Soil Ecology SOILS 412W
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Torrey Wyman V
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This 0 page Class Notes was uploaded by Torrey Wyman V on Sunday November 1, 2015. The Class Notes belongs to SOILS 412W at Pennsylvania State University taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/233069/soils-412w-pennsylvania-state-university in Soil Science at Pennsylvania State University.
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Date Created: 11/01/15
Lecture 45 Sept 7 2000 Carbon and Energy Inputs into the Soil Food Web Gross primary production Gross primary production is the amount of carbon dioxide converted to organic carbon by primary producers autotrophs A portion of the gross primary production is converted back to C02 by respiration of primary producers Remaining organic carbon is the net primary production available to consumers heterotrophs Primary producer groups in soil ecosystems Primary producers are the foundation of all food webs Consist predominantly of plants which convert light energy into chemical energy through photosynthesis May include photosynthetic microbes eg prokaryotic cyanobacteria eukaryotic algae but their role is subordinate to that of higher plants May include autotrophic chemolithotrophic soil bacteria but these contribute much less to primary production ammoniaoxidizing bacteria nitriteoxidizing bacteria Primary producers in harsh environments Some harsh environments prevent the growth of higher plants so that microbes may be the predominant primary producers in these habitats exposed rock surfaces cyanobacteria in lichens polar land surfaces psychrophilic or coldloving photosynthetic bacteria highsalt environments halophilic or saltloving photosynthetic bacteria highly alkaline hot springs Chloro exus spp hightemperature environments cyanobacteria in desert crusts Lecture 45 Page 2 of 10 Net primary productivity 0 Consumption of organic matter by detritivores and subsequent grazing of detritivores involves conversion of some organic carbon back to C02 respiration Net gain in organic matter produced by photosynthesis and not converted back to C02 is net primary productivity Positive net community productivity accumulates organic matter within the system Negative net productivity requires inputs of organic matter otherwise the community will dissipate available energy and disappear or become dormant Net primary productivityquot of some natural and agricultural ecosystems grams of dry organic matter per m2 per year Corn eld l0006000 Temperate grassland up to 1500 Temperate forest 1200 1600 Cattail swamp 2500 Freshwater pond 950l500 Rice paddy 340l200 Tropical rain forest up to 2800 Tundra 400 Desert 200 Coastal seawater 200 Open ocean 100 Note that l g of dry biomass contains 50 carbon and corresponds to 5 kcal energy stored From Microbial Ecology 2quotd ed by Ron Atlas p 314 Lecture 45 Page 3 oflO Soil Food Web Grazers and Predators This portion of the soil food web is dominated by macro and microfauna Food web is based on interrelated transfers of stored energy among soil organisms Each energy transfer step represents a trophic level with only about 1015 of the biomass transferred to the next higher trophic level In general the higher the trophic level the smaller its total biomass In reality many consumersgrazers will feed on more than one trophic level Soil Food Web Decomposition and Secondary production This portion of the food web is dominated by heterotrophic microorganisms which degrade organic polymers and release soluble substances from particulates Secondary production is the conversion of dissolvedparticulate organic compounds to new cell material An important contribution of bacteria to food webs is their ability to assimilate dissolved organic carbon from extremely dilute solutions Bacteria convert mineral nutrients to biomass which becomes suitable food for organisms that cannot use dissolved nutrients directly Lecture 45 Page 4 of 10 Comparison of food web groups in marine and forest ecosystems Dominant primary producers in marine systems are photosynthetic plankton algae cyanobacteria while in terrestrial systems they are plants In terrestrial habitats a higher proportion of energy enters the decomposition portion ofthe food web from EP Odum 1962 cited in Microbial Ecology by R Atlas GrazersPredators 75 phagotrophic microflagellates Marine Phytoplankton 25 Decomposers bacteria GrazersP redators macro and microfauna Forest Plants 83 Decomposers fungi and bacteria
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