15:365 Plant Ecology - Midterm

Ecology

• Interactions of organisms and their physical and biological environments

  • Patterns and causes of distribution and abundance

• The study of distribution and abundance

  • Relates to impact and outcome

• All the organisms together, the ENTIRE community

Plant Ecology

• Subset of ecology with a a focus on the unique physiological processes of plants

Issues with Sedentary Lifestyles

• Problems with finding a mate

• Dispersal

  • Plants use fruit

Individual

• Is made of a genet and ramet(s)

Genet

• The genetic individual, can be divided into several discrete physical plants

  • Entirety of the genetic individual

Ramet

• An individual, physically distinct unit produced by a clonal plant through vegetative (asexual) reproduction

• Discrete physical individuals, may be only part of the genet

  • Separate individual within the genet

Population

• A group of one species

Community

• All the populations of all the species put together

Biome

• A major region with a distinctive vegetation type

• Can be subdivided, and can be incorporated into larger regional variations

• E.g. Canadian prairies

Habitat

• Features or attributes of the place where the organism grows

• Focuses on the environmental features and attributes of the location

  • Attributes are summarised into a phrase that characterise the entirety of the location where the organism resides

  • E.g. Under the canopy

Microhabitat

• The immediate environment

• Examples: hummocks or a hollows, and ridges or depressions

  • Differentiated from habitat by scale

  • Can be found within habitats, both can exist together at the same time

• Can differ from conditions in the surrounding area

Aspect

• The compass direction you are facing

Niche

• The range of conditions

• Used in some reference to some metric → e.g. pH

• Can be categorised into fundamental and theorised. Usually refer to the realised as thats how we actually see it

• Example: cranberries have a narrow pH range, found in the field from 4 - 5.5 (acidic)

Physiological Ecology

• Looking at the adaptations of plants to their environment

• Anatomical changes and adaptations

  • Example: water physiology and how to retain water in drought conditions

Functional Ecology

• Looking at keystone species

  • Keystone species that have a big impact on other species

Ecosystem Function

• The movement of energy and nutrients through the ecosystem

Community Structure

• Considered for a particular community and not the entire ecosystem

  • How many species, and how many individuals of each species

  • Invariably, we find a few common species and many rare species

• Example: vascular plants

The Scientific Method

1. Observation

2. Hypothesis

3. Experiment

Types of Experiment

• Manipulative

• Natural

• Observational

Manipulative Experiments

• Change is conducted on a certain aspect in hopes for a response

• Downside → run the risk of artifacts (unintentional as a result of the experiment)

  • Must have negative and positive controls to avoid artifacts as much as possible

Natural Experiments

• Where (usually) a calamity occurs

  • Example: Wildfire → we then observe what happens after the fire and record what happens next

• Downside → can tell statistical differences but hard to tell due to there being no replication and no randomisation

  • Example: Wildfire → cannot replicate a fire and randomise it

Observational Experiments

• Looking at some pattern in either space or time, without human intervention

  • Example: looking at El Niño cycles and how it affects the surroundings

• Downside → interpretation is tricky because we don’t know the cause and effect, too many variables to consider

  • Example: observing the effects of a slope on plant life (we don’t know the water, amount of light, etc. over time)

Model

• Simplified version of the real world

Conceptual Models

• Example → A’s relationship to B

  • A and B are species with some kind of interaction. B eats A

  • Or A and B are communities, with the relation being time, where community A turns into community B

Mathematical Models

• Example → change in population with time

Generalisation Model

• Thought method of observing the world and trying to provide an explanation

  • Pattern, process, and theory

Generalisation Model - Pattern

• What we see

  • Example: Lichens are observed in greater abundance on field trips in pristine environments → what is the process at work here

• Is attributed to process of work

Generalisation Model - Process

• Are the cause(s) of the pattern

  • Example: Lichens won’t suffer pollution

Generalisation Model - Theory

• The explanation for what’s happening in the process

  • Example: Why are lichens intolerant to pollution → soil acts as a cleaning mechanism, and lichens don’t grow on soil

Research Categories

• Primary

• Secondary

Primary Research

• Doing something that nobody has ever done before

Secondary Research

• Taking a textbook and reading the chapters to write an essay

  • The information is not brand new

Science Caterogies

• Basic

• Applied

Science Caterogies - Basic

• Fundamental

  • Example: studying patterns of bird migration

    • Understanding the world as we see it

Science Caterogies - Applied

• Has relation to the user

  • Example: how much weight can this wire carry before it breaks?

  • Example: Looking at how weeds can be mitigated for the prairies (user is observing the weeds, so it has relation to the user)

Components of Experimental Design

• Treatment

• Control

  • Negative and positive

• Replication

• Randomisation

Statistical Design

• Possible options:

  • 1. Treatments randomised completely

  • 2. Split-plot design

C3 Photosynthesis

• The standard form of photosynthesis

• Utilises rubisco, the calvin cycle, and 3 energy (ATP)

• Photolysis occurs in the chlorophyll → water is split to make protons and electrons, and oxygen

• First product of the process is C3

• Performs better in cooler conditions

Rubisco as an Oxygenase

• Happens in 2 scenarios:

  • When there is low CO2 levels

  • Warm conditions (20+, 30+ degrees C)

Why C4 Plants do Worse in Cool Conditions

• Artificially elevates the CO2 levels in the cells

  • C4 is changed to malate before transfer, malate is then converted to CO2

C4 Metabolism

• Is a strategy to avoid photorespiration for plants growing under warm conditions

• Rubisco can act as an oxygenase or a carboxylase

• Oxygenase yields C2 + C3 instead of C3 + C3

• Photorespiration is pronounced when growth is under warm conditions, and photorespiration removes the C2 and liberates CO2

• Artificially elevates CO2 levels at the expense of energy

Water Efficiency - C4 & C3 Plants

• C4 plants water use efficiency is higher than C3 plants

  • C3 plants lose more water, since they have to keep stomata open

• C4 plants can tolerate aridity because they keep their stomata closed more of the time

C3 & C4 Grasses Locations

• C3 → found in cooler locations

• C4 → found in warmer and drier locations

Crassulacean Acid Metabolism (CAM) Strategy

• Open stomata only at night

• Capture CO2 and store as a C4 in the vacuole → then release the CO2 the next day

• Originally discovered in the stonecrop family (Crassulaceae)

• Found in cacti, members of Crassulaceae, and Bromeliaceae

C4 Products from CAM

• Are acidic, specifically malate (malic acid), in an ironised form

Bromeliaceae

• Usually epiphytes, found in the wet tropics

  • Grows in places without a lot of soil → helps to conserve water

Ultra-Violet Exposure

• Is elevated in alpine ecosystems, because light has passed through less atmosphere

  • As a result, alpine plants:

    • Have increased levels of protective pigments, e.g. the flavonoid called luteolin

    • Have more antioxidant enzymes, which prevent cell damage from oxidising agents formed by U.V light

    • Invest more in DNA repair systems to fix damage from U.V light

Flavonoids

• A category of organic molecules

U.V Light

• Generates chemical species in the tissues, which can be remedied by berries (or the pigments, in the case of plants)

  • The chemical species can be modified by the enzymes created by the berries

PPFD

• Photosynthetic photon flux density, basically light intensity

  • Sunlight → 1600 u mol m^-2 s^-1

  • Greenhouse → 400 u mol m^-2 s^-1

  • Growth chamber → 250 u mol m^-2 s^-1

  • Below the forest canopy → 10 - 200 u mol m^-2 s^-1

Compensation Point

• The specific level of light intensity or carbon dioxide concentration at which the rate of photosynthesis exactly equals the rate of cellular respiration

  • Mitochondria → uses up oxygen to create ATP and releases CO2

Tiarella

• Has a low compensation point

  • Allows for net photosynthesis under the canopy shade

• Modifies the system to have the compensation point as low as possible

Tropical Forest Adaptations to Deep Canopy Shade

• Satin sheen

  • Epidermal cells focus light on the chloroplasts, the cells are configured in a certain way

• Blue iridescence

  • Leaf cells scatter blue light to maximise capture of red light for photosynthesis

Sun Leaves

• Thicker in dimension

• Have more palisade layers

• Have greater density of chlorophyll cm^-2 (more per unit area)

Phenotypic Plasticity Example

• Sun leaves and shade leaves sometimes being formed at different positions on the same plant

Plants in Well-Lit Environments

• Direct resources to leaves

Shade Leaves

• Have limited potential

  • Cannot use the light even if it has an abundance of it

Cuticle

• Wax layer on the exterior of the plant (outside of the epidermis on leaves and stems)

• Non-living, waterproof, and made of cutin

• Possessed by all land plants

Xylem

• Is composed of lignin → only thing that provides the strength

• Not present in bryophytes

• Seen as tracheids in all vascular plants, and vessels in angiosperms

Tracheids

• Elongated, primitive water-conducting cells found in the xylem of vascular plants

  • Water movement occurs through the cohesion-tension mechanism within the plant’s xylem tissue

• Possessed by every plants

Vessels

• Are like a pipe, the end can be open or have a ladder-like structure

• Water and minerals move inside like a continuous pipe

Stomata

• Microscopic pores on the surface of leaves that allow gas exchange, letting CO2 in and oxygen and water vapour out

  • Aperture → the size of the central pore flanked by two specialised guard cells on the surface of plant leaves and stems. The shoot sends a signal to close the stomata via a chemical originating from the roots

Guard Cells

• Are a specialised pair of crescent-shaped cells that flank each stoma and control its opening and closing by changing water pressure (turgor pressure)

• Contain chloroplasts

  • These chloroplasts generate the ATP needed to power the ion movements that open and close the stomatal pore

Water Potential

• The energy for water to move

  • Energy per unit volume (in the context of plants) → given as pressure units (mega pascals)

  • Energy per unit mass (in the context of soil) → positive and negative heads

• Everything is less than zero (all negative values), can be lowered even more by addition of solutes (water molecule wants to stay in association with salt)

• Can put surfaces in contact → can become more stable if it is in contact with surfaces

Water Potential - Water Removal Gradient

• Water is removed from the void spaces, starting with the large void spaces first, then gradually the smaller spaces

• Gradient exists across the plant

Wilting Point

• When the plant cannot obtain the water anymore because it is being held too tightly in the soil pores and cannot move into the plants

• Is considered a soil property, but is actually a plant property (driven by the plant but expressed as a soil property)

• Also called “the lower limit of extraction”

Physiological Drought

• A condition where plants suffer from water deficit and cannot absorb water, even though water is physically present in the soil

  • Water is too salty for plants to uptake

Plant Water Strategies

• Mesophytes

• Hydrophytes

• Hygrophytes

• Xerophytes

• Halophytes

Halophytes

• A salt-tolerant plant that naturally grows and completes its life cycle in soil or water with high salinity

  • The plants tissue’s water potential is lower than the saline water it grows in/around

  • Can have sodium in the vacuole, in the cytoplasm they will put a compatible solute (an amino acid not used in proteins) which makes the cytoplasm more salty

Mesophytes

• Terrestrial plant adapted to moderate environmental conditions with a balanced, average supply of water and soil moisture

  • Most plants

Hydrophytes

• Aquatic or wetland plants that have adapted to live either partly or completely submerged in water, or in waterlogged, oxygen-poor soil

  • Usually referring to plants that grow in standing water

  • Can be divided into submerged, floating, emergent variants

Hygrophytes

• A terrestrial plant that lives in wet, damp, or waterlogged environments

  • Plants found alongside water, where is oil is always moist

Xerophytes

• Any plant species adapted to survive and grow with a limited supply of water in dry, arid, or desert conditions

  • Plants that grow in arid conditions

Mesophyte Stomata Status in Differing Conditions

• When water is available, stomata is open and transpiration proceeds

• In dry conditions, the stomata close up and photosynthesis is reduced

Levels of Transpiration from Different Plant Environments

• Tropical rainforest tree → 1000 kg H2O day^-1

• Temperate broadleaf tree → 150 kg H2O day^-1

• Boreal conifer → 30 kg H2O day^-1

• Maize plant → 1.5 kg H2O day^-1

Why Water-Use Efficiency Low

• Air is dry, and so concentration gradient for H2O is 20x that for CO2

  • Water concentration is far steeper than the concentration gradient for CO2

• H2O = 18, whereas CO2 = 44, and so H2O diffuses faster

  • CO2 has long path to chloroplast, whereas H2O evaporates from cell surface

Ways to Grow in Dry Places

1. Stay dormant as a seed until rain

2. Send roots deep to underground water

3. Drop leaves using dry periods

4. Have a shallow root system to capture and store rain

5. Low ratio of surface-area-to-volume

6. CAM

7. Modify anatomy

Ways to Grow in Dry Places - Stay Dormant as a Seed until Rain

• Stay as a seed until rain, then germinate

• Example: Osteospermum

Ways to Grow in Dry Places - Send Roots Deep to Underground Water

• Some roots can grow deep that reaches below the water table

• Example: Tamarix

• Phreatophytes → plants that send taproots deep to groundwater

Phreatophytes

• Deep-rooted plant that obtains its water supply primarily from the water table or the saturated capillary fringe just above it

  • Plants that send taproots deep to groundwater

Ways to Grow in Dry Places - Drop Leaves During Dry Periods

• Tends to occur where there is no winter

• Area must have a consistent dry season, E.g. parts of India and Brazil

• E.g. Deciduous tropical tree, Tabeuia in flower in Panama, and Parkinsonia

• Drought-deciduous forests → Southern Brazil, Southern India, flowers are made visible and flowers are the only food available to pollinators

Ways to Grow in Dry Places - Shallow Root System to Capture & Store Rain

• Placing roots close to the surface ti intercept the rainfall when it comes. Then store the water in the tissues (to be succulent)

Ways to Grow in Dry Places - Low Ratio of Surface-Area-to-Volume

• Predominantly found in succulents but can be done by non-succulents

  • Non-succulent examples: Ephedra (mormon tea) and Lygodesmia (skeleton weed)

• Principle is to have a low surface area-to-volume ratio

Ways to Grow in Dry Places - CAM

• Found in Cactaceae, Crassulaceae, and Bromeliaceae

• Principle is to only open stomata at night when there is less evaporative demand

Ways to Grow in Dry Places - Modify Anatomy

• Leaves to stop H2O loss

• Presence of stomatal crypts and a non-turbulent boundary layer

Anatomical Features to Grow in Dry Places

• Leaf modifications to conserve water:

  • Stomatal crypts, hairs, and a thick cuticle

• High capacity for photosynthesis following:

  • Infrequent rain: isobilateral and amphistomatous leaves

Features Associated with Xerophytes

• Fibre-rich tissue

• Stem growths forming thorns

• Leaves modified as spines

• Hairs modified as prickles

  • All related to slow growth and the need to defend against herbivory

Plants in Mesic Conditions

• O2 diffuses to the roots via air spaces in soil

  • When the soil is saturated, the pores are water-filled, and O2 moves far more slowly to the roots

Plants in Saturated Conditions

• Oxygen moves far too slowly

  • Plants can last for a little while being waterlogged but anything past 6 weeks, the plants will die

  • In short, ATP cannot be made

Ways to Grow in Wet Places

• Aerenchyma delivers O2 from shoot to root via air channels

  • E.g. Nuphar (waterlily)

• Pneumatophores deliver O2 from above water to roots

  • E.g. Taxodium (swamp cyprus)

Particle Size - Sand

• 0.05 mm to 2 mm

Particle Size - Silt

• 0.002 mm to 0.05 mm

Particle Size - Clay

• < 0.002 mm (2 microns)

Development of Prairie Soil from Loess Deposited by Wind

• Must be a permanent grassland, soils cannot support trees (too dry for trees to grow)

• Litter comes mostly from the dead roots, and the root litter deposition is the source of nutrients

• Calcium gets washed down the profile

• Soil type is called Chernozem or Mollisol

Cation Exchange Capacity

• Ability of soil to hold cations

• Units: centimoles (of charge) kg^-1 (of soil)

• Basic cations → Ca²⁺, Mg²⁺, and K+

• Acidic cations → H⁺ and Al³⁺

Where Protons Come From

• In the atmosphere, CO2 combines with water to make carbonic acid → carbonic acid dissociates into a proton and a bicarbonate anion

• Pristine rainwater pH is 5.5

Clay Particles

• Are sheets with negative charges around the edges

• Cations will be held alongside the negative charges

Organic Matter / Humus

• Polymeric

• Black in colour

• Negative charges (carboxyl, phenyl, benzyl)

• Provides cation-exchange capacity and water-holding capacity

  • Can be a reservoir for basic cations, water, and nitrogen

Nitrogen

• Organic N has C-N bond, 99% of soil N is organic N

• Mineral is NO^3- + NH⁴⁺, only mineral N is available to plants

• Slow mineralisation of organic N is rate-limiting for plant nutrition

Field Capacity

• How much water can be held in the soil when gravity has completed its draw down of water

• The equal state