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States of Activity
2. Quiescent (needs good conditions to germinate)
When seed will not germinate under conditions of moisture,
temperature, and aeration known to be suitable for the environment.
Types of Dormancy:
- Hard Seed-
- seed coat prevents uptake of water or exchange of gases (used for
- survival, bred out of most common crops)
- Immature embryo- forms after uptake of water,
- undergoes after ripening process
- Embryo dormancy- Incapable of germination due to
- a true physiological dormancy, (needs something to break dormancy: temperature,
Germination Vs. Emergence
- Germ: emergence of the radical from the seed coat, Emergence: seedlings break through the soil
- surface. Prior to emergence feeds on reserve (Heterotrophic) After emergence
Types of Emergence
- Epigeal- cotyledons brought above soil by
- hypocotyl (soybean)
- Hypogeal- cotyledons and bulk of seed remain
- below soil surface (Corn, wheat)
Respiratory Quotient = CO2 released/O2 consumed.
- RQ for starch=1.0 and 0.7 for fats: Fats need more O2 to
Factors preventing germ and emergence
- Seed vigor (ability to germinate under non
- optimal conditions) two tests: cold test, and Accelerated aging tetrazolium
Vigor vs germination test for %germination over time
- Vigor starts out lower and steadily decreases. Germination under optimal conditions
- decreases at a slower rate (oil type starts out lower than wheat type)
Why don’t we report vigor?
- Sellers don’t want buyers to know
What does seed longevity depend on?
- of crop developmental events (Growth Stages)
Increase in plant/crop dry weight
- sequential production differentiation,
- expansion, and loss of the structural units of the plant.
- Growth increases plant dry weight. The plant can keep increasing in dry weight
- without expanding and going on to reproduction. The plant can also go through developmental
- stages without increasing in dry weight.
- A short plant may still go through reproductive stages but not increase
- in dry weight. Depends on environmental
- conditions (light, temp, etc.)
- plant building block e.g. leaf, node
- time between first visible appearance of a leaf and
- appearance of next younger leaf.
- – time between first visible appearance of a leaf and the
- appearance of the next younger primordium.
first stage of development of an organ
- growth pattern. Rather strict demarcation between vegetative and reproductive
- growth (flower from top down)
- – grows throughout season – overlapping vegetative and
- reproductive growth (keep flowering, bottom ages differently than top).
Tu = [(Tmax + Tmin)/2]-Tb (base temp of growth)
- If Tmax gets above a critical number for some crops use the
- Tmax designated for that crop.
- Rate of developmental processes are determined by temp
- (Linear) unless the plants are exposed to environmental stresses.
- – length of day
- plant response to length of day (ex. Soybean under street lamp)
Types of plants
- Short day plants (summer crops, soybeans)
- flowering promoted by day lengths shorter than critical maximum
- Long day plants (winter crops, wheat) flowering
- promoted by day lengths longer than a critical maximum
- Day neutral plants (corn) work off of Tu
- Period of uninterrupted night in is more important than
- uninterrupted day.
cold requirement in addition to day length
Leaf Area of a plant at a given time is determined by
- Date of plant emergence
- Rate of leaf production
- Rate of expansion of the leaf lamina
- The duration of expansion
- The rate of branching or tillering
- Timing of leaf senescence, removal or damage
LAI- Leaf area/ unit of soil area (unitless)
Leaf area of a crop canopy determined by
- Plant population density
drymatter/unit of land area/time (g/m^2Groundarea/day
- accumulation of dry matter/unit leaf area/ time (does not
- account for branches and stems)
active radiation (PAR)
crop has LAI of
- absorbed PAR
So as LAI increases the critical LAI photosynthesis increases to a certain point and stays
- constant while photosynthesis and respiration of the optimum LAI decreases
- after a certain amount of leaves are produced.
Compare and contrast individual leaf vs. crop canopy
Individual leaf is more productive at low light intensitybut as intensity increases net photosynthesis for the crop canopy increases andis more productive. Like studentsworking in a field.
Lambert- beer extinction Law
I= Irradiance at a particular level in the canopy
Io= irradiance above the canopy
- K=extinction coefficienct (leaf angle; 1is flat 0 is
L=Layers of leaves
- K = constant (wheat=0.3-0.4 erect; corn=0.4-0.8 plagiophile;
- sunflower = 0.8-0.9 planophile)
Greater the value of k the more horizontal the leaf surface
- Degrees from horizontal 0
- 30 45 60 75 85
- Light penetration % 0
- 13 29 50 74 91
- Leaf photo rate decreases as leaf angle increases. Canopy photo rate
- increases as leaf angle increases.
Would you expect increase plant pop and decrease row spacing of effect
short season or long season plants?
More beneficial for short season
Plant response to increasing plant population density (diminishing returns)
- Phase I – 1-2 plants no interplant competition
- yield per plant is maximized
- Phase II- plants compete for needed resources
- yield increases as plant pop increases with marginal increases are smaller for
- each additional plant
- Phase III – populations in excess of that
- required for 95% insolation
Calvin Cycle (C3 cycle)
CO2+RuBP à 3PGA
- 16 subunits coded from chloroplast
- Large subunits coded from chloroplast genes
- Small subunits coded from genes in the nucleus
- Most common enzyme in leaves
- Approx. ½ of soluble protein in a C3 leaf
- Affinity for CO2 and O2
When there is a limit to CO2 (water stressed; closed
stomata) photorespiration occurs. Uses a lot of energy. Allows plant to recover 75% of the C that would
otherwise be lost as Pglycolate
Compare and contrast CO2 concentration on a calm vs. windy
- Starts out lower (310ppm) for a windy day decreases slightly
- around 12 hours then increases around 16 hours.
- On a calm day starts out higher and decreases sharply and then increases
Boundary layer almost non existant on a windy day.
CO2 movement into the leaf is a diffusive process.
C4 vs C3 rate of photosynthesis and temperature
- C3 is more efficient at lower temps. C4 more efficient at higher temperatures As Temp increases, )2 becomes more soluble
- than CO2 more O2 for photorespiration in C3. As Temp increases rubisco’s
- affinity for o2 increases.
- Q=quantity of PAR
- I = fraction of Q intercepted IPAR
- E = photosythetic efficiency
- H = harvest index (grain biomass/total biomass)
Source vs. Sink
- source= where plant materials are synthesized
- sink = where plant materials are utilized
movement is a accropetal (from bottom to top)
movement is bidirectional
phloem movement between cells is via the ____
phloem transport operates via _____
water potential gradient.
substances that move to the phloem across the phospholipid bilayer via diffusion
- organic acids
- plant hormones
Rate of movement in phloem depend on
- 1. Rate of acceptance by the sink
- 2. Chemical nature of compound
- 3. rate of movemeent out of the source
- 4. environment
- movement can be up to 500cm hr-1, normal is 30-150 cm hr-1
strongest sink? most photosynthetically active?
New leaves. fully expanded leaves
leaf is a net _____ of photosynthate to about ____% at that point the leaf starts _____.
impoter. 50%. exporter
movement of compounds from an area where they were once deposited to an area where they are reutilized. (Storing assimilate)
Not all stored assimilate can be removilized. Which can and cannot?
- Cannot- structural (Cellulose)
- Can- storage compounds (carbs, lipids, proteins)
Estimates of crop water needed
- wheat 26 in
- soybean 26 in
- corn 31
- sugarcane 96 in
Most water is used for ____ rather than ____
evaporative cooling rather than photosynthesis.
water potential of air, leaf, stem, root, and moist soil
- air = -100 Mpa
- leaf = -1 to -4
- stem = -0.2
- root = -0.1 to 10.5
- moist soil = -0.01 to -0.1Mpa
water moves from ____ potential to ___ potential.
high to low
as the water potential becomes morenegative the moisture available to the plant _______
Factors affecting transpiration
- 1. Irradiance
- 2. wind speed - removes boundary layar
- 3. soil moisture
- 4. plant anatomical/morphological features
As transpiration increases biomass ____
increases linearly. Slope depends on the crop.
adaptation vs acclimation
- adaptation - heritable modification in structure or function that increases the probability of survival in a particular environment
- Acclimation - non-heritable
what are YA and Yp
- YA=actual yield- depends on the environment
- Yp= yield potential--> depends on seed.