phosphorus Hybrid of gaseous and sedimentary cycles occur Sulfur

22.1 There Are Two Major Types of Biogeochemical Cycles http://myweb.nutn.edu.tw/~hycheng/ Both gaseous and sedimentary cycles Involve biological and nonbiological processes Are driven by the flow of energy through the ecosystem Are tied to the water cycle Biogeochemical cycles could not exist without the water cycle. All biogeochemical cycles have a common structure Inputs Internal cycling Outputs

Figure 22.1 Fig. 22.1 A generalized representation of the biogeochemical cycle of an ecosystem. The three common components– inputs, internal cycling, and outputs– are shown in bold.

22.2 Nutrients Enter the Ecosystem via Inputs http://myweb.nutn.edu.tw/~hycheng/ The input of nutrients depends on the cycle. Nutrients with a gaseous cycle enter the ecosystem via the atmosphere. Nutrients with a sedimentary cycle enter the ecosystem via weathering of rocks and minerals.

22.2 Nutrients Enter the Ecosystem via Inputs http://myweb.nutn.edu.tw/~hycheng/ Supplementing soil nutrients (of terrestrial habitats) are carried by rain, snow, air currents, and animals. Wet fall are those nutrients supplied by precipitation. Dry fall are the nutrients brought in by airborne particles and aerosols. The sources of nutrients for aquatic ecosystems From the surrounding land in the form of drainage water, detritus, sediment. Form the atmosphere in precipitation.

22.3 Outputs Represent a Loss of Nutrients from the Ecosystem http://myweb.nutn.edu.tw/~hycheng/ The output (export) of nutrients depends on the cycle. Release of CO2 from expiration of heterotrophic organisms. Organic matter can be carried out of an ecosystem Through surface flow of water or underground flow of water. By herbivores. Nutrients are released slowly from organic matter as it is decomposed.

22.3 Outputs Represent a Loss of Nutrients from the Ecosystem http://myweb.nutn.edu.tw/~hycheng/ Human harvesting (farming and logging) Nutrient loss must be replaced by fertilizers. Fire converts a portion of the standing biomass and soil organic matter to ash. Leaching and erosion of soil.

22.4 Biogeochemical Cycles Can Be Viewed from a Global Perspective http://myweb.nutn.edu.tw/~hycheng/ Often, the output from one ecosystem represents an input to another. The exchange of nutrients among ecosystems requires us to view the biogeochemical processes on a broad spatial scale. This is particularly true of nutrients that go through a gaseous cycle.

22.5 The Carbon Cycle Is Closely Tied to Energy Flow http://myweb.nutn.edu.tw/~hycheng/ Carbon is so closely tied to energy flow that the two are inseparable. Ecosystem productivity = grams C fixed/m2/year Inorganic carbon dioxide is the source of all carbon. The inorganic carbon is fixed into the living component through photosynthesis. Carbon dioxide is again released following respiration.

22.5 The Carbon Cycle Is Closely Tied to Energy Flow http://myweb.nutn.edu.tw/~hycheng/ Terrestrial cycling of carbon Input: photosynthesis Output: respiration, decomposition, combustion Net primary productivity = carbon uptake (photosynthesis) – carbon loss (respiration) Net ecosystem productivity = difference in rates

22.5 The Carbon Cycle Is Closely Tied to Energy Flow http://myweb.nutn.edu.tw/~hycheng/ The rate of carbon cycling is determined by the rates of primary productivity and decomposition. The rates of primary productivity and decomposition are directly affected by temperature and precipitation . In warm, wet ecosystems (e.g., tropical rain forest), production and decomposition rates are high and carbon cycles through the ecosystem quickly. When dead material has not completely decomposed in the past (e.g., in swamps) the matter has formed fossil fuels.

22.5 The Carbon Cycle Is Closely Tied to Energy Flow http://myweb.nutn.edu.tw/~hycheng/ Aquatic cycling of carbon Input: photosynthesis, diffusion, transport Output: respiration, decomposition, diffusion. Significant amounts of carbon can be bound as carbonates incorporated into exoskeletons (e.g., shells) of many aquatic organism. Carbon dioxide concentration fluctuates throughout the day This is a function of the difference in photosynthetic activity in response to sunlight and temperature.

Fig. 22.2 The carbon cycle as it occurs in both terrestrial and aquatic ecosystems. Figure 22.2

Figure 22.3 Fig. 22.3 Daily flux of CO2 in a forest. Note the consistently high level of CO2 on the forest floor– the site of microbial respiration. Atmospheric CO2 are highest at night, when photosynthesis shuts down and respiration pumps CO2 into the atmosphere.

22.6 Carbon Cycling Varies Daily and Seasonally http://myweb.nutn.edu.tw/~hycheng/ The production and use of carbon dioxide fluctuates with the seasons. This is a function of temperature and timing of the growing and dormant seasons. With the onset of the growing season, the atmospheric concentration begins to drop as plants withdraw carbon dioxide through photosynthesis. The fluctuations are greater in terrestrial environments as compared to aquatic ecosystems Fluctuations are much greater in the Northern Hemisphere due to the larger land area.

Figure 22.4 Fig. 22.4 Variation in atmospheric concentration of CO2 during a typical year at Barrow, Alaska. Concentrations increase during the winter months, declining with the onset of photosynthesis during the growing season (May-June).

The Earth contains 1023 grams (or 100 million gigatons) of carbon! 22.7 The Global Carbon Cycle Involves Exchanges among the Atmosphere, Oceans, and Land http://myweb.nutn.edu.tw/~hycheng/ Earth's carbon budget is linked to the atmosphere, land, and oceans and to the mass movements of air currents The Earth contains 1023 grams (or 100 million gigatons) of carbon! All but a small fraction of this carbon is buried in sedimentary rock and is not actively involved in the global carbon cycle.

22.7 The Global Carbon Cycle Involves Exchanges among the Atmosphere, Oceans, and Land http://myweb.nutn.edu.tw/~hycheng/ Carbon pool involved in the global carbon cycle amounts to 55,000 gigatons (Gt) Fossil fuels: 10,000 Gt Oceans: 38,000 Gt (mostly as bicarbonate and carbonate ions) Dead organic matter: 1650 Gt Living matter (mostly phytoplankton): 3 Gt Terrestrial Dead organic matter (in soil): 1500 Gt Living matter: 560 Gt Atmosphere: 750 Gt

Figure 22.5 Fig. 22.5 The global carbon cycle, The sizes of the major pools of carbon are labelled in red, and arrows indicate the major exchanges (fluxes) among them.

22.7 The Global Carbon Cycle Involves Exchanges among the Atmosphere, Oceans, and Land http://myweb.nutn.edu.tw/~hycheng/ The surface water acts as the site of main exchange of carbon dioxide between atmosphere and ocean Uptake of CO2 depends on its reaction with carbonate ions (CO32–) to form bicarbonates (HCO3–) Carbon circulates physically by means of currents and biologically through photosynthesis and movement through the food chain. Net uptake of carbon in oceans = 1 Gt/year Net loss of carbon in oceans (due to sedimentation) = 0.5 Gt/year.

22.7 The Global Carbon Cycle Involves Exchanges among the Atmosphere, Oceans, and Land http://myweb.nutn.edu.tw/~hycheng/ Recent studies suggest that the terrestrial surface is a carbon sink, with a net uptake of CO2 from the atmosphere. Uptake of CO2 from the atmosphere by terrestrial systems is determined by photosynthesis. CO2 losses from terrestrial systems are a function of respiration (especially decomposition).

More carbon is stored in soils than in living matter. 22.7 The Global Carbon Cycle Involves Exchanges among the Atmosphere, Oceans, and Land http://myweb.nutn.edu.tw/~hycheng/ More carbon is stored in soils than in living matter. The average carbon/volume of soil increases from the tropical regions poleward to the boreal forest and tundra. The greatest accumulation of organic matter occurs in areas where decomposition is inhibited (e.g., frozen or waterlogged soils)

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Nitrogen is an essential constituent of protein, a building block of all living tissue Nitrogen is available to plants in two forms Ammonium (NH4+) Nitrate (NO3–) The Earth's atmosphere is 80 percent nitrogen in the form of N2 This form is unavailable to plants for assimilation.

Fig. 22.6 The nitrogen cycle in terrestrial and aquatic ecosystems. Figure 22.6 Fig. 22.6 The nitrogen cycle in terrestrial and aquatic ecosystems.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Nitrogen enters the ecosystem via two pathways. Atmospheric deposition via wetfall and dryfall provides nitrogen in a form already available for plant uptake. High-energy fixation occurs when gaseous nitrogen (N2) is converted to ammonia and nitrate by energy from cosmic radiation, meteorite trails, or lightning — this accounts for only 0.4 kg N/ha annually. Atmospheric nitrogen can be converted into a usable form biologically — this accounts for 10 kg N/ha annually.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ This fixation is carried out by: Symbiotic bacteria living in mutualistic associations with plants. Free-living aerobic bacteria Cyanobacteria (blue-green algae) Nitrogen fixation requires considerable energy. To fix 1 g of nitrogen, nitrogen-fixing bacteria must expend about 10 g of glucose!

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Rhizobium bacteria are symbiotic organisms and form nodules in the roots of host plants. Associated with leguminous plants Free-living soil bacteria (Azotobacter, Clostridium) are prominent in converting nitrogen into a usable form. Cyanobacteria (Nostoc, Calothrix) fix nitrogen in terrestrial and aquatic ecosystems. Certain lichens may also fix nitrogen.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Ammonification occurs when ammonium (NH4+) is converted to NH3 as a waste product of microbial activity. Loss of gaseous NH3 from the soil to the atmosphere is influenced by soil pH. Nitrification is the stepwise conversion of NH4+ to NO2– (by Nitrosomonas) and then conversion of NO2– to NO3– (by Nitrobacter). Denitrification is the chemical reduction of NO3– to N2O and N2 (by Pseudomonas) which are then returned to the atmosphere

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Nitrification is the stepwise conversion of NH4+ to NO2– (by Nitrosomonas) and then conversion of NO2– to NO3– (by Nitrobacter). The nitrate may be taken up by plant roots or returned to the atmosphere. Denitrification is the chemical reduction of NO3– to N2O and N2 (by Pseudomonas) which are then returned to the atmosphere This reduction requires anaerobic conditions This process is common in wetland ecosystems and bottom sediments of aquatic ecosystems

Fig. 22.7 Bacterial processes involved in nitrogen cycling. Figure 22.7 Fig. 22.7 Bacterial processes involved in nitrogen cycling.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Nitrate is the most common form of nitrogen exported from terrestrial ecosystems in stream water. The amount of nitrogen recycled is usually much greater than inputs or outputs of nitrogen. Nitrogen fixation and nitrification are influenced by environmental conditions. Bacterial activity is affected by temperature, moisture, and soil pH. In highly acidic soils, bacterial action is inhibited.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ The internal cycling of nitrogen is fairly similar from ecosystem to ecosystem Assimilation of NH4+ and NO3– by plants Return of nitrogen to the soil, sediments, and water via decomposition. The nitrogen pool Atmosphere: 3.9 × 1021 g Terrestrial Biomass: 3.5 × 1015 g Soils: 95 × 1015 to 140 × 1015 g

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Nitrogen loss Terrestrial and aquatic denitrification: 200 × 1012 g/yr Sedimentation Nitrogen input Freshwater drainage: 36 × 1012 g/yr Precipitation: 30 × 1012 g/yr Biological fixation: 15 × 1012 g/yr

Figure 22.8 Fig. 22.8 The global nitrogen cycle, Each flux is shown in units of 1012 g N/yr.

22.8 The Nitrogen Cycle Begins with Fixing Atmospheric Nitrogen http://myweb.nutn.edu.tw/~hycheng/ Human activity has significantly influenced the global nitrogen cycle. Conversion of native forests and grasslands to agricultural fields. Application of chemical fertilizers to agricultural fields. Auto exhaust and combustion add N2O, NO, and NO2 to the atmosphere, which leads to an increase in ozone concentration of the stratosphere.

22.9 The Phosphorus Cycle Has No Atmospheric Pool http://myweb.nutn.edu.tw/~hycheng/ Phosphorus (P) can only be cycled from land to sea and is not returned via the biogeochemical cycle. The main reservoirs of P are rock and natural phosphate deposits. Phosphorus is released by weathering, leaching, erosion, and mining. In most soils, only a small fraction of total phosphorus is available to plants.

Fig. 22.9 The phosphorus cycle in aquatic and terrestrial ecosystems. Figure 22.9 Fig. 22.9 The phosphorus cycle in aquatic and terrestrial ecosystems.

22.9 The Phosphorus Cycle Has No Atmospheric Pool http://myweb.nutn.edu.tw/~hycheng/ In freshwater and marine ecosystems, the phosphorus cycle moves through three states Particulate organic phosphorus (PP) Dissolved organic phosphates (PO) Inorganic phosphates (Pi)

22.9 The Phosphorus Cycle Has No Atmospheric Pool http://myweb.nutn.edu.tw/~hycheng/ Organic phosphates are taken in by all forms of phytoplankton, which are eaten by zooplankton. Zooplankton may excrete as much phosphorus daily as it stores in its biomass. Some phosphorus is deposited in sediments  surface waters may become depleted while the deep waters become saturated. This phosphorus can be returned to the surface waters and accessed by organisms when upwelling occurs.

22.9 The Phosphorus Cycle Has No Atmospheric Pool http://myweb.nutn.edu.tw/~hycheng/ The phosphorus cycle Little atmospheric component although airborne transport of ~1 × 1012 g P/yr River transport = 21 × 1012 g P/yr (only 10 percent is available for NPP) Ocean waters are a significant global pool of P simply due to large volume. Organic phosphorus in the surface waters is recycled very rapidly. The phosphorous deposited in sediments or deep waters is unavailable to phytoplankton until upwelling.

Figure 22.10 Fig. 22.10 The global phosphorus cycle. Each flux is shown in units of 1012 g P/yr.

Ecological Issues Nitrogen Saturation http://myweb.nutn.edu.tw/~hycheng/ NPP in most terrestrial forest ecosystems is limited by soil nitrogen availability. Anthropogenic activity and high-intensity agriculture have increased inputs of nitrogen oxides in the atmosphere far above natural inputs. Generally, nitrogen is deposited in the region where it originated and thus will vary with geography and human population density.

Figure 1 Fig. 1 Estimated inorganic nitrogen deposition from nitrate and ammonium in 1998.

Ecological Issues Nitrogen Saturation http://myweb.nutn.edu.tw/~hycheng/ Soil nitrogen concentration influences the rate of N uptake and plant tissue concentration. Up to a point, as nitrogen concentration increases, net primary productivity increases. As the ecosystem approaches "nitrogen saturation," the soil and plant community suffer negative impacts. Release of other important soil cations (e.g., Mg) as ammonium concentration increases. Soil acidification that may contribute to toxic levels of aluminum ions.

Figure 2 Fig. 2 Hypothesized response of temperate forest ecosystems to long-term nitrogen additions. In stage 1, N-mineralization increases, which results in increased NPP. In stage 2, NPP and N-mineralization decline due to decreasing Ca:Al and Mg:N ratios and to soil acidification. Nitrification also increases as excess ammonium is available. Finally, in stage 3, nitrate leaching increases dramatically.

22.10 The Sulfur Cycle Is Both Sedimentary and Gaseous http://myweb.nutn.edu.tw/~hycheng/ The sulfur cycle has both sedimentary and gaseous phases. In the long-term sedimentary phase, sulfur is tied up in organic and inorganic deposits and is released by weathering and decomposition. The gaseous phase permits sulfur to circulate on a global scale.

Figure 22.11 Fig. 22.12 The sulfur cycle. Note the two components: sedimentary and gaseous. Major sources from human activity are the burning of fossil fuels and acidic drainage from coal mines.

22.10 The Sulfur Cycle Is Both Sedimentary and Gaseous http://myweb.nutn.edu.tw/~hycheng/ Atmospheric sulfur sources (as H2S) Combustion of fossil fuels Volcanic eruptions Ocean surface exchange Decomposition Atmospheric sulfur dioxide (SO2) is carried back to the surface in rainwater as weak sulfuric acid (H2SO4)

22.10 The Sulfur Cycle Is Both Sedimentary and Gaseous http://myweb.nutn.edu.tw/~hycheng/ Sulfur is incorporated into plants via photosynthesis and building of sulfur-bearing amino acids. Excretion and death return sulfur from living material back to the soil and sediments. Bacteria release it as hydrogen sulfite or sulfate Colorless, green, and purple bacteria each have a unique interaction with sulfur.

22.10 The Sulfur Cycle Is Both Sedimentary and Gaseous http://myweb.nutn.edu.tw/~hycheng/ Pyritic rocks (硫化鐵礦)(those that contain FeS) can be a source of sulfur if weathered or uncovered by humans (during coal mining). These products (e.g., sulfuric acid) can be extremely detrimental to aquatic ecosystems. The annual flux of sulfur compounds (SO2, H2S, sulfate particles) through the atmosphere ~300 × 1012 g Wetfall and dryfall of sulfate particles

22.11 The Global Sulfur Cycle Is Poorly Understood http://myweb.nutn.edu.tw/~hycheng/ Oceans are a large source sulfate aerosols, though most are redeposited in precipitation and dryfall. Dimethylsulfide [(CH3)2S] is the major sulfur gas emitted (16 × 1012 g S/yr) from the oceans and is generated by biological processes. H2S is the dominant sulfur form emitted from freshwater wetlands and anoxic soils. Forest fires emit 3 × 1012 g S annually. Volcanic activity contributes to the global cycle of sulfur.

Figure 22.12 Fig. 22.12 The global sulfur cycle. Each flux is shown in units of 1012 g S/yr.

22.12 The Oxygen Cycle Is Largely Under Biological Control http://myweb.nutn.edu.tw/~hycheng/ The major source of oxygen (O2) that supports life is the atmosphere and may originate from two processes Breakup of water vapor = 2 H2O  O2 + 4 H+ Photosynthetic production The input of oxygen must have exceeded its loss (due to respiration) for an overall abundance of oxygen. Water and carbon dioxide are other sources of oxygen. Oxygen is also biologically exchangeable in various molecules that are transformed by living organisms (e.g., hydrogen sulfide to sulfates).

Fig. 22. 13 A simple model for the global biogeochemical cycle of O2 Fig. 22.13 A simple model for the global biogeochemical cycle of O2. Data are expressed in units of 1012 moles of O2 per year or the equivalent amount of reduced compounds. Note that a small misbalance in the ratio of photosynthesis to respiration can result in a net storage of reduced organic materials in the crust and an accumulation of O2 in the atmosphere. Figure 22.13

22.12 The Oxygen Cycle Is Largely Under Biological Control http://myweb.nutn.edu.tw/~hycheng/ Due to oxygen's reactivity, its cycling in the ecosystem is complex. Carbon dioxide + calcium  carbonates Nitrogen compounds  nitrates Iron compounds  ferric oxides Ozone (O3) is an atmospheric gas In the stratosphere (10 to 40 km above Earth) it acts as a UV shield Close to the ground, it is a pollutant

22.12 The Oxygen Cycle Is Largely Under Biological Control http://myweb.nutn.edu.tw/~hycheng/ In the stratosphere, O2 is freed by solar radiation and freed oxygen atoms rapidly combine with O2 to form O3 (this reaction is reversible). Under natural conditions, a balance exists between ozone formation and destruction. Human activity has interrupted this balance, and various molecules (e.g., CFCs) reduce the production of O3

22.13 The Various Biogeochemical Cycles Are Linked http://myweb.nutn.edu.tw/~hycheng/ The biogeochemical cycles are linked through their common membership in compounds that form an important component of their cycles Nitrate and oxygen in nitrate Autotrophs and heterotrophs require nutrients in different proportions for different processes Stoichiometry (化學計量學) is the branch of chemistry that deals with the quantitative relationships of elements in combination.

Chap.22 Biogeochemical cycles 問題與討論 Ayo NUTN website: http://myweb.nutn.edu.tw/~hycheng/