Soil and Plant Nutrition Flashcards
Layers of soil
horizons
Upper layers of soil
topsoil
Soil particles in order of smaller to largest
clay
silt
sand
what does topsoil consist of?
mineral particles, living organisms, and decaying organic material, humus
humus
decaying organic material
Loams
soils that support highly productive plant growth - composed of roughly equal parts sand, silt, and clay
Inorganic components
cations (K+, Ca2+, Mg2+ adhere to negatively charged soil particles; this prevents them from leaching out of soil as water flows through
cation exchange
cations are displaced from soil particles by other cations
Displaced cations enter the soil solution and can be taken up by plant roots
Negatively charged ions
do not bind with soil particles and can be lost rom the soil by leaching from percolating groundwater
Agriculture impacts on soil
depletes nutrients
increases erosion
taxes water resources
soil compaction
Where is usable fresh water from
surface water (lakes and streams) or ground water (aquifers)
depleting of aquifers can result in
subsidence
subsidence
the settling or sinking of land
irrigation can lead to salinization
the concentration of salts in soil as water evaporates
Advantages of drip irrigation
requires less water and reduces salinization
Fertilization
replaces mineral nutrients that have been lost from the soil
Commercial fertilizers are enriched in
nitrogen, phosphorus, and potassium
organic fertilizers composed of
manure, fishmeal, or compost
Large monoculture farms with high fertilizers have _____ dominated soil food webs
bacteria
Natural systems and organic farms have ____ based soil food webs
fungal
Erosion
Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the US
Erosion of soil causes loss of nutrients
Erosion can be reduced by
planting trees as windbreaks
terracing hillside crops
cultivating in a contour pattern
practicing no-till agriculture
essential element
if a chemical element is required for a plant to complete its life cycle
Macronutrients
9 of the essential elements,
plants require them in relatively large amounts
What are the macronutrients
carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium
Micronutrients
remaining seven, plants need them in very small amounts
what are the micronutrients
chlorine, iron, manganese, boron, zinc, copper, and molybdenum
Rhizosphere
the layer of soil bound to the plant’s roots
The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots
Rhizobacteria
free-living
Function in the rhizosphere
can enter roots
What roles do rhizobacteria play
produce hormones that stimulate plant growth
produce antibiotics that protect roots from disease
absorb toxic metals
make nutrients more available to roots
What can increase crop yields
Inoculation of seeds with Rhizobacteria
_____ can be an important limiting nutrient for plant growth
nitrogen
nitrogen cycle
transforms nitrogen and nitrogen-containing compounds
Most soil nitrogen comes from
actions of soil bacteria
Plants absorb nitrogen as
either NO3- or NH4+
Bacteria break down organic compounds or use _____ to produce _____ which is converted to ______
N2
NH3
NH4+
Nitrification
carried out by bacteria that convert NH3 into NO3-
Nitrogen fixation
the conversion of nitrogen from N2 to NH3
Symbiotic relationships with nitrogen-fixing bacteria
provide some plant species with a built-in source of fixed nitrogen
Key symbioses occur between
nitrogen-fixing bacteria and plants, including those in the legume family (peas, beans, and other similar plants)
Along a legume’s roots are swellings called
nodules
nodules
composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria
Inside the root nodule, Rhizobium bacteria assume a form called
bacteroids
bacteroids
are contained within vesicles formed by the root cell
Bacteria of a root nodule obtain sugar from
the plant and supply the plant with fixed nitrogen
where do carnivorous plants grow
acidic soils that lack nitrogen
How is prey digested in carnivorous plants
digested with enzymes secret from specialized glands
Pitcher plants
have pitcher-shaped leaves with cavity filled with digestive fluid
Venus flytrap
when hairs are touched, the two halves of the leaf snap together
Sundews
Glandular trichomes secrete both sticky mucilage and digestive enzymes
Waterwheel
Uses trigger hairs and snaps to capture and digest small aquatic animals
Snap-trap mechanism
was acquired by a common ancestor of the Venus flytrap and the aquatic waterwheel
Parasitic Plants
may be photosynthetic or non-photosynthetic
At least 3,000 types of plants
Dodder
nonphotosynthetic
wraps around its host
Relies on host for its nutritional needs
Indian pipe
non photosynthetic
hooks into host trees through mycorrhizae
Calvin cycle
fixes CO2 into sugar
Ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) catalyzes the first step
Can bind CO2 or O2
I
If CO2 binds
a 3-C sugar is made, that can be used to make glucose and sucrose
If O2 binds
photorespiration occurs
neither nutrient nor energy storage
C3 photosynthesis
occurs in mesophyll cells
C4 photosynthesis
uses an extra pathway to shuttle carbon deep within the leaf
This reduces photorespiration by limiting the Calvin cycle to cells surrounding the vascular tissue where O2 levels are low
In C3 plants, as CO2 increases
the Calvin cycle becomes more efficient
should lead to increased photosynthesis and plant growth
plants have less nitrogen and minerals per unit mass - ratio of carbon to nitrogen increases
results in lower nutritional value for herbivores
As CO2 levels increase, relatively less nitrogen and other macronutrients are found in leaves
Herbivores need to eat more biomass to obtain adequate nutrients, particularly protein
Protein deficiencies in human diets could result from decreased nitrogen in crops
Phytoremediation
use of plants to concentrate or breakdown pollutants
Phytodegradation
contaminant is taken up from soil and broken down
Phytovolatiliation
contaminant is taken up from soil and released through stomata
Phytoaccumulation
contaminant is taken up from soil and concentrated in shoots
These are later harvested
Trichloroethylene
May be removed from the soil by poplar trees
Degraded into CO2 and chlorine
A fraction moves rapidly through the xylem ad is released through stomata
Trinitrotoluene
May be removed from soil and degraded by poplar and bean plants
But at high concentrations, it is toxic to these plants
Use of Phytoremediation
Phytoremediation is a promising technique
costs are 50-80% lower than cleanup methods involving mechanical removal of contaminated soil
