Some soil microbes discovered 2 miles beneath the surface
Number of earthworms found in a square foot of good soil (according to Teaming with Microbes 2010)?
up to 50
bacteria that derive energy from sulfur, nitrogen or iron compounds?
What do most soil bacteria need to eat to sustain life?
something containing carbon
chemicals produced by plants, secretated through the roots
a good portion of energy produced during photosynthesis is used to produce these
they are in the form of carbohydrates and proteins and attract beneficial bacteria and fungi
the zone immediately around the roots
where the secretion of exudates and sloughing off of cell root material occurs
what soil organisms can be found in the rhizosphere?
bacteria, fungi, nematodes, protozoa and larger organisms
two functions of soil food web
help provide nutrients to roots in the rhizosphere
members' activities bind soil particles together (slime) while they provide for the passage of air and water through the soil
the state where nutrients are locked up inside soil organisms
nutrients are eventually released as wastes or mineralized
How do healthy soil food webs control disease?
Diversity increases competition for food sources, ensuring that one species does not get all available nutrients
Nets or webs formed by fungi around roots act as physical barriers to invasion
Bacteria coat surfaces so others can't attach themselves
Some fungi and bacteria produce inhibitory compounds (vitamins or antibiotics, for example, that help maintain or improve plant health)
establish a symbiotic relationship with roots
physical protection and nutrient delivery
plant gives exudates, fungi provide water, phosphorus and other nutrients
Most important nutrient
it's a basic building block of amino acids
When could soil scientists measure the amount of bacteria and fungi in soils?
1980s - Dr. Ingham at Oregon State
Ratio of fungal to bacterial (F:B) biomass for agricultural soils?
1:1 or less
Forest soils have 10 times or more fungi to bacteria
In general, what types of plants prefer fungi-dominated soils?
Perennials, trees, shrubs
In general, what types of plants prefer bacteria-dominated soils?
annuals, grasses, vegetables
When soil organisms are eaten, some of their nitrogen is retained by the eater. The rest is released as waste in what form?
Plant-available ammonium NH4
In fungally dominated soils, much of the nitrogen remains in ammonium forms
Depending on the soil environment, ammonium can either remain as-is or be converted to NO3 (nitrate) by special bacteria. When does that occur?
When ammonium (NO4) is released into soils dominated by bacteria
Bacterial dominated soils generally have an alkaline (high) pH due to bacterial bioslime, which encourages nitrogen-fixing bacteria to thrive
Who is regarded as the "man who saved a billion people" and what did he accomplish in order to be awarded the Nobel Peace Prize in 1970?
Developed a strain of disease-resistant wheat
T/F In a mass-selected variety, overall genetic diversity is much greater than that of any individual
T/F Throughout history, humans manipulated the genetic makeup of crops and livestock without explicit knowledge of genetics
T/F Because of inbreeding depression assoicated with their mutation, polyploid plants often produce fewer seeds or smaller fruits than their normal diploid parents
T/F While the crop production industry has narrowed its genetic basis over time, the livestock industry, which relies more on cross-breeding, has maintained a high level of diversity.
T/F Of the major grains we rely upon in the USA, only corn and oat are native species
T/F in the Penn and Teller: Norman Borlaug video, Dr. Terri Lomax indicated that no plants containing animal genes had been released into the environment. However, rice has now been used on a test scale to synthesize human proteins to use in treating illness from dehydration.
T/F People in the poorest nations normally spend between 20 and 80% of their disposable income on food.
USA Citizens, on average, now spend what percent of their disposable income on food?
About 10 percent
Southern corn leaf blight (1970-71)
D. Both A and C
_______ has been observed to occur naturally.
D. All of the above
If you were to cross two different true-breeding inbred lines to produce a hybrid, how many of the four offspring would have the dominant trait?
4 (All Tt)
In static terms, an adaptation is
any aspect of an organism or its parts that is of value in allowing the organism to withstand conditions
could enable an organism to better use resources, provide protection, modifify local environments to the benefit of an organism or facilitate reproduction
the genetic information carried by an individual
The physical and behavioral expression of the genotype
If variation in a trait were graphed as a frequency distribution, what would it look like
A normal curve of probability (a bell-shaped curve)
Does phenotypic variation correlate directly with genotypic variation?
No, but it usually has a significant genotypic basis
The genetic variability within a species is due mainly to:
Most mutations are simply single changes in the nucleotide sequence of DNA molecules. What does this mean?
By themselves, they may have no significant effect, but added together over time they can result in fundamental changes
Ex: bigger fruit, resistance to frost, addition of tendrils for climbing
genetic material carried in the gametes is mixed in novel ways when gametes combine during fertilization
formation of gametes
variation is also introduced here, when chromosomes are deleted or translocated, or when homologous chromosomes fail to separate at first meiotic division
a gamete that has two copies of each chromosome
an "error" created during meiosis
a gamete with one chromosome
this is the most common
If a diploid gamete fuses with a haploid gamete, what happens?
A zygote with three times the number of haploid chromosomes can reslut
When one of those is fused with an unreduced diploid gamete, a zygote with four times the haploid number can be formed
more than one diploid number of chromosomes
polyploid plants typically have different characteristics than their diploid forebears
occur relatively common in nature
the process by which environmental conditions determine which traits confer an advantage and therefore increase in frequency in the population
Does natural selection act on a species as a whole?
No, it works on populations
each distinct population of a species
ecotypes can become distinct enough from other ecotypes to become a distinct species in its own right
the process by which humans "direct" genetic change in agricultural populations
we determine which traits are most desirable and select these traits in the way we cultivate and propogate the species
human cultures have both caused changes in the genetic makeup of certain useful species and been transformed as a result of those changes
How long ago did agriculture starte to arise in the world
Between 4,000 and 10,000 years ago, it arose independently in several different areas of the world
How does carbon partitioning operate in crop plants versus wild species?
Crop plants store a much greater proportion of their biomass in their edible or harvestable parts
the ability to withstand stresses, threats or limiting factors in the environment
What are some natural abilities plants have to withstand herbivory and what are the consequences of these traits being lost because other traits were developed/selected?
morphological adaptations, mutualistic interactions, production of obnoxious compounds
agroecosystems have become dependent on pesticide use to prevent loss of crop through herbivory
collecting seed from individuals in a population that show one or more desirable traits and using that seed for planting the next crop
mass selection maintains adaptations to local conditions and allows for maximum genetic variability
Pure line selection
for self-pollinating plants
select superior-appearing plants and study over generations, releasing lines distinct and superior to existing varieties
can also transfer genes between existing pure lines through artificial cross-pollination (can be accomplished by backcrossing progeny with a parent)
the underlying principle is to limit the parental genotypes to a few that are known to have superior characteristics and to cross well
have more genetic variability than pure line varieties, but far less than mass-selected varieties
What is the primary method of directed selection today in many crop plants (especially corn)?
Production of hybrid varieties
A hybrid is a cross between two v. different parents, each from a different pure-breeding line
Two steps involved in the hybrid process
1. The two distinct pure-breeding lines are produced
2. The pure-breeding lines are crossed to produce the hybrid seed that is planted by farmers for crop production
introducing genetically controlled male sterility
also known as hybrid vigor
the hybrid offspring of two slectively inbred parents are usually quite different from either parent
often larger, produce larger seeds or fruits
An advantage of hybrid crosses (from the standpoint of conventional agriculture)
genetic uniformity - all hybrid seeds of a particular cross will have the same genotype
disadvantage of hybrid varieties
seeds produced by hybrid parents will have different traits, most of which will not have the hybrid vigor of parents
farmers must purchase hybrid seed each year from seed producers
Once a hybrid is produced in crop types with tubers or other means of asexual reproduction, how is it propagated?
asexually as a clone
Why are so many of our crop types (wheat, corn, coffee, cotton) polyploids?
They are often more robust and have larger fruits or seeds than their diploid parents, so people found them desirable when they occurred in early cropping systems
how can scientists induce polyploidism
through the use of colchicine or other chemical stimulators during the first steps of meiosis
induced polyploidy has produced some of the most useful lines of wheat such as hexaploid Triticum aestivum
what does genetic engineering enable crop geneticists to do?
introduce specific traits such as resistance to freezing or herbivory into a crop species and to create customized organisms, each with its own unique suite of traits
how has genetically engineered crops changed agriculture?
area planted has increased regularly every year since the mid-1990s
in 2004, an estimated 200 million acres were planted with GE crops
Monsanto has maintained an 80 to 90% share of the market
one way farmers, geneticists, plant breeders and others responded to the dangers of losing genetic diversity in food crops
establishment of gene banks
why are gene banks limited?
1. the vast majority of current banks only have a limited number of crops, preserving a fraction of genetic diversity
2. management and evaluation of genetic resources within banks is lacking so deterioration of material occurs
3. germplasm collections are static, not incorporating the processes that maintain and create genetic diversity (environmental and cultural selection)
the result of gene transfer and backcrossing techniques to incorporate one gene's resistance into a specific crop pedigree
what are two weaknesses of vertical resistance?
resistance continues to function only as long as the limiting factor does not change (limiting factors such as pests, disease and resistance to weeds are not static - they adapt due to natural selection)
genes providing partial resistance to the wider spectrum of pathogens are lost in the process of breeding for vertical resistance
results from breeding based on durable resistance
requires the accumulation of many resistance characters using population-level breeding methods
International Board of Plant Genetic Resources (IBPGR)
Formed in 1974, it's an international network of ex situ (off-site) crop germplasm repositories
Crop Diversity Trust
An independent international organization charged with assuring the long-term security of our most important collections of crop diversity.
Seeks to salvage collections that are at risk and to assist developing countries with managing their collections
According to FAO estimates, how many of the world's livestock breed are threatened with extinction?
As many as 43%
Why are plants autotrophic (self-nurishing)?
They can synthesize carbohydrates using only water, carbon dioxide and energy from the sun
the process of photosynthesis
the solar energy-driven production of glucose from water and carbon dioxide
What are the two distinct processes of photosynthesis?
1. light reactions
2. dark reactions
Light reactions convert light energy into chemical energy in what forms?
ATP (adenosine triphosphate)
NADPH (oxidized from of nicotinamide adenine dinucleotide phosphate)
light reactions use water and give off oxygen
dark reactions take carbon atoms from carbon dioxide in the atmosphere and use them to form organic compounds
driven by the ATP and NADPH produced by light reactions
direct end product of photosynthesis, it's made up mainly of glucose
the plant's main structural material
storage form of glucose
CO2 Compensation Point
This is where photosynthesis equals respiration, yielding no net energy gain by the plant
It's a result of the closing of the stomata in response to high temperatures or moisture stress, so carbon dioxide becomes limiting and slows down the photosynthetic process
Another drawback of closing stomates in response to stress
eliminates the leaf's evaporative cooling process, which increases the leaf O2 concentration
that stimulates photorespiration (O2 is substituted for CO2 in the dark reactions of photosynthesis, producing useless products that require further energy to metabolize)
another name for what occurs during the light reactions
the basis of dark reactions
The most common type
Named because the first stable compound formed in the dark reactions is a three-carbon compound
Carbon dioxide is taken in during the day through open stomata and used in dark reactions to form glucose
Benefits of C3 photosynthesis
plants do well under relatively cool conditions since their optimum temperature for photosynthesis is relatively low
Drawbacks of C3 photosynthesis
Because stomata must be open during the day to take in carbon dioxide, C3 plants are subject to photosynthetic limitations during times of heat or drought stress
closure of stomata limits intake of carbon dioxide and increases photorespiration
Types of crops that use C3 photosynthesis
CO2 is incorporated into four carbon-fixing compounds before it enters the dark reactions
takes place in special chlorophyll containing cells in the leaf
the four carbon compound goes to bundle sheaths, where enzymes break loose the extra carbon as CO2, which is used to form the three-carbon compounds used in the dark reactions
Benefits of C4
photosynthesis can take place while the stomata are closed (carbon dioxide is liberated by interal respiration)
prevents photorespiration from occuring because it makes it more difficult for oxygen to compete with carbon dioxide in the dark reactions)
photosynthesis can occure under conditions of moisture and temperature stress
Crops that use C4 photosynthesis
(also bermuda grass and pigweed)
Crassulacean Acid Metabolism (CAM) Photosynthesis
Similar to C4
During the night, when stomata is open, carbon dioxide is taken in and the four-carbon compound malate is formed and stored in vacuoles
Stored malate serves as a source of carbon dioxide during the day to supply the dark reactions
Examples of CAM plants
succulents and cactus, bromeliads that live as epiphytes
What types of photosynthetic plants are responsible for the majority of world food production?
how a plant districutes the carbon compounds derived from photosynthesis and allocates them to different physiological processes and plant parts
Photosynthesis has an efficiency of energy capture of about 20%. How much energy is involved in converting photosynthate into biomass?
Rarely exceeds 2%
this is low because internal respiration uses up much of the photosynthate and because photorespiration limits photosynthetic output when photosynthetic potential is highest
The actual transfer from vasular strands to sink tissue is often based on
a sugar concentration gradient
source, path, sink phenomena
what carbon partitioning is refered to in ecological terms
source: leaves (chloroplasts especially)
complex set of chemical locators and enzymes are active in tranfering carbon out of the chloroplast and into transport paths
Once in the phloem, carbon moves through the stem to grain, flowers, fruits, tubers or other parts (sinks)
Products of photosynthesis are compounds of carbon, oxygen, and hydrogen. How much of plant dry matter do they make up on average?
indicates a close relationship between whole plant photosynthesis and whole plant productivity
After the canopy closes, crop photosynthesis and growth depend mainly on what
net CO2 fixation per unit leaf area
What makes up 95 percent of the average plant's fresh weight?
carbon and oxygen
Why are essential nutrients needed?
form the structures of the plant
form the nucleic acids directing various plant processes
enzymes and catalysts regulating plant metabolism
help maintain internal osmotic balance
play a role in the absorption of ions from the soil solution
where do essential nutrients come from?
Three nutrients required in relatively large amounts
Nitrogen, phosphorus and potassium
most needed, most universally deficient nutrient
occurs in every amino acid (so is a major component of proteins)
required in enzyme synthesis
invovled in some way with up to 50% of dry plant biomass
Nitrogen deficient plants show a yellowing. Why?
Nitrogen forms part of chlorophyll and is required in its synthesis
How much of a proportion of dry weight is nitrogen
commonly 1-2%, but conents about 5% are not uncommon
Some plants have a symbiotic relationship with microorganisms that help them obtain nitrogen. But most obtain their nitrogen from what?
ion exchange with the soil solution as NO3- or NH4+ adsorbed to humus or clay minerals
available forms in the soil are generally kept at low levels by rapid uptake of nitrogen when it's available coupled with nitrogen's high potential for leaching loss with rainfall or irrigation percolation
component of nucleic acids, necleoproteins, phytin, phospholipids, ATP and some sugars
built into the DNA of chromosomes and RNA of nucleus and ribosomes
Cell membranes need it
Phosphorus is absorbed by
Phosphates from the soil solution through plant roots
readily available and taken up by plants
plants opportunistically take up large amounts of this when it's available
Signs of phosphorus deficiency
purpling, especially on the undersides of the leave
root and fruit development are severely restricted when phosphorus is limiting
function is primarily regulatory
it is involved in stomatal movement and as a cofactor for enzyme systems
Signs of potassium deficiency
signs of disruptions in water balance - drying tips or curled leaf edges
Ca Mg S
Ca and Mg are readily absorbed through cation exchange (as Ca2+ and Mg2+) while Sulfur is taken up as an anion SO42-)
the continual flow of water from the soil to the atmospher along a pathway that extends from the soil into the roots up the stem to the leaves and out of the leaves through the stomata
plant responses which are triggered by some external stimulus
responses come about as a result of a certain condition but the condition doesn't have to be maintained for the response to continue
tobacco seed requires light to germinate - a flash will do
plant responses that depend on the continued presence of a particular external condition
leaf production on the spiny stems of ocotillo only last as long as moisture levels are sufficient in the soil - leaves drop upon reaching the wilting point
plant responses that occur regardless of conditions in the immediate environment
a corn plant flowers because of a particular stage in growth and development
a species with a broad set of tolerances of environmental conditions
a species with a narrow set of tolerances and a very specialized niche
Any soil above a pH of 7(neutral)
Any soil with a pH below 6.6
general range of agricultural crop pH preference
when a particular nutrient is not present in the soil in sufficient quantity, it's called a limiting nutrient
In natural ecosystems, the organic matter content of the A horizon can range up to 15 or 20% or more, but in most soils it averages
How can you estimate soil organic matter content?
by either multiplying the total carbon content by 2 or the total nitrogen content by 20
the process of metabolizing or decomposing complex carbon compounds in fresh plant litter
humification eventually imparts a darker color to the soil as it produces humic residues (humus)
The first step in developing soil organic matter
maintain constant inputs ofr new organic matter to replace that which is lost through harvest and decomposition
How might incorporation of crop residue be done while minimizing the potential of passing on pest or disease organisms to the subsequent crop?
Proper timing of incorporation of the residue into the soil
rotation of crops
composting the residue away from the field and returning the finished compost to the field
a plant cover is grown specifically to produce plant matter for incorporation as a "green manure" into the soil
cover crop plants are usually grown in rotation with a crop or during a time of the year that the crop can't be grown
Some drawbacks of animal manure?
smells and flies
nitrogen loss through ammonification
runoff of nitrates and other soluble materials
1 days production of manure from a 120 cow dairy operation is equivalent to
soil cultivatin is limited to the actual seedbed and is done at the time of seed planting
fertilization and weed control can be completed at the same time as planting
drawback- many zero tillage systems rely heavily on herbicides