Plant Environment Interactions

What influence does biotic competition have on species competition?

herbivory, disease, competition with other plants and organisms for resources

fundamental niche

determined by the physiological amplitude where conditions are suitable for a plant to grow and reproduce

realised niche

determined by the ecological amplitude and is constrained by biotic interactions/competition

What are the different types of resource use efficiencies?

Light, nutrient, water, photosynthetic

light use efficiency

dry matter production is a linear function of the amount of radiation intercepted

nutrient use efficiency

requirements and capacity of plants to acquire nutrients differ between species and can limit plant growth

nitrogen use efficiency (NUE)

ratio of dry matter production and whole plant nitrogen content

water use efficiency

the amount of water lost during photosynthesis or in relation to biomass production

law of limiting factors

the rate of photosynthesis process is limited by the pace of the lowest factor

Irradiance

energy from the visible and neighbouring wavelength

spectral distribution of energy

influenced by location and absorption by gases in the atmosphere

How does global irradiation varies?

time of day, season, latitude, altitude, atmospheric conditions

Where does reflected global irradiation occur?

the lower leaf surfaces

Amount of infrared radiation absorbed by a leaf

a function of effective temperatures of the sky and plant surroundings

What determines plant distribution?

temperature

What are the 3 possible mechanisms of heat loss?

long wave radiation emitted from leaf, heat used to drive transpiration having a significant cooling effect, sensible heat loss through conduction to cooler surrounding air

conduction

thermal collision of gas molecules

free convection

occurs when transferred heat warms the air surrounding the leaf, the air expands which decreases its density making it more buoyant moving it away from the leaf

forced convection

caused by the turbulent mixing of air by wind which removes heat from the layer of air surrounding the leaf

leaf boundary layer

comprised of laminar sublayer and turbulent layer

What determines the thickness of the leaf boundary layer?

wind velocity, leaf size, leaf shape

What are the mean global temperatures in regard to latitude and altitude?

60C for latitude, 40C for altitude

What does the temperature of a leaf depend on?

time of say, season, location, cloudiness, wind speed, position in canopy, height above soil, leaf shape/dimensions

What does root temperature depend on?

rooting depth, soil properties like type, porosity, bulk density, moisture content

Why is it difficult to investigate impacts of temperature?

fluctuating thermal regimes across soil-plant-atmosphere continuum, influence of many factors, different growth stages having different optimum temperature, influence and variability of air and soil temperatures

cardinal temperature

the optimum cardinal temperature defines temperature at which growth and performance are at their maximum

temperature coefficient

describes the effect of temperature on chemical processes

characters of low temperature environments

low air and soil temperature, short photoperiod, low radiation flux densities, high winds, low water availability, low rates of soil microbial activity, mechanical stress, atmospheric composition

chilling injury

caused by loss of membrane fluidity, leading to increase permeability and ionic imbalance

freezing injury

ice forms within the cells or organs disrupting the structure of the protoplasm

examples of freezing injury

ice formation, bleaching, frost heave, cracking, desiccation

adaptations to low temperature stress

production on antioxidants, xanthophyll cycle, morphology, ice barriers in vascular tissues, increasing proportion of fatty acids in chloroplast membrane, physical avoidance

characteristics of high temperature environments

high air and soil temperatures, high radiation flux densities, high winds, low water availability, salinity, mechanical stress

high temperature stress

increase membrane fluidity, denature of proteins, increase transpiration, photosynthesis decreases

What are some adaptations to high temperature?

adjustment to leaf angle, leaf properties aid reflectance, secondary metabolites produced, heat shock proteins,

What are some environmental drivers of photosynthesis?

light, temperature, CO2, humidity, soil water availability, nutrient status

What are the 4 main points of resistance to CO2 diffusion into a leaf?

boundary layer resistance, stomatal resistance, intercellular airspace, liquid phase/mesophyll resistance

How do leaves absorb light?

epidermal cells, chloroplasts, general leaf anatomy

When does maximum incident irradiance occur?

when incoming sunlight is perpendicular to leaf surface

diaheliotrophic

plants that maximise light interception

paraheliotrophic

plants avoid exposure to minimise heat load and water loss

maximum quantum yield

describes the ratio between the number of photons absorbed and molecules of CO2 fixed

soil plant atmosphere continuum (SPAC)

the gradient in water potential across SPAC drives water transport through plants

water potential

describes the availability of water in soils, plant, and the atmosphere; can be positive or negative depending on the sum of the components

osmotic potential

the chemical potential of water due to the presence of dissolved materials; value always negative

hydrostatic pressure

the physical pressure exerted on water within a plant system

vapour pressure

transpiration from plants is driven by differences in vapour pressure between the internal air spaces in leaves and the atmosphere

relative humidity

describes the water content of the air relative to the amount of water the air can hold at a given temperature

How does soil type influence water availability?

type and porosity influence how water will drain

forces required to move water through a plant

root pressure, xylem, phloem, capillary action, cohesion-tension theory

cohesion-tension theory

water covers mesophyll cells in thin film, as the water evaporates the film retreats into spaces between the cells, this increases surface tension generating negative pressure which draws more water to the surface

What are points of resistance to water movement?

boundary layer, cuticle, stomata, transport resistance in mesophyll, conduction resistance in xylem, transport resistance in roots, hydraulic resistance in soil

adaption to water stress

desiccation avoidance, desiccation tolerance, photosynthetic pathway, resurrection plants

water use efficiency (WUE)

amount of water lost during photosynthesis or in relation to biomass production

What are essential elements to plants?

nitrogen, sulphur, phosphorus, silicon, boron, potassium, calcium, magnesium, chlorine, manganese, sodium, iron, zinc, copper, nickel, molybdenum

Where to plants get their nutrients from?

atmospheric deposition, symbiotic associations, absorption through leaves, carnivory

key role of nitrogen

vital component of proteins, nucleic acids, and chlorophyll

key role of potassium

enzyme development, regulation of stomatal aperture, disease resistance

key role fo phosphorus

vital component of plant cell membranes and ATP

ectotrophic mycorrhizae

form thick mantle of mycelium around roots, penetrates root between cortical cells to form Hartig net, common in tree species

arbuscular mycorrhizae

penetrates cortex cells to form vesicles and arbuscules, which is the site of nutrient transfer, common in crop species

toxic elements

heavy metals like aluminum

nutrient productivity

relative growth rate/whole plant nutrient content

What happens when soils become waterlogged?

diffusion of oxygen decreases, soil microorganisms consume o2, can make rooting zone anaerobic

Redox potential of waterlogged soils

as o2 diffusion decreases microorganisms use a series of less eager electron acceptor

What are the implications of hypoxia?

inhibits many metabolic pathways, plants use fermentation pathways to delay effects of hypoxia

What are some physiological adjustments to waterlogging?

epinastic growth of leaf shoots, porosity of roots increase, aerenchyma formed by targeted death and dissolution of cortical cells

How are saline soils formed?

net downward movement of water minimises potential salt accumulation, high evapotranspiration results in net upward movement of water accumulating salts in rooting zone, high water table can inhibit removal of salts

impacts of saline soil on plants

creates problems with water balance and water potential, similar to drought response, osmotic stress, stomatal closure, production of ROS

adaptive mechanisms of plants in saline soils

halophytes keep salt concentration low in cytosol by accumulation in vacuole, compatible solutes in cytosol to keep water potential low

What is considered plant growth?

increment of dry mass, volume, length, area involving division, expansion, and differentiation of plant cells

What are some of the commonly assessed parameters driving plant growth?

leaf area, net assimilation rate, mineral nutrients

relative growth rate

determined by differences in physiology, morphology, and biomass partitioning to provide information on the increase in plant mass per unit plant mass already present

leaf area ratio

amount of leaf area per unit toral plant mass

net assimilation rate

the rate of dry mass gain per unit lead area

What are the three key storage categories?

accumulation, reserve formation, and recycling

What are the 4 key pillars of crop breeding?

environmental adaptation, phenotypic characterisation, genetic diversity, genetic information

What can eddy covariance techniques tell us?

temporal patterns of C uptake and release, identification of driving/limiting factors