76848 (1).pptx

Plant Physiology
Morphology
Seasonality and
Life Cycles
Grazing and
Plant Growth
Seasonal
Growth Rates
Germination
and Seedling
Establishment
Grazing
Optimization
Carbohydrates
and
Allocation
Reproduction
Grass
Anatomy
Forb
Anatomy
Shrub
Anatomy
You are here
Secondary
Compounds
Grazing
Resistance
Forage
Quality
RANGE PLANT GROWTH AND DEVELOPMENT
RDM
Grazing
Effects
Photosynthesis
Water and
Nutrients
Life Cycles
and
Phenology

Seasonality and Life Cycles
 Terminology
 Life Cycles
 Seasonal growth rates
 Forage Quality
 RDM
Seasonality and
Life Cycles
Seasonal
Growth Rates
You are here
Forage
Quality
RDM
Life Cycles
and
Phenology

 The Phenology Handbook, pg 1-15
 George et al. 2001. Annual Range Forage Production
 George and Bell. 2001. Using Stage of Maturity……..
Return to Course Map
Seasonality and
Life Cycles
READING AND REFERENCES
SEASONALITY & LIFE CYCLES

 Terminology
 Life Cycles
 Forage Quality
 RDM
Plant Physiology

TERMINOLOGY
 Annual  Perennial
Seasonality and
Life Cycles

Grass: monocot, most
are not woody
Forb: dicot, non-woody
 Shrub
Dicot, woody
Seasonality and
Life Cycles
TERMINOLOGY

Seasonality and
Life Cycles
TERMINOLOGY
 PHENOLOGY is the science
that measures the timing of
life cycle events for plants,
animals, and microbes, and
detects how the environment
influences the timing of those
events.
 In the case of flowering plants,
these life cycle events, include
leaf budburst, first flower, last
flower, first ripe fruit, seed set,
leaf shedding, others.

LIFE CYCLES
Seasonality and
Life Cycles

ANNUAL LIFE CYCLES
 Annuals
 Germination
 Vegetative
 Seedling
establishment
 Leaf growth
 Winter growth is slow
 Growth accelerates
in spring
 Flowering
 Seed Set, Drying
 Dry and Die
Seasonality and
Life Cycles

ANNUAL LIFE CYCLE CALENDAR
N D J F M A M J J A S O
Germination & Seedling
Establishment
Slow Vegetative Growth
Rapid Vegetative
Growth
Little or No Vegetative Growth
Tiller Development
Flowering
Seed Development
Seed Set
Drying Stems &
Leaves
Dry & Dead Stems & Leaves
Seasonality and
Life Cycles
Timing of phenological events

PERENNIAL LIFE CYCLES
 Perennials
 Lives several years
 Sexual reproduction
 Vegetative reproduction
 Stolons and Rhizomes
 Winter dormancy
 Dry season dormancy
 Vegetative phase
 Flowering
 Seed set and dispersal
 Dormancy
Seasonality and
Life Cycles

PERENNIAL LIFE CYCLE CALENDAR
N D J F M A M J J A S O
Dormant or Slow Vegetative Growth Rapid Vegetative Growth
Slow Vegetative
Growth
Dormant Tiller Development Tiller Development
Dormant Carbohydrate Use Carbohydrate Storage
Apical Meristems Near Soil Surface
Flower Stems
Elongate
Flowering
Seed
Development
Seed Set
Drying Stems &
Leaves
Dry & Dead
Stems &
Leaves
Seasonality and
Life Cycles
Timing of phenological events

PHENOLOGY AND LIFE CYCLES
Seasonality and
Life Cycles
Phenological events

Crude protein decreases in annual grasses with stage of maturity
(see ANR Publications 8019 and 8022)
PHENOLOGY AND FORAGE QUALITY
Seasonality and
Life Cycles

SEASONAL GROWTH RATES
0
500
1000
1500
2000
2500
3000
3500
lbs/ac
Average Monthly Peak Standing Crop at UC SFREC
D1 J1 F1 M1 A1 M1 Peak
http://groups.ucanr.org/sierrafoothill/files/67089.pdf
Seasonality and
Life Cycles

SEASONAL GROWTH RATES
 Growth rates of perennials in northeastern
California
0
200
400
600
800
1000
1200
1400
1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul
lbs/ac
Seasonality and
Life Cycles

 Terminology
 Life Cycles
 Forage Quality
 RDM
Plant Physiology

LITTER: RESIDUAL DRY MATTER
Moderate grazing results in
recommended RDM levels
Heavy grazing results in low
RDM levels
Light grazing results in high
RDM levels
Seasonality and
Life Cycles

SUMMARY
Seasonality and
Life Cycles
 In this section you have learned the differences
between annual and perennial life cycles and
how plant growth rates and forage quality
change as range and pasture plants move
through their life cycle.

Plant Physiology
Seasonality and
Life Cycles
Grazing and
Plant Growth
Seasonal
Growth Rates
Germination
and Seedling
Establishment
Grazing
Optimization
Carbohydrates
and
Allocation
Reproduction
Grass
Anatomy
Forb
Anatomy
Shrub
Anatomy
You are here
Secondary
Compounds
Grazing
Resistance
Forage
Quality
RANGE PLANT GROWTH AND DEVELOPMENT
RDM
Grazing
Effects
Photosynthesis
Water and
Nutrients
Life Cycles
and
Phenology
Morphology

Morphology
 Grass Anatomy
 Forb Anatomy
 Shrub Anatomy
 Reproduction
You are here
Reproduction
Grass
Anatomy
Forb
Anatomy
Shrub
Anatomy
Morphology and
Development

 Briske, 1991. Chp 4. Dev. Morph and Phys of Grasses.
Introduction and Developmental Morphology Sections.
 Skinner and Moore. Growth and Dev of Forage Plants
 How Grass Grows
MORPHOLOGY

MORPHOLOGY
 Grass Anatomy
 Forb Anatomy
 Shrub Anatomy
 Reproduction
Plant Physiology

GRASS ANATOMY
 Please review “How Grass Grows” at the link below.
 Overview of the Grass Plant
 Shoot Development
 Crown
 Leaf Formation
 Leaf Expansion Dynamics
 Tillering
 Rhizome and Stolon Development
 Flowering
 Root Development
 Germination Process
 Seasonal Development
http://www.files.ahnrit.vt.edu/files/flash/howgrassgrows/howgrassgrows.swf
Morphology and
Development

GROWING POINTS
 Apical meristems (flower)
 Axillary buds (give rise to tillers,
rhizomes and stolons)
 Intercalary meristems or collar
(leaf expansion)
 Some growing points become
elevated as the growing season
progresses.
 Buds near the ground are less
likely to be grazed
 Delaying bud elevation reduces
risk of bud removal by grazing
Morphology and
Development

 Intercalary meristems or collar
(leaf expansion)
 Some growing points become
elevated as the growing season
progresses.
 Buds near the ground are less
likely to be grazed
 Delaying bud elevation reduces
risk of bud removal by grazing
Morphology and
Development
GROWING POINTS

 Intercalary meristems or collar (leaf
expansion)
 Some growing points become elevated
as the growing season progresses.
 Buds near the ground are less likely to
be grazed
 Delaying bud elevation reduces risk of
bud removal by grazing
Morphology and
Development
GROWING POINTS

 Intercalary meristems or collar (leaf
expansion)
 Some growing points become elevated
as the growing season progresses.
 Buds near the ground are less likely to
be grazed
 Delaying bud elevation reduces risk of
bud removal by grazing
Apical
meristem
rising
Morphology and
Development
GROWING POINTS

VEGETATIVE PHASE
 In the vegetative phase,
shoots consist
predominantly of leaf
blades.
 Leaf blade collars remain
nested in the base of the
shoot and there is no
evidence of sheath
elongation or culm
development.
Morphology and
Development

ELONGATION (TRANSITION) PHASE
 Floral induction - Apical meristems is
gradually converted from a vegetative
bud to a floral bud.
 During the transition phase, leaf
sheaths begin to elongate, raising the
meristematic collar zone to a grazable
height.
 Culm internodes also begin elongation
in an "un-telescoping" manner
beginning with the lowermost
internode thereby raising the
meristematic zone (floral bud and leaf
bases) to a vulnerable position.
Morphology and
Development

REPRODUCTIVE PHASE
 The flowering phase begins
with the conversion from
vegetative to floral bud.
 Much of this is unseen until
the emergence of the seed
head from the sheath of the
flag leaf (boot stage).
 Within a few days,
individual florets within the
seed head are ready for
pollination.
Apical
meristem
rising
Morphology and
Development

FORB ANATOMY
Morphology and
Development

FORB GROWING POINTS
Morphology and
Development

SHRUB ANATOMY
 Coast live oak resprouts  Chamise resprouts
Morphology and
Development

REPRODUCTION
 Long Day Plants
 Short Day Plants
 Sexual Reproduction (flowers and seeds)
 Vegetative Reproduction (stolons, rhizomes)
Morphology and
Development

 Some plants are long-day plants
and others are short-day plants.
 The long-day plants reach the
flowering phenological stage after
exposure to a critical photoperiod
and during the period of increasing
daylight between mid April and mid
June.
 Generally, most cool-season plants
with the C3 photosynthetic pathway
are long-day plants and reach
flower phenophase before 21 June.
Morphology and
Development
REPRODUCTION -
LONG DAY PLANTS

 Short-day plants are induced into flowering
by day lengths that are shorter than a critical
length and that occur during the period of
decreasing day length after mid June.
 Short-day plants are technically responding
to the increase in the length of the night
period rather than to the decrease in day
length.
 Generally, most warm-season plants with the
C4 photosynthetic pathway are short-day
plants and reach flower phenophase after
21 June.
 The annual pattern in the change in daylight
duration follows the calendar and is the
same every year for each region.
Morphology and
Development
REPRODUCTION
SHORT DAY PLANTS

REPRODUCTION
 Plant populations persist through
both asexual (vegetative)
reproduction and sexual
reproduction.
 The frequency of true seedlings
produced from seed is low in
established grasslands and
occurs only during years with
favorable moisture and
temperature conditions in areas
of reduced competition from older
tillers, and when resources are
easily available to the growing
seedling.
Morphology and
Development

 Sexual reproduction is necessary for a population to maintain
the genetic diversity enabling it to withstand large-scale
changes.
 However, production of viable seed each year is not necessary
to the perpetuation of a healthy grassland.
Morphology and
Development
REPRODUCTION
SEXUAL

 Reproductive shoots are
adapted for seed production
rather than for tolerance to
defoliation
 Grass species that produce a
high proportion of
reproductive shoots are less
resistant to grazing than are
those species in which a high
proportion of the shoots
remains vegetative.
Morphology and
Development
REPRODUCTION
SEXUAL

 Vegetative growth is the dominant form of
reproduction in semiarid and mesic grasslands
 Annual plants are dependent on seed production
each year for survival.
 Short-lived perennials depend on seed production.
 Long-lived perennials rely more on vegetative
reproduction.
Morphology and
Development
REPRODUCTION
ASEXUAL OR VEGETATIVE

TILLERING
Morphology and
Development

REPRODUCTION
 Bunch grasses spread by the production
of tillers.
 Stoloniferous grasses spread by lateral
stems, called stolons, that creep over
the ground and give rise to new shoots
periodically along the length of the
stolon.
 Rhizomatous grasses spread from below
ground stems known as rhizomes.
Morphology and
Development
ASEXUAL OR VEGETATIVE

SUMMARY
.
Morphology and
Development
In this section you learned about plant growing points, how
plants grow, phases of plant growth and reproduction. You
learned that vegetative reproduction in the form of tillers,
stolons and rhizomes are more important than reproduction
via seeds in most grasslands. You also learned that buds
close to the ground are less vulnerable to grazing than when
they are elevated.

Plant Physiology
Morphology
Seasonality and
Life Cycles
Grazing and
Plant Growth
Seasonal
Growth Rates
Germination
and Seedling
Establishment
Grazing
Optimization
Carbohydrates
and
Allocation
Reproduction
Grass
Anatomy
Forb
Anatomy
Shrub
Anatomy
You are here
Secondary
Compounds
Grazing
Resistance
Forage
Quality
RANGE PLANT
GROWTH AND DEVELOPMENT
RDM
Grazing
Effects
Photosynthesis
Water and
Nutrients
Life Cycles
and
Phenology

Plant Physiology
 Germination &
Seedling
Establishment
 Photosynthesis
 Carbohydrates and
Carbohydrate
Allocation
 Water and Nutrients
 Secondary
Compounds
Plant Physiology
Germination
and Seedling
Establishment
Carbohydrates
and
Allocation
Secondary
Compounds
Photosynthesis
Water and
Nutrients

 McKell, C.M. 1974. Morphogenesis and management of
annual range plants in the United States. Pg 111-116.
Grazing Resistance Section.
 Waller and Lewis. 1979. Occurrence of C3 and C4
photosynthetic pathways in North American grasses.
 Carbohydrate Reserves: What you learned may be wrong.
PLANT PHYSIOLOGY

PLANT PHYSIOLOGY
 Germination and Seedling Establishment
 Photosynthesis
 Carbohydrates and Carbohydrate Allocation
 Secondary Compounds
Plant Physiology

GERMINATION & SEEDLING
ESTABLISHMENT
Plant Physiology

 See Anatomy
 Embryo
 Endosperm (food
reserves)
 Seed coat (pericarp)
 Variable seed
production
 Empty seeds
Empty Seeds
Seed Coat
Plant Physiology
ESTABLISHMENT

Plant Physiology
ESTABLISHMENT

PHOTOTROPISM
Plant Physiology

 Oxygen is required for
respiration during
germination.
 Oxygen is found in soil pore
spaces but if a seed is
buried too deeply within the
soil or the soil is
waterlogged, the seed can
be oxygen starved.
 Some seeds have
impermeable seed coats
sometimes called hard
seed.
 Hard seed is common in
legumes
Plant Physiology
ESTABLISHMENT

 Temperature also influences
germination.
 Seeds from different
species and even seeds
from the same plant
germinate over a wide range
of temperatures.
 Seeds often have a
temperature range within
which they will germinate,
and they will not do so
above or below this range.
Plant Physiology
ESTABLISHMENT

 Some seeds require exposure to
cold temperatures (vernalization)
to break dormancy.
 Seeds in a dormant state will not
germinate even if conditions are
favorable.
 Some seeds will only germinate
following hot weather and others
exposed to hot temperatures
during a forest fire which cracks
their seed coats.
 Some seeds need to pass through
an animal's digestive tract to
weaken the seed coat enough to
allow the seedling to emerge.
Plant Physiology
ESTABLISHMENT

 Variability in the rate of
germination exists between
and within species.
 Seed size has been shown
to be a critical factor in
promoting seedling vigor.
 In legumes and other forbs,
seed coat hardness or
impermeability often retards
germination but spreads
germination over years
which is a survival
advantage for the species.
Plant Physiology
ESTABLISHMENT

 On annual rangelands estimates
of germinable seed exceed
20,000 per m2.
 On annual rangelands the
number of plants early in the
growing season has been
reported to vary from 20 to nearly
100 per square inch.
 Considerable reduction in this
number takes place as the
season progresses. The lost
seedlings decay and provide a
flush of nutrients early in the
growing season.
Plant Physiology
ESTABLISHMENT

 Rapid root growth is
fundamental to establishment
and development of annual
rangeland plants.
 Individual plants and species
may gain an advantage over
competitors if they exhibit rapid
root growth and are able to
maintain both rapid root and top
growth.
 Annual grasses frequently
exhibit root growth rates greater
than native perennial grasses
Annual grass (cheatgrass) roots
(b) grew faster in this study than
blue bunch wheatgrass (native
perennial ) roots (a) (Harris
1977, JRM)
Plant Physiology
ESTABLISHMENT

CO2 + H2O CH2O + O2
Sunlight
Chlorophyll
Plant Physiology
PHOTOSYNTHESIS

FOUR FUNDAMENTAL CONCEPTS
 Plants are the only source of energy for grazing animals.
 The formation of sugars, starches, proteins and other foods
is dependent on photosynthesis.
 Plants do not get food from the soil. They obtain raw
materials needed for photosynthesis and subsequent food
production
 When leaves are removed from plants, food-producing
capacity is reduced.
Plant Physiology

To learn more about Photosynthesis:
http://www.youtube.com/watch?v=_wO9f3
ER17M
Plant Physiology
PHOTOSYNTHESIS

4. Physiological efficiency
5. Soil nutrients
6. Water supply
7. Temperature
Factors that influence photosynthetic rate
1. Leaf area
2. Light intensity and quality
3. CO2 content of the air
Plant Physiology
PHOTOSYNTHETIC RATE

Relationship between light interception and leaf area (Brougham 1956)
Plant Physiology
LEAF AREA AND LIGHT INTENSITY

Lightly grazed
Closely grazed
Plant Physiology
PHOTOSYNTHESIS & LIGHT INTENSITY

(Parsons et al. 1983)
Plant Physiology
PHOTOSYNTHESIS & LEAF AREA

Relationship between leaf area and herbage yield (Brougham 1956)
Plant Physiology
PRODUCTION & LEAF AREA

Gross & Net Production
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Leaf Area Index
Photosynthesis
(%
of
maximum
GPP)
GPP NPP R
GROSS & NET PRIMARY PRODUCTION
 NPP=GPP - R
 GPP and NPP
increase as leaves
are added until
upper leaves
begin shading
lower leaves then
R increases
resulting in
decrease in NPP
Plant Physiology

STOMATES AND WATER RELATIONS
Guard Cells
Stomate
Plant Physiology

 Water required for
photosynthesis
 Lost through stomates
(transpiration)
 Arid and semi-arid lands
frequently subjected to water
stress
 Drought tolerant
Plant Physiology
WATER RELATIONS

PHOTOSYNTHETIC PATHWAYS
Plant Physiology
C3, C4 & CAM Pathways

 C3 because CO2 is first incorporated
into a 3-carbon compound.
 Stomata are open during the day.
 Photosynthesis takes place
throughout the leaf.
 Adaptive Value:
 more efficient than C4 and CAM
plants under cool and moist
conditions and,
 under normal light conditions.
 Most plants are C3.
Plant Physiology
C3 PHOTOSYNTHESIS

 CO2 is first incorporated into a 4-carbon compound
 Stomata are open during the day.
 Photosynthesis takes place in inner bundle sheath
cells
 Adaptive Value:
 Photosynthesizes faster than C3 plants under
high light intensity and high temperatures.
 Better water use efficiency than C3 because
CO2 uptake is faster and so does not need to
keep stomata open as much (less water lost by
transpiration) for the same amount of CO2 gain
for photosynthesis
 C4 plants include several thousand species in at
least 19 plant families
 Examples: fourwing saltbush, corn, and many
summer annual plants
Plant Physiology
C4 PHOTOSYNTHESIS

 Crassulacean Acid Metabolism (CAM)
 Stomata open at night and are usually closed during
the day.
 The CO2 is converted to an acid and stored during
the night.
 During the day, the acid is broken down and the
CO2 is released for photosynthesis
 Adaptive Value:
 Better Water Use Efficiency than C3 plants
 CAM-Idle
 When conditions are extremely arid, CAM plants
can just leave their stomata closed night and
day.
 CAM plants include many succulents such as cactuses
and agaves and also some orchids and bromeliads
Plant Physiology
CAM PHOTOSYNTHESIS

Plant Physiology
Waller, S.S. and J.K. Lewis. 1979. Occurrence of C3 and C4
Photosynthetic Pathways in North American Grasses. Journal of Range
Management 32:12-28 for an review and list of C3 and C4 range plants.
COOL & WARM SEASON GRASSES

Plant Physiology
ROOT GROWTH TEMPERATURES

Plant Physiology
WATER USE EFFICIENCIES
C3 VS C4

Plant Physiology
CO2 CONCENTRATION

Plant Physiology
LIGHT, TEMPERATURE AND CO2
C3 VS C4:

Carbohydrates are the plant’s energy source
Energy needed for:
• Root replacement
• Leaf and stem
growth following
dormancy
• Respiration during
dormancy
• Bud formation
• Regrowth following
top removal
REDUCED CARBOHYDRATE STORAGE
Plant Physiology

Plant Physiology
CARBON DISTRIBUTION/ALLOCATION

CARBON DISTRIBUTION/ALLOCATION
Plant Physiology

WATER AND NUTRIENT UPTAKE
Plant Physiology
For more information on plant water movement see these two videos:
http://www.youtube.com/watch?v=tRNe_UHw7F4
http://www.youtube.com/watch?v=umUn8D6gEOg&feature=related

AVAILABLE WATER
Plant Physiology

NUTRIENT UPTAKE
Plant Physiology

MYCORRHIZAE
Plant Physiology

SECONDARY COMPOUNDS
Plant Physiology
Many secondary compounds are toxic to livestock and humans.
For more information see “Livestock-Poisoning Plants of California.

SECONDARY COMPOUNDS
Conifers accumulate monoterpenes
Plant Physiology
TERPENES

 Lignin
 Flavenoids
 Tannin
isoflavenoids in legumes
Tannins in oak leaves
Plant Physiology
SECONDARY COMPOUNDS
PHENOLICS

 Alkaloids
SECONDARY COMPOUNDS
 Cynanogenic glycosides
Plant Physiology
NITROGEN CONTAINING COMPOUNDS

SECONDARY COMPOUNDS
Plant Physiology
ALLELOPATHY

SUMMARY
Plant Physiology
In the plant physiology section you learned about germination and
seedling establishment, photosynthesis, carbohydrate storage and
allocation, plant water relations and nutrient uptake and secondary
compounds. You learned that fire and heat can influence germination
along with soil moisture and temperature. You also learned that
photosynthetic rate increases with leaf area to some optimum level and
then slows with continued increases in leaf area. You learned about
three photosynthetic pathways (C3, C4 and CAM) and their adaptive
value. You learned that carbohydrates produced during photosynthesis
are used for plant growth or stored to meet future needs. And finally you
learned about secondary compounds

Grazing and Plant Growth
 Grazing Effects
 Grazing Optimization
 Grazing Resistance
Grazing and
Plant Growth
Grazing
Optimization
Grazing
Resistance
Grazing
Effects

Grazing Resistance Section.
 Trlica, J. 2006. Grass Growth and Response to Grazing.
 A quick lesson in plant structure, growth and regrowth for
pasture-based dairy systems.
 Noy-Meir, I. 1993. Compensating growth of grazed plants and
its relevance to the use of rangelands.
GRAZING & PLANT GROWTH

GRAZING AND PLANT GROWTH
 Grazing Effects
Grazing and
Plant Growth

GRAZING EFFECTS
 Detrimental Effects
 Growth Promoting Effects
Grazing and
Plant Growth

Grazing and
Plant Growth
DETRIMENTAL GRAZING EFFECTS
 Removal of photosynthetic
tissue
 Reduced carbohydrate
storage
 Reduced root growth
 Reduced seed production

Grazing and
Plant Growth
1. Grazing that is too heavy can reduce leaf area and reduce
photosynthesis and carbohydrate production.
Grazing can influence leaf area
REDUCED LEAF AREA FOR PHOTOSYNTHESIS

Grazing and
Plant Growth
1. Heavy grazing can weaken root systems increasing moisture
stress
Grow leaves,
stems, roots and
buds.
REDUCE GROWTH

Grazing and
Plant Growth
1. Heavy grazing can weaken root systems increasing moisture
stress
Leaves, stems,
roots and other
plant parts
REDUCE GROWTH

Grazing and
Plant Growth
Seed production
REDUCE GROWTH

Grazing and
Plant Growth
Carbohydrates are the plant’s energy source
REDUCED CARBOHYDRATE STORAGE

Grazing and
Plant Growth
 Detrimental Effects
 Growth Promoting Effects
GRAZING EFFECTS

Grazing and
Plant Growth
 Increased photosynthesis
 Increased tillering
 Reduced shading
 Reduced transpiration
GROWTH PROMOTING EFFECTS

Grazing and
Plant Growth
1. Intensity
2. Timing
3. Frequency
4. Grazing of surrounding plants
INFLUENCES ON GRAZING EFFECTS

Grazing and
Plant Growth
1. Decreases evapotranspiration
2. Moderates surface microclimate during germination and seedling
establishment
3. Slows surface runoff and increases infiltration
4. Protects soil from erosion
LITTER

Grazing and
Plant Growth
Grazing too close reduces reserves
and slows recovery following grazing
GRAZING TO CLOSE

Grazing and
Plant Growth
 Plant A was allowed to grow for
three months without clipping.
Healthy root system
 Plant B was clipped to 3 inches
every three weeks for 3
months. Healthy root system
 Plant C was clipped to 1 inch
every week for 3 months. Very
weak root system and might not
survive a drought
A C
B
DETRIMENTAL EFFECTS OF GRAZING

Grazing and
Plant Growth
Heavy Grazing:
 Decreased photosynthesis
 Reduced carbohydrate storage
 Reduced root growth
 Reduced seed production
 Reduced ability to compete with
ungrazed plants
 Reduce accumulation of litter or
mulch which decreases water
infiltration and retention, plus it
protects soil from erosion.
Light to Moderate Grazing:
 Increased plant productivity
 Reduced shading of lower leaves
 Reduced transpiration losses
 Reduced ability to compete with
ungrazed plants
 Reduction of excessive litter or
mulch that can physically or
chemically inhibit vegetative
growth. Excessive mulch
promotes pathogens and insects
that can damage forage plants.
Negative effects of heavy grazing vs. possible effects
of light to moderate grazing on range plant physiology
SUMMARY

Grazing and
Plant Growth
 Grazing Effects

GRAZING OPTIMIZATION
 There are levels of grazing that can result in
increased productivity
 G.O. is a complex and sometime controversial
subject.
Grazing and
Plant Growth

GRAZING OPTIMIZATION HYPOTHESIS
Grazing and
Plant Growth

GRAZING OPTIMIZATION HYPOTHESIS
Grazing and
Plant Growth
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Leaf Area Index
Photosynthesis
(%
of
maximum
GPP)
GPP NPP R
 NPP=GPP - R
 GPP and NPP
increase as leaves
are added until
upper leaves
begin shading
lower leaves then
R increases
resulting in
decrease in NPP

0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Photosynthesis
(%
of
maximum
GPP)
Leaf Area Index
GPP NPP R
 NPP=GPP - R
 GPP and NPP increase as
leaves are added until
upper leaves begin shading
lower leaves then R
increases resulting in
decrease in NPP
 Grazing reduces leaf area
 G.O. says if grazing keeps
LAI near 4, NPP is
optimized.
 May occur in some
species, more likely in
pasture.
 Some species are
extremely susceptible to
grazing even at light
intensities.
Grazing and
Plant Growth

Grazing and
Plant Growth
C = ‘control’ no clipping
TB = terminal bud removed only
60 = 60% current annual growth removed

Grazing and
Plant Growth

MECHANISMS CONTRIBUTING TO
COMPENSATORY PLANT GROWTH
Grazing and
Plant Growth
Herbivore-induced physiological processes
 Accelerated photosynthesis per unit leaf area
 Accelerated nutrient absorption per unit root mass
 Greater resource allocation to shoots
 Increased tiller initiation
 Improved water status
Herbivore-mediated environmental modification
 Increased irradiance on remaining leaves and young tillers
 Conservation of soil water following leaf area removal
 Accelerated rate of nutrient cycling
 Increased activity of decomposer organisms

Grazing and
Plant Growth
Grazing Effects
Grazing Optimization
Grazing Resistance

GRAZING RESISTANCE
Grazing and
Plant Growth

GRAZING AVOIDANCE
 Mechanical
 Biochemical
Grazing and
Plant Growth

Grazing and
Plant Growth
PLANT MORPHOLOGY
 Grass, forb and shrub species produce viable axillary
buds have greater potential to regrow following grazing
 Grass, forb, and shrub species that protect meristems
have the potential to regrow quickly following grazing.
 Grasses that develop tillers at different times during
the grazing season tolerate grazing better than plants
that do not
GRAZING TOLERANCE

Grazing and
Plant Growth
PLANT PHYSIOLOGY
 Ability to regrow quickly following grazing
 Ability to compete for water and nutrients enable
some plants to regrow more quickly
 In some plant grazing stimulates absorption of
nutrients. However, in many species removal of
leaves and stems decreases nutrient absorption.
 Ability to quickly move nutrients and carbohydrates
between roots and shoots
GRAZING TOLERANCE

Grazing and
Plant Growth
Grasses
 Higher proportion of culmless (stemless)
shoots than species with low resistance
 Greater delay in elongation of the apical
buds than species with low resistance
 Sprout more freely from basal buds after
defoliation than species with low resistance.
 Higher ratio of vegetative to reproductive
stems than species with low resistance.
GRAZING RESISTANCE FACTORS

Grazing and
Plant Growth
Forbs
 Produce a large number of viable seeds
 Delayed elevation of growing points
 Poisons and chemical compounds that
reduce palatability

Grazing and
Plant Growth
Shrubs
 Spines and thorns
 volatile oils and tannins that
reduce palatability
 Branches make removal of inner
leaves difficult
 Only current year’s growth is
palatable and nutritious for
most species.

Grazing and
Plant Growth
Most to least resistant
1. Grasses
2. Shrubs
3. Forbs
*Many exceptions do occur.
GRAZING RESISTANCE OF FORAGE

Grazing and
Plant Growth
 In the final section you learned about grazing
and plant responses to grazing.
 You learned that grazing can have detrimental
as well as growth promoting effects on plants.
 We discussed the theory of grazing
optimization and some of the mechanisms
that can result in compensatory plant growth.
 And finally we discussed mechanisms that
allow plants to resist the effects of grazing.
SUMMARY

 Grass Anatomy
 Growing Points (buds, meristems)
 Developmental Anatomy
 Forb Anatomy
 Growing Points (buds, meristems)
 Reproduction
 Sexual
 Asexual
Morphology

PLANT PHYSIOLOGY
 Germination and Seedling Establishment
 Photosynthesis
 Factors that influence photosysnthesis
 C3, C4, CAM Photosynthesis
 Secondary Compounds
Plant Physiology

Grazing and Plant Growth
 Grazing Effects

Plant Physiology
Morphology
Seasonality and
Life Cycle
Grazing
and Plant Growth
Life Cycles
And
Phenology
Seasonal
Growth Rates
Germination
and seeding
establishment
Grazing
Optimization
Carbohydrates and
Carb. Allocation
Reproduction
Grass
Anatomy
Forb
Anatomy
Shrub
Anatomy
You are here
Secondary
Compounds
Grazing
Resistance
Forage
Quality
PHYSIOLOGY AND MORPHOLOGY
OF RANGE PLANTS
RDM
Grazing
Effects
Photosynthesis
Water and
Nutrients

CHAPTER 5: RANGE PLANT PHYSIOLOGY
1. Basic concepts of plant growth
2. Importance of carbohydrate reserves
3. Grazing effect on forage plants
4. Grazing resistance in grasses, forbs and shrubs
5. Grazing theory
a. Why palatable plants dominate rangelands with
good grazing management?
b. Why unpalatable plants dominate rangelands
under sustained heavy grazing (over grazing)?

A FEW BASIC PRINCIPLES CONCERNING THE INFLUENCE OF
GRAZING ON PLANTS
1. Plants must have leaves for photosynthesis.
2. Grazing has the least effect on plants during the dormant
season when they are photosynthetically inactive.
3. Grazing has the most severe effect on plants towards the
end of the growing season ( seed formation to seed
hardening) because the plant’s demands for
carbohydrates are higher and little time remains of
optimal temperature and moisture conditions for regrowth.
4. Grazing early in the growing season has less effect on
plants than late in the growing season because
considerable time remains when temperature and
moisture are optimal for regrowth.

WHY PLANTS MUST STORE CARBOHYDRATES
1. Root replacement and growth
2. Regeneration of leaves and stems after
dormancy
3. Respiration during dormancy
4. Bud formation
5. Regrowth after top removal by grazing.

PHOTOSYNTHESIS AND CARBOHYDRATES
 Factors that influence photosysnthesis
 C3, C4, CAM Photosynthesis

REPRODUCTION
 Recruitment maintains plant community
 Sexual Reproduction (flowers and seeds)
 Vegetative Reproduction (stolons, rhizomes)
 Annuals dependent on seed production
 Short-lived perennials depend on seed production
 Long-lived perennials rely more on vegetative reproduction.

Relationship between herbage dry matter and leaf area (Brougham 1956)

Increased tillering
 Increased photosynthesis
 Reduced transpiration

SUMMARY
EFFECTS OF LIGHT TO MODERATE GRAZING
 Increased plant productivity
 Reduced shading of lower leaves
 Reduced transpiration losses
 Reduced ability to compete with ungrazed plants
 Reduction of excessive litter or mulch that can physically or
chemically inhibit vegetative growth. Excessive mulch
promotes pathogens and insects that can damage forage
plants.

LIFE CYCLES Return to Course Map

Bilbrough and Richards (1993)
C = ‘control’ no clipping
TB = terminal bud removed only
Grazing and
Plant Growth

Grazing and
Plant Growth

CARBOHYDRATE STORAGE
1. Root replacement and growth
2. Regeneration of leaves and stems after
dormancy
3. Respiration during dormancy
4. Bud formation
5. Regrowth after top removal by grazing.
Grazing and
Plant Growth
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Plant Growth
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