How plants grow l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 37

How Plants Grow PowerPoint PPT Presentation


  • 127 Views
  • Uploaded on
  • Presentation posted in: General

How Plants Grow. Mort Kothmann Texas A&M University. Plant Development and Responses to Grazing. Objective 1 Review the developmental morphology and growth form of grass plants. Objective 2. Evaluate some major physiological and morphological plant responses to grazing. Objective 3.

Download Presentation

How Plants Grow

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


How plants grow l.jpg

How Plants Grow

Mort Kothmann

Texas A&M University


Plant development and responses to grazing l.jpg

Plant Development and Responses to Grazing

Objective 1

Review the developmental morphology and growth form of grass plants.

Objective 2.

Evaluate some major physiological and morphological plant responses to grazing.

Objective 3.

Explore the mechanisms that convey grazing resistance to plants.


Functional categories of plants l.jpg

Functional Categories of Plants

Annual (grass, forb)

Perennial (grass, forb)

Woody

Deciduous or evergreen

Sprouting or non-sprouting (basal)

Cool season or warm season

Anti-herbivory

Chemical

Physical


Major plant groups on rangelands l.jpg

Major Plant Groups on Rangelands

Tree

Dicots

Monocots

  • Grass

  • Grasslike

Shrub

Forb


Slide5 l.jpg

Surviving plants have strong drought resistance and well developed chemical or structural anti-herbivory.


Slide6 l.jpg

Grassland with scattered shrubs and small trees on upland. Competition is for light and soil resources. Fire is a major determinant of the dominant vegetation. Grazing tolerance is more important than anti-herbivory.


Developmental morphology l.jpg

Developmental Morphology

Ligule

Blade

Tiller 1

Phytomer 4

Sheath

Tiller 2

Intercalary

Meristems

Phytomer 3

Internode

Tiller 3

Phytomer 2

Axillary

Bud

Node

Phytomer 1

Phytomer Organization

Plant Organization

Tiller Organization


Tiller cross section l.jpg

Tiller Cross Section

Intercalary Meristem

Leaf Blade

Emerging Tiller

Leaf Sheath

Apical Meristem

Axillary Bud

Adventitious Root


Culmless versus culmed tillers l.jpg

Culmless Versus Culmed Tillers

Culmed

Apical Meristem

Culmless

Axillary Buds


Basal location of grass regrowth in cumless tillers l.jpg

Basal Location of Grass Regrowth in Cumless Tillers


Meristematic contribution to grass growth l.jpg

Meristematic Contribution to Grass Growth

Contribution to Biomass Production

Intercalary Meristems

Apical Meristems

Axillary Buds

Days

Hours

Weeks

Rate of Growth Following Defoliation

Leaf production

Leaf elongation

Tiller production

(Activation of dormant buds)

(Cell division & differentiation)

(Cell enlargement)


Factors limiting plant growth l.jpg

Factors Limiting Plant Growth

Heat (optimal temperature)

Below-Ground (roots)

Water

Nitrogen and other nutrients

Above-Ground (shoot)

Light

CO2

Meristems (apical, intercalary, axillary)


Resources and meristems l.jpg

Resources and Meristems

Intercalary meristems are primarily involved with cell enlargement which requires primarily CHO and has low N requirement.

Axillary meristems are sites of cell division and differentiation. Cell division requires N; thus N availability will limit the number of active meristems.

N content of leaves is generally 2X that of roots; thus, low N results in less shoot growth relative to root growth.


Allocation of plant resources l.jpg

Allocation of Plant Resources

Plants allocate resources (phytosynthetate) with the priority towards acquiring the most limiting resource(s).

If water is limiting, allocation is shifted towards root growth over shoot growth.

If leaf area is limiting, allocation is shifted towards leaf growth over shoot growth.


Key concepts l.jpg

Key Concepts

N uptake is with water; if water is limiting, N will be limiting

Higher levels of available N increase water use efficiency

Level of available NO3 in the soil affects the species composition of the vegetation

Weeds require higher levels of NO3 than do climax grasses


Physiological responses to grazing l.jpg

Physiological Responses to Grazing


Effects of grazing on plants l.jpg

Effects of Grazing on Plants

Removal of photosynthetic tissues reduces a plant’s ability to assimilate energy.

Removal of meristems (apical & intercalary) delays or stops growth.

Removal of reproductive structures reduces a plant’s ability to produce new individuals.

Grazing is a natural ecological process and overgrazing occurred prior to humans.

Properly managed grazing is a sustainable enterprise, but destructive grazing can occur.


Compensatory photosynthesis l.jpg

Compensatory Photosynthesis

120

110

100

90

Control

Moderately clipped

Heavily clipped

80

70

6

4

10

8

0

2

PN (% of preclipping Ps rate)

Time From Clipping (days)


Resource allocation l.jpg

Resource Allocation

Biomass partitioning to roots and sheath is reduced much more than to leaves following partial defoliation.

TreatmentTotal growthBlade growthSheath growthRoot growth

mg mg % total mg % totalmg % total

Undefoliated69 23 33 17 2520 29

Defoliated 38 20 53 8 21 7 18

Detling et al. 1979


Root responses to defoliation l.jpg

Root Responses to Defoliation

50%

70%

90%

All roots stopped growing for 17 days

50% of roots stopped growing for 17 days

No roots stopped growing


Root responses to defoliation22 l.jpg

Root Responses to Defoliation

Root growth decreases proportionally as defoliation removes greater than 50% of the plant leaf area.

Frequency of defoliation interacts with defoliation intensity to determine the total effect of defoliation on root growth.

The more intense the defoliation, the greater the effect of frequency of defoliation.


Consequences of reduced root growth l.jpg

Consequences of Reduced Root Growth

The net effect of severe grazing is to reduce:

Total absorptive area of roots.

Soil volume explored for soil resources e.g. water and nitrogen.

How may this alter competitive interactions?


Tnc contribution to shoot regrowth l.jpg

TNC Contribution to Shoot Regrowth

Carbohydrate reserves exist and they provide a small amount of energy to contribute to initial leaf growth following severe grazing or leaf damage e.g., fire, late spring freeze.

Current photosynthesis is the primary source for growth of new shoots.


Growth is exponential l.jpg

Growth is Exponential

The initial or residual amount of plant tissue is very important in determining the rate of plant growth at any point in time.

The total amount of root and shoot biomass is more important than the concentration of reserve CHO.


Morphological characteristics l.jpg

Morphological characteristics

Primary growth forms of grasses

Bunchgrasses

Turf or sod grasses


Stolons and rhizomes l.jpg

Stolons and Rhizomes

Stolon

Rhizome


Variation of the grass growth form l.jpg

Variation of the Grass Growth Form

Bunchgrass Growth-form

Intermediate Growth-form

Sodgrass Growth-form


Bunchgrass growth form l.jpg

Bunchgrass Growth Form


Herbivory resistance l.jpg

Herbivory Resistance

Grazing Resistance

(Mechanisms enabling plants to survive in grazed systems)

Tolerance

(Mechanisms that increase growth following grazing)

Avoidance

(Mechanisms that reduce the probability of grazing)

Physiological

Characteristics

Morphological

Characteristics

Biochemical

Compounds

Morphological

Characteristics


Anti quality factors in forages l.jpg

Anti-quality Factors in Forages


Classes of anti quality l.jpg

Classes of Anti-quality

Structural plant traits

Plant parts

Spines, Awns, Pubescence

Plant maturity

Leaf:Stem ratio

Live:Dead

Reproductive:Vegetative tillers

Tensile/shear strength


Structural anti quality l.jpg

Structural Anti-quality

Fiber components

Cell walls

Lignin

Silica


Anti quality mineral imbalances l.jpg

Anti-quality Mineral imbalances

Excess

Silicon

Se

Mo

NO3

Deficiency

N, P, K, Mg (macro minerals)

Cu, Co, Se, Zn


Anti quality alkaloids l.jpg

Anti-qualityAlkaloids

Western plants

Largest class of secondary compounds

Found in 20-30% of plant species

Highly toxic

Eastern plants

Ergot alkaloids

Fescue pastures

Dallisgrass

Perennial ryegrass


Toxicity of anti herbivory compounds l.jpg

Toxicity of anti-herbivory compounds

Plants with highly toxic compounds do not allow animals to learn from negative post-ingestive feedback.

Plants with less toxic compounds allow animal to learn and develop aversions.

When nutritious forage is limited, positive feedback may override negative feedback and animals will consume toxic plants.


  • Login