Plant Physiology Morphology Seasonality and Life Cycles Grazing and Plant Growth Seasonal Growth Rates Germination and Seedling Establishment Grazing Optimization

Plant Physiology

Morphology

Seasonality andLife Cycles

Grazing and Plant Growth

SeasonalGrowth Rates

Germinationand SeedlingEstablishment

GrazingOptimization

Carbohydrates and

Allocation

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy

You are hereSecondary Compounds

GrazingResistance

Forage Quality

RANGE PLANT GROWTH AND DEVELOPMENT

RDM

Grazing Effects

Photosynthesis

Water andNutrients

Life Cycles and

Phenology

Seasonality and Life Cycles Terminology Life Cycles Seasonal growth

rates Forage Quality RDM



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 andLife CyclesREADING AND REFERENCES

SEASONALITY & LIFE CYCLES


Terminology Life Cycles Forage Quality Seasonal growth rates RDM


Plant Physiology

TERMINOLOGY

Annual Perennial



Grass: monocot, most are not woody

Forb: dicot, non-woody

ShrubDicot,

woody


Seasonality andLife CyclesTERMINOLOGY

http://images.google.com/imgres?imgurl=http://weeds.montana.edu/images/WeedWebImages/Geranium_closeup.jpg&imgrefurl=http://weeds.montana.edu/crop/redstem.htm&h=1024&w=1536&sz=241&hl=en&start=2&sig2=kzxQV30BLi9kYYlBi6uXVA&tbnid=Y94wOwR8xiOQuM:&tbnh=100&tbnw=150&ei=5KSUSLmTCJe8iAGztvG_Cg&prev=/images?q=filaree&gbv=2&hl=en


Seasonality andLife CyclesTERMINOLOGY

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.




Plant Physiology

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



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


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



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


Timing of phenological events

PHENOLOGY AND LIFE CYCLES



Phenological events




Plant Physiology

Crude protein decreases in annual grasses with stage of maturity(see ANR Publications 8019 and 8022)

PHENOLOGY AND FORAGE QUALITY






Plant Physiology

SEASONAL GROWTH RATES

Series10

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



SEASONAL GROWTH RATES

Growth rates of perennials in northeastern California


1-Feb 1-Mar 1-Apr 1-May 1-Jun 1-Jul0

200

400

600

800

1000

1200

1400

lbs/

ac



Terminology Life Cycles Seasonal growth rates Forage Quality RDM


Plant Physiology

LITTER: RESIDUAL DRY MATTER

Moderate grazing results in recommended RDM levels

Heavy grazing results in low RDM levelsLight grazing results in high

RDM levels



SUMMARYSeasonality 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 PhysiologySeasonality and

Life Cycles




GrazingOptimization

Carbohydrates and

Allocation

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy


GrazingResistance

Forage Quality


RDM

Grazing Effects

Photosynthesis

Water andNutrients

Life Cycles and

Phenology

Morphology

Morphology Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction

You are here

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy

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

READING AND REFERENCESMORPHOLOGY

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





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



Apical meristems (flower) Axillary buds (give rise to

tillers, rhizomes and stolons) Intercalary meristems or collar






Morphology and DevelopmentGROWING POINTS

Apical meristems (flower) Axillary buds (give rise to tillers,

rhizomes and stolons) Intercalary meristems or collar







Apical meristems (flower) Axillary buds (give rise to tillers,

rhizomes and stolons) Intercalary meristems or collar





Apical meristem rising



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.



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.



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



Plant Physiology

FORB ANATOMY



FORB GROWING POINTS


Growing point or apical bud


MORPHOLOGY



Plant Physiology

SHRUB ANATOMY

Coast live oak resprouts

Chamise resprouts



MORPHOLOGY



Plant Physiology

REPRODUCTION

Long Day Plants Short Day Plants Sexual Reproduction (flowers and seeds) Vegetative Reproduction (stolons, rhizomes)



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 DevelopmentREPRODUCTION -

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 DevelopmentREPRODUCTION

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.



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.



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.



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.



ASEXUAL OR VEGETATIVE

TILLERINGMorphology 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.



ASEXUAL OR VEGETATIVE

SUMMARY

.



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





GrazingOptimization

Carbohydrates and

Allocation

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy


GrazingResistance

Forage Quality


RDM

Grazing Effects

Photosynthesis

Water andNutrients

Life Cycles and

Phenology

Plant Physiology Germination &

Seedling Establishment

Photosynthesis Carbohydrates

and Carbohydrate Allocation

Water and Nutrients

Secondary Compounds

Plant Physiology


Carbohydrates and

Allocation

Secondary Compounds

Photosynthesis

Water andNutrients

McKell, C.M. 1974. Morphogenesis and management of annual range plants in the United States. Pg 111-116.

Briske, 1991. Chp 4. Dev. Morph and Phys of Grasses. 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

READING AND REFERENCES

PLANT PHYSIOLOGY

Germination and Seedling Establishment

Photosynthesis Carbohydrates and Carbohydrate

Allocation Water and Nutrients 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 PhysiologyGERMINATION & SEEDLING ESTABLISHMENT



PHOTOTROPISMReturn to Course Map

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



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.



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.



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.



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.



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





Plant Physiology

CO2 + H2O CH2O + O2

Sunlight

Chlorophyll


Plant PhysiologyPHOTOSYNTHESIS

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=_wO9f3ER17M

Plant PhysiologyPHOTOSYNTHESIS




4. Physiological efficiency

5. Soil nutrients6. Water supply7. Temperature

Factors that influence photosynthetic rate1. Leaf area2. Light intensity and quality3. CO2 content of the air


Plant PhysiologyPHOTOSYNTHETIC RATE

Relationship between light interception and leaf area (Brougham 1956)


Plant PhysiologyLEAF AREA AND LIGHT INTENSITY


Lightly grazed

Closely grazed

Plant PhysiologyPHOTOSYNTHESIS & LIGHT INTENSITY

(Parsons et al. 1983)


Plant PhysiologyPHOTOSYNTHESIS & LEAF AREA

Relationship between leaf area and herbage yield (Brougham 1956)


Plant PhysiologyPRODUCTION & 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

Pho

tosy

nthe

sis

(% o

f m

axim

um G

PP

)

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 PhysiologyWATER 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 PhysiologyC3 PHOTOSYNTHESIS

http://images.google.com/imgres?imgurl=http://media-2.web.britannica.com/eb-media/54/120954-004-A11E21B1.jpg&imgrefurl=http://www.britannica.com/EBchecked/topic-art/431235/114775/Orchard-grass&usg=__yf7NltwiyUsW7JKPfJrxxg5ib2M=&h=450&w=302&sz=46&hl=en&start=14&sig2=kZoyJuNdqk4mTF-bgRUwsw&um=1&tbnid=eQSb5cxTNpIZIM:&tbnh=127&tbnw=85&prev=/images?q=orchard+grass&hl=en&rlz=1T4GZAZ_enUS329US329&sa=N&um=1&ei=HhuUSoTWOJb6tAP3vOnVDw

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 PhysiologyC4 PHOTOSYNTHESIS

http://plants.usda.gov/java/largeImage?imageID=atca2_012_ahp.jpg

http://en.wikipedia.org/wiki/File:MatureSweetCorn.jpg

http://images.google.com/imgres?imgurl=http://www.geni.org/globalenergy/library/technical-articles/generation/biomass/science-daily/biofuel-major-net-energy-grain-from-switchgrass-based-ethanol/080109110629.jpg&imgrefurl=http://www.geni.org/globalenergy/library/technical-articles/generation/biomass/science-daily/biofuel-major-net-energy-grain-from-switchgrass-based-ethanol/index.shtml&usg=__4dCvgYQVRbAxAwTefWreFqKq8eg=&h=293&w=300&sz=24&hl=en&start=6&sig2=NcR6QhMfoUQAHaC8ldfzZw&um=1&tbnid=lut0ysWBF_QxVM:&tbnh=113&tbnw=116&prev=/images?q=switchgrass&hl=en&rlz=1T4GZAZ_enUS329US329&sa=N&um=1&ei=-RuUSpekIZH4tAOkufzJDw

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 PhysiologyCAM PHOTOSYNTHESIS

http://wc.pima.edu/~bfiero/tucsonecology/plants/cactus_family.htm


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 PhysiologyROOT GROWTH TEMPERATURES


Plant PhysiologyWATER USE EFFICIENCIES

C3 VS C4


Plant PhysiologyCO2 CONCENTRATION


Plant PhysiologyLIGHT, TEMPERATURE AND CO2

C3 VS C4:

PLANT PHYSIOLOGY





Plant Physiology

Carbohydrates are the plant’s energy sourceEnergy 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 PhysiologyCARBON DISTRIBUTION/ALLOCATION

CARBON DISTRIBUTION/ALLOCATION


Plant Physiology





PLANT PHYSIOLOGY





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_UHw7F4http://www.youtube.com/watch?v=umUn8D6gEOg&feature=related

AVAILABLE WATER


Plant Physiology

NUTRIENT UPTAKE


Plant Physiology

MYCORRHIZAE


Plant Physiology

PLANT PHYSIOLOGY





Plant Physiology

SECONDARY COMPOUNDS


Plant Physiology

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

http://anrcatalog.ucdavis.edu/pdf/8398.pdf

SECONDARY COMPOUNDS

Conifers accumulate monoterpenes


Plant Physiology

TERPENES

Lignin Flavenoids Tannin

isoflavenoids in legumesTannins in oak leaves


Plant PhysiologySECONDARY COMPOUNDS

PHENOLICS

http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/en/thumb/6/6d/Large_Blue_Oak.jpg/240px-Large_Blue_Oak.jpg&imgrefurl=http://wiki.verkata.com/en/wiki/Blue_Oak&usg=__WK_i17GdjFJLV365nk9jCVH8udo=&h=214&w=240&sz=18&hl=en&start=5&sig2=d9hhH-cT4U5zGLXd2QnyhQ&um=1&tbnid=COheQ7b_i_5qqM:&tbnh=98&tbnw=110&prev=/images?q=blue+oak&hl=en&rlz=1T4GGLL_enUS356US357&um=1&ei=LIM2S9maD4yGtAOlod0G

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

Plant Physiology

Morphology





GrazingOptimization

Carbohydrates and

Allocation

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy


GrazingResistance

Forage Quality


RDM

Grazing Effects

Photosynthesis

Water andNutrients

Life Cycles and

Phenology


Grazing Effects Grazing

Optimization Grazing Resistance


GrazingOptimization

GrazingResistance

Grazing Effects


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 Optimization Grazing Resistance



GRAZING EFFECTS

Detrimental Effects Growth Promoting Effects




Grazing and Plant GrowthDETRIMENTAL GRAZING EFFECTS

Removal of photosynthetic tissue

Reduced carbohydrate storage

Reduced root growth Reduced seed

production



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



1. Heavy grazing can weaken root systems increasing moisture stress

Grow leaves, stems, roots andbuds.


REDUCE GROWTH



1. Heavy grazing can weaken root systems increasing moisture stress

Leaves, stems, roots and other plant parts

REDUCE GROWTH



Seed production

REDUCE GROWTH



Carbohydrates are the plant’s energy source

REDUCED CARBOHYDRATE STORAGE



Detrimental Effects Growth Promoting Effects

GRAZING EFFECTS



Increased photosynthesis

Increased tillering Reduced shading Reduced transpiration

GROWTH PROMOTING EFFECTS



1. Intensity 2. Timing3. Frequency4. Grazing of surrounding plants

INFLUENCES ON GRAZING EFFECTS



1. Decreases evapotranspiration2. Moderates surface microclimate during germination and

seedling establishment3. Slows surface runoff and increases infiltration4. Protects soil from erosion

LITTER



Grazing too close reduces reserves and slows recovery following grazing

GRAZING TO CLOSE



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 CBReturn to Course Map

DETRIMENTAL EFFECTS OF GRAZING



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 Increased tillering 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 Effects Grazing Optimization Grazing Resistance


GRAZING OPTIMIZATION

There are levels of grazing that can result in increased productivity

G.O. is a complex and sometime controversial subject.



GRAZING OPTIMIZATION HYPOTHESIS



GRAZING OPTIMIZATION HYPOTHESIS




0

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80

100

0 1 2 3 4 5 6 7 8 9 10

Leaf Area Index

Pho

tosy

nthe

sis

(% o

f m

axim

um G

PP

)

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 10P

ho

tosyn

thesis

(%

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G

PP

)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.






C = ‘control’ no clippingTB = terminal bud removed only

60 = 60% current annual growth removed100 = 100% current annual growth removed




MECHANISMS CONTRIBUTING TO COMPENSATORY 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 EffectsGrazing OptimizationGrazing Resistance


GRAZING RESISTANCE



GRAZING AVOIDANCE

Mechanical Biochemical





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



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



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



Forbs Produce a large number of viable

seeds Delayed elevation of growing points Poisons and chemical compounds

that reduce palatability




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.




Most to least resistant1. Grasses 2. Shrubs 3. Forbs

*Many exceptions do occur.

GRAZING RESISTANCE OF FORAGE



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

THE END: UNUSED SLIDES

The Phenology Handbook, pg 1-15 George et al. 2001. Annual Range Forage Production George and Bell. 2001. Using Stage of Maturity……..


Seasonality andLife CyclesREADING AND REFERENCES


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

READING AND REFERENCESMORPHOLOGY





PLANT PHYSIOLOGY



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






PLANT PHYSIOLOGY


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

Carbohydrates and Carbohydrate Allocation

Water and Nutrients Secondary Compounds

Plant Physiology


Grazing and Plant Growth Grazing Effects Grazing Optimization Grazing Resistance


Plant Physiology

Morphology

Seasonality andLife Cycle


Life CyclesAnd

PhenologySeasonal

Growth Rates

Germinationand seeding

establishment

GrazingOptimization

Carbohydrates andCarb. Allocation

Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomyYou are here

Secondary Compounds

GrazingResistance

Forage Quality

PHYSIOLOGY AND MORPHOLOGY OF RANGE PLANTS

RDM

Grazing Effects

Photosynthesis

Water andNutrients

Plant Physiology

Morphology



Life CyclesAnd

PhenologySeasonal

Growth Rates


establishment

GrazingOptimization


Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomy

You are here

Secondary Compounds

GrazingResistance

Forage Quality


RDM

Grazing Effects

Photosynthesis

Water andNutrients

Plant Physiology

Morphology



Life CyclesAnd

PhenologySeasonal

Growth Rates


establishment

GrazingOptimization


Reproduction

GrassAnatomy

ForbAnatomy

ShrubAnatomyYou are here

Secondary Compounds

GrazingResistance

Forage Quality


RDM

Grazing Effects

Photosynthesis

Water andNutrients

CHAPTER 5: RANGE PLANT PHYSIOLOGY

1. Basic concepts of plant growth2. Importance of carbohydrate reserves3. Grazing effect on forage plants 4. Grazing resistance in grasses, forbs and

shrubs5. 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 growth2. 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 Carbohydrates and Carbohydrate

Allocation

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 photosynthesis

Increased tillering

Increased photosynthesis Reduced transpiration

Reduced shading

Reduced transpiration

SUMMARY EFFECTS OF LIGHT TO MODERATE GRAZING

Increased plant productivity Increased tillering 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 clippingTB = terminal bud removed only

60 = 60% current annual growth removed100 = 100% current annual growth removed





CARBOHYDRATE STORAGE1. Root replacement and growth2. Regeneration of leaves and stems

after dormancy 3. Respiration during dormancy 4. Bud formation 5. Regrowth after top removal by

grazing.



We can probably delete this slide




Can probably delete this slide

Documents

Plant Physiology Morphology Seasonality and Life Cycles Grazing and Plant Growth Seasonal Growth Rates Germination and Seedling Establishment Grazing Optimization