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180 Cards in this Set
- Front
- Back
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Shoot protoderm
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produces epidermis
-w/ waxy cuticle (waxy coating) -may have lenitcels for gas exchange, -some develop into guard cells (stomata), hairs, glands etc |
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shoot ground meristem
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produces cortex (will form cork cambium) & pith for storage
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shoot procambium
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produces vascular bundles
-primary phloem, primary xylem & fasicular cambium (wil form a complete ing w/ xylem inside & phloem outside; will be growth rings) |
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procambium produces:
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PRIMARY PHLOEM
-living cells that transport foods, hormones, etc PRIMAR XYLEM -dead, hollow cells for transport of water, minerals & nutrients. Direction of flow usually only upwards VASCULAR CAMBIUM --secondary meristems for secondary growth |
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ground meristem produces:
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CORTEX
-storage, lateral water/nutrient transport into 'stele' (centre of root) ENDODERMIS -regulates flow of material into stele; cell walls suberized (have casparian strip) PERICYCLE -similar to cortex, but areas ca become meristematic, forming new apical meristems for lateral roots |
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Root Cap
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protects the end of the root
lubricates the root for growing between soil particles |
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root apical meristems
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under root cap
produces cells in all directions meristematic region: area of active longitudinal cell division at root apex |
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primary growth stages
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1) cell division via mitosis
-daughter cells produced from meristematic cells (apical initials: mother cells) 2) cell expansion: daughter cells grow to functional size 3) cell differentiation and maturation: cells develop the physical/physiological characteristics necessary for specialized functions |
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Angiosperms:
Vessel Elements Fibres |
specialized for transport more efficient than tracheids
specialized for support |
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leaf formation
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-leaf primordia develop near shoot apex
-it elongates and a cambial strand develops into it forming leaf mid vein -meristems on either side form leaf blade -further cell division, elongations and maturation produces mature leaf -w/ cuticle layer on epidermis for protection |
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Trichomes
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hairs over stoma to prevent/reduce water loss and reduce herbivory
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stomatal crypt
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pit that contains the stoma; sometimes with trichomes as a way to prevent water loss
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angiosperm leaves
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epidermis
mesophyll veins |
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epidermis
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-typically 1 cell thick
-has cuticle (usually thicker on top side of leaf) -has stomata: stomatal pore, guard cells for gas exchange (usually on lower surface) -may have trichomes or stomatal pits |
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mesophyll
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-main leaf tissue; produces by ground meristems
-consists of photsynthetic parenchyma, usually 2 layers: upper - palisade (high PS) lower - spongy |
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veins
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-derived from procambium, contain vascular tissue
-primary xylem on top -primary phloem on bottom -surrounded by bundle sheath |
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conifer leaves
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-cuticle usually thick
-stomata often in pits/crypts covered in wax -many have palisade and spongy parenchyma (pine only has spongy) -1 or 2 vascular bundles, surrounded by transfusion tissue and endodermis ( w/ casparian strips) -resin ducts |
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leaf morphology varies w/
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environment
age season |
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leaf morphology - ENVIRONMENT
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ie/ sun leaves vs. shade leaves
sun leaves: smaller cells, smaller surface area, thicker cuticles and thicker (more layers) palisade parenchyma |
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leaf morphology - AGE
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ie/ W. red cedar have needles in juvenile form, scale leaves when older
Blk cottonwood - lanceolate in juveniles, deltoid or ovate when mature |
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leaf morphology - SEASON
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of development,
ie/ preformed or neoformed |
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secondary growth
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growth in circumference produced by lateral meristems
-wood and bark tissue -herbaceous plants have little to none -hardwoods and softwoods do |
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secondary vascular cambium
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1) FUSIFORM INITIALS
-produces ling, vertically oriented secondary xylem mother cells to inside and secondary phloem mother cells to outside -these then = xylem and phloem for axial transport through periclinal divisions 2)RAY INITIALS -horizontal ray mother cells -vascular rays for radial transport and storage |
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secondary xylem gymnosperms
TRACHEIDS (& ray parenchyma) |
-elongated cells that taper at ends with support and conduction function
-xylem tracheids elongate, cell walls are lignified and protoplasmic contents lost at maturation leaving large lumen through which water is transported -longitudinal tracheids: vertical transport, water conduction -ray tracheids: horizontal transport |
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secondary xylem gymnosperms
(trachieds &) RAY PARENCHYMA |
-living cells that carry out conduction and storage function in rays
-production and secretion of resin into resin canals -only living cells in xylem |
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secondary xylem angiosperms
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VESSEL MEMBERS
-primary vertical water conduction cells, shorter and wider than tracheids; dead at maturity TRACHEIDs -provide support FIBERS -longitudinal cells that provide support and some storage RAY PARENCHYMA -conduction, storage and secretion (but not resin, only in gymnosperms) |
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phloem cells types gymnosperms
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SIEVE CELLS
for axial food conduction, living but no nucleus ALBUMINOUS CELLS -connect to sieve cells (but from different mother cell) with plasmodesmata -loading/unloading of carbs PARENCHYMA CELLS -living cells in rays, conduction/storage, secretion in resin canals FIBERS -provide support |
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phloem cell types angiosperms
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SIEVE-TUBE MEMBERS
-food conduction, no nucleus, hace sieve plates with pores COMPANION CELLS -living and connected to sieve tube members; for loading/unloading; have nucleus PARENCHYMA -various types in phloem FIBERS -provide support |
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annual growth rings
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EARLYWOOD
-xylem formed early in growing season -large lumes, thin cell walls -high water conductivity, -structurally weaker than latewood LATEWOOD -xylem formed late in the growing season (summer) -smaller lumens, thicker cells walls -therefor stronger and more dense than earlywood |
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false ring
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growth slows down early in season because of stress, then resumes with earlywood-type cells
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frost ring
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poorly formed xylem caused by damage to cambium (cold injury)
-false ring caused by frost |
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cork cambium (phellogen)
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= secondary lateral meristem
-develops from cortical cells beneath epidermis in young stem -produces cork (phellum) to outside, dead, suberized -produces a thinner layer of phelloderm to inside |
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periderm
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phellogen + cork + phelloderm
= outer bark |
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inner bark
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living phloem
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outer bark
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periderms and old, dead phloem
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cambial divisions
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PERICLINAL
-tangental to cambium -produces phloem or xylem mother cells ANTICLINAL -in a few angiosperms -increases the circumference of the cambium itself OBLIQUE ANTI-CLINAL (or PSUEDO TRANSVERSE) -increases cambial circumference, 2 cells grow to length of the original cell DIVISION PRODUCING RAY INITIAL |
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lateral buds
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-new apical meristems develop in leaf axils
-produces bud scale primordia -then leaf primordia dvlp into leaves next year -sometimes new sylleptic shoots begin to grow right away (sometimes lammas growth) |
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terminal buds
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-in mid-summer apical meristem switches from forming leaf primordia to bud scale primordia
-budscales cover shoot apex, forming terminal bud -then apical meristem switches back to leaf primordia |
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sympodial growth
monopodial growth |
a lateral apical meristem bud becomes new psuedoterminal apical meristem next spring (growth terminates with shoot-tip abscission)
terminal buds |
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determinate growth
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buds containing all leaf primordia for next years growth
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indeterminate growth
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no buds, or buds with apical meristems capable of initialing additional leaf primordial during growing season
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neoformed
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leaves are initiated and developed in same year, not preformed
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photoperiod
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environmental cue triggering growth cessation and terminal bud formation
-2 types of phytochrome (Pr + Pfr) measure it -exposure to red light converts Pr to Pfr, while in dark it slowly converts back -when night length reaches threshold growth inhibitors produced, growth cessation, bud form, leaf abscission |
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sylleptic shoots
lammas growth |
shoot grows out into a branch in year of formation (w/o bud forming)
bud flushes in the year of formation |
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leaf abscission
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triggered by photoperiod
ABSCISSION ZONE 2 layers: pectinases digest middle lamella of top layer, cells of lower layer expand with water - forces separation of leaf -wound sealed with suberized cork -in angiosperms: tyloses grow through pits from parenchyma cells to plug vessels |
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fall colours
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pigments other than chlorophyll found in plastids or vacuoles
yellow = breakdown of chlorophyll red = anthocyanines high light = bright colours |
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growth resumption in buds
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1) adequate chilling requirement met
2) adequate heat sum defined in degree days heat sum = (# of days) x (Te -To) where Te = environment temp and To = threshold temp |
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frost hardiness
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-full rapid dvlpment requires frost
-some species respond to temperature alone (Thuja) -sugars etc increase to help decrease freezing point -roots dvlp hardiness to a lesser extent than above ground plant parts (due to snow insulation) |
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(deep) supercooling
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-water stays liquid below freezing point by preventing ice nucleation (creation)
-due to increases concentration of solutes from nucleating agents -won't work <-40C therefor not in boreal forest |
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freeze dehydration
(intercellular freezing) |
-water leaves protoplast and freezes in intercellular spaces (leaves living part of cell)
-promoted by 'ice-nucleating' proteins in outer cell wall -anti freeze proteins in inner cell wall, controls ice formation; don't prevent water from freezing, changes shape of ice crystals so they aren't sharp -super cooled and very rigid |
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cold hardiness phases
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FIRST PHASE
-photoperiod induced, leads to dormancy starting SECOND PHASE involves rapid increase in hardiness in response to lowering temps -max hardiness reached in Nov/Dec |
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growth of terminal buds/shoots
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-height growth of lifetime is sigmoidal
(slow, fast, slow) DETERMINATE growth of leader rapid and completed relatively early on INDETERMINATE -growth generally slower, but lasts longer |
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determinate species
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-normally 1 bud flush/year; >1 = lammas growth
-number of leaves and internodes determined during bud formation -amount of growth depends on condition in this year and last year -bud scale primordia start to form during may, then leaf primordia -bud ready and fully dormant by sept. |
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indeterminate species
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-no buds or small buds with more leaf primordia than bud scale primordial (turn into new formed leaves)
-small/no buds, growth slows, ready for winter by Oct. |
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growth of lateral buds/shoots
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same pattern as leader but for shorter time
-also sigmoidal |
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short shoots
vs. long shoots |
SHORT
-lower laterals, tend to be determinate LONG -usually upper laterals, tend to be indeterminate -can switch back and forth -some terminal buds do this too -short shoots may go long after terminal buds removed |
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epicormic shoots
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-lateral buds that stay dormant and don't flush for many years
-cause knots and decrease wood quality -grow a bit each year to keep pace with stem diameter growth -released in response to light or warmth after injury -frequency varies with species (high in angiosperms) |
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adventitious shoots
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-not from buds (not from leaf axil)
-don't come from where you would expect them to come from: from wounds or roots -allows crown to recover from stress/damage |
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branching paterns
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main shoot: first order, then second order etc (most trees don't go past 3 or 4)
UNINODAL (monocyclic) -one ring of branches around stem each year (many conifers) MULTINODAL (polycylic) -more than one "node" of branches per year |
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estimating age of trees
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-counting "whorls" and adding 1 (for first year)
-count series of bud scars (+ 1) -count wood rings (must do near base of tree to get first year) |
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crown form
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affects quality and quantity of harvestable wood
affected by: -relative growth of different shoots -branch size/angle/number *is under genetic control, but expression modified by environment and age |
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decurrant
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-laterals @ sharper angle with first order shoot
-results in broad rounded crown |
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fastigate
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-all branches long and grow vertically @ very narrow angle to stem
-results in columnar crown |
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excurrent
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-laterals @ wide angle, often perpendicular to stem
-first order shoot grows more than laterals -yields single stem with conical crown -almost all trees start this was, conifers stay this way in mature form |
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apical dominance (A.D.)
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the terminal bud or leader controls growth and angle of laterals
-mediated by hormones *an example of epistasis |
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epistatsis
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where one organ affects the position or growth of another
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topophysis
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retention of characteristics in an organ no longer subject to original controlling influence
ie/ removal of leader causing no change in orientation of laterals *not well understood |
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crown form - SPACING
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CLOSE
-lower branches receive low light and die early -some trees self prune -crown "recedes" upwards WIDE -lower branches retained longer and reach larger size |
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self pruning
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actively dropping branches that aren't receiving enough light/nutrients to actively photosynthesizes
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crown form - FORKING
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unwelcome, causes rot and reduces yield
caused by: 1) species that normally lose shoot tip every year and 2 lateral buds take over 2) lammas growth of laterals 3) apical meristem splits 4) when >1 lateral is released after accidental death of terminal |
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crown form - INJURY
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-exposure to wind and blowing snow (or sea salt spray) may decrease trees to low gnarled forms and cause flagging and trailing in direction of wind
damage due to disease, insects, parasites, frost, snow press, humans & other animals |
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stem form
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-because of light and wind, trees in the open taper more rapidly than trees in a stand
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stem form - ABSENCE OF LIGHT
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-seedling tall and skinny and lack chlorophyll, leaves don't expand
-become etiolated -stem growth over root growth (seen in saplings in stands) -branching also inhibited |
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etiolation
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-controlled by phytochrome
-low levels of red light relative to far red light under canopies leads to stem elongation (very shade tolerant species don't do this) |
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wind throw
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along cut block edges due to etiolation
-trees not used to wind will "firm up" by increased carbon allocation to base of stem |
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progressive windthrow
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trees fall over along edges of cut block, increasing the fetch, allowing more wind to come in, causing further wind throw
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damage to stem form
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-by humans (ie/ culturally modified trees)
-gravity -snow movement -soil creep -sun exposure higher on one side than the other |
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root systems
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-type characteristic of species, but influenced by environment
-also responds to stress (ie/ swaying tree = "I beam" uneven thickening of roots) 3 main types: -tap root -flat -heart root |
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tap root system
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-primary root well developed
-penetrates deeply into soil (good for dryer locations) -laterals not particularly well developed -ie/ douglas fir, ponderosa pine |
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flat root system
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-laterals well developed, but not primary root
-suitable for shallow soils, wet locations, permafrost -ie/ sitka spruce |
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heart root system
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-intermediate of tap/flat root
form buttresses on very wet or very shallow soils |
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buttresses
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base of tree swells
-extra wood growth on top surface of primary lateral roots |
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roots/grafting
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-spread out up to 10x further than crown, therefor they overlap and may graft together with roots of other plants of same species
-promotes spread of disease and carbon |
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short lived fine feeder roots
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-mostly in top 20cm of soil
-total up to several km -all roots need oxygen *can be damaged by trampling and soil compression: can lead to death |
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when do roots grow?
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on coast:
-root growth peaks in spring, decrease in summer, peaks again in fall -season more compressed in interior, shoot/root growth coincident |
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root form in container seedlings
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-roots spiralling around container cavity and grow/graft together
NOW: -no longer a big problem -copper in walls of containers inhibits growth of roots |
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hormones
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needed to co-ordinate growth processes
-are organic compounds made in one plant part and moved to another, where they cause a response -don't need to move far -are effective at very low concentrations 5 general groups: -auxins -gibberellins -cytokinins -abscisic acid (ABA) -ethylene |
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auxins
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-first one identified by effect on mimicking phototropism
-4 natural ones (ie/ IAA = indole acetic acid) & many synthetic ones -cell growth and expansion -made by growing tissues -polar transport -apical dominance -prevents abscission & heals wounds -promotes root initiation from stem |
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polar transport
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very slow: approximately = 1 cm/hr
-moves mostly down in shoots (in phloem and parenchyma) -moves mostly up in roots (in cortex and endodermis) |
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auxin & apical dominance
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removal of terminal = removal of auxin pool
-releases laterals -won't happen if auxin is applied to wound |
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auxin & leaf abscission
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when auxin production stops, ethylene production starts; causes leaf abscission
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cytokinins (CK)
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-promotes cell division etc
-first one: zeatin (now >30) -high in young organs and root tips (important site of production) -NO polar transport (moves in all directions) but lots goes from roots to shoots -stimulates shoot production |
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CK/Auxin interaction
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high CK/Auxin = shoots
low CK/Auxin = roots therefore helps control root/shoot balance high CK/Auxin can overcome apical dominance |
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brroms
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proliferation of shoots:roots caused by parasitic plants
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gibberellins
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-discovered as fungus that promotes stem elongation (now >125 known)
-made all over but especially by seed and young leaves -stimulate height and cone production -also stimulates seed germination, bud break, fruit growth (but doesn't affect flowers) |
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ethylene (C2H4)
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-simple gas discovered because of effects on leaf abscission
-produced all over, especially when wounded or stressed -inhibits cell elongation, promotes stem thickening -stimulates fruit ripening -turns on defensive mechanisms against disease -very important in flooding stress |
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abscisic acid (ABA)
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-a stress hormone that was discovered in 1963
-increases rapidly during drought, responsible for closing stomata -plants can be hardened to (water) stress by ABA application -needed for normal embryo development |
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more hormones
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Salisylic acid (induces systemic disease resistance)
Systemin Jasmonic Acid FT (flowering time) protein |
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photosynthesis
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6 O2 + 12 H2O (+light) => C2H12O6 + 6 O2 + 6 H2O
-there are many hundreds of reactions involved in this process -O2 (released as waste) comes from water NOT CO2 2 parts: -light reactions -dark reactions |
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light reactions
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-light absorbed by chlorophyll (most) and carotenoids
-chlorophyll absorbs green light badly -chlorophyll molecules arranged in photosystems and funnel light energy into photosystem centres -at center special chlorophyll (P680) loses an electron, which then travels down photosynthetic electron transport chain (series of proteins and carriers) |
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photosynthetic electron transport chain
+ electron flow used to produce |
a complicated set of proteins and chemicals arranged in a series
-produces a proton gradient across thylakoid membrane, harnessed to make ATP needed to power carbon fixation -electrons themselves are used in carbon fixation as reducing power -continuous electron flow needed, they are obtained by the "splitting" of water in the photosystem centre (free oxygen (O2) is released as waste product into atmosphere - 2 H2O needed to produce 1 O2) |
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photosystem centres
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several hundred chlorophyll molecules per photosystem
*more in shade leaves because need to capture more light |
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carbon (dark) reactions
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uses CO2 & photosynthates from light reaction
-plants very good at absorbing CO2 -RUBISCO fixes CO2, is most abundant protein -attaches CO2 to a 5C substrate -produces two 3C molecules -these are reshuffled in calvin cycle to regenerate substrate and produce sugar |
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photorespiration
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when O2 competes with CO2 in being used by rubisco
-this isn't useful, the plant must try to fix this mistake, which is energy wasteful |
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increase in CO2
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lowers photorespiration
increase in plant growth so long as there are no other limiting factors |
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visible light
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between ultraviolet and infrared
plants/chlorophyll absorb lots of this light @ red and blue |
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solarization
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= sun scald or photooxidation
-bleaching, then browning -caused by excess light energy, electron transport becomes overloaded -"shorts out" to O2 (picks up electron) producing oxygen radicals, and damaging chlorophyll |
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oxygen radicals
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react with chlorophyll and other constituents causing damage/death to cells
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photoinhibition
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minor damage caused by solarization that results in a decrease in photosynthesis
-causes decrease in maximum chlorophyll fluorescence |
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chlorophyll fluorescence
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chlorophyll reemits some energy as red light
-can be determined with fluorometer -a useful measure of environmental stress/damage (i.e./frost damage) |
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herbicides
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Atrazine
-a triazine -blocks electron transport in photosynthesis -plants "fry" Paraquat -a diquat -makes oxygen radicals |
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herbicides used in forestry
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nexazinone/sirmazine
-triazines 2, 4-D -mimics auxin Glyphosate -blocks synthesis of essential amino acids -round up Triclopyr -hormone analog -release |
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pressure potential
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positive if water is under pressure (in a confined space)
negative if water is under tension (being pulled from cell) can be generated by osmosis |
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matric potential
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caused (mainly) by hydrogen bonding to surfaces
-always negative -not usually important UNLESS in dry soils, seeds, dry wood etc |
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total water potential
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= solute potential + pressure potential + matric potential
in a happy plant will approximately = -0.5 MPa (-1.5 + 1.0 + 0) |
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soil-plant-air continuum (SPAC)
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is soil total water potential is 0 MPa (or so) then..
-water moves from soil to plant (high to low potential) -water potential of air VERY negative (if relative humidity is <100%) -water moves from soil to air through xylem of tree along the water potential gradient in soil is higher than xylem xylem higher than leaf leaf higher than air |
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water movement
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angiosperms - only goes through one living cell
gymnosperms - goes through 2 living cells |
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ascent of sap (water movemnt through trees)
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pulled up by transpiration by cohesion of water to itself because of hydrogen bonding(SPAC)
-xylem water is under tension -water columns sometimes break (cavitations) *can pull a tube of water up 3000m |
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cavitations
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water columns in xylem breaking
-caused by wind, drought or freezing -tracheids are less susceptible because of bordered pits -can be heard by insects (signalling plant under stress) -occurs first in petiole |
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water movement not done by:
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Osmosis
-root pressure not enough, and movement too slow NOT another living pump -poisoned/dead trees can continue to transpire Capillary action -too slow -only "lifts" water about 0.5m up in wood |
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speed of water movement in trees
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up to 40 m/hr in ring porous species
1-7 m/hr for diffuse porous species 1-2 m/hr in gynosperms |
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proof of xylem tension
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1) trunks shrink during transpiration
2) when stem cut water "snaps" away from cut surface in both directions 3) pressure probes measure tension directly or place cut shoot in a pressure bomb |
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pressure bomb
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indirectly measures xylem tension
= balancing pressure x -1 this will equal the total water potential of xylem and therefor of the shoot more tension = more negative total water pressure = more stress |
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xylem water
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-usually very dilute
-exceptions: birch, maple, & grape sap in spring contain sugar (and have positive pressure in xylem) -when water pulled into roots dissolved materials can be filtered out and left in soil (ie/ mangroves making sea water saltier) |
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water stress
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from lack of water
-increases susceptibility to other issues -decreases growth -wiliting indicates dying; needs to replaces at night to remain alive -planting also water stressful time -some species are more water tolerant then others garry oak > ponderosa pine > lodgepole pine > white spruce > black spruce |
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ways plants decrease water stress
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-stomatal closure
-develop thicker cuticle -change leaf orientation -leaf abscission -leaf rolling (grasses) -produce more roots (genetically controlled but plastic) root:shoot ratio dryland shrubs => 9:1 young pine in plantations => 1:5 |
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hydraulic lift
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water lifted from depth at night by plant roots and deposited closer to soil surface
=redistribution |
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phloem transport
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-bidirectional
-materials transported: photosynthate (sugars), amino acids, hormones, vitamins, some minerals -moved from source to sink (where they are used or put into storage) -transport mostly down in tree trunks in summer -slower than xylem transport: max speed => 1m/hr |
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evidence of phloem transport
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1) girdling causes accumulation of material above (more) and below (less) wound
2) radioactive labelling -give leaf 14CO2 => creates radioactive photosynthate, can follow it's movement 3) aphid stylets: phloem sap oozes out under pressure |
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pressure-flow hypothesis
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1) sugar, usually sucrose, loaded into phloem @ source
2) water follows by osmosis, increasing the pressure in sieve cells at source end 3) sugar unloaded or used up @ sink 4) water exits by osmosis, decreasing pressure at sink end |
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phloem loading/unloading
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angiosperms: companion cells
gymnosperms: albuminous cells -requires metabolic energy because is being forced against pressure gradient |
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apoplastic
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water moves from cell to cell via spaces in cellulose in cell walls until it reaches endodermis
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symplastic
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water moves from cell to cell in cytoplasm vis plasma membranes and plasmodesmata
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transcellular
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water movement is through the cells
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allelopathy
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chemical inhibition of one plant by another
-many plants produce toxic chemicals themselves, competition is usually indirect but can be direct by chemical competition |
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respiration
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process by which energy stored in sugar molecules is released and re-packaged for use driving other chemical reactions and processes
C6H12O6 + 6 O2 => 6 CO2 + 6 H2O + energy (ATP) *basically reverse of photosynthesis, numerous separate reactions involved |
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glycolysis
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6C glucose molecule broken down to pair of 3C pyruvate molecules
-also yields 2 ATP and 2 NADH2 Pyruvate is decarboxylated for 2-C acetyl groups -these then enter the Krebs Cycle (by way of acetyl CoA) |
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Krebs cycle
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acetyl group broken in series of reactions to yield CO2
-and more reducing power and 1 ATP *donates electron to the electron transport chain |
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mitochondrial electron transport change
(respiration) |
electrons establish a proton gradient, used to produce ATP
Cytochrome oxidase: -catalyzes electron being accepted by O2 to yield H2O |
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ATP yields of respiration
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aerobic:
-approximately 36 ATP/glucose molecule consumed anaerobic: -produces only 2 ATP -plus: potentially toxic by-products, particularly ethanol => may build up and damage plants |
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alternate oxidase
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occurs at end of an extra electron transport chain
-doesn't produce as much ATP, simply yields heat directly -can't be poisoned by cyanide -skunk cabbage, cones or cycads (smelly, insect pollinated) |
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ecophysiology
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experimental science that seeks to describe the physiological mechanisms that underlie ecological observations
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photosynthetic capacity
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-peaks when leaves reach full size, then begins to decline again
-decline lasts 1 growing season in deciduous trees -extended over several seasons for evergreens |
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leaf longevity/leaf nitrogen content
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nitrogen content/unit dry mass
-negative relationship between leaf longevity and leaf nitrogen content -same relationship reflected in photosynthetic capacity |
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evergreen vs. deciduous leaves
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evergreen leaves
-higher cost of formation per unit area -last longer -cost is from the formation of thick, waxy, somewhat succulent needle leaves |
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photosynthetic recovery after cold
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after cold storage photosynthesis in seedlings recovers within a few days, can reach compensation (PS = Resp) within a few hours
after winter: -recovers after a few warm spring days and well under way before bud break |
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winter photosynthesis
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can be especially tolerant for shade tolerant evergreens growing under deciduous trees
-peak photosynthesis usually occurs for these trees in fall and spring *spring likely better because of longer days, more intense light, high solar angle |
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dark respiration
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-rate linked to availability of photosynthesis
highest just after dark, lowest just before dawn (reflects availability of respiratory substrate) -otherwise consistent on a day to day basis respiration peaks in spring (growth) & in leaves during senescence |
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respiration & tissues
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varies with tissue
fruits/flowers > leaves >= roots > stems -most respiration from branches/trunks is in living bark, but also in cambium and sapwood (ray parenchyma) |
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respiration in seasons/times of day
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during summer is approximately 10% as fast as photosynthesis
continues at night & in winter in all plants parts -25-50% of carbon fixes is respired away |
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influence of temperature
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-photosynthesis, respiration and growth increase with temperature (to a plateau)
-high temperature inhibits photosynthesis more than respiration (heat limit @ compensation) -high temp. promotes photorespiration -solubility of CO2:O2 decreases with temp -CO2 enrichment promotes thermal tolerance |
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temperature acclimation
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-some species show seasonal adjustment of optima, this is induced by temp. & photoperiod
-others show change in capacity but not optima *important in predicting effects of climate change |
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homeostasis
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growth at low temperature results in high respiration capacities
-change in capacity in a compensating fashion |
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light attenuation
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Beer's law
I = (Io)e ^ -KL Io = PPFD upper canopy e = 2.718 K = canopy extinction coefficient L = leaf area index (leaf area/ground area) |
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K
(Beer's law) |
depends on leaf thickness, chlorophyll concentration and leaf angle
-high values (0.8 - 1.0) for horizontal leaves -low values (0 - 0.2) for vertical leaves -about 0.5 is typical |
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L
(Beer's law) |
typical values = 6 (in a forest)
-@ "canopy closure" L = 5 (>90% light absorption) -can reach up to 18 -20 in conifer forests |
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Beer's law doesn't consider
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-difference between diffuse and direct light
-solar angle -patchiness -changes in leaf angle through canopy |
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sun leaf characteristics
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narrow
thick more/longer pallisade more vascular tissue thick epidermis/cuticle lower chlorophyll (dry weight basis) dense on branches short petioles often at an angle "sun" chloroplasts on top, "shade" ones on bottom |
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shade leaf characteristics
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wide
thinner only one pallisade layer less vascular tissue thin epidermis/cuticle more chlorophyll (dry weight basis) sparse on branches long petioles perpendicular to light "shade" chloroplasts |
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to regulate PPFD
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leaf angle
leaf thickness pigmentation (ie/ anthocyanin, rhodoxanthin) leaf/chloroplast movement (PPFD = photosynthetic photon flux density) |
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light saturation point
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PPFD needed for maximum photosynthesis
-typically 25-50% of full sun in sun leaves (less than shade leaves) |
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light compensation point
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where photosynthesis = respiration
-near PPFD 40 micro mols/sm^2 -less in shade leaves because they have lower respiration rates (lower maintenance costs) |
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more shade/sun stuff
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-leaves/branches that are below compensation are abscised
-leaf longevity depends on shade tolerance, available light, stress, etc -high leaf angle of sun leaves decreases incident PPFD & permits light penetration -this in combination with self-shading causes light response curve of whole canopy to be "smooth" |
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sunflecks
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-important for understory plants (30-60% of photosynthesis)
-intensity, duration and size depend on canopy structure and height -taller canopy: sunflecks have a lower PPFD -most last <30s -rates of induction/de-induction important to shade tolerance -because of "post illumination CO2 fixation" can exceed efficiency of continuous light utilization |
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carbon allocation
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typically...
(fixed carbon) -about 2/3 of carbon = below ground (mostly fine roots) -about 1/3 of carbon = to shoot (some used in reproduction) -what isn't used is stored as reserves for winter |
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large tree mortality
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-because of sheer size (too much biomass and respiring surface area to support) or hydraulic limitations
-may also approach compensation or become structurally unstable leading to damage from ice/snow, wind, diseases etc *can speed up forced succession |
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water cycle
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earth has 1.2 billion km^3 of water; 97% in oceans, rest on land but mostly ice
precipitation = evaporation over entire Earth approximately equal to 90 cm/yr 1/6 of evaporation over land >1/6 of ppt overland |
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main function of water in plants
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1) medium for biochemical reactions
2) participant in biochem reactions 3) solvent for movement of material 4) maintenance of turgidity for growth, function and form 5) temperature regulation |
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plant water content
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varies with species (hardwood > softwoods), tissue, season (spring > others)
-largest total amount is in wood -% water content, higher in sapwood then in heartwood -leaves next -inner bark, cambium, apical meristems have high water content because they are active areas of growth |
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use of water by forests
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-doesn't vary much with species
-related more to forest region (ie/ climate) need ppt: -40 cm/yr min in boreal forest -20 cm/yr in taiga -60 cm/yr in mid latitudes -120+ cm/yr in tropics |
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water loss
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99.7% of water taken up is transpired, only 0.1% incorporated into dry matter
-rest is fresh mass -must expose wet surface to get CO2 for photosynthesis -must compromise by closing/opening stomata (depends on relative humidity of air) |
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stomata/water loss
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if water in short supply the stomata close
-during mild drought partial stomatal closure lower transpiration > lower photosynthesis -stoma close completely before leaf wilts |
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water structure
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2 H & 1 O = 3 nuclei
10 electrons, including one lone pair positively and negatively charged ends, result in hydrogen bonding between water molecules |
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hydrogen bonding
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association of hydrogen atom of one molecule with lone pair of electron on another
-gives water unique properties, increasing tensile strength and surface tension (water beads on surfaces) |
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hydrogen bonding in ICE
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crystalline water
-each molecule bound to 4 others |
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hydrogen bonding in LIQUID WATER
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semi-crystalline
-hydrogen bonding constantly forming and breaking |
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water potential
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= the potential of water to do work
-units of pressure: Pa or MPa -salty water more negative potential -water under pressure has more positive water potential -water always moves from higher to lower potential |
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solute potential
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becomes more negative as quantity of dissolved substances increases
-differences in solute potential drives osmosis solute potential of sea water = -3.0 MPa solute potential of sea water = ~0 MPa |
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osmosis
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the diffusion of water across a semi-permeable membrane separating 2 solutions of different solute potentials
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turgid pressure
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caused by water moving into cell to balance solute potential, causes pressure potential to increase inside cells
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