Agronomy 334 Fall 2013 -- Where you are from
Black River, MI
~ 870 m
Forage Anatomy & Morphology
Reassessing plant tissues and
parts as they relate to forage
nutritive quality and digestibility …
Delevan, IL
(~320 mi)
So Sudan
(~8000 mi)
Lees Summit, Mo
(~ 240 mi)
Carbohydrates
Forage Carbohydrates
‘Soluble carbohydrates’ / ‘Free sugars’ / ‘Spendable sugars
Role in Plant / Function
Role in Animal Nutrition
Formed by photosynthesis
Energy metabolism
Energy used in metabolism
Rumen function
Energy translocated
Stimulation of salivation
(rumen buffering)
predominantly monosaccharides
--- glucose
--- fructose
--- xylose
--- arabinose
etc..
Energy storage
‘Building blocks’ of
plant structure
Nonstructural Carbohydrates
% of dry matter
Storage Polysaccharides
Starch
CH2OH
(polymers of glucose)
Function - Storage
O
H
OH
H
OH
O
H
O
H
OH
Amylose
D-Glcp-[(1 4)--D-Glcp]n
Amylopectin
-(1 6)--D-Glcp-[(1 4)--D-Glcp]n
OH
H
O
(Made up of chains and branched chains)
Fructans
(polymers of glucose & fructose)
n
Soluble
Sugars
2-5
3-6
1-5
Starch
1 - 11
0-2
1-5
Fructans
-
3 - 10
-
(primarily in grasses)
Function - Storage in cell vacuole
Inulin
Phlein
Temperate Cool-Season Warm-Season
Legumes
Grasses
Grasses
H
O
CH2 OH
-D-Glcp-(1 2)--D-Frucf-[(1 2)--D-Frucf]n
-D-Glcp-(1 2)--D-Frucf-[(6 2)--D-Frucf]n
Alfalfa
Clovers
Ky bluegrass
Orchardgrass
Oats
Big bluestem
Bermudagrass
Corn
1
Plant Cells
Vacuole
Plant Cells
‘Free’ Sugars
Storage carbs.
Amino acids
Other N compds.
Minerals
Lipids
Cell ‘Contents’
Membrane & what’s inside
Nucleus
Mitochondria
Chloroplasts
Cell Membrane
Plant Cells
Structural Polysaccharides of primary cell walls
Primary & Secondary Cell
Walls (outside the membrane)
Structural Carbohydrates
Cellulose D-Glcp- (1 4)--D-Glcp]n
Note! Similarity to starch but with
different linkage configurations
between glucose units. This is
an important difference in terms of
digestibility.
H
O
CH2
H O
O
OH
CH2 O H
O
O
H O
OH
O
O
OH
H
OH
H
H
OH
CH2OH
H
O
O
n
H
O
CH2
O
O
O
OH
H
O
H
OH
O
CH2 O
H O
H
O
O
H
H
O
CH2
O
O
O
OH
CH2
O H
O
OH
OH
O
H
O H
CH2
O
H
Structural Polysaccharides of primary cell walls
Pectins - a ‘matrix’ of polysaccharides contained in
Primary Cell Wall
cell walls, acting as a form of cement
between cells and the base upon which
primary cell walls form
2
Hemicellulose - structural polysaccharides
closely associated with cellulose
Structural Carbohydrates
% of dry matter
(Made up of other 5 & 6-carbon sugars -- Xylans (including arabinoxylans)
glucuronoxylans glucuronoarabinoxylans) and Xyloglucans
Temperate
Legumes
Hemicellulose forms at the same time during
primary cell wall formation . It serves to bind
to the cellulose mcrofibril layer as a ‘hard gel’
layer,' holding’ microfibril layer orientation.
Cell Wall Development
Cool-Season Warm-Season
Grasses
Grasses
Cellulose
20 - 35
15 - 45
22 - 40
Hemicellulose
4 - 17
12 - 27
25 - 40
Pectin
4 - 12
1-2
1-2
(28-74)
(48-82)
(28-64)
Secondary Cell Wall
(forms after cells have reached their final size/shape
Primary Wall
Elongated Cell
Cell Membrane
As the newly divide, young cell
enlarges (or elongates),
additional primary cell wall is
added to accommodate the new
volume.
More complex ‘phenolic’ compounds are
important constituents of lignin and the
secondary cell wall.
Phenolics impart :Steric Interference (blocking) of digestion
Hydrophobic Effects on microbial
‘attachment's & digestion
In some cases, toxicity which inhibits
digestion microflora
Subunits are joined to each other and to other cell wall constituents
via ether and ester bonds
The most common ‘lignin
sub-units are the cinnamic
acids forms :
Cell Wall Development
Mature Cell
Primary Wall
Secondary Cell Wall
Cell Membrane
The secondary cell wall forms
between the primary cell
wall and the cell membrane
Proportion of DM in Cell wall
Proportion of DM in Cell Contents
3
Distribution of secondary cell wall in the plant
(also can be called
lignification
Structural Carbohydrates
)
Approx. Range --- % of dry matter
- very limited in ‘young’ plant tissues (areas of
cell division, rapid growth and elongation)
generally a greater component of ‘older’
plant tissue and plant parts
- generally greatest in ………
‘epidermal tissue’ layers
xylem tissue
tissues surrounding vascular tissues
In plants, structural carbohydrates serve as :
• Structural composition / rigidity
• Cell recognition
• Etc.
Temperate
Cool-season
Grasses
Warm-season
Grasses
Cellulose
20 - 35
15 - 45
22 - 40
Hemicellulose
4 - 17
12 - 27
25 - 40
Pectin
4 - 12
1-2
1-2
Lignin
6-12
3-6
5-9
Forage Carbohydrates – Utilization
by animals
Class of compounds
Pectins
In animal usage we consider the same
compounds as ‘fiber’
Cool-Season Warm-Season
Temperate
Legumes
Cellulose
Hemicellulose
Lignin
Bioavailability
(Digestibility)
Complete
Variable
Variable - but high %
Virtually none
• Nutritional entity
• Resistant to digestion
• Biophysical properties
During ruminant fermentation (digestion), microbial & gastric
enzyme encounter constituents of variable digestibility
4
Legume Stem Anatomy
Rumen microorganisms
beginning to digest
forage fiber
Lignified
areas
Epidermis
Vascular
Bundles
Pith
Photos: Dr T Bauchop
After a period of digestion
What tissues
are lignified ?
Alfalfa
Stem
Digested
48 hrs in
rumen
fluid
Lignified
areas
Corn Stem Cross Section
Cool-Season Grass Leaf
Which tissues are Lignified ?
Corn Stem Digested in Rumen Fluid
Corn Leaf
5
Cool-Season Grass Leaf Digested in Rumen Fluid
Corn Leaf Digested in Rumen Fluid
TRUE DIGESTIBILITY
Digestion Model:
Bioavailability of Forage Carbohydrates
CI
Undigested Fiber
CD
Digested Fiber
CS
Cell Solubles
L



Think about your understanding of the
definition of these ?
Lignin
Cellulose
Hemicelluloses
Sugars
Starches
Fructans
Pectins
• Annual
• Biennial
• Perennial
FERMENTATION TIME
Note that there is a ‘lag period’ before fiber digestion begins
-- time for microbial ‘attachment’ and enzyme activity
to increase
Annual -- completing the life cycle in one year
(Or does it mean in one growing season?
• cool season (C3) species
• warm season (C4) species
‘Cool-season’
C3 photosynthesis
(optimum 50 - 70 F)
Ex. orchardgrass
Where do we classify ‘winter annuals’?
( planted in autumn / grow vegetatively;
following spring/early summer, produce seed & die )
‘Warm-season’
Biennial -- living for two years, first yr.
vegetative, second year reproductive
C4 photosynthesis
(optimum 70 - 95 F)
- more efficient use of CO2
( ‘less wasteful’ potosynthesis)
- specialized vascular bundle
sheath tissue
Perennial -- living for more than two years
Ex.
switchgrass & maize
6
What are meristems ?
Meristems -- areas of actively dividing cells;
-- undifferentiated tissue capable of
differentiating into specialized tissue
•
Constitutes a very small part of the plant
but gives rise to and regulate growth
(initial and regrowth)
•
Increase in cell numbers is localized in the
meristems
-- the ‘growing point’ is only one of
the meristems present in plants
Growth can be defined as an increase in:
• cell number
• cell size / plant height / plant size
• cell weight / plant weight, dry matter
Meristems
1.
(5 types)
• maturation More often referred to as
DEVELOPMENT -- usually by
identifiable ‘stages of development’
–
Apical meristems, ‘true growing points’
Stem terminal meristems in grasses remains below
the soil surface until jointing; generally above soil
surface for dicots
For a while at tips of leaves
Apical or terminal meristem in monocots
becomes the inflorescence (seed heads).
In dicots, terminal meristems are vegetative
but may become an inflorescence
(flower cluster)
Alfalfa
2. Axillary meristems
Apical meristem
White clover
Located in the axial of the leaf which is
attached to the stem at the node
Activity controlled by hormones from growing
point and/or light
7
Axillary meristems
Axillary meristems
Contributes to branching in dicots when the
terminal meristem is removed
•
Crown buds in perennial legumes
Tillering in grasses often before the terminal
meristem is fully developed
•
Provides regrowth if growing point has been
removed or winterkilled
3.
Intercalary meristems -- located between differentiated
(mature) tissue
Contributes to growth & plant height
Base of the internode; found just above the node
-- will cause the internode to elongate;
-- more distinct in grasses than dicots
Intercalary meristems -- located between differentiated
(mature) tissue
…and at the
Base of the blade of grass leaf,
allows for blade elongation,
even if the tip of the blades
are removed
Base of the petiole of the dicot leaf
Base of the sheath of the grass leaf
elongates with the internode
Base of the peduncle of some
legume flowers (subterranean
clover and peanuts)
5. Lateral meristems
4. Marginal meristems
-- Active only in very early
leaf expansion
•
•
•
•
Contributes to size & maturation
Found in dicots and woody plants
Meristematically active cambium layer
that allows the stem to increase in
diameter
Ex. alfalfa taproot and stem diameter;
and increase in turnip ‘bulb' size
8
Legume Morphology
Where are the meristems ?
Stolon
Crown
Rhizome
Crown
Taproot
Rhizome
Taproot
Node
Leaf
Blade
Taproot
Taproot
Where are the meristems ?
Collar
Internode
Leaf
Sheath
Node
‘Crown’
Availability and type of meristematic tissue
Fast ‘regrowth’
Intercalary
meristems
Plant Material Produced
(quantity)
slow regrowth
apical
meristems
axillary
buds
less
more
9
Roots
• Function - absorb and transport water
and nutrients; anchor the plant; store
carbohydrate used for spring growth or
regrowth
Root development, mass and function is influenced by:
-- closeness and frequency of defoliation
(leaf area, photosynthesis, carbohydrate ‘reserves’)
• Morphology - fibrous root system for grasses;
taproot system for legumes; deeper roots for
drought tolerant species
-- the environment of the soil
soil moisture
nutrient levels
temperature
oxygen
-- soil impedances (compaction, rocks, water table)
Stems
Stem Morphology – Grasses
• Numerous functions –
Significant component of harvested yield
– Size and development influenced by:
species
vegetative vs. reproductive stages
temperature,
harvest management
photo period
– Examples of stem mass among forage species
Bermudagrass
Smooth bromegrass
Upright, vertical
stems, tillers
Horizontal stems,
above ground,
stolons
• Alfalfa, stems and reproductive parts - 56% total
dry matter
all stems have nodes and internodes, and axillary
(lateral) buds develop in the leaf axils
• Timothy, stems, leaf sheath, reproductive parts -
70% of total dry matter (1st cut)
• Horizontal stems, below ground, rhizomes;
Solid enlarged internodes below
the soil surface, haplocorms or
corms; timothy
sod forming grasses; sod density is related to
the number of rhizomes; axillary buds that
give rise to new plantlets; length of the
internode is variable;
•
short internode length- big and little bluestem,
switchgrass, tall fescue
lower stem morphology
longer internode length -smooth bromegrass,
reed canarygrass, quackgrass
Turnip bulbs are roots
10
Stem Morphology of legume stems
Morphology of legumes
• Upright, vertical stems, branches (tillers)
(alfalfa, red & alsike clover, soybeans, etc.)
Alfalfa
alsike clover
forage soybeans
• Horizontal stems, above ground,
stolons;
white clover
• Decumbent, or vines
Ex. Hairy vetch, kudzu, field peas
Morphology of legumes
• Horizontal stems, below ground,
What is the nutritive value of stems ?
‘Rhizomes’ ; kura clover, some alfalfa
High ?
Low ?
Variable ?
Influenced by:
Segment of stem (age / lignification)
Leaves
• Function, photosynthesis, transpiration
Leaf location is an indication of the tolerance of close
and frequent defoliation
ex.
What is the nutritive value of leaves?
High ?
Low ?
Variable ?
white clover, perennial ryegrass & KY bluegrass
abundant leaf material is near the soil surface
reed canarygrass, bromegrass, timothy,
dicots have few basal leaves
Influenced by:
Part of leaf; (lignified tissues)
11
Leaf Area Index (LAI) = leaf area (m2) / ground area (m2)
So what about LAI - leaf area index
Why should a producer care about the LAI of a field of
forage crops?
A crop with a
LAI of 3 means
that 3 meter2
crop surface
leaf area is
present above
a meter2 of soil
advantages & disadvantages
+ Photosynthesis, capturing sunlight which used as the
energy to fix CO2, producing sugar, used for growth
+ Capturing sunlight so that no sunlight reaches the soil
surface, reducing weeds,
- inhibiting low growing forages in a mixture of species
+ Covering the soil surface, reducing evaporation and
soil temperature, erosion from rain falling directly on
the soil surface
Ground area= meter2
+ Leaves harvested either by machines or animals, yield
Anatomy & Morphology – Key Points
Know the important structural and non-structural
Carbohydrates in forages and their relative
Bio-availability
Be able to discuss the ‘Digestion Model’ diagram
Know and be able to discuss the 5 types of meristems
found in forage plants and their management
Know the morphology (plant parts) of grasses & legumes
What is LAI? Be able to discuss its importance in
forage management.
12