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