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Plants require at least seventeen essential nutrients
chemical composition of plants
thought that the soil provided the substance for plant growth and the leaves
were used to protect the fruit.
van Helmont postulated that plants grew from the water in the soil.
Hales said that plants were nourished by air.
extract minerals from the soil.
of herbaceous plants are water.
truly be considered a nutrient because it provides the plant with the hydrogen
necessary for photosynthesis.
90% of the water absorbed is lost through transpiration.
50 elements have been identified in plants.
essential nutrient is a particular chemical element that is required for the
plant to grow from a seed and complete the life cycle by producing more seeds.
have been used to identify many of these essential nutrients.
are elements required by plants in relatively large amounts.
oxygen, hydrogen, nitrogen, sulfur, phosphorus, calcium, potassium, magnesium
(See p. 713 for uses)
are elements needed in small amounts.
chlorine, copper, manganese, zinc, molybdenum, boron, and nickel.
as cofactors of enzymatic reactions.
enzymatic activity, they are found in small amounts but can weaken or kill a
plant if not present.
The symptoms of mineral deficiency depend on the function and mobility of
depend on function.
magnesium causes leaves to yellow because it is found in chlorophyll.
causes the same problem but is a cofactor to the production of chlorophyll.
also depend of mobility.
mineral moves freely about the plant, the symptoms will be found in the older
organs first because the newer parts have “drawing power”.
mineral does not move freely, the symptoms will be found in the younger part of
the plant because the older tissues may have adequate amounts stored in the
of nitrogen, potassium, and phosphorus are the most common.
in micronutrients are less common and tend to be geographically localized.
characteristics are key environmental factors in terrestrial ecosystems.
texture and chemical composition of soils
weathers of solid rock.
seeps into crevices and freezes in winter fractures the rock and acids dissolved
in the water also help to break it down.
accelerate the decomposition.
a mixture of decomposed rock of varying texture, living organisms, and humus
(made of decayed organic materials).
topsoil and other distinct soil layers or horizons are often visible in vertical
texture of topsoil depends on the size of its particles which are classified
from coarse sand to microscopic clay particles.
fertile soils are usually loams made up of a mixture of sand, silt, and clay.
enough fine particles to provide a large surface area for retaining minerals and
provides air spaces continuing oxygen that can be used for cellular respiration.
does not drain, the roots suffocate because the air is replace by water and mold
has an astonishing number of organisms and these affect the physical and
chemical properties of the soil.
aerate the soil by burrowing and adding mucus that holds fine soil particles
change the mineral composition of the soil by fixation.
the decomposing organic material formed by the action of bacteria and fungi on
dead organisms, feces, fallen leaves, and other organic refuse
clay from packing
soil to stay crumbly and allows for air pockets and water retention.
availability of soil water and minerals.
heavy rainfall, water drains away from the larger spaces of the soil but smaller
spaces retain water because of its attraction for the soil particles which have
electrically charges surfaces.
adheres to hydrophilic soil particles that cannot be extracted by plants.
tiniest spaces of the soil a film of water can be found.
It is not tightly bound and is not pure water but called soil solution.
solution contains many dissolved minerals.
minerals in soil are positively charged like potassium, calcium, and magnesium
and adhere to the negatively charged soil particles.
prevents leaching during heavy rain.
charged minerals are made available to the plant when hydrogen ions in the soil
displace the mineral ions from the clay particles.
called cation exchange and is stimulated by the roots themselves.
Soil conservation is one step toward sustainable agriculture
take centuries for a soil to become fertile through decomposition but human
mismanagement can destroy that fertility within a few years.
used manure to fertilize their crops.
Americans buried fish along with seeds when they planted corn.
farmers now days use fertilizers that have been mined or processed.
are usually enriched in nitrogen, phosphorus, and potassium.
fish meal, and compost are organic fertilizers but must be processed before
their inorganic molecules can be used.
conserve these fertilizers, the pH of the soil must be paid attention to.
not only affects cation exchange but also influences the chemical form of all
availability of water most often limits the growth of plants.
can help but it also puts a huge drain on water resources.
also make the soil very salty and then infertile.
the soil solution hypertonic to root cells so the lose water instead of gaining
lost to wind and water erosion.
precaution can help reduce this by planting trees as a windbreak or alfalfa or
wheat provides good ground cover for the soil.
agriculture is a commitment that are conservation-minded, environmentally safe,
The metabolism of soil bacteria makes nitrogen available to plants.
is the one that most limits the growth of plants and the yields of crops.
ingredient of proteins, nucleic acid, and other important organic molecules.
cannot use nitrogen in its gaseous form and it must be converted to ammonium or
bacteria restock nitrogenous minerals in the soil by converting N2 to NH3 by
by nitrogen fixing prokaryotes.
nitrogenase that catalyzes the entire reaction sequence that reduces N2 to NH3
by adding electrons and hydrogen ions.
the legume family have built in sources of nitrogen fixation.
roots have swellings called nodules composed of plant cells that contain the
nodule the bacteria forms bacterioids which are contained within the vesicles
formed by the root cell.
This is a
supply the legume with nitrogen and the plant provides the bacteria with
carbohydrates and other organic compounds.
is an iron-containing protein that binds reversibly to oxygen for the intense
respiration that must take place for nitrogen fixation.
keeps the concentration of free oxygen low because nitrogenase is inhibited by
the ammonium is used to make amino acids that are transported to the shoot and
leaves via the xylem.
bacteria can over produce ammonium that is released into the soil to help other
plants may use other nitrogen fixing organisms.
Improving protein yield of crops is a major goal of agricultural research
breeding to improve the protein content of plants.
productivity of symbiotic nitrogen fixation by using enzymes other than
the ability to induce root nodule formation in nonlegumes.
Predation and symbiosis are evolutionary adaptations that enhance plant
photosynthetic but use haustoria to tap into the xylem of the plant they are
are sometimes mistaken for parasites.
nourish itself but grows on the surface of another plant.
anchored to the plant but gets its water and minerals from rain that falls on
that occasionally feed on animals.
own carbohydrates from photosynthesis but obtain some of their nitrogen and
minerals by killing and digesting insects.
that contain glands that secrete digestive juices.
associations between roots and fungi
secrete growth factors that stimulate the roots to grow and branch.
root develops into the mycorrhizae, the fungus either sheathes the root and
extends hyphae among the cortex cells or invades the root cells themselves.
are more efficient in absorbing these minerals and secrete acid that increases
the solubility of some minerals.
provides the minerals and the plant provides the carbohydrates.