ENST 200- Exam 3
Ecological Engineers: Earthworms
"natures tillers" create channels through the soil that plants roots use casts (poop) break down micro aggregates and from new ones increase nutrient availability
Oxydation: Redox changes of S in sulfide and sulfate
- in oxy: sulfides, elemental sulfur (S0), thiosulfates (S2O32-), and polythionates (S2xO3x 2-). - oxi of sulfites and sulfides only chemical -most sulfur oxidation is done by autotroph bact -oxidation at pH <2 to >9 INSERT PIC
S cycle (similarities to N cyle)
-4 forms: sulfides, sulfates, organic sulfur, elemental sulfur. - atmosphere important source -held largely in the SOM -microbe oxy-redox -leave/enter soil as gas -can leach in anionic form
reasons for growing deficiency of S
-industrial SO2 emmissions, took soil for granted
P role in eutrification
-overfertilization -phosphorus stimulates algae growth and kills the floating plants
Reduction: Redox changes of S in sulfide and sulfate
-sulfate ions unstable in anaerobic enviro -two bacteria Desulfovibrio & Desulfotomaculum -in poor drained: S reacts w/ Fe or Mg -hydrolysis of sulfide = gas hydrogen sulfie
Buffering soil acidity
1. Hydrolysis, dissolution, or precipitation of aluminum and iron hydroxyoxide clay minerals 2. Protonation or deprotonation of OM functional (R-OH) groups 3. Protonation or deprotonation of pH dependent charge sites on clay minerals 4. Cation exchange reactions 5. The dissolution or precipitation of carbonate minerals
C/N Ratios
30:1 legumes 500:1 sawdust and charred material 8:1-15:1 in OM 30-40:1 in Forests O
6 ways roots contribute to soil carbon
1. sloughing off of root cap cells 2. excretion of mucigel 3. spilling of cell contents when epidermal cells are lysed 4. exudation of specific compounds produced by root hairs 5. exudation of various compounds by cortical cells 6. export of organic compounds to symbolic fungi
6 fates of nitrogen in Nh4
: (1) immobilization by microorganisms; (2) removal by plant uptake; (3) anammox—the anaerobic oxidation of NH4+ in conjunction with nitrite (NO2-) to produce N2O gas; (4) volatilization after being transformed into ammonia gas; (5) nitrification—the microbial oxidation of ammonium to nitrite and subsequently to nitrate; and (6) fixation or strong sorption in the interlayers of certain 2:1 clay minerals
Micro organism
<0.1mm nematodes, single celled protozoans
Macro organism
>2mm moles, gophers, earthworms, millipedes
1:1 clay minerals (kaolinite)term-14
1:1 clays like kaolinite exhibit less plasticity, stickiness, cohesion, shrinkage, and swelling and can also hold less water each layer contains one tetrahedral and one octahedral sheet low ability to absorb exchangeable cations the hydroxyl plane is exposed on the clay particle surface, so removal or addition of hydrogen ions can produce either positive or negative charges, depending on the pH of the soil, also the hydrocyl plane can react with and strongly bind specific anions adjacent layers are bound together by hydrogen bonding good for building, can be cultivated and productive
Saline Seeps
An area of land in which saline water seeps to the surface, leaving high salt concentration behind as water evaporates
K strategists
An organism that maintains a relatively stable population by specializing in metabolism of resistant compounds that most other organisms cannot utilize
pOH
A measure of hydroxide ion (OH-) concentration. It is used to express the alkalinity of a solution
Mutualism
A relationship between two species in which both species benefit (+/+) aka symbiosis
Saline-sodic soil
A soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants and containing appreciable quantities of soluble salts pH 8.5 or less exchangeable sodium adsorption rate is >13
How to keep potential from becoming active
CaCO3 can eventually neutralize H2SO4, best to prevent S oxidation
2:1 clay minerals
One octahedral sheet between two tetrahedral sheets smectite, vermiculite, hydrous micas (illite), chlorite can be expanding or non-expanding
rhizobial bacteria
Plants of the legume family are famous for their distinctive ability to provide the major biological source of fixed nitrogen in agricultural soils. They do so in association with several genera of bacteria (in the subclass Alpha-Proteobacteria) collectively termed rhizobial bacteria Rhizobium
feeder roots
Roots at or near the soil surface that absorb most of the water and nutrients needed by the tree. can become deficient in oxygen even if the overburden of exces soil is no more than 5-10 cm in depth should build a protective wall (a dry well) or install a fence around the base of a valuable tree before grading operations begin to preserve the original soil surface and avoid compaction in a zone around the trunk, the size of the protected zone varying with the size of the tree.
Humus vs. Clay
Humus particles and clay particles are negatively charged humus has 30 to 40 times more attraction to positively charged nutrients than clay particles humus is very stable, the strong negative charge helps to hold on to positively charged mols in the soil thus preventing leaching Clay is smaller than humus and formed in thin, flat plates
Reversible
It will go to the left if sodium is added to the system. This reversibility is a funda- mental principle of cation exchange.
Encourage soil dispersion and puddling
Low salt (ion) concentration and weakly attracted ions (Na)
Role of Na+ v. Ca 2+
Main ions associated with salinity Na is much more water soluble than Ca, and the reactions produce more hydroxyl ions and a high pH which is bad because the pH can rain above 10, so its better that Ca is more dominant in soil
fauna
all the animal life in a particular region
Nitrogen's role in Plants
amino acids- the building blocks of all proteins, including the enzymes, which control virtually all biological processes nucleic acids- in which hereditary control is vested chlorophyll- which is at the heart of photosynthesis nutrient uptake- stimulates root growth and development, as well as the uptake of other nutrients like carbohydrates
nitrification
ammonia ions in the soil are oxidized into nitrate ions (NO3-) by bacteria
Carbon sequestration
a natural or artificial process by which carbon dioxide is removed from the atmosphere and held in solid or liquid form. opportunities for sequestering carbon are greatest for degraded soils that currently contain only a small portion of the organic matter levels they contained originally under natural con- ditions. Reforestation of denuded areas is one such opportunity. Conversion of cultivated land to perennial vegetation may sequester carbon at twice these rates. reducing or eliminating tillage generally enhances soil quality and surface soil carbon level oceans, soils, plants, organisms, etc.
Mold
break down soil OM, found in all pH but dominate in acid surface
Carbonic and other organic acids
carbonic acid is formed when co2 dissolves in water dissociating H+, microbes break down organic matter generating organic acid
acid cations
cations, principally Al3+, Fe3+, and H+, that contribute H+ ion activity
antagonism
certain soils become disease-suppressive; the pathogenic organisms are inhibited by antagonism from beneficial bacteria and fungi General Suppression: caused by high levels of overall microbial activity in a soil, especially at times critical in the development of a disease, such as when the pathogenic fungus is generating propagules or preparing to penetrate the plant cells (basically there is too much competition against the pathogens, so they can't survive) Specific Suppression: attributable to the actions of a single species or a narrow group of microorganisms that inhibit or kill a particular pathogen; usually has to do with build up of a monoculture of one pathogen, and the something else comes along to prey on said pathogen, eliminating it
Impacts of climate change
changes in rainfall distribution and growing season length, increases in sea level, and greater frequency and severity of storms and droughts
Permanent charge
charge imbalance brought about in some clay crystal structure by the isomorphic substitution of one cation by another of similar size but different charge
Saline soil
an nonsodic soil containing sufficient soluble salts to impair its productivity pH is <8.5 exchangeable sodium adsorption rate is less than 13
Fine roots
anchor root as it pushed through soil increase the amount of surface area available to absorb water and nutrients
Primary consumers
animals and microbes that use energy stored in plant residues
predators
animals that kill and eat other animals
shredder
animals that physically shred and chew the plant debris responsible for most actual decomposition of dead plant and animal debris also called saprophytes break down all kinds of plant and animal compounds, from simple sugars to woody materials, feed on detritus, dead animals (corpses), and animal feces
alkaline soil locations
areas with precipitation to evaporation ratio is .75 or less, flat areas with high water table, weathering of primary minerals in rocks and parent materials
Mites/Collembolans
arthropods that are prominent among the mesofauna that play important roles in soil food web mites are arachnids collembolans/springtails are insects springtails get their name from their springlike furcula or "tail" (arrows) eat detritus, fungi, smaller arthropods, nematodes, and other denizens of the soil
Sodic soil
a soil that contains sufficient sodium to interfere with the growth of most crop plants and in which the sodium adsorption ratio is 13 or greater low levels of neutral sodium salts relatively high levels of sodium on the exchange complex very high pH (8.5-10+) low soil organic matter that moves to surface due to pH low permeability to water/air due to clay dispersion poor to no plant growth
lower soil pH
add acid OM and inorganic chemicals
Soil food web
complex network of interconnected food chains in an ecosystem; in this case, in the soil.
C/Ration on plant growth
as plants mature their C/N increases because proteins in plants decline while lignin and cellulose increase
Ecological Engineers: Termites
eat dead plant material invert soil while building their mounds create islands of soil fertility
Expanding silicate clays: Smectite groups
flake-like crystals high amount of mostly negative charge resulting from isomorphous substitution; most of the charge derives from Mg2+ ions substituted in the Al3+ positions of the octahedral sheet, but some also derives from substitution of Al3+ ions for Si4+ in the tetrahedral sheets capacity to adsorb cations is very high adjacent layers are only loosely bound to each other by very weak oxygen-to-oxygen and cation-to-oxygen linkages and the space be- tween is variable Flake-like smectite crystals tend to pile upon one another, forming wavy stacks that con- tain many extremely small ultramicropores; adsorption of water in these ultramicropores leads to significant swelling; when they re-dry, the soils shrink in volume expansion upon wetting contributes to the high degree of plasticity, stickiness, and cohesion that make smectitic soils very difficult to cultivate or excavate
roles of fauna
food web sources of energy and carbon producers consumers decomposers ecosystem engineering soil fertility
Roles that fungi play in the ecosystem
form and stabilize OM and soil aggregates
Effect of pH on microorganisms
fungi predominate in low pH bacteria dominate in intermediate to high pH
Root exudate
further stabilize soil aggregates by supporting myriad of fungi and bacteria
Sodium Absorption Ratio (SAR)
gives information on the comparative concentrations of Na+, Ca2+, and Mg2+ in soil solutions An SAR value of 13 for the solution extracted from a saturated soil paste is approximately equivalent to an ESP value of 15. The SAR of a soil extract takes into consideration that the adverse effect of sodium is moderated by the presence of calcium and magnesium ions. The SAR also is used to characterize irrigation water applied to soils For Equation: [Na+], [Ca2+], and [Mg2+] are the concentrations (in mmol of charge per liter) of the sodium, calcium, and magnesium ions in the soil solution
Shrooms
grow in moist and organic residues, above and below ground
Ways to ameliorate soil acidity
gypsum application, OM, selecting adapted plants
Promote clay flocculation and soil permeability
hight salt concentrations and strongly attracted ions (Ca)
Soil fungal to bacterial ratio
hundreds of species of fungi to thousands of species of bacteria
pH dependent charge
hydroxyls and other functional groups on the surface of the colloidal particles that may release or accept H+ ions thus providing either negative or positive charges
Exchangeable Sodium Percentage (ESP)
identifies the degree to which the exchange complex is saturated with sodium ESP levels greater than 15 are associated with severely deteriorated soil physical proper- ties and pH values of 8.5 and above
Net positive charge
if the substitutiong cation has a higher charge than the ion for which is substitutes
liming materials
increase pH using alkaline materials that provide CB of weak acids (CO3 2-, OH-, SiO3 2-) most often applied in their Ca of Mg forms
Hyphae
individual fungal filiments
Exchangeable (salt replaceable) soil acidity
involves the al and h that are easily exchangeable by other cations in a simple unbuffered salt solution (HCl)
Nonexpanding Silicate Clays: Chlorite
iron or magnesium, rather than aluminum, occupy many of the octahedral sites Commonly, a magnesium-dominated trioctahedral hydroxide sheet is sandwiched in between adjacent 2:1 layers; thus chlorite is sometimes said to have a 2:1:1 structure nonexpansive because the hydroxylated surfaces of an intervening Mg-octahedral sheet are hydrogen-bonded to the oxygen atoms of the two adjacent tetrahedral sheets, binding the layers tightly together. colloidal properties of the chlorites are therefore quite similar to those of the fine-grained micas
Soil Organic Matter vs Soil Organic Carbon
matter-entire organic portion of soil carbon- about half of SOM is C
Secondary consumers
microbes (bacteria and fungi) and animals that consume other animals
Causes of Soil Alkalinity
minimal leaching in dry environments decreases soil acidification dissociation of calcite and carbonic acid to form carbonate (CO3 2-) and bicarbonate (HCO3-)
Fe and Al oxide clays
modified octahedral sheets with either fe or al, do not have large negative charge, strongly adsorb and combine with anions, construction, nonexpansive and generally exhibit relatively little stickiness
Reclamation of sodic soils
must reduce level of exchangeable na+ with gypsum or sulfur then keep rooted vegetation and air injection
Reclamation of saline soils
need to leach salts from soil depending on effective drainage and availability of irrigation deep rooted plants artificial drain
mycelia
networks of branched hyphae adapted for absorption
forms of N taken up by plants
nitrate (NO3-) for growth and development ammonium (NH4+) for proteins
Rhizobia
nitrogen fixing bacteria, grow right on plant roots
Mucigel
nonwater, soluble gel like substance that is used to lubricate the roots pushing through the soil
N roles in human nutrition
nucleic acids- DNA amino acids- proteins
How salts effect plants
nutrient deficiency soluble salts lower the osmotic potential of soil water Na can take the place of K limited air and water
Autotrophs
obtain their carbon from carbon dioxide and energy from photosynthesis (photoautotrophs) or oxidation (chemoheterotrophs)
Protozoa
one celled eukaryotic organisms such as amoeba
Inner sphere complexes
one or more direct bonds formed between the adsorbed ion and the atoms in the colloid surface, no water
Anion Exchange capacity
opposite of CEC, decrease with increasing pH
Role of bacteria in ecosystem
oxidation and reduction of certain chemicals including in orange ions such as fe and mg
ideal pH
pH 5.5-7
humid region pH
pH tends to be lower, dry higher
Algae
photoautotrophs, produce substantial amount of OM in some fertile soil contribute to the forming of macrobiotic crusts
Bad effects of soil fungi and bateria
plant pests and parasites, plant disease
Legumes
plants of the bean and pea family, with seeds that are rich in protein compared with other plant-derived foods famous for their distinctive ability to provide the major biological source of fixed nitrogen in agricultural soils
Decomposition
plants store C so when they die and are broken down the C is added back
Functional Redundancy
presence of many organisms that carry out each task
Detritivores
primary consumers that feed on detritus
Nitrogen Fixation
process converts the inert dinitrogen gas of the atmosphere (N2) to reactive nitrogen that becomes available to all forms of life through the nitrogen cycle. carried out by a limited number of bacteria, including several species of Rhizobium, actinomycetes, and cyanobacteria (formerly termed blue-green algae).
Salinization
process of accumulation of salts in the soil
Archea
prokaryotic, live in extreme environments, all live without oxygen and get energy from inorganic molecules and light most are unicellular
Slow Organic Matter
properties intermediate between the active and passive pools and half-lives typically measured in decades experiments have shown that under warm conditions a greater proportion of a soil's carbon will turn over at rates rapid enough to be characterized as active organic matter than would be the case when the same soil is kept cold.
CO2 evolution
reacts with soil to produce carbonic acid and carbonates and bicarbonates that are soluble and taken up by plants
Heterotrophs
rely on organic compounds for their carbon and energy
Plant roots
responsible for a quarter to a third of respiration in soil, heavily influence chemical and physical properties
Cation Exchange Reactions
reversible, charge equivalent, ration law, mass action (precipitates, volatilizes, strongly associates and therefore not reversible, cation selectivity, complementary ions,
Anion exchange
same at CE but colloids are positive, and the exchange is among negatively charged particles
Forms of Nitrogen Taken Up by Plants
dissolved nitrate (NO3-) and ammonium (NH4+ ) ions certain plants grow best when provided mainly with one or the other of these forms, a relatively equal mixture of the two ions gives the best results with most plants nitrite ions (NO2-) can also be taken up, but fortunately only trace quantities of this toxic ion usually occur in field soils.
Microbial Metabolism
driving force behind the development and maintenance of the planet's biosphere basically just organisms converting one organic molecule into another for energy microbial metabolism produces chemicals that can be beneficial or harmful to other organisms survival
Complementary
the likelihood that a given adsorbed cation will be displaces from a colloid is influenced by how strongly its neighboring cations are adsorbed to the colloid surface
Leaching (forms lost)
the main form of nitrogen subject to leaching loss is nitrate: negatively charged nitrate ions are not adsorbed by the negatively charged colloids that dominate most soils, so they move downward freely with drainage water and are readily leached from the soil Subsurface flow of dissolved nitrogen is commonly the pathway accounting for the greatest losses of nitrogen from upland ecosystems, especially agroecosystems in some cases subsurface flow carries substantial amounts of DON
pKa
the negative log of the acid dissociation constant or Ka value. A lower pKa value indicates a stronger acid. That is, the lower value indicates the acid more fully dissociates in water.
pH
the negative logarithm of the hydrogen ion activity (concentration) of a soil
CEC roles in ecosystem
the percentage saturation of essential nutrient cations such as calcium and potassium greatly influence the uptake of these elements by growing plants
Immobilization
the process in which nitrate and ammonium are taken up by soil organisms and therefore become unavailable to crops Basically, mineralization in reverse
Acid saturation
the proportion or percentage of a cation exchange site occupied by acid cations
Isomorphous substitution
the replacement of one atom by another of similar size in a crystal lattice without disrupting or changing the crystal structure of the mineral isomorphous substitution of similarly sized ions can occur in both types of sheets and is responsible for the charges of the clays due to differences in the charges if the subsituted ion from they typical one
Nitrogen cycle
the series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition.
Cation exchange capacity (CEC)
the sum total of exchangeable cations that a soil can absorb
basic cations
those cations that do not react with water by hydrolysis to release H+ ions to the soil solution Ca2+, Mg2+, K+, Na+
root hairs
tiny hair-like extensions that increase the surface area of the root allowing it to absorbs more water and nurtients 10-50 μm in diameter
Root cap
tip of the root that is tougher and consists of expendable cells that slough off ass the root pushed through the soil
Primary producers
vascular plants, mosses, algae, lichens, bacteria that do photosynthesis
Humus
very large net negative charge
Nematodes
very small (most microscopic) unsegmented round worms, prey on fungi and bacteria, can be good or bad wriggle their way through the labyrinth of soil pores, sometimes swimming in water-filled pores (like their aquatic cousins), but more often pushing off the moist particle surfaces of partially air-filled pores term-99 Moist, well-aggregated, or sandy soils typically have especially high nematode populations, as these soils contain abundant pores large enough to accommodate their movements. when there is too little water they can go into a cryptobiotic or resting state , in which they seem to be nearly impervious to environmental conditions and use no detectable oxy- gen for respiration feed on fungi, bacteria, and algae or prey on other soil animals microbial activity can be stimulated by light grazing or reduced by heavy grazing microbial-feeding nematodes excrete considerable soluble nitrogen (30-40% of the plant available nitrogen released in some ecosystems) can also give insects diseases (entomopathogenic) to kill them before they eat, making them an alternative to pesticides for farmers
Allophane
volcanic ash, bond to humus to protect it from decomposing have high amounts of both positive and negative charge, and high water-holding capacities plastic when wet, but not sticky extremely high capacities to strongly adsorb phosphate and other anions, especially under acid conditions
cycling of N in animal and human wastes
waste remains in soil as OM, whered it is then processed by microbes into soluble organic nirtogen, absorbed and fixed by clay colloids, converted to ammonia by bacteria, or lost from runoff and leaching
Outer sphere complexes
water molecules form a bridge between the adsorbed ion and the charged colloid surface
Challenges associated with alkaline soils
water supply for plants and desert pavement
Volatization of Ammonia
when ammonia gas (NH3) is produced from the breakdown of plant residues, animal excrement, and from such fertilizers as anhydrous ammonia and urea, it may diffuse into the atmosphere, resulting in a loss of valuable nitrogen from the soil and environmentally detrimental increases on nitrogen deposition from the atmosphere increased at higher pH because OH- ions drive the reaction to the right ammonia gas-producing amendments or the addition of water will drive the reaction to the left, raising the pH of the solution in which they are dissolved increased at higher temperatures ammonia losses are greatest where low quantities of soil colloids are present or where the ammonia is not in close contact with the soil examples if sistuations where loss is greatest: ammonia losses can be quite large from sandy soils and from alkaline or calcareous soils, especially when the ammonia-producing materials are left at or near the soil surface and when the soil is drying out
Dentrification
when nitrate ions are converted to gaseous forms of nitrogen by a series of widely occurring biochemical reduction reactions mostly done by facultative anaerobic bacteria, but some archea and fungi can also do it (usually done by a heterotroph) the oxygen released at each step would be used to form CO2 from organic carbon final nitrogenous gas released dependent mainly on the degree of oxygen depletion, as well as the prev- alent pH, temperature, and concentrations of nitrate and nitrite ions available
Yeasts
single celled, live in waterlogged, anaerobic soils
Effect of sodicity on soil physical properties
slake- tendency of aggregates to break up upon becoming wet swelling- na increases ability to swell, as they swell the large water draining pores are shut Dispersion- clay separates from itself making a gel like consistency
Benefits of soil bacteria and fungi
soil OM formation and nutrient cycling, breakdown of toxic compounds, inorganic transformations, nitrogen fixation, plant protection
C/N effect of microbial deomposition
steep slope int he beginning then even out, because a metabolic pool with high rates of initial decomposition representing with mainly cytoplast contents, a structural pool with slower initial decomposition that represents mainly cell wall constitutes
rhizosohere
that portion if the soil in the immediate vicinity of plant roots in which the abundance and composition of the microbial population are influenced by the presence of roots
Composting/Decay Process
(1) During a brief, initial mesophilic stage, sugars and readily available microbial food sources are rapidly metabolized, causing the temperature in the compost pile to gradually rise from ambient levels to over 40 °C. (2) A thermophilic stage occurs during the next few weeks or months, during which temperatures rise to 50-75 °C while oxygen-using thermophilic organisms decompose cellulose and other more resistant materials. Frequent mixing during this stage is essential to maintain oxygen supplies and assure even heating of all the material. The easily decomposed compounds are used up, and humuslike compounds are formed during this stage. (3) A second mesophilic or curing stage follows for several weeks to months, during which the temperature falls back to near ambient, and the material is recolonized by mesophilic organisms, including certain beneficial microorganisms that produce plant-growth-stimulating compounds or are antagonistic to plant pathogenic fungi
6 fates of N in No3
(1) immobilization by microorganisms; (2) removal by plant uptake; (3) microbial reduction to NO2- followed by conversion, along with ammonium, by anammox to N2O gas; (4) denitrification—microbial reduction forming N2 and other nitrogen-containing gases which are lost to the atmosphere; (5) dissimilatory reduction by microbes to ammonium; and (6) loss to groundwater by leaching in drainage water
Sources of Sulfur
(1) organic matter (2) soil minerals (3) sulfur gases in the atmosphere
P mineralization
-SUBJECT TO TEMP, MOISTURE, TILLAGE -READILY ABSORBED BY PLANTS -WHEN FORESTED SOILS ARE CULT THE P released by mineralization is high -degredation of everglades
Residual soil acidity
H and Al ions that are bound in nonexchangeable forms by OM and clay
changes in S deposition (acid rain)
-changes rain to ppH4 or lower -damage lakes, soils, plants -
scarcity of P v eccess P
-deforestation -pollutes aquatic systems
sulfur roles in plant nutrition
-essential amino acids: methionine, cysteine, cystine -vitamins and enzymes that regulate photosynthesis and N fixation -S-S links in amino acids
soil properties affected by SOM
-growth promoting compounds (vitamin, amino acids, hormones --encourages granulation and aggregate stability -reduce plasticity, cohesion, stickiness -increased infiltration rate & water-holding capacity -carbon abcorbing
3 main pools of combined P
-plant, animal, and human waste -rocks -ammendments (fertilizers)
N roles in plant nutrition
-plants are 2-4% N - amino acids, proteins enzymes -stimulate root growth Too little: plants go through chlorosis (older leaves broken down to feed new leaves) Too much: susceptibal to fungal disease
soil properties affecting SOM
-residue placement (surface=slower decomp) -Allelochemical effects: plant infuses soil with chemical
Meso organism
.1-2mm springtail mites
Expanding silicate clays: Vermiculite Group
2:1-type minerals in which the octahedral sheet is aluminum dominated (dioctahedral), but some magnesium-dominated (trioctahedral) vermiculites also exist. have consid- erable substitution of aluminum in the silicon positions, giving rise to a cation exchange capacity (CEC) that usually exceeds that of all other silicate clays interlayer spaces of vermiculites usually contain strongly adsorbed water molecules, Al-hydroxy ions, and cations such as magnesium; these interlayer constituents act primarily as bridges to hold the units together, rather than wedges driving them apart; the degree of swelling and shrinkage is, therefore, considerably less for vermiculites than for smectites. vermiculites are considered limited-expansion clays, ex- panding more than kaolinite, but much less than the smectites.
Competition
A common demand by two or more organisms upon a limited supply of a resource; for example, food, water, light, space, mates, nesting sites. It may be intraspecific or interspecific.
Effect of pH on plants
Al damages membrane sites where Ca is taken up and restricts cell wall, metabolism, DNA, and seed germination
role of Al in soil acidity
Al3+ ions are released in h+ exchange and then become adsorbed on the colloid cation exchange sites Al3+ ions also tend to split water and bond with OH, leaving H+ ions in the soil
Silicate clay
Crystalline: closely packed layers of two to four sheets of tightly bonded oxygen, silicon, and aluminum atoms; usually negative, but they are highly variable Noncrystalline Silicate Clays: consist mainly of tightly bonded silicon, aluminum, and oxygen atoms, but do not exhibit ordered, crystalline sheets; can be positive or negative; high water holding capacity; not sticky
sulfur cycle
Cyclic movement of sulfur in various chemical forms from the environment to organisms and then back to the environment.
greenhouse gasses
Gasses such as carbon dioxide, methane and water vapor that trap heat in the Earth's atmosphere and change Earth's climate. these gases allow short-wavelength solar radiation in but trap much of the outgoing long-wavelength radiation.
Effect of SOM on Soil Properties
Humus tends to give surface horizons dark brown to black colors Granulation and aggregate stability are encouraged, especially by the bacteria polysaccharides and fungal glomalin-associated glycoproteins produced during decomposition The protected particulate organic matter, char, and sorbed biomolecules in the humus help reduce the plasticity, cohesion, and stickiness of clayey soils, making these soils easier to manipulate. soils higher in organic matter tend to be more productive is their enhanced ability to supply plants with water because organic matter increases both infiltration rate and water-holding capacity water-holding capacity of very sandy soils can be improved by adding stable organic amendments humus colloids and high surface area char hold nutrient cations (potassium, calcium, magnesium, etc.) in easily ex- changeable form, wherein they can be used by plants but are not too readily leached out of the profile by percolating waters provides much of the pH buffering capacity in soils organic matter alleviates aluminum toxicity by binding the aluminum ions in nontoxic complexes
Sulfur Compounds to Raise Acidity
If nitrogen is needed for fertility, its supply as ammonium sulfate (NH4)2SO4) will promote rapid acidification. As the sulfur undergoes microbial oxidation in the soil (see Section 13.20), 2 moles of acidity (as sul- furic acid) are produced for every mole of S oxidized: 2S + 3O2 + 2H2O -----> 2H2SO4
Main sources of human influenced soil acidity
Nitrogen fertilizers (NH4+ oxidized), Acid deposition, Exposure to potential acid sulfate materials (introducing oxygen to normally anaerobic soils oxidizes sulfur)
N role in eutrophication
Nitrogen fertilizers run off into water, inducing overgrowth of algae, which blocks out the sun, causing other plants to die, causing O2 levels to drop, eventually resulting in a "dead zone"
Accumulation of Organic Matter
OM forms soluble complexes with cations such as Ca and Mg, therefore the soil losses these cations OM contains numerous acid functional groups from which H+ ions can disassociate
Soil Organic Matter incorportation
OM is adsorbed onto soil colloid surface or occluded inside soil aggregates where it is protected from further metabolism
R strategists
Opportunistic organisms with short reproductive times that allow them to respond rapidly to presence of easily metabolized food sources
Oxidation of Nitrogen (Nitrification)
Oxidation reactions have h+ as a product, Nh4+ from OM go through oxidation to get NO3-
Cyanobacteria
Photosynthetic, oxygen-producing bacteria (formerly known as blue-green algae). fix nitrogen
Protected Carbon/Humus
Protection of at least some C from microbial respiration in the form of humus enables soils to accumulate increasing amounts of organic matter over years and centuries Humus colloids include tiny particles of char as well as multiple layers of organic compounds with varying degrees of polarity sorbed to clay surfaces exhibit very high levels of surface area and negative charge—similar per unit volume to those of high-activity clay, but much greater than clay when compared per unit mass. based on pH, the cation exchange capacity of humus may range from about 150 to as high as 500 cmolc/kg (about 40-120 cmolc/L). water-holding capacity of humus on a mass basis (but not on a volume basis) is four to five times that of the silicate clays. promotes aggregate formation and stability, and, in turn, the aggregate structures help protect the humus from decay. humus imparts a black color to soil as is most characteristic of O, A, and Bh horizons
Acids in Precipitation
Rain, snow, fog all have H+ ions that contribute to the soil
Active soil acidity
Results from the h+ ions in the soil solution
Building Blocks of Layered Silicates
Silica Tetrahedral Sheets and Aluminium Octahedral Sheets Two to four of these sheets may be stacked together in sandwich-like arrangements, with adjacent sheets strongly bound together by sharing some of the same oxygen atoms The specific nature and combination of sheets in these layers (The relationship between planes, sheets, and layers) vary from one type of clay to another and largely control the physical and chemical properties exhibited. isomorphous substitution of similarly sized ions can occur in both types of sheets and is responsible for the charges of the clays due to differences in the charges if the subsituted ion from they typical one
Aluminium Octahedral Sheets
Six oxygen atoms coordinating with a central aluminum or magnesium atom form the shape of an eight-sided geometric solid Numerous octahedra linked together horizontally constitute the octahedral sheet
Effect of sodium on plant growth
Soil dispersion causes clay particles to plug soil pores, resulting in reduced soil permeability low soil porosity damages plants ability to get water and oxygen needed for growth
biodiversity
The amount of biological or living diversity per unit area. It includes the concepts of species diversity, habitat diversity and genetic diversity.
Grazing Microbial Colonies
The grazing by these meso- and microfauna on microbial colonies may stimulate faster growth and activity among the microbes, in much the same way that grazing animals can stimulate the growth of pasture grasses. Sometimes, the attack of the microphytic feeders may kill off so much of a microbial colony as to inhibit the work of the microorganisms.
Passive Organic Matter
The more stable and well-protected portion of the humus fraction where carbon is not readily accessible to microbes and remains in the soil for hundreds or even thousands of year closely associated with the colloidal properties of soil humus and is responsible for most of the cation- and water-holding capacities contributed to the soil by organic matter. includes most of the humus physically protected in clay-humus complexes, POM protected inside microaggregates, and chemically stable bits of char. Passive organic matter accounts for 60-90% of the organic matter in most soils its quantity is increased or diminished rather slowly.
Nonexpanding Silicate Clays: Micas
The more weathered fine-grained micas, such as illite and glauconite, are found in the clay fraction of soils. main source of charge in fine-grained micas is the substitution of Al3+ in about 20% of the Si4+ sites in the tetrahedral sheets. This results in a high net negative charge in the tetrahedral sheet, even higher than that found in vermiculites The negative charge attracts cations, among which potassium (K+) is just the right size to fit snugly into certain hexagonal "holes" between the tetrahedral oxy- gen groups and thereby get very close to the negatively charged sites. By their mutual attraction for the K+ ions in between, adjacent layers in fine-grained micas are strongly bound together; the fine-grained micas are quite nonexpansive. more like kaolinite than smectites with regard to their capacity to adsorb water and their degree of plasticity and stickiness.
active organic matter
The organic matter of the labile carbon pool consists of labile (easily decomposed) materials with half-lives (the time it takes for half of a mass of material to decay) of only a few weeks to a few years has a relatively high average C/N ratio (about 15-30) includes such organic matter fractions as the living biomass, tiny pieces of unprotected detritus, and many biomolecules Active organic matter rarely comprises more than 10-20% of the total soil organic matter. provides most of the readily accessible food for soil organisms and most of the readily mineralizable nitrogen responsible for most of the beneficial effects on structural stability that lead to enhanced infiltration of water, resistance to erosion, and ease of tillage. it can be readily increased by the addition of fresh plant and animal residues it is very readily lost when such additions are reduced or tillage is intensified.
Carbon Inputs
The original source of soil organic matter is plant tissue, and the amount of organic mat- ter accumulated in soils is partly a function of the net plant productivity that provides this material animals are secondary sources
Priming Effect
The peak level of microbial activity appears to accelerate the decay of the original humus, but the humus level is increased by the end of the process basically microbes use up a lot of the existing humus before dying and replenishing it, plus extra
Mineralization
The process by which fungal and bacterial decomposers break down the organic matter found in dead bodies and waste products and convert it into inorganic compounds that can be used again by organisms Steps: 1. Microbial decomposition breaks large, insoluble N-containing organic molecules into smaller and smaller units with the eventual production of simple amino compounds, or amine groups (R—NH2). 2. by the use of enzymmes that break C—H and C—NH2 bonds, the amine groups are hydrolyzed, and the nitrogen is released as ammonium ions (NH4+ ), which can be oxidized to the nitrate form
Basic saturation
The proportion of percentage of a cation-exchange site occupied by nonacid cations
Carbon Cycling
This one sucks, but it was easier to just put in the book's explination for the diagram than to try to rewrite it myself lol "The microbial biomass (upper right) produces (mainly exocellular) enzymes that break down plant residues and microbial compounds from previous decomposition cycles, transforming components into dissolved organic C compounds. When these compounds are metabolized by microbes to obtain energy, most of their C is released as CO2 while their other elements (N, P, S, etc.) may be released into the soil solution. The labile C (upper half of diagram) is subject to rapid metabolism, some components become stabilized (lower half of diagram). The soil environment and microbial activity control this stabilization and accumulation of organic matter. Bits of plant tissue and microbial cell walls (particulate organic matter)may become inaccessible to microbial attack as microaggregates form around them. Microbial oxidation creates zones of polarity in formerly hydrophobic biomolecules, allowing their C to become protected by bonding to mineral surfaces. Low temperatures or oxygen levels preserve plant and microbial compounds. Fires produce black carbon materials, which may resist enzymatic oxidation. Over time an individual C atom may move among any number of these pools."
How to Increase/Decrease SOM Level
To increase active organic matter: addition of fresh plant and animal residues To decrease active organic matter: additions are reduced or tillage is intensified. productive soils managed with conservation-oriented practices contain relatively high amounts of organic matter fractions associated with the active pool, including microbial biomass, free particulate organic matter, and easily oxidizable organic matter
Measuring Salinity
Total Dissolved Solids- boil water off salt and weigh solids in mg/L Electrical Conductivity- conductivity increases with more and more salt in water Electromagnetic (EM) Induction- done in the field to conductivity and therefore salinity
Tertiary consumers
Use secondary consumers as prey
Salinization of irrigated soil
Water is poured onto soil and evaporates, leaving behind salts. Over time, as this is repeated, nothing will grow there anymore due to heightened salt concentrations.
Pathogen
a biological agent that causes disease or illness to its host.
Actinomycetes
a group of bacteria that form branched mycelia that are thinner, but somewhat similar in appearance to fungal hyphae their biomass often exceeds that of the other bacteria pH values between 6.0 and 7.5 Streptomyces, produce compounds that kill other microorganisms (antibiotics) fix atmospheric nitrogen gas into ammonium nitrogen Generally aerobic heterotrophs, the actinomycetes live on decaying organic matter in the soil or on compounds supplied by plants with which certain species form parasitic or symbiotic relationships. Important for decomposition and the nutrients released back into the soil produced by this process earthy aroma of OM rich soils due to these guys
Endo mycorrhiza
a symbiotic association of the mycelium of fungi and roots of a variety of plants in which the fungal hyphae penetrate directly into the root hairs, other epidermal cells, and occasionally cortical cells, individual hyphae also extend from the root surface outward into the surrounding soil
ecto mycorrhiza
a symbiotic association of the mycelium of fungi and the roots of certain pants in which the fungal hyphae for a compact mantel on the surface of the roots and extend into the surrounding soil and inward between cortical cells but not into these cells
Ecological Engineers: Dung beetles
cut round balls from large mammal feces, enabling them to roll the dung balls to a new location, nutrient cycling and conservation in grazed ecosystem
Detritus
debris of dead tissues left by plants on the soil surface and within the soil pores
Oxidation of Sulfur
decomposition of plant residues or oxidation of sulfur in minerals (pyrite) results on -SH groups to yield H2SO4
Fungi
eukaryotes- have a nuclear membrane and cell walls yeasts, molds, and mushrooms Biochemically and genetically they are more closely related to us humans than they are to such other microorganisms as bacteria or archaea. heterotrophs- they depend on living or dead organic materials for both their carbon and their energy. aerobic organisms- although some can tolerate the rather low oxygen concentrations and high levels of carbon dioxide found in wet or compacted soils.
Measuring sodicity
exchangeable sodium percentage- identifies the degree to which the exchange complex is saturated with sodium Sodium adsorption ratio- gives info on the comparative concentrations of Na+, Ca 2+, and Mg 2+
parisites
feed off living host
Saprophytes
feed on dead tissues
Net negative charge
isomorphic substitution of a lower charged ion (Mg 2+) for a higher charged ion (Al 3+)
Nitrogen Fixation by Legumes
known to develop nodules and to accommodate symbiotic nitrogen fixation when their root hairs are invaded by soil actinomycetes of the genus Frankia can colonize soils that are newly formed or infertile due to ability to fix their own nitrogen Once nitrogen-fixing plants become established and begin to build up the soil nitrogen supply through leaf litter and root exudation, the land becomes more hospitable for colonization by other species
Main pools of global C
soil, oceans and lakes
Conditions that favor soil fungi
some can tolerate low oxygen but prefer more, heterotrophs, tolerate low pH
Conditions that favor soil bacteria
some can tolerate no oxygen or oxygen, optimal moisture potential for plants, temp 20-40
Arbuscule
specialized branch structure formed within a root cortical cell by endomorphic mycorrhizal fungi
Herbivores
spol organisms that eat live plants
Nitrogen deposition
the addition of atmosphere-borne reactive nitrogen compounds (ammonium and nitrogen oxide) to soils through rain, snow, dust, and gaseous absorption. Deposition is greatest in high-rainfall areas downwind from cities (nitrate from nitrogen oxides in car exhaust and coal burning power plants), concentrated animal-feeding operations (CAFOs) (ammonium volatil- ized from manure), and fertilized wetland rice production The ratio of nitrate to ammonium nitrogen deposited varies with location, the nitrate share ranging from about one-third to two-thirds. leads to soil acidification methane oxidation capacities are decreased by deposition
Effective CEC
the amount of cation charges that a material can hold at the pH of the material
Phosphorus cycle
the cyclic movement of phosphorus in different chemical forms from the environment to organisms and then back to the environment
Ionic double layer
the distribution of cations in the soil solution resulting from the simultaneous attraction towards colloid particles by the particles negative charge and the tendency of diffusion and thermal forces to move the cations away from the colloid surfaces
charge equivalence
the ex- change takes place on a charge-for-charge basis Therefore, although one H+ ion exchanged with one Na+ ion in the reaction just shown, it would require two singly charged H+ ions to exchange with one divalent Ca2+ ion. If the reaction is reversed, one Ca2+ ion will displace two H+ ions.
Silica Tetrahedral Sheets
two planes of oxygens with mainly Si in-between , basic shape is one Si surrounded by four O
Liming
used to change the chemical makeup of a substantial part of the root zone
Aluminium toxicity
when pH drops from 5 to 4 not a problem in OM The water draining from acidified soils often contains elevated levels of aluminum, as well as sulfate and nitrate. When this alumi- num-charged soil drainage eventually reaches streams and lakes, these bodies of water become lower in calcium, less well-buffered, more acid, and higher in aluminum. The aluminum is directly toxic to fish, partly because it damages gill tissues. aluminum can be effectively detoxified in acid soils by strong binding to high molecular weight organic com- pounds associated with stable soil organic matter or by weaker bonding with small organic molecules associated with microbial decomposition and root exudates.
Plant Uptake of Cations
when plants take up far more cations than they do of anions, plants oxide H+ ions