Lecture 9a Biogeochemical Cycles

1. Lecture 9aBiogeochemical Cycles • Biogeochemical Cycles- Cycling of energy, and various chemical elements and compounds through the biosphere due to the feeding of organisms on each other • This includes: carbon, nitrogen, phosphorus, water...almost anything that temporarily inhabits a living thing

2. Ecosystem Ecology Food Webs: The "levels"which organisms eat which one's "lower" on the chain"— are called TROPHIC LEVELS (from the Greek troph, meaning "food" or "nourishment") The Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystems via the trophic levels. The efficiency with which trophic levels convert energy from the previous trophic levels varies greatly with ecosystem, but usually ranges between 5% - 20%.

3. Organisms in the food web • Autotrophs: Organisms that can feed themselves by harnessing light energy to make organic molecules such as carbohydrates, proteins, lipids, and nucleic acids out of inorganic raw materials (such as carbon dioxide, water, nitrogen compounds, etc.) • Autotrophs = Primary Producers, because they are the first link in the food web/chain. Without their ability to capture light and "harness" it as solid, organic matter, life as we know it would not exist. · Heterotrophs: Organisms that feed on other organisms to obtain energy. + =

4. Primary Producers are eaten by PRIMARY (1o) CONSUMERS. • Primary Consumers are eaten by SECONDARY (2o) CONSUMERS. • Secondary Consumers are eaten by TERTIARY (3o) CONSUMERS. • Tertiary Consumers are eaten by QUATERNARY (4o) CONSUMERS...and so on, throughout the web.

5. Carbon Cycle C6H12O6 • All organic matter eventually is oxidized (burned) and converted back to carbon dioxide and water. Photosynthesis

7. Soil Food Web • The community of organisms living all or part of their lives in the soil • Fueled by primary producers • plants, lichens, moss, photosynthetic bacteria, and algae • http://www.agron.iastate.edu/~loynachan/mov/ • Or foodchain.rm

8. Photosynthesizers • First trophic level • Plants • Algae • Bacteria • Role: • Capture solar energy to fix CO2 • Add organic matter to soil (biomass such as dead cells, plant litter)

9. Decomposers • Second trophic level • Bacteria • Fungi • Protozoa • Role: • Breakdown residue • Immobilize nutrients in their biomass • Create new organic compounds • Bind soil aggregates

10. Mutualists • Second trophic level • Two organisms living in beneficial association • Bacteria • Fungi • Role: • Enhance plant growth • Fix nitrogen

11. Pathogens/Parasites • Second trophic level • Bacteria • Fungi • Nematodes • Arthropods • Role: • Promote disease • Consume roots • Parasitize nematodes or insects

12. Root-feeders • Second trophic level • Nematodes • Arthropods • Role: • Consume plant roots • Crop yield losses

13. Shredders • Third trophic level • Earthworms • Arthropods • Role: • Breakdown residue • Enhance soil structure • Provide habitat for bacteria in gut

14. Measurement of Microbial Activity • Counting • Direct counts • Plate counts • Activity levels • Respiration • Nitrification rates • Decomposition rates • Cellular constituents • Biomass C, N, or P • DNA/RNA fingerprinting

15. Food Web Structures • Fungi to bacteria ratios • Grasslands:Ag soils = 1:1 • Deciduous Forest 5:1 to 10:1 • Conifer Forest 100:1 to 1000:1 • Organism communities reflect their food source

16. Soil management affects the fungal and bacterial populations in soil • Fungi and bacteria differ in their responses to changes in agricultural practices. • Fungi are usually more sensitive to these changes. The fungal-to-bacterial ratio is therefore an indicator of environmental changes in the soil. • When plant residues are surface applied - fungi prosper because their hyphae are able to grow into the litter layer. • Tilliage - destroys large amounts of the fungal hyphae. • Incorporation of plant residues into the soil favors the bacterial population because the contact surface between the substrate and bacteria is increased. • Fungi are the predominant cellulose decomposers. Bacteria, which have a smaller C:N ratio than fungi, need food rich in nitrogen (e.g. green manure, legume residues). • A high nitrogen fertilizer favors the bacterial community in a soil • Substrate additions with a relatively wide C:N ratio enables growth of the fungal population.

17. Rates of Plant Residue Decomposition • Kind of material (FAST --> Sugar, starches, proteins --> hemicelluloses, cellulose, --> Fats waxes --> lignin SLOW • Rate decreases after the easy material has decomposed • Soil Conditions - water, temp., oxygen, nitrogen, phosphorus, • Decay Products = Energy (heat), carbon dioxide, N,P,S & Humus

18. Carbon Dioxide & Global Warming • The use of fossil fuels and practice of deforestation to meet the world's energy demands has lead to increasing concentrations of carbon dioxide (CO2) and methane (CH4) in the atmosphere. • Both gases absorb terrestrial infrared radiation and have the potential to affect earth's climate by warming it.

19. Sources of Atmospheric Carbon Atmospheric carbon represented a steady state system, where influx equaled outflow, before the Industrial Revolution. Currently, it is no longer a steady state system because the influx exceeds the outflow. Therefore, we are experiencing an increase in atmospheric carbon, mainly in the form of CO2 Dennis L. Hartmann

20. Half of the solar energy that reaches Earth passes through the atmosphere and is absorbed at the surface. • About 90% of the infrared radiation emitted by the surface is absorbed by the atmosphere before it can escape to space.

21. The characteristics of the atmosphere that enable it to raise the temperature of the surface of Earth are: • 1) atmosphere is transparent to sunshine • 2) but is almost opaque to infrared radiation. • So the atmosphere lets in the heat from the sun, but is reluctant to let it escape again due to the “greenhouse gasses”

22. If CO2 is suddenly added to the atmosphere, it takes between 50 and 200 years for the amount of atmospheric CO2 to establish a new balance, compared to several weeks required for water vapor.

23. Soil Carbon Sinks • Large amounts of carbon have been released into the atmosphere through the conversion of grasslands and forests to agricultural and grazing land, as well as through unsustainable land practices. • Soils can regain lost carbon by absorbing or "sequestering" it from the atmosphere. But the ability of soils to act as carbon "sinks“ depends on sound land management.

25. No. 1 Environmental Enemy in Production Agriculture D.C. Reicosky USDA - ARS -Morris Lab Intensive Tillage

26. Holding carbon in the soil! Keeps Carbon out of the atmosphere!

27. Gaining Carbon Losing Carbon Soil Carbon “C” : easy come, easy go! Improved management can make C easy to come with more cropping intensity and/or cover crops and result in net carbon sequestration. Improved management can make C slow to go with residue management and/or less tillage and result in net carbon sequestration.

28. Fossil carbon cycle. CO2 CO2 CO2 C Biological carbon cycle. Atmospheric Carbon as CO2 Energy from fossil fuels Energy from bio-fuels Plant biomass and roots left on or in the soil contribute to Soil Carbon or Soil Organic Matter and all associated environmental and production benefits. Nonrenewable Renewable

29. Carbon Carbon Global environmental quality depends on Conservation Agriculture and soil quality. Carbon inputs Tillage intensity Our food supply Sustainable agriculture = Soil organic carbon

30. Soil is meant to be covered. Manage soil carbon - make the world a better place. D.C. Reicosky USDA - ARS -Morris Lab

31. The End