Extreme Environments and Light

Floristic Kingdoms

Taxonomic groupings that reflect geological and evolutionary history

Holarctic

Most of North America and temperate Laurasia

• a Floristic kingdom

South American

From South Florida to Patagonia

• a Floristic kingdom

African

All of Africa except the Mediterranean area

• a Floristic kingdom

Indo-Pacific

From India to Pacific Island (Southeast Asia)

• a Floristic kingdom

Australian

Australia and some surrounding islands

• a Floristic kingdom

biomes

distinct region defined by its ecology and vegetation

Tundra

Small-sized plants adapted to short seasons

Taiga

Conifer Forests ‘northern’

• ex: Canada

Deciduous Forests

Broad-leaf temperate forests (us in east America)

Grasslands

Prairies, Steppes, Savannah, Pampas

Shrublands

Chaparral, Scrub, etc. (westcoast US like California)

Desert

Plants are further apart than in shrublands, little water

Tropical Forests

Humid and warm with peak diversity

Environmental Factors

external influences that can impact the operation of the system

• can be abiotic or biotic

Biotic factors

Resulting from interactions with other organisms such as : herbivory, infection, symbiosis, competition

• ALIVE

Abiotic Factors

Nonliving components of environment. Includes parameters (temperature, pH, humidity, soil) and resources (light, water, minerals) that determine growth - as well as others that can add stress (ex: pollutants)

Limiting Factors

One environmental factor at suboptimal level can limit plant processes. things preventing plant from thriving

• ex: At a given light intensity level photosynthetic rate can be limited by level of CO2

Stress

Occurs when essential factors (such as light, water, oxygen, nutrients) are at inappropriate levels (higher OR lower) outside of optimal range

• diff from environmental noxa!

Environmental Noxa

Factors that trigger stress at ANY concentration. never good, bad at all lvls

• heavy metals, pollutants, etc.

State of Latent Life

Minimal life processes occur when stress factors are too high/low

• ‘coma’ not doing much but not dead

Dormancy

an adapted latent life stage - triggered by environmental cues. Involves physiological changes (e.g. abscession (shedding) of leaves, production of bud scales, etc).

• avoiding bad temperatures until conditions improve

Avoidance Strategy

Seeds and spores allow annual/ephemeral plants to avoid moments of highest environmental stress.

• complete life cycle super quickly. will be dormant for most of life, then in small period where env. is good, they do everything in that short time

Mesophiles

Plants that require moderate temperatures to grow.

Hardening

The process by which tolerable stress levels trigger the plant to prepare for extreme conditions

• a heads up to prep for extreme conditions

what are some changes plants make to adapt to extreme high temps?

dormancy or avoidance

in leaves:

• change surface hairs

• smaller, thicker leaves in high temp

• angle leaves to reduce sunlight exposure

general:

• increase transpiration if in hot wetlands

• find shade or make it

Leaf Changes - Surface

Hairs can reduce evaporation and reflect intense sunlight

• in high temps

Leaf Changes - Size

Smaller, thicker leaves help minimize effect of high light intensity

• in high temps

Leaf Changes - Angle/Position

Some species (e.g. legumes) can move leaves to reduce exposure to sunlight.

• in high temps

Transpiration

increased transpiration can help maintain the plant cooler than surrounding environment

• adaptation to high temp if plant is in a wetland or swamp

Shading

Plants use some structures to protect others from direct sunlight

• in high temps

Avoidance Strategy - Temperature

In hot environments, many species are short-lived annuals (ephemeral) - avoiding worst conditions

what r some adaptations to cold environments?

• Rosettes/low growing plants → protect against weight of snow flattening them and env. is warmer closest to ground

• Evergreen → high concn of sugar in leaves to reduce freezing pt.

• Deciduous → lose leaves (abcession) and bud scales to protect axillary meristems

Rosette/Low growing plants

Protected against weight of snow & environment warmer close to ground

• in cold env.

Evergreen Plants

High concentrations of sugar in leaves act as anti-freeze (reduces freezing pt.)

• in cold env.

Deciduous Plants

Leaf abscission (shedding) and bud scales to protect axillary meristems in cold environemnts

Photosynthesis

A process that requires sunlight, carbon dioxide, and water as reactants and produces sugars and oxygen.

Chlorophyll

A green pigment found in the chloroplasts of plants, algae, and some bacteria

• captures sunlight in the thylakoid membranes of chloroplasts

Thylakoid

A flattened membrane sac inside the chloroplast, used to convert light energy into chemical energy.

Sunlight

(via photosynthesis) produces the vast majority of energy for life on Earth.

• intensity + composition vary w location, time, and season

Light - Too Low

Negative energy balance - not enough photosynthesis to cover plant's metabolic requirements

Light - Too High

Unused energy can lead to oxidative stress.

what can plants move to control exposure to light?

many can change position of their leaves

• pulvini → joint like thickenings @ base of leaf that allows them to move

ferns, mosses, and some seed plants can move their chloroplasts to diff parts of the cell

Pulvini

Joint-like thickening at base of leaves ( in petiole) (ex: legumes) that allows for movement of leaves. do this to control their exposure to light

Chloroplasts

Capture energy from sunlight and use it to produce food for the cell. They will move to different parts of the cell

to increase or reduce exposure to light!

Sun Leaves

Smaller and thicker, with well- developed mesophylls and several layers of palisade cells - epidermal hairs might

minimize excess sunlight.

• exposed to lots of sunlight so have chloroplasts w small grana and few stromal thylakoids. Photosystem has small properotion of antenna and many rxn centers

Shade Leaves

Larger and more tender, with weakly develop mesophylls - epidermal cells might act as lenses to increase/magnify light capture!

• have large grana and many stromal thylakoids to maximize sunlight. Photosystems have large proportions of antenna and few rxn centers

Sun Leaves - Subcellular Level

Chloroplast with small grana and few stromal thylakoids cuz dont need to maximize sunlight since they alr get so much

Photosystem (Sun Leaves)

Small proportion of antenna and many reaction centers

Shade Leaves - Subcellular Level

Chloroplast with large grana and many stromal thylakoids cuz have to maximize sunlight

Photosystem (Shade Leaves)

Large proportion of antenna and few reaction centers

which type of leaf has few reaction centers and large proportions of antennas in their photosystem?

shade leaves

which type of leaf has small grana with few stromal thylakoids?

sun leaves

what r some ways plants spread (horizontal) to look for light?

• stolons

  • aboveground stems! dvlp plantets

• stoloniferous rhizomes

  • belowground stems! same as stolon

• suckers

  • root instead of stem but does same thing

Stolons

Aboveground stems; emerge from crown and bend downwards; develop plantets where they touch the ground

• Asexual!

Stoloniferous Rhizomes

Belowground stems; upright shoots develop from axillary buds in nodes; adventitious roots in underside

Suckers

Upright roots/shoots growing from horizontal roots (aka "adventitious shoots")

• same as belowground stem function but diff tissue!

how can plants climb to search for light?

• twiners

  • stems of vines grow in spirals. supports itself

• tendrils

  • modified leaf or short stem that hugs + provides support for main stem

• adhesive pads

  • at tips of tendril-like short stems that allows them to stick to walls

Twiners

Stems of vines that grow in spirals around objects such as small trunks.

• These stems support themselves!

Tendrils

Modified leaf or short stem that wraps around objects they touch. “hug”

• These leaves/stems provide support for main stem

Adhesive Pads

At the tips of tendril-like short stems. These pads allow plants to attach to walls

Supportive Roots

Roots that plants form in soft wet soils to help them grow taller

• buttress roots

• prop roots

Buttress Roots

Roots that are wedge-shaped, tall and wide - they prevent shallow-rooted trees from falling over in soft, wet soils

• a type of supportive root

Prop Roots

Advetitious/aerial roots that arise from the trunk (or large branches) and grow downwards to provide support in

shifty wet soil conditions (e.g. mangroves)

• a type of supportive root

how can plants steal light?

• epiphytes

  • grow in wet areas and use roots to grasp tree branches and take water

• lianas

  • in rainforests. spread horizontally in canopy of rainforest

Epiphytes

Plants that grow in wet areas. They use their roots to grasp tree branches (instead of water absorption)

• steal light

Lianas

Typically in rainforests; woody, creeping vines that spread through the canopy of rainforests spreading their leaves to the sun.

• steal light

Raunkiaer hypothesis

Scientist that proposed a sequence of life forms/classification based on how they deal with protecting their meristem.

• tried to explain why lower latitude flora is dominated by trees vs higher latitude by smaller herbaceious plants (shorter in cold)