Exam 2 Terms

evaporation

transforamtion/loss of H2O from a liquid to gaseous form; transformation of liquid H2O to H2O vapor

transpiration

loss of H2O vapor from leaves through stomates

evapotranspiration

total return of H2O to the atmosphere from the Earth’s surface, including evaporative loss from surface H2O and loss of H2O from plants

water balance equation

P = SS + ET + D

interception

water caught by canopy

antecedent conditions

conditions that occur prior to an event

throughfall

the precipitation that percolates down through the plant canopy

stem flow

amount of precipitation that flows down the stem of a tree

fragipan

area of a soil resistant to root growth and water movement

-0.015 MPa

typical soil water potential at field capacity

-0.2 MPa

typical root water potential

-0.6 MPa

typical stem water potential

-1.5 MPa

typical leaf water potential

-100 MPa

typical atmosphere water potential

hydraulic redistribution

ability of roots to both take up and to release water

hydrophyte

plant that is adapted to very high water content soils, and thereby also adapted to low oxygen in soil

aerenchyma

plant adaptation that allows oxygen to diffuse through tube into roots

pneumatophores

roots that grow down into the substrate and then back up allowing access to oxygen in hydrophytes

mass flow

movement of air physically through pores in soil

diffusion

movement of materials in response to concentration gradient

nitrogen fixation

method by which specialized bacteria utilize gaseous nitrogen

redox potential

tendency or potential for electrons to be transferred from one substance to another

frost heaving

forcing of objects upward in the soil by alternative freezing and thawing

albedo

measure of whiteness/reflectiveness

specific heat

amount of energy required to increase temperature by 1 degree C

colloid

A very finely divided substance which is scattered throughout another substance in soil

colloidal fraction

clay and humus particles in soils

internal surface area

the area of surface exposed within clay crystal between the individual crystal layers

cation

positively charged ion

cation exchange

the interchange between a cation in solution and another cation on the surface of any surface-active material, such as clay or organic matter

adsorbed ions

cations swarming swarming about near the colloidal surface, loosely held

exchangeable ions

cations that can change places with those moving freely about in a soil solution

ionic double layer

distribution of cations in the soil solution resulting from the simultaneous attraction toward colloid particles by the particles’ negative charge and the tendency of diffusion and thermal forces to move the cations away from the colloid surfaces

kaolinite

1:1 crystalline silicate clay with no interlayers, low ability to absorb water, low carrying capacity, used in construction

smectite

expanding 2:1 crystalline silicate clay with isomorphous substitution leading to high interlayer negative charge and high CEC, allowing significant interlayer expansion

montmorillonite

an aluminosilicate clay mineral in the smectite group with a 2:1 expanding crystal lattice; highly adsorptive, has interlayers

crystalline silicate clays

includes smectite, vermiculite, fine mica, kaolinite, and chlorite

Fe/Al Oxides

includes gibbsite, geothite

phyllosilicates

silicate clays with leaf-like, or planar structure, composed of 2 kinds of horizontal sheets

dioctahedral

octahedral sheet in 2:1 type clay dominated by aluminum

trioctahedral

octahedral sheet in 2:1 type clay dominated by magnesium

isomorphous substitution

one element fills a position usually filled by another of similar size

noncrystalline silicate clays

includes allophane, imoglite; nonsilicate colloids with either Fe3+ or Al3+ in the cation positions; have niether tetrahedral sheets nor silicon; isomorphous substitution occurs rarely

Humus

noncrystalline heterogeneous organic substances

cation exchange capacity

sum total of the exchangeable cationic charges that a soil can absorb

ratio law

states that, at equilibrium, the ratio of Ca2+ to Mg2+ on the colloid will be the same as the ratio in the solution and both will be the same as the ratio in the overall system

buffer CEC methods

method for determining cation exchange capacity in which a buffer solution is used; exaggerates the true CEC of acid soils

Effective CEC

method of determining cation exchange capacity in which the reaction occurs at the actual pH of the soil; measures potential or maximum CE

organic soil colloids

includes humus

protonation

attachment of protons to exposed OH groups on the surface of soil particles resulting in an overall positive charge on the particle surface

ecology

study of the interactions of organisms and their environment

functional diversity

biodiversity

heterotroph

organism that gains carbon through combined organic carbon

autotroph

organism that gains carbon thorugh carbon dioxide or carbonate

chemotroph

organism that gets energy from biochemical oxidation

phototroph

organism that gets energy from solar radiation

primary producer

trophic level that contains primary producers and the most energy

primary consumers

trophic level that directly consumes primary producers, including herbivores, detritivores, and saprophytes

saprophytic microbes

organisms that consume dead material and decompose it without eating it

secondary consumers

trophic level that consumes primary consumers, including earthworms, nematodes, and mites

higher level consumers

trophic level that consume secondary consumers and beyond, such as amoebas, earthworms, mites, athropod predators, nematodes, mammals, and birds

anecic earthworm

very long earthworm that burrows deeply

middens

casts created by anecic earthworms containing aggregation of dead plant material

parasatoids

parasite-like organisms that kill their hosts

rhizosphere

small zone outside fine roots used for nutrient uptake

rhizodeposition

all materials lost or excreted from plant roots

mucigel

gel-like substance excreted by cells near root tip to lubricate its push through the soil

mycorrhizae

mutualistic relationship between plants and fungi

cyanobacteria

soil algae that photosynthesizes and fixes nitrogen

hyphae

fungal filament

mycelium

twisted together fungal hyphae

soil actinomycetes

long filamentous bacteria that are beneficial to increasing fertility of soil