FOREST 3

Plants contribute extensively to the water cycle?

Vegetation type both depends on and affects water availability (locally and regionally)

Evapotranspiration cools land surface: deforestation = warming

Plants keep water from flowing downstream, produce transpiration

Anthropogenic land cover change affects water cycle?

US Geological Survey

2022 water cycle diagram

Includes humans for the first time

Human influence is a major factor – find all components

most limiting abiotic factor to plant growth and productivity?

water

What can be some differences between different environmental systems?

Precipitation

soil water content

vapor pressure deficit

leaf area index

stomatal conductance

rooting depth

duration of water availability after rain

Temperature (affects ET, depends on specific heat (buffering capacity) of land cover

Atmospheric Demand (Sink)?

Humidity

Vapor pressure deficit (VPD) = Dryness

Holding of moisture in the air cause of saturation

Increases with temperature

Soil moisture (source)?

Water falling into soil cause of gravity

Only certain levels of thickness in soil can keep water

Saturatin

Field capacity

wilting point

Saturation?

all pares are full of water

Gravitational water is lost

Field Capacity?

Immidietly after rain fall

Available water for plant growth

Held by gravity

Wilting point?

No more water is available to plants

“Soil-plant-atmosphere continuum”?

Once water falls, its taken up through the roots and then released into the air from the leaves

Roots→plant→leaves→atmosphere

Capillary pores move to where it is negative, have the most pull

Pulling water against gravity

Trees move water at incredibly negative pressures (tension)?

Water up

-1 to -10 MPa (MegaPascals)

-1 to -10 MPa (MegaPascals)?

This is really negative

1MPa ~ 9.8 atmospheres

A human can suck through a straw at about -25 kPa, or 0.025 Mpa

Water transport structures?

Guard cells, intercellular spaces

Apoplastic route – in cell walls

Symplastic route – through live cells

Casparian strip – a suberized band in the endodermis cell walls, serving as a barrier for all apoplastic transport. Protects roots from pathogens through dense fibers

Properties of Water?

Cohesion

Adhesion

“Bipolar” molecule – negative charge on the oxygen atom and positive on the hydrogen.

Thus, they are held together by hydrogen bonds. Charged particles also make them attracted to different surfaces

Forced used to fight against gravity

Cohesion?

water is attracted to water

Adhesion?

water is attracted to other substancess

Adhesion of water molecules to xylem walls is like Alex Honnold clinging to a rock face on El Capitan

Cohesion -tension theory?

Cohesion of water molecules to each other

Adhesion of water to conduit walls

Drawn up in a “continuous” columns

Tension is the force needed to overcome the downward force from gravity (negative pressure)

Tension?

force needed to overcome downward force from gravity (negative pressure)

Capillary rise is proportional to vessel diameter?

Capillary rise occurs due to adhesion to tube walls

In xylem cells (diameter 20-200 µm) capillary forces can lift water about 1m Capillary rise is proportional to vessel diameter

𝐾 (capillary) = − (𝜋r^4/8n)

Vessel size affects pressure drop, helps work against gravity?

The larger the vessel, the less pressure needed

What is the ultimate driving force behind water movement in the xylem?

the sun

heat from the sun evaporates the water which drives the pulling force of water

According to Domec, how does water availabilty related to tree height?

The tension-driven makes the pit aperture diameter of tracheids decrease steadily with height,

Conductive tissues?

Xylem conducts water, carries resources from soil to leaves

The larger the diameter, the lower the resistance, and the greater the risk of cavitation

As cells get older, minerals begin to plug up pores and reduce the abilities of xylems

Becomes hardwood

Vessels vs. Tracheids (Tracheary elements of the xylem) Angiosperms vs Gymnosperms?

Variation in the size of pores.

Angiosperms have larger holes with smaller amounts of cell walls

Size is dependent on the amount of water available and the strength of the water column

Xylem structure?

Not all conduits are the same

Vessels

Tracheids

Vessels?

Found in angiosperms

Length 1-1000+cm

Diameter 15-500 µm (0.015-0.5 mm) – large size range

Faster maximum transport rate • Greater vulnerability to cavitation

Tracheids?

Found in gymnosperms (conifers)

Length 0.1 – 1.0cm

Diameter 5-80 µm – narrow size range

Lower maximum flow rate – the conductance of the hydraulic system of the plant may limit leaf water availability

Xylem structure influences plant hydraulics?

primarily two kinds of resistance

Pit resistance and Lumen resistance

Longer vessels could increase lumen resistance but decrease pit resistance, due to fewer end wall-crossings

DaVinci’s “rule of trees”?

The cross-sectional area of branches adds up to the cross-sectional area of the trunk

DaVinci’s a=2

Murray’s Law – a=3, for blood flow

Sopp & Valbuena’s clarification?

The cumulative hydraulic resistance remains constant

Diameter decreases with height to counter gravity

Also associated with a mechanical support function (greater decline of radius in gymnosperms, similar to Murray’s Law in ring-porous angiosperms)

Embolism or cavitation?

A critical point where the tension exceeds that required to pull air from an empty conduit to a filled conduit across a pit membrane — this aspiration is known as air seeding

An air seed creates a void in the water, and the tension causes the void to expand and break the continuous column.

Air seeding thresholds are set by the maximum pore diameter found in the pit membranes of a given conduit.

Caused by excessive water potential gradient, and affected by evaporative demand, flow rate and gravity

Embolism or cavitation 2?

There are billions and trillions of conduits in trees (so cavitation of a million of them isn’t necessarily fatal)

Trees can isolate embolized conduits

Redundant pathways

How can trees recover from embolism?

Divert water around embolized conduits

Grow new xylem

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

Some cannot recover from embolism.

Torus?

specialized thickening in the pit membranes of conifer xylem, acting as a valve to prevent air embolism

Injured vessels are often isolated by suberization of the cell walls next to the injury.?

Illustration of coniferous tracheids’ sealing mechanism;

Torus is displaced when tension exceeds a threshold

Another example of xylem staining?

Top sample was freshly cut from the tree and stored in water to prevent drying

Bottom sample was left out to dry for two days

Only the functioning (water - filled) xylem get stained; non -functional (air -filled) xylem do not get stained

Isohydric plants?

maintain their internal water potential relatively constant across a range of environmental water availabilities

E.g. cherry

More conservative

Last better in a drought

Anisohydric plants?

leaf water potential changes more in response to environmental water availability

E.g. oaks, ash

Isohydric vs anisohydric species?

Continuous spectrum, some species can vary

E = transpiration, ψ = leaf water potential

Cavitation events can also be detected acoustically?

breaking of water column

Ultrasonic acoustic emissions sensors

Can detect sounds beyond the range of human hearing

Cavitation curves: water potential & acoustic events?

Number of acoustic emissions increases as the branch dries out

Water potential in the branch gets more and more negative as the tension on the water column increases (as the branch dries out)

Measuring transpiration using sap flux probes?

Temperature difference is logged as trees transpire water

Temperature difference is highest when there is no flow and lowest when there is high flow

Why do cavitation limits vary within plants?

Trade-off between large, efficient conduits and increased vulnerability to cavitation

Year-round growing patterns

Need a good temperature

Evolution of xylem tissues?

Tracheids were the only highly specialized elements in the first upright land plants (about 300 million years ago)

With flowering plants, xylem tissues evolved into separating for water conduction and mechanical support

Fibers – cells which specialized for ‘support’ function

Vessel elements – water-conducting cells

Earliest vascular plants?

Cooksonia – the earliest known vascular plant (Silurian period – 430 to 400 MYA)

All plant growth begins with energy from the sun?

Primary producers

Primary producers?

Plant photosynthesis

Scales from individual leaf process to whole ecosystem processes

Light is the necessary ingredient for most Life?

photosynthesis

light-use efficiency

Photosynthesis?

The light-driven process of carbon uptake and assimilation in green plants.

Light-use efficiency?

Only 3-6% of absorbed light is converted into chemical energy by leaves.

Phototropism?

growing toward light

Happens cause of phototropins

Phototropin?

protein that changes in response to blue light (shade)

Differential growth on the sun vs shade side

Genetic control still unclear?

heliotropism (turning toward Sun) does not respond to same triggers as phototropism (other light source)

Light absorption by foliage?

Chlorophyll absorbs light in blue and red wavebands

Not all the energy from light is absorbed

More leaves/foliage means more light/energy absorbed

Light is also?

Absorbed by non-photosynthetic material

Transmitted

Reflected

Chl vs leaf absorption spectrum?

Non-photosynthetic absorption

Reflectance

Definitions for leaf photosynthesis?

Gross photosynthesis (PG)

Respiration (R)

Net photosynthesis (PN = PG – R)

Respiration (R)?

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

Photosynthesis and photorespiration?

Add phosphate to create energy

Can now collect oxygen through CO2

Create a 6 carbon sugar, broken up into 3 carbon sugar

Gross photosynthesis (PG)?

Total amount of CO2 assimilated through the process of photosynthesis (in leaves)

Net photosynthesis (PN = PG – R)?

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

Metabolic hubs?

Photosynthesis occurs in the chloroplasts; key enzyme Rubisco

Respiration occurs in mitochondria (same as us!); ATP synthesis

Steps in photosynthesis?

Energy capture & conversion to chemical form = light reactions (light dependent)

CO2 absorption and conversion of chemical energy to new biomass = dark reactions

Light independent (does not require either light or darkness)

Light reactions of photosynthesis?

Absorbed quanta excite electrons in chlorophyll, which get transferred to other molecules – electron transport chain

Electrons are replenished by splitting water

Electron transport across the membrane drive proton transport and proton gradient, which …

… drives ATP synthesis (create O2)

occur in thylakoid membranes

Have a barrier

Dark reactions of photosynthesis?

Rubisco enzyme combines CO2 with 5-carbon RuBP, forming

2 3-carbon sugars

Phosphate groups are added to increase the reactivity (ATP)

2 3-carbon sugars combine to make glucose

RuBP is regenerated with additional investment of ATP

5x3C sugars—>3x 5C sugars

Dark reactions occur in the chloroplast stroma

Recipient molecule recreated

Respiration – energy production?

Glycolysis and citric acid cycle (or Krebs cycle) break down glucose and harness the chemical energy in energy carrier molecules (ATP, NADH and FADH2)

The reducing power (NADH, FADH2) gets converted to ATP (1-to-3)

Bribing other reactions with ATP to break bonds and create energy

Factors affecting photosynthesis?

Light

Water availability in soil and air

Temperature

Nutrients (N, P, K, …)

Growth-limiting factors: #1. Light?

Light saturation of photosynthesis

Photosynthesis increases with light, up to a point

Leaves have grown to optimally suit their light environment

Canopy response to light is the sum total of sun and shade leaves

Sun vs. shade leaves?

Inhabit different light microenvironments

Have different responses to light

Plateaus represent higher competition

Sun leaves?

In full sun

Higher photosynthetic rates but also higher rates of respiration.

Higher leaf angle (seem to avoid light during hottest part of day).

Shade leaves?

In the shade of others

Lower rates of photosynthesis per unit mass but larger display area and lower respiration.

Lower leaf angle (capture more light).

Canopy response to light?

greater than leaf response

more linear over a broader light range than for any one leaf

Impact of shade

Growth-limiting factors: #2. Temperature?

Enzymes that control the rates of photosynthesis and respiration have different sensitivities to temperature.

Warmer temperatures increase photosynthesis up to an optimum temperature.

Respiration increases exponentially with a linear increase in temperature

Gross photosynthesis is lowest at temperature extremes and thus carbohydrate gain is limited

Respiration increases exponentially with a linear increase in temperature?

Microbial respiration – enzymatically controlled, based on cell’s energy needs

At extreme temps – cellular degradation, constant repair

Net photosynthesis increases with temperature but then decreases with very high temperature?

Net PS declines at supraoptimal temperature:

Enzymes denature (lose function) at high temperature, and free electrons damage membranes

Constant repair = high respiration cost

Net photosynthesis?

Gross photosynthesis - respiration

Respiration is the loss of CO2 from plants as mitochondria use carbohydrates to produce energy

Balance between carbon gained and carbon loss

Growth-limiting factors: #3. Water availability?

Affects photosynthesis by causing plants to open or close stomata, and CO2 diffusion

Water availability depends on soil texture, on pore size

Water potential gradient as the driving force of T (transpiration)?

Water evaporating at leaf surface and adhesion and cohesion of water creates upward pull of water

Water needed to move solutes within plant

Decoupling between photosynthesis and growth?

Canopy photosynthesis has longer seasonality than radial growth

Especially in conditions of limited sink strength

GPP versus annual ring-width correlation with climate factors

Growth controlled by CHO availability, environmental resources, genetics

Conditions of limited sink strength?

Higher leaf area

Drought

Low temperature

GPP versus annual ring-width correlation with climate factors?

They disagree

Radial growth actually has negative correlation with radiation

Radial growth actually has negative correlation with radiation?

—>sink limitation of growth – other resources are limiting (water, nutrients)

—>water needed to transport carbohydrates

There is a lag between GPP & growth

Drought and other stresses suppress cambial activity before they affect GPP

Decoupling between photosynthesis and growth 2?

Correlation between environmental conditions (T, PDSI, Radiation) and gross photosynthesis (left) and tree ring width growth (right)

1.GPP and ring width growth differ

2. sensitivity to different factors varies by season

3. different factors affect GPP & RW differently

Growth-limiting factors: #4. Nutrients?

Nitrogen is especially important to photosynthesis because RuBisCO, the primary enzyme involved in fixing carbon, requires lots of nitrogen

Photosynthesis vs net carbon gain (True Photosynthesis=source)?

Carboxylation (GPP),

binds CO2

Oxygenation=photorespiration,

binds Oxygen

Carboxylation (=GPP)?

Net photosynthesis

Mitochondrial respiration

Mitochondrial respiration?

Ion gradients

Protein turnover

Lipid turnover

Carbon use?

Gross photosynthesis (= carboxylation) as source

Two sinks

carboxylation sinks?

Maintenance (~50%)

Net photosynthesis (~50%)

Maintenance (~50%) sink?

Ion gradients

Protein turnover

Lipid turnover

Net photosynthesis (~50%) sink?

Growth

Storage

Defense

Reproduction

Carbon allocation: Where a plant puts the photosynthate (carbon)?

TBCA = total belowground carbon allocation

In areas with higher nutrient levels, plants put less C toward roots and belowground biomass and more toward leaves and wood.

Human appropriation of NPP?

NASA Goddard Space Center: human appropriation of NPP has increased from ~20% to 25% of NPP

Ceiling of usable NPP is NOT 100%. It is much lower, but we do not know where. 33%? 40%???!

Current human appropriation of NPP?

crops for food and fiber

timber for wood products and paper

livestock grazing (Gough 2011)

Limits to human appropriation of NPP?

Rancher David Daigle telling ESSM 319 silviculture class that he cannot let cattle graze more than 25-30% of growth

Milk-carton analogy:

1/3 cream

1/3 water

1/3 carton

Norman Borlaug & agricultural revolution?

“The father of the Green Revolution”, forester, plant pathologist and geneticist by training

Nobel Peace Prize in 1970 & government honors

Developed disease-resistant & high-yield wheat varieties in Mexico

These varieties saved a billion people from starvation

Wheat yields doubled in 5 years in India and Pakistan

Costs of agricultural revolution?

Wide-spread monocultures

Intensive cultivation methods (benefitting agrobusiness more than the people)

High pesticide use

Nutritional limitations of individual crops

Growing food supply has increased global population

Essential Elements?

Carbon, Oxygen, Hydrogen

Make up 90% of tree’s dry mass

Obtained from atmosphere & water

Remaining elements come from soil

What are nutrients?

Substances that an organism needs for growth and survival, but cannot make itself

Essential elements?

building blocks of organic molecules (>90% of dry weight)

Hydrogen (H), carbon (C), oxygen (O)