Module 26Describe the four vertical horizons found in mature soils; what are soil aggregates 1. O horizon- layer of under composed plant material2. A horizon- surface soil (dark in organic matter and color)3. B horizon- subsoil (minerals, little organic matter)4. C horizon- soil base (develops directly from underlying bedrock)Explain how and why oxygen levels change in the microenvironments within soil aggregates; why are microbial fermentation pathway products found within soil aggregates Oxygen levels change in the microenvironments within soil aggregate due to different levels of sand, silt, clay, and organic matter. Microbial fermentation pathway products are wound within soil aggregates because it can no longer use oxygen inside therefore it must adapt and use fermentation for energy.Why are strict anaerobic bacteria such as Clostridium able to live within soil aggregates There are strict anaerobic bacteria such as Clostridium about to live within soil aggregates because of the microbial activity in the soil is influenced by oxygen/liquid relationships. Diagram the process of rhizodeposition, tracing carbon from the atmosphere into soil microbes near plant roots Why is N2-fixing symbiosis important to certain plants and to agricultureDescribe the sequence of steps in establishment of plant-rhizobia symbiosis; what chemicals areused for plant↔microbe communication 1. Flavonoid compounds2. Flavonoids= bacteria3. Nod factors synthesized4. Root hair curling5. Infection thread forms6. Formation of bacteroid stateReview the nitrogen fixation pathway inside bacteroids; what is the overall reaction for nitrogen fixation; explain the source of energy, how much energy is expended for each N2, and the role of leghemoglobin Its energy is supplied by aerobic respiration. The amount of energy expanded for each N2 is 16, the role of leghemoglobin is that it is an oxygen carrier.What are the two types of associations of fungi with plant roots; how do plants and mycorrhizal fungi benefit from each other Ectomycorrhizea- form a sheath around the outside of the rootEndomycorrhizae- has fungal mycelia that colonize the roots interior. Mycorrhizal function in bidirectional nutrient exchange, acts as functional root extensions to take up nutrients from surrounding soil and convert into more readily available for
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