Root Systems and

1
Chapter 7

• Root Systems and
• Plant Mineral Nutrition

2
Roots

• Plants get H2O thru roots
• Most plants have a below ground life and an above
  ground life
• roots are adapted to the dark, relatively moist
  and mineral-rich underground
• shoots use H2O/nutrients to make sugar and other
  organic molecules sent to the roots to grow

3
Taproot System

• Have 1 large 1 root (from radicle) and smaller
  branch roots
• Most dicots have a prominent taproot and 2 or
  lateral roots
• Common in cone bearing trees and dicots
• Sugar beets/carrots have a fleshy taproot that
  stores carbohydrates made in photosynthesis

4
Form Dictates Function

• Form of structures reveals and is directly
  related to function
• Taproot function is to store food and absorb H2O
  from deep in the soil
• not all taproots store food
• Taproots grow faster than the branch roots and
  usually is very long

5
Fibrous Root System

• Mass of similar sized roots
• Most monocots have
• Radicle is short lived and replaced by
  adventitious roots
• roots that form on organs other than roots
• Edible on a few plants such as sweet potato
• Some plants have both tap and fibrous roots like
  clover

6
Adventitious Roots

• Corn has fibrous root system and adventitious
  roots above grove called prop roots that support
  the corn
• Adventitious roots can be underground rhizomes
  in ferns, club mosses and horsetails

7
Adventitious Roots

• Primary means of vegetative or asexual
  reproduction making offspring without egg or
  sperm
• raspberries, quaking aspen
• Use to make cuttings of houseplants
• force parenchyma to become meristematic tissue to
  make roots
• usually in response to hormones

8
Root Cap

• Protects the growing end of the root and as it
  grows thru the soil
• Secrete mucigel a slimy substance made of
  sugar, enzymes and amino acids from the outermost
  cells of the root cap
• makes 100 mg/g of root/day

9
4 Functions of Mucigel

• Protection prevent drying out of root, may have
  compounds to inhibit other roots
• foxtail grass can inhibit nearby corn roots by
  33
• Lubrication as roots move thru soil
• H2O absorption soil clings to mucigel and helps
  maintain continuity between soil and root
• Nutrient absorption helps minerals to absorbed
  with the H2O
• No similar structure in shoots to mucigel

10
Subapical Region

• Just behind the root cap
• 3 regions
• zone of cell division
• apical meristem new roots form here
• zone of cell elongation
• cells get longer and helps move root thru soil
• zone of cell maturation
• begin to take on specific function and develop
  root hairs
• root hairs are only behind the start of this zone
• No real demarcation between the zones

11
Root Tissue

• Mature dicot root has primary structure
• epidermis with no cuticle
• xylem/phloem packed in the center of the root
• cortex cells store most of the starch
• outer layer of cortex is the hypodermis cells
  lined with suberin and no H2O passes thru slows
  the movement of H2O/nutrients
• endodermis inner most layer of cortex packed
  tighter than other parts and no intercellular
  space

12
Casparian Strips

• Cells of the endodermis have 4 of 6 sides with
  Casparian strips made of lignin and suberin
• looks like rubber band around the cell
• redirects inward movement of H2O/nutrients

13
Casparian Strips

• Acts like a valve to help eliminate leaks,
  conserves some minerals in vascular, negative H2O
  pressure so that H2O moves thru the endodermis

14
Stele

• Within the endodermis
• Contains the vascular tissue, pericycle and
  sometimes a pith

15
Pericycle

• Outermost layer meristem cells, 1 to several
  layers thick
• Produce branch roots that grow from the center,
  cell division in pericycle
• Branch root also has root cap and vascular tissue
  linked to the parent root

16
Pith and Vascular Tissue

• Vascular tissue in dicots and few monocots (wheat
  and barley) have a core of xylem with the phloem
  in between lobes of xylem

• Pith is in the center of most monocots and few
  dicots center of the vascular tissue

17
Rhizoshere

• Narrow zone of soil surrounding a root and is an
  ever changing environment
• Modified by growing roots and their metabolism
• Roots force way thru soil and later die leave
  open channels aerating soil
• may result in acidic pH as by-product of
  metabolism
• May decrease the ability to absorb minerals pH
  based

18
Soil Enrichment

• Roots enrich soil with organic material
• sugar is made in the shoot and moved to roots
• ends up in the soil as mucigel and other
  compounds
• dying/dead roots leave behind many minerals that
  are reused by other plants
• some plants secrete proteins to protect roots and
  against disease causing bacteria
• may also help plants absorb more minerals

19
Hydropnics

• Plants grown in H2O
• Generate plants that make proteins and then
  collect the protein
• may be a way to make important molecules

20
Root Growth and Development

• Controlled by several factors
• Learn much from a rhizatron a growth chamber
  that is used to study roots

21
4 Factors

• Gravity - gravitropic, want to grow towards
  gravity, grow laterally and then move towards
  gravity
• Genetic differences determines whether taproots
  or fibrous roots, deep or shallow
• Stage of development when flowering/fruiting,
  all energy goes here
• Soil properties loose packed soil is usually
  better, as is well aerated soil

22
Growth

• Competition is prevented by plants growing in the
  same area by growing to different depths
• mesquite grows a deep taproot but the saguaro
  cactus has shallow roots that spread out 30 m to
  get the most H2O when it rains
• As plant ages there is a shift between the roots
  and shoots root/shoot in seeding is large but
  as time passes the ration becomes smaller

23
Special Adaptations

• Storage starch, glucose in leaves move to the
  roots and converted to starch, may also store
  sugar as in sweet potatoes, may hold H2O for
  personal use
• Vegetative reproduction produce suckers from
  roots makes new plant
• cherry, apple and pear trees
• clones of original plant
• Aeration specialized roots to collect
  atmospheric O2 to prevent plant growing in
  stagnant H2O
• aerenchyma tissue act like snorkels

24

• Vegetative reproduction

• Aeration

25
Nutrition as an Adaption

• Parasites have special roots to get nutrients
  from host tree
• tree with mistletoe plants on it
• lack chlorophyll usually meaning all sugar from
  host
• may have chlorophyll but cant make sugar

26
Epiphytes

• Grow above ground, independently on other plants
• orchids, staghorn ferns and some cacti
• Grow slowly need to get nutrients from sources
  other than soil or plant growing on with
  adventitious roots

27
Aerial Root Functions

• H2O retention prevents drying in orchids
• Photosynthesis philodendron have photosynthetic
  roots
• Support prop roots are aerial roots that grow
  into the soil corn
• Buttress roots at base of trunk plank-like
  and contain many fibers

28
Specialized Epiphyte

• Spanish moss
• lacks roots
• absorbs H2O and nutrients thru hairs on stems and
  leaves

29
Roots in Ecology/Evolution of Plants

• 1000s of microorganisms, fungi, algae,
  protozoans, nematodes, worms and insects all
  influence the soil by mixing and aerating it
• earthworms process gt1 ton of soil a year,
  refining the soil by passing it thru its
  intestines
• also add humus decaying organic matter
• much from grasses rye can add 11,000 km or
  roots and root hairs to soil
• makes nutrients more available by adding them
  directly or changing the pH that releases things
  like phosphates
• some have a negative effect such as nemotodes,
  soft-leaved purple sage which makes a chemical
  that prevents other plant growth
• chemical warfare is called allelopathy

30
Mycorrhizae

• Mutualistic relationship between plant and fungus
• fungus gives nutrients to plant and plant gives
  sugar etc to fungus
• increase up to 4-fold the uptake of phosphorous
• See in pine and oak trees fungus invades the
  root forming net-like structure between cells of
  cortex

31
Mycorrhizae

• Plant has no root hairs
• 2 factors 1) fungus have many hyphae to
  increase surface area and 2) hyphae can permeate
  a greater volume of soil
• Mycorrhizae can increase plant growth
  dramatically over those without them
• used to reclaim some strip-mined areas
• pioneer plants grow on bare or disturb soil
  that is nutrient-deficient, just like millions of
  years ago

32
Mutualistic Relationships

• Fungi and plants co-evolved at same time
• Hypothesis on how this came to be
• A is good at job 1 but B is bad at job 1
• B is good at job 2 but A is bad at job 2
• A and B exchange the excess from each of the jobs
  and everyone is happy
• usually involve the uptake of nutrients job 1
  by the fungus and excess sugar job 2 by plant

33
Legumes and N2 Fixing Bacteria

• N2 is deficient in most soils but atmosphere is
  80 and unusable by organisms
• Some soil bacteria have an enzyme called
  nitrogenase that can convert 1 molecule of N2 to
  2 molecules of NH3
• Legumes such as beans and alfalfa have a
  mutualistic relationship with these bacteria
  forming nodules
• NH3 to plants and sugar to bacteria

34
Using N2-Fixing Bacteria

• Use N2-fixing bacteria in aquatic ferns that grow
  in the rice paddies of Asia, when drain the
  fields to harvest rice the ferns die and are
  incorporated into the N-deficient soil
• Farmers rotate crops to keep the N levels high
  without so much fertilizer
• Scientists are trying to engineer the nitogenase
  gene into non-legume plants to take advantage of
  this in N poor soils that cant support legume
  growth

35
Root System

• Affects ecology of an entire community
• Tamarisk tree brought from Asia/Mediterranean to
  control erosion along stream banks
• produce millions of seeds and have spread rapidly
  considered a pest
• Except in the Grand canyon, where became habitat
  for SW willow flycatcher which was endangered and
  in Colorado where beavers help control the trees
  dams and lodges
• No natural pest in the US but in China there is
  the leaf-eating beetle to counteract -
  ecologists worry about them eating native
  vegetation

36
Roots Economically Important

• Carrots
• Sugar beets table sugar
• Horseradish
• Sweet potatoes 5 protein, Ca, Fe and minerals
• Turnips
• Tapioca no protein but starch from cassava
• Sasparilla root beer
• Other roots used to make drugs

37
Soils Source of Minerals

• Levels vary
• Surface litter only a few cm deep and mostly
  leaves
• Top soil 10-30 cm, not acidic and usually has
  10-15 organic matter
• Subsoil 30-60 cm, larger particles, little
  organic matter, usually large amounts of minerals
  washed down from the topsoil, roots grow to here
• Weathering bedrock rock fragments, no organic
  matter

38
Physical Environment of Soil

• Controls plant growth
• 5 same components in varying amounts that dictate
  plants the soil can support
• mineral particles
• humus
• air
• H2O
• living organisms

39
Weathering Breaks Down Rock

• Smallest parts are the soil particles
• Made of minerals used as building blocks in
  plants
• 3 components of soil
• sand nutrient poor and largest
• silt in the middle size
• clay retain large amounts H2O, tightly packed
  poor for plants, little O2
• Combo of the 3 make up loam

40
Humus

• 1-30 soil composition
• some gt90 in swamps and bogs very acidic so
  decomposers cant grow so humus doesnt break
  down
• Helps retain H2O, decrease run-off and erosion,
  aerates soil, reservoir of nutrients
• Plants grow best in 10-20 humus
• Need to replace humus and can accomplish by
  composting
• Remaining soil volume is made up of air 25-50

41
Essential Elements

• Plants obtain from soil
• Van Helmont did an experiment where he planted a
  willow and watch for several years
• plant gained 70 kg but the soil only decreased
  60 grams
• predicted the growth was from the water added
• Now know that the growth was also from CO2 and
  minerals in the soil

42
Essential Minerals

• 3 criterion for being essential
• required for normal growth and reproduction
• no other element can replace it and correct the
  deficiency
• has direct or indirect action in plant metabolism

43
Hydroponics

• Grow plant in water and defined chemicals rather
  than soil
• add test mineral one at a time
• Plant mineral nutrition is the study of how
  plants use nutrients

44
Minerals

• Macronutrients required in large amounts
• C, H, O, P, K, N, S, Ca, Mg
• Micronutrients or trace elements required in
  very small amounts
• Fe, Cl, Cu, Mn, Zn, Mo, B
• 2 generalizations
• plants require different amounts of different
  elements
• elements may have different function in different
  plants or parts of plants

45
4 General Categories

• Required for
• parts of cell structures
• parts of compounds involved in energy-related
  chemical reactions
• activate or inhibit enzymes
• alter osmotic potential guard cells of the
  stomata

46
Deficiencies

• Disrupt plant growth
• N, P and K can limit growth dependent on
  absorbing these nutrients
• Deficiency is usually in the soil
• Micronutrient deficiencies are easy to fix
• Zn deficiencies can be remedied by placing
  galvanized nail in the tree or dirt the plant is
  growing in

47
Deficiencies

• K deficiencies cause the leaves to curl
• Fe/Mn deficiencies cause chlorotic leaves
• white or yellow leaves
• both are important for chlorophyll production

48
Essential Elements and Functions
49
Accumulation of Elements

• Plants can accumulate large amounts of minerals
  called hyperaccumulators concentrate minerals
  at 100x normal
• used as protection against predators most cant
  handle high concentration of the chemical
• can concentrate NaCl, Pb, strontium dependent on
  if exposed
• plants on old gold strip mines can accumulate 1
  mg Au/1 g dry plant material
• Phytoremediation use plants to reclaim land
  from toxic substances such as oil, heavy metals
  and strip mining
• could save billions of dollars a year on
  environmental clean-up

50
Rainforests

• They are deficient in many nutrients
• Tropical rains leech many nutrients from the
  leaves of plants
• pick up the nutrients as the rain runs down the
  stems
• Have extensive shallow roots systems to pick up
  the nutrients as they get to the soil

51
Special Adaptations

• Some trees send up roots along the bark of other
  trees and collect nutrients this way
• may also send roots up their on trunks
• re-cycle own nutrients as well as other plants
• Roots grow in response to nutrients
• 3 fake trees
• 1 with cattle manure all had climbing roots
• 1 with leaf litter 25 had climbing roots
• 1 with nothing no roots