Module 8: Extreme environments and light (adaptations)

What are the Floristic kingdoms?

Taxonomic groupings that reflect geological and evolutionary history, including holartic, south american, africa, indo pacific, and australian

Holartic

most of north America and temperate laurasia

South american

From south florida to patagonia

African

all of africa except mediterannean area

Indo pacific

From india to pacific islands

Austalian

Australia and surrounding islands

Tundra

small sized plants adapted to short seasons

Taiga

Conifer forest

Deciduous forests

broad leaf temperate forests

Grasslands

Prairies, steppes, savannahs, pampas

Shrublands

chapparral, scrub, etc

Desert

plants are further apart than shrub lands

Tropical forests

humid and warm, peak diversity

What is distibution of an organism defined by?

Its reaction to individual external influences, called environmental factors

Biotic factors

result from interaction with other organisms ex: herbivory, infection, symbiosis

Abiotic factors

Includes parameters (temperature, humidity, PH) and resources (light, water, minerals) that determine growth, as well as others that can add stress (pollutants)

What are limiting factors?

one environmental factor at suboptimal level can limit a plants process ex: at a given light intensity level photosynthetic rate can be limited by level of CO2

How common are optimal growing conditions in nature?

rare

When does stress occur?

when essential factors ( such as light, water, oxygen, and nutrients) are at inappropriate levels

Environmental noxa

factors that trigger stress at any concentration ( heavy metals, pollutants)

What is a state of latent life?

Minimal life processes occur when concentration of stress factors is too high or low

Dormancy

An adapted latent life stage triggered by environmental cues involves physiological changes (abscission of leaves production of bud scales etc)

Avoidance strategy

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

Mesophiles

require moderate temperatures to grow

Hardening

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

How do leaves adapt to high temperatures?

Hairs can reduce evaporation and reflect intense sunlight, small, thicker leaves help to minimize the effect of high light intensity. Some species (legumes) can move leaves to reduce sun exposure

Transpiration

Evaporation of water from the leaves of a plant

Why is transpiration important?

Increased transpiration can help maintain the plant cooler than the surrounding environment

Shading

plants use some structures to protect others from direct sunlight

Avoidance strategy

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

What are some adaptations to cold weather?

Rosette/low growing plants are protected against weight of snow and environment and are warmer close to the ground, evergreen plants have high concentrations of sugar in the leaves that act as antifreeze, in deciduous plants leaf abscission and bud scales protect axillary meristems

leaf abscission

Aging and dropping of leaves

bud scales

modified leaves that protect buds

ephemeral

short-lived annuals

What is photosynthesis?

A process that requires carbon dioxide and water as reactants and produces sugars and oxygen requires sunlight ,which is captured by chlorophyll molecules located in the thylakoid membranes of chloroplasts

Sunlight

produces the vast majority of energy for life on earth, its intensity and composition vary with location, time of day, and season

When does light become a stressor?

If it is too low there is not enough photosynthesis to cover a plants metabolic requirements, if it is too high unused energy can lead to oxidative stress

Pulvini

joint like thickening at the base of leaves that allows for movement of leaves (legumes)

Chloroplast movement

In ferns. mosses, and some seed plants chloroplast move to different parts of the cell to increase or reduce exposure to light

What type of leaves do sun plants have?

Smaller and thicker leaves

What is well developed in the leaves of sun plants?

Mesophylls

How many layers of palisade cells do sun leaves typically have?

Several layers

What feature might minimize excess sunlight in sun leaves?

Epidermal hairs

What is the structure of chloroplasts in sun leaves?

Small grana and few thylakoids

What is the proportion of antenna to reaction centers in the photosystem of sun leaves?

Small proportion of antenna and many reaction centers

What are the characteristics of shade leaves?

Shade leaves are larger and more tender.

How is the mesophyll in shade leaves developed?

Shade leaves have weakly developed mesophylls.

What role do epidermal cells play in shade leaves?

Epidermal cells might act as lenses to increase light capture.

What is the structure of chloroplasts in shade leaves?

Chloroplasts in shade leaves have large grana and many thylakoids.

What is the composition of the photosystem in shade leaves?

The photosystem in shade leaves has a large proportion of antenna and few reaction centers.

Stolons (searching for light)

aboveground stems that emerge from crown and bend downwards, develop plantets where they touch the ground

Stoloniferous rhizomes (searching for light)

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

Suckers (searching for light)

Upright shoots growing from horizontal roots (aka adventitious shoots)

Twiners

stems of vines that grow in spirals around objects such as small trunks to support itself ( climbing to search for light)

Tendrils

modified leaf or short stem that wraps around objects they touch and provides support or main stem ( climbing in search of light)

Adhesive pads

at tips of tendril-like short stems and allow plants to attach to walls ( climbing in search of light)

Supportive roots

roots that help plants grow taller in soft, wet soils ( tropical and coastal areas)

Buttress roots

Wedge-shaped tall, and wide roots that prevent shallow-rooted trees from falling over

Prop roots

adventitious/aerial roots that arise from the trunk for large branches and grow downwards to provide support in shifty conditions ( mangroves)

Epiphytes

Grown in wet areas, they use their roots to grasp tree branches (instead of water absorption)

Lianas

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

What is Raunkiaers approach?

He proposed a sequence of life forms based on how they deal with protecting their meristem. It attempted to explain why lower latitude flora is dominated by more trees and higher latitude by smaller herbaceous plants, while temperature is important, growth form is the consequence of multiple interacting factors