plant nutrients

what are the macromolecules

carbon, hydrogen, oxygen, and nitrogen

aside from being a source of energy what does fixed carbon molecules from photosynthesis form

the physical building blocks from which the plant body is constructed.

where do plants obtain most of their nutrients

from the soil

what is a soil solution

within the soil, minerals dissolve in water as ions, forming a solution that contacts the roots of plants

what is an essential element

a plant nutrient that if the element is absent of insufficient the plant fails to complete its life cycle or grows abnormally

what are the two types of essential elements in plants

• macronutrients

• micronutrients

how much macronutrients does a plant need

a plant needs macronutrients in concentrations of at least 1 gram per kilogram of the plant’s dry matter

how much micronutrients does a plant need

a plant needs micronutrients in concentrations of less than 100 milligrams per kilograms of the plat’s dry matter

mineral elements required by plants (just a chart don’t memorize this)

what is a deficiency symptom

when a plant is deficient is an essential element, it displays characteristic symptoms

how are essential elements identified in plants

plants were grown hydroponically (in a nutrient solution instead of soil) which allows for a great control of nutrient availability. This way they can add and remove different nutrients to see how the plant reacts

most plant dry biomass is built from what

the CO2 in air

how are plants able to obtain all their nutrients if they cant move

plant growth is their version of movement. Roots grow through the soil to obtain mineral nutrients and water. Stem and leaf growth helps a plant get more light and CO2

how does the soil direct root growth

different situations can create soil that is more alkaline, or acidic. And such microenvironments encourage or discourage further growth of a root system and help direct its growth

what happens to root growth when phosphorus is deficient

Low phosphorus levels cause the root system in the topsoil to branch out more, as well as grow longer root hairs, where the likelihood of reaching phosphorus rich patches of soil may increase.

what happens to root growth when nitrogen is deficient

Low nitrogen levels cause the root system to grow deeper into the soil where the likelihood of reaching nitrate-rich patches of soil may increase

how are nutrients transported into a cell

ions are actively transported with transport proteins across the cell membrane of epidermal cells into the symplast because their concentrations in the soil solution are generally lower than their concentrations inside the cells.

why is nutrient uptake so highly regulated

the levels of ions inside cells must be maintained at constant levels

how is nutrient uptake regulated

The number of transporters for a given nutrient can be regulated in response to nutrient availability. Low nutrient levels stimulate transcription, whereas high levels repress transcription

functions of soil

• mechanical support

• mineral nutrients and water from the soil solution

• O2 for root respiration

living components of soil

bacteria, fungi, protists, and animals (earthworms and insects)

nonliving components of soil

rock fragments that range in size from large stones to sand to silt, to clay. Soil also contains water and dissolved mineral nutrients, air spaces, and dead organic matter

name the typical percentages of living and nonliving components in soil

• particles: 45%

• water: 25%

• air:25%

• organisms:5%

what is the A horizon of soil

A horizon is the topsoil that supports the plant’s nutrient needs. it contains most of soil’s living and dead organic matter

what is the B horizon of soil

B horizon is the subsoil, which accumulates materials from the topsoil above it and from the parent rock below

what is the C horizon of soil

C horizon is the parent rock, also called bedrock, which is in the process of breaking down to form soil

what is soil fertility

a soil’s ability to support plant growth

what factors determine a topsoil’s fertility

their proportions of sand, silt, and clay

mineral leaching in sand

dissolved minerals are readily leached from sandy soil because sand particles are relatively large and cannot hold water. This carries the nutrient to deeper horizons, where they are unavailable to plant roots.

mineral leaching in clay

clay particles are tiny and pack tightly together, leaving little space for air. But it also binds more water than sand, and the charged surfaces of clay particles bind mineral ions that plant roots ultimately take up.

what is loam

the optimal mixture of sand, silt, and clay and thus has sufficnet levels of air, water, and available nutrients for plants

what is humus

dead organic mater, like leaves or other plant organs that break down into humus

role of humus

its used as a food source by microbes that break down complex organic molecules and release simpler molecules into the soil solution. Humus also provide air spaces that increase O2 availability to plant roots

why are there ionic bonds in soil

humus and clay particles often carry negative charges which form ionic bonds with charged ions of minerals

what needs to happen for minerals to become available to the plants

the cations of minerals must be detached from the clay particles

how can the ionic bond between cations and clay particles be broken

cellular respiration releases CO2, root hairs pump out protons. They form carbonic acid which ionizes into bicarbonate and a free proton and this increases the proton concentration in the soil surrounding the root allowing cation exchange to happen.

what is the cation exchange

protons bind more strongly to clay particles than do mineral cations so they trade places with the cations in a process called cation exchange. It releases important cations into the soil solution, where they are available to be taken up by the roots

how is soil fertility affected by soil pH

proton concentration affects the binding of cations and anions to soil particles, it affects the solubility of other nutrients. And it affects the absorption of nutrients by plant root

why are fertilizers important

leaching and the harvesting of crops can deplete a soil of its nutrients, so that new crops grow poorly on that soil. Soil fertility can be restored with fertilizers

how does shifting agriculture work

when soil could no longer support plant growth, they would move location, letting organic matter slowly, naturally fertilize the soil.

how do microorganisms fertilize soil

microorganisms in the soil break down organic molecules into smaller, simpler molecules. These simpler molecules can dissolve in soil water and enter plant roots

how does organic fertilizers work

the nutrient content of soil can be increased by adding organic materials such as compost or manure. This allows for a slow release of ions as the materials decompose

how do inorganic fertilizers work

they supply mineral nutrients in forms that can be taken up immediately by plants. fertilizers can be used in varying amounts, depending on the crop and soil type.

common inorganic fertilizer types

ammonia, urea, and salts like potassium, ammonium, nitrate, phosphate, and sulfate

how do plants influence the type and abundance of the organisms that live near their roots

plants spend a significant amount of their photosynthate to produce and secrete a wide range of compounds from their roots.

what is the rhizosphere

this is the region of soil close enough to a root to be affected by their secretions

what are mycorrhizae associations

the association of fungi with plant roots

what are fungal hyphae

the long, thread-like filaments that make up the structural body of most fungi and molds

what is the first step in the formation of arbuscular mycorrhizal

Plant roots produce strigolactones that stimulate rapid growth of fungal hyphae toward the root

what does fungi do in response to strigolactones (step 2)

the fungi produces signals that stimulate expression of genes that promote symbioses with other organisms. These genes give rise to the prepenetration apparatus

what is the prepenetration apparatus (step 3)

it guides the growth of the fungal hyphae into the root cortex

what is step 4 of the formation of arbuscular mycorrhizal fungi

fungus grows along the root length

what are arbuscules

the sites of nutrient exchange between fungus and plant

what is step 5 of arbuscular mycorrhizal formation

hyphae induce formation of new prepenetration apparatus structure inside cortical cell

what is step 6 of arbuscular mycorrhizal fformation

hyphae enter prepenetration apparatuses and branch to form arbuscules, where nutrients are exchanged

what are periarbuscular membrane

its a specialized, host-derived membrane that envelops fungal arbuscules inside plant root cells during arbuscular mycorrhizal symbiosis.

what do legumes form symbioses with

soil bacteria in several genera collectively known as rhizobia

how do legume roots attract the rhizobia

legume roots release flavonoids and other chemical signals to attract the rhizobia to the vicinity of the roots

what is step 1 of the formation of a nitrogen-fixing root nodule

root hairs release flavonoids and other chemical signals that attract rhizobia

what is step 2 of the formation of a nitrogen-fixing root nodule

rhizobia proliferate and cause a root hair to curl and an infection thread to form

what is an infection thread

a tubular, tunnel-like structure formed by a plant cell during its symbiotic relationship with nitrogen-fixing bacteria. it acts as a safe pathway that allows the microbes to travel deep inside the plant’s root to form nodules.

what is step 3 of the formation of a nitrogen-fixing root nodule

stimulated by Nod factors secreted by bacteria, root cells begin to divide

what are Nod factors

flavonoids trigger the transciption of nod genes, who synthesize Nod factor. these factos, when secreted by the bacteria, cause cells in the root cortex to divide, leading to the formation of a primary nodule meristem

what is step 4 of the formation of a nitrogen-fixing root nodule

the infection thread grows into the cortex of the root

what is step 5 of the formation of a nitrogen-fixing root nodule

the infection thread releases bacterial cells, which become bacteroids in the root cells

what is step 6 of the formation of a nitrogen-fixing root nodule

the nodule forms as plant cells continue to divide and become infected with bacteria

how does bacteria enter the root

through an infection thread, which is analogous to the prepenetration apparatus in mycorrhizal associations

what happens when the bacteria reaches cells inside the root nodule

here the bacteria is internalized by nodule cells, enclosed in membrane vesicles.

what happens to the bacteria enclosed in membrane vesicles

the bacteria differentiate into bacteroids - the form of the bacteria that can fix nitrogen

why is fungi symbiosis important for plants

most vascular plants cannot reach all the nutrients available in the soil. Mycorrhizae expand the root surface area 10 to 1000 times, increasing the amount of soil that can be mined for nutrients.

what is the primary nutrient that plants receive from mycorrhizae interactions

phosphorus

what do the fungi get in return for being in symbiosis with plant root

fungus obtains an energy source. Around 20% of the products from photosynthesis.

why is nitrogen fixation necessary

while nitrogen makes up almost 4/5s of Earth’s atmosphere, plants cannot use nitrogen direction as a nutrient.

why can’t nitrogen from the atmosphere by used directly by plants

the tripble bond linking the two nitrogen is extremely stable, and a great deal of energy is required to break it

what is nitrogen fixation

some prokaryotes have an enzyme that enables them to convert nitrogen (N2) into a more reactive and biologically useful form

what are the two types of organisms that can fix nitrogen

1. free-living organisms living in soil and water

2. symbiotic organisms living in other organisms

what is required for nitrogen fixation to happen

1. a strong reducing agent to transfer hydrogen atoms to N2 and to the intermediate products of the reaction

2. a great deal of energy, which is supplied by ATP

3. the enzyme nitrogenase, which catalyzes the reaction

what prevents nitrogenase from being active all the time

nitrogenase is strongly inhibited by oxygen. but rhizobia are aerobic and fix nitrogen in aerobic plant roots.

how can nitrogenase function under aerobic conditions

plants typically house nitrogen-fixing bacteria in root nodules. Within a nodule, O2 is maintained at a low level that is sufficient to support respiration, but no so high as to inactivate nitrogenase.

what is leghemoglobin

a plant-produced protein, which is an O2 carrier.

what is the result of nitrogen fixation

it formes ammonia, and most of it is rapidly ionized to form ammonium which can be taken up by plant roots and is then used as a source of amino groups.

what are nitrifiers

type of soil bacterial that oxidize ammonia to nitrate ions (another form that plants can take up) by the process of nitrification