SOM. Bugs! Plants are a major source of SOM First remember that SOM is food ROOT EXUDATES. Rhizosphere. Microbes

Transcription

1 SOM Plants are a major source of SOM First remember that SOM is food Soil organic matter ROOT EXUDATES 10-20% OF PLANT PHOTOSYNTHESIS GOOD EATING Rhizosphere Root zone - area of greatest microbial activity Area of highest food supply The soil is one giant food web and on the bottom there are the Bugs! Microbes Most primitive organisms Single celled Responsible for plant matter decomposition This enables recycling of nutrients Only with nutrient recycling do you have sustainability 1

2 First level consumers Bacteria - 5 x 10 6 Actinomicetes - 9 x 10 5 Fungi - 2 x 10 3 Per gram of soil Population will rise and fall very quickly in response to food supply How much? I ha of soil = 1 traincar load or 30,000 kg of SOM 1 ha of soil = 1 dump truck or 3,000 kg of bacteria, antinomycetes and funghi Bacteria initial breakdown of organics may be initially 80-90% of activity accounts for the heat generated Some of these also form associations with plants Nitrogen fixing bacteria Take N 2 gas and turn it into NH 3 (solid) Major source of N for plants Plants give photosynthate (food) in return Will only form associations with certain types of plants Legumes- Clovers Peas Soybeans Red alder This gives these plants an advantage over non leguminous species in low N soils Actinomycetes somewhere between bacteria and fungi breakdown of cellulose responsible for earthy odor 2

3 One type you recognize Fungi similar role as actinomycetes active in cellulosic/lignaceous compounds activity increases when undisturbed Visible, edible portion is the fruiting body of the fungus Each have preferences Funghi - can tolerate acid soils, sandy soils, soils with fluctuating moisture Bacteria - very tolerant of high temperature, some can tolerate anaerobic conditions (no air) Antinomycetes like things just so Ever heard of: Streptomycine or penicillin? Produced by antinomycetes and funghi Soil microbes produce a range of substances to compete against other microbes These are antibiotics and are the origin of the antibiotics that we use Plant disease Range of plant diseases associated with soil organisms Potato scab - antinomycetes Lower ph Club root - fungus Raise ph Damping off - fungus Keep dry MYCHORRIZAE TYPE OF FUNGHI FORMS ASSOCIATION WITH ROOT ECTO AND ENDO OUT AND IN 3

4 Ecto vs Endo MYCHORRIZAE Ecto Outside - a white sheath coating the root Visible to the eye Important with conifers Endo Invisible to the eye Colonize into the root Most annuals and perienniels Provide access to soil nutrients (P) Again in exchange for photosynthate Not associated with brassicacae Very important for certain tree species Very important in poor soils Things that eat the bugs Second level consumers Whiteworms potworms (Enchytraeids) mm In addition to eating the bugs Eat larger plant material (hard for a microbe to fit a tap root into its mouth) Eat each other Soil flatworms (Turbellarians) mm Mold mite (Acarina) Earthworms mm Land snails and slugs 2-25 mm Beetle mites 1 mm Millipedes mm Featherwinged beetles (Ptiliids) 1-2 mm Springtails (Collembola) mm Protozoa mm Rotifera mm Nematodes Nematodes Myriad of types Primarily beneficial Some detrimental Put pincer into root and feast away Love peach trees and pepper plants Marigolds natural control method 4

5 Third level consumers Major players ground beetles (carabid) 8-20 mm Psuedoscorpion 1-2 mm Centipedes 30 mm Worms Eat soil- recycle nutrients improve aggregation castes Predatory mite mm Ant (Formicid) 5-10 mm Rove beetles (staphylinid) 10 mm Major players Ants and termites Move enormous amounts of soil Ants generally beneficially For soil structure and nutrient cycling Focus on air and water (how they work together) Inorganic Organic Air Water Let s talk about eating When you eat a portion of the food (carbon) is released as energy Remainder is incorporated into body tissue What is respiration? Process of getting energy from food 5

6 Aerobic Respiration Most things do this C 6 H 12 O 6 + 6O 2 (sugar) 6CO 2 + 6H 2 O How we get energy from food C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O This means that we need O 2 to eat Here the we are plants, aerobic micro-organisms, larger biota (worms, nematodes, moles ) It also means that we produce CO 2 in the process This means that we take C in a reduced state (C 6 valence = 0 H 12 O 6, ) and release energy by oxidizing C (6C valence = 4+ O 2 ) We take the electrons from the C and dump them on the O (that is why its aerobic respiration) 6O 2(valence = 0) 6CO 2 + 6H 2 O (valence = -2) Photosynthesis Only plants do this How plants make food 6CO 2 +12H 2 O C 6 H 12 O 6 + 6O 2+ 6H 2 O Plants need water and CO 2 to photosynthesize CO 2 fixation takes place in the leaves Respiration takes place in the roots and leaves This means That there is a lot of CO 2 being released in the soil By all the creatures that use aerobic respiration Also a demand for O 2 in the soil By the same creatures And That the demand for CO 2 is being satisfied by the leaves above the soil This means you need good air exchange between soil air and the air to maintain sufficient O 2 in the soil In addition Certain gases can be produced by roots that can be phytotoxic in small concentrations Ethylene These need to move out of soil as well 6

7 Review - What air contains Nitrogen 78.1% Oxygen 21% Carbon dioxide 0.03% Argon 0.09% Respiration Use 6O 2 Give off 6CO 2 Oxygen 21% Carbon dioxide 0.03% Tendency to accumulate CO 2 in the root zone For a soil to function well Need rapid air exchange Wind generally does not blow through the soils Diffusion - things move to reach equilibrium Move as a function of concentration Macropores provide for most efficient movement 7

8 So when the soil stays waterlogged for extended periods The macropores are filled with water instead of air Plants start to die - they can t breath For forests and fields, this is how things work However, there are specialized plants that have developed ways to grow in waterlogged soil Rice - aerenchyma pipe air down Mangrove - surficial roots Wetland species Wetlands What is the big fuss about wetlands? Remember how aerobic organisms (humans and plants) use carbon for energy and dump the electrons on oxygen? In wetlands, there is not enough oxygen to go around Alternative electron acceptors Without oxygen As the number of electrons needing a home goes up eh ( or electron pressure) goes down Alternatives, such as N, Fe, Mn, S, are used by specialized organisms (anaerobes) as a home for the electrons N (valence = 5+) O - 3 N 2(valence = 0) N is an ion N is a gas This is why wetlands are so good at getting rid of excess nutrients 8