ESSM 309 Final Review

How much water can plants retain?

Plants retain only a FRACTION of the water they take up through their roots for cell expansion and plant growth.

Where does the rest of the water go, if not retained?

The rest is loss through TRANSPIRATION.

Transpiration

loss of H2O (WATER) and O2 (OXYGEN) from leaves

What is the MOST LIMITING FACTOR to plant growth and productivity?

WATER

Stomata

Greek for "mouths"; pores in leaves that allow for CO2 to enter and O2/H2O to exit leaf

What must the stomata do for plants to build sugars? What does it risk?

STOMATA MUST BE OPENED; risks being dried out

SPAC (Soil Plant Atmosphere Continuum)

cycling of water from the soil, through the plant into the atmosphere and back to the soil. (CONTINUOUS WATER TRANSPORT PATHWAY)

Cohesion-tension theory

water movement thru plants by cohesion, adhesion, and negative pressure generated by the evaporation of water from the leaves. (transpiration)

Adhesion

the property of water that allows it to cling to other surfaces

Cohesion

the property of water that bonds water molecules to other water molecules

Negative Pressure

-1 to -10 MPa (megapascals); pressure that moves water thru trees because of gradient difference due to water loss thru transpiration.

At what pressure can humans suck through a straw?

About -25 kPA, or .025 MPa

Cavitation

when a water cavity collapses due to extreme negative pressure; can be detected acoustically with sensors

Embolism

obstruction of a water cavity caused by an air bubble formed from metastable water

Conduit

paths that water follows on its way up the tree (piping)

Tracheid

conduits found in conifers; shorter in length (0.1-1.0 cm) and diameter (5-80 um) than angiosperms.

Vessel

conduits found in angiosperms; longer in length (1-1000+ cm) and longer in diameter (15-500 um) than gymnosperms

True/False - Water can't flow through xylem conduits that have been embolized (or filled with air).

TRUE

True/False - Cavitation of a million conduits IS FATAL.

FALSE

What are Ultrasonic Emissions Sensors?

The detect sounds beyond the range of human hearing.

What results can be achieved from XYLEM STAINING?

Only the FUNCTIONING (water-filled) xylem get stained;
NON-FUNCTIONAL (air-filled) xylem DO NOT get stained

True/False - All conduits are the same.

False

True/False - Xylem Size can change through the growing season.

True

Earlywood

xylem vessels grown at the beginning of the spring growing season

Latewood

xylem vessels grown later in the growing season (summer)

primary producers

plants; create their own food source; don't need to consume others to produce energy (usually)

What are embolized conduits?

Redundant pathways

What is the tradeoff between growth rate and vulnerability to cavitation?

FAST GROWING SPECIES tend to have large, efficient conduits that are vulnerable to cavitation.

SLOWER-GROWING SPECIES tend to have smaller, less efficient conduits that are more resistant to cavitation.

True/False - SLOWER GROWING SPECIES tend to survive better during droughts.

True

What ABIOTIC FACTORS can disrupt water transport?

• Drought

• Freezing Temperatures

What BIOTIC factors can disrupt water transport?

• Root Pathogens (bacteria or fungi)

• Foliar Pathogens (bacteria or fungi)

• Insects

How can trees survive from an EMBOLISM?

• Divert water around embolized conduits

• Grow new xylem

• Some plants can refill embolized conduits, but the mechanism is not understood.

Primary Producers

An autotroph, usually a photosynthetic organism. (PLANTS) Collectively, autotrophs make up the trophic level of an ecosystem that ultimately supports all other levels.

True/False - All plant growth begins with energy from the sun.

True

Photosynthesis

light driven process of carbon uptake and assimilation in green plant to produce energy; (6CO2 + 6H2O + light = C6H12O6 + 6O2)

Light Use Efficiency (LUE)

only 3-6% of absorbed light is converted into chemical energy

Gross Photosynthesis (Whole Canopy or Ecosystem)

Total amount of CO2 assimilated through the process of photosynthesis.

Respiration

Opposite of photosynthesis; CO2 lost to atmosphere through consumption of carbohydrates (in leaves and all living tissues)

Another RESPIRATION Definition

Plants & animals/microbes use oxygen and release CO2 in order to access stored energy to grow and maintain functions.

Net Photosynthesis

Net CO2 gain by leaves (the starting point for carbon allocation and growth)

Net Photosynthesis Equation (relation to leaf level)

Gross Photosynthesis (leaves) - Respiration (leaves)

Where does photosynthesis occur?

Chloroplast

What is the key enzyme in photosynthesis?

Rubisco

Where does respiration occur?

mitochondria (same as us); ATP synthesis

Factors Limiting Photosynthesis

Light
Water
Temperature
Nutrients

True/False - Photosynthesis increases with higher light intensities, but saturates at a maximum rate.

True

Sun Leaves

higher photosynthetic rates but also higher rates of respiration
higher leaf angle - seems to avoid sunlight during the hottest part of day.
- lighter in color; smaller; thick; higher light saturation point

Shade Leaves

lower rates of photosynthesis per unit mass but larger display area and lower respiration.
lower leaf angle - captures more light
- darker green; bigger; thin; more chlorophyll

True/False - Warmer temperatures increase photosynthesis up to an optimum temperature.

True

True/False - Respiration increases exponentially with a linear increase in temperature.

True

True/False - Gross Photosynthesis is LOWEST AT TEMPERATURE extremes and thus carbohydrate gain is LIMITED.

True

Why does NET PHOTOSYNTHESIS increase with temperature but then decreases with very high temperature?

Respiration increases and leaf enzyme lose function.

True/False - Respiration is the loss of CO2 from plants as mitochondria use carbohydrates to produce energy.

True

What limiting factor affects photosynthesis by causing plants to open or close stomata?

Water availability

True/False - Water availability DOES NOT depend on soil texture.

False, IT DOES

Why is NITROGEN is especially important to the limiting factor of NUTRIENTS?

Rubisco, the primary enzyme involved in fixing carbon requires a lot of nitrogen.

What type of forests are generally more likely to be Nitrogen limited?

Temperate and Boreal Forests

What type of forests are more likely to be Phosphorus limited?

Tropical Forests

Why do we care so much about photosynthesis?

• Plays very important role in global carbon cycle

• Primary production by plants forms basis of food chains and manny, many products that humans consume.

Why does NPP (net primary production) matter so much?

Nearly 25% of global NPP is used by humans annually in production of crops for food and fiber, timber for wood products and paper, and in support of livestock grazing.

gross primary production (GPP)

whole ecosystem photosynthesis

net primary production (NPP)

GPP - R autotroph;
GPP - autotrophic respiration
Plant growth or the addition of new tissue

autotrophic respiration (R autotroph)

respiration by plants/primary producers

heterotrophic respiration (R heterotroph)

respiration by animals

net ecosystem production (NEP)

Net accumulation of carbon in the ecosystem
NPP - Heterotrophic respiration
GPP - (R autotroph + R heterotroph + other losses due to herbivory, leaching, etc.)

True/False - Absorbed light can remotely sensed with (with satellites or airplanes) and converted to NPP with light use efficiency (LUE)

True

What variables correlate with NPP?

• Leaf Area Index

• Length of Growing Season

In areas with higher nutrient levels plants put less CARBON toward roots and below-ground biomass and more towards leaves and roots. Why?

Amount of respiration emitted?

Relationship between NPP & enviro. factors (Precipitation & Temperature)

On a global scale ecosystem productivity increases with increasing mean annual temperature (heat) and precipitation;

Forest Biomass

The total dry mass of living organisms and dead organic matter per unit area (hectare). Indexed in (tons/ha)

How is LIVING FOREST biomass separated?

• OVERSTORY (canopy trees)

• UNDERSTORY (young trees that grow into canopy, or species that live near the ground)

How is DEAD MASS separated from LIVE BIOMASS?

• FOREST FLOOR (leaves, twigs, decomposed material not in mineral soil - the O Horizon)

• SNAGS (standing dead trees)

• COARSE WOODY DEBRIS

• SOIL ORGANIC MATTER

What are the essential elements?

Hydrogen (H), Carbon (C), Oxygen

Macronutrients

Nutrients required in large amounts: N, P, K , Ca, Mg , S.

Micronutrients

Nutrients required in small amounts: Cu, Zn, Cl, Mn, Fe, B, Mo, Ni.

What are the beneficial elements?

Sodium (Na), Silicon (Si), Cobalt (Co)

Phytoremediation

use of plants to clean up environmental hazards by improving soils, water and air contamination / quality.

Chelation

• many metals are insoluble at normal pH

• roots & mycorrhizal fungi release organic compounds that grab metal ions (Fe, Cu, Zn) so they can be available to plants & microbes

Atmospheric Deposition

• "dry" deposition or dust

• "wet" deposition or nutrients in solution

How do plants receive nutrients they can use? (Sources of Nutrients

• Weathering of Rocks

• Atmospheric Deposition

• Removal from air: nitrogen fixation by bacteria, lightening

• Deposition from upslope/upstream erosion

relationship between nutrient concentration and growth

Nutrients are deficient, critical, luxury consumption, toxicity

Forest Fertilization

• widely used strategy in industrial forestry

• mostly N and P fertilization

• micronutrient deficiencies in some older weathered soil (Australia, South America, SE United States (Ultisols and sandy Spodosols)

• has become STANDARD OPERATING PROCEDURE for most regions of world with intensive plantation forestry.

True/False - Forest fertilization has increased dramatically over the past 40 years in loblolly pine stands in SE US.

True

What are the 4 COMPONENTS OF SOILS?

Mineral Water (45%)

Organic Matter (5%)

Water (25%)

Air (25%)

What are the COMPONENTS OF MINERAL SOILS?

Derived from igneous rock (volcano), metamorphic rock, and sedimentary rock

Sand (.05 to 2 mm)

Silt (.002 - .05mm )

Clay (less than .002mm)

What is WEATHERING?

The chemical and physical transformation of rocks or mineral soil constituents by pressure, temperature change, water, and organic acids

What is Field Capacity?

The amount of water held against gravity due to cohesion to other water molecules and adhesion to soil particles

What is a Permanent Wilting Point?

The point at which soil moisture potential has dropped beyond the plants ability to uptake water and the plant cannot recover and will wilt and die

Cohesion and adhesion forces exceed most plants' ability to draw water

What is Hygroscopic Water?

Water that is tightly bound to soil particles - cannot be drawn up

What is Soil Organic Matter?

Plant residues and living & dead microbial biomass

Soils can vary greatly in % SOM; - grassland may have 5-6% in surface horizon
- sandy desert soil may have

What is turnover?

When small roots grow and die every couple of years

What is Cation Exchange Capacity (CEC)?

A soils ability to hold on to and supply nutrients like calcium, magnesium, and potassium over time

Mycorrhizosphere

Zone affected by roots and mycorrhizal fungi - roots and microbes exude hormones, chelators (grab metals), enzymes

lots of microbes

lots of Organic Matter deposited here

lots of decomposition occurs

Why is soil organic matter important?

Helps to maintain soil structure

Stores air & water

Carboxyl groups increases cation exchange capacity

Reduces stickiness of clays (easier to till in agricultural systems)

Food source for many organisms

Stores Carbon

What is the primary source of Nitrogen for a plant?

Soil Organic Matter

Soil Horizons (O, A, E, B, C, R)

Layers of soil

Erosion or agriculture may mean not all horizons exist

O - organic; fresh decaying organic material

A - mineral mixed with humus, dark colored

E - zone of eluviation, leaching

B - zone of accumulation (Fe & Al)

C - zone of unweathered parent material

R - regolith / bedrock

Soil Horizon Development
(Pedogenesis)

Additions

Losses

Translocations

Transformations

O Horizon

Organic horizon consists of fresh and decaying plant residue from leaves, needles, twigs, moss, lichens

Typically dark in color

A Horizon

Mainly mineral material

Generally darker than the lower horizons because of the varying amounts of organic matter

Where most ROOT activity occurs

Most PRODUCTIVE layer of soil

E Horizon

Zone of eluviation is generally bleached or whitish

As water moves down through this horizon, soluble minerals and nutrients dissolve and some dissolved minerals are washed (LEACHED) out

Main feature of this horizon is the loss of silicate clay, iron, aluminum, humus, or some combination of these, leaving a concentration of SAND AND SILT PARTICLES