Two Ambrosia Species: An Overview

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Two Ambrosia Species An Overview
Ana L. Karim Dept. Horticulture and Crop Science
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Habitat

• A. bidentata - (Lanceleaf ragweed) An annual
  weed commonly found in pastures and untilled
  areas from Texas to Louisiana.
• The southern two-thirds of Missouri, and the
  eastern quarter of Oklahoma and Kansas, and
  southern Arkansas are heavily infested.
• Structure cointaining seed called an achene
  simple, dry one seeded, indehiscent fruit
  attached to wall (McIntyre and Peters,1972).

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Morphological Description (contd)

• A. bidentata - Branching annual, stems
  spreading- hirsute leaves sessile, opposite
  below, alternate above, upper leaves lanceolate,
  entire. Staminate spikes solitary, heads
  crowded, sessile. Involucre ovoid, 4-angled or
  ribbed, the angles extend into 4 stout spines.
  Found near pond margins, prairies, pastures,
  roadsides, and railroads.

Dicotyledoneae of Ohio, 1988
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Morphological Description (Contd)

• A. bidentata - ranges from 6 to 36 inches tall,
• long- pointed, hairy, lanceolate leaves pointing
• upward.
• Flowers reduced and monoecious
• Female flowers borne in the axils of the lower
• leaves
• Male flowers borne above in terminal spike

McIntyre and Peters, 1972
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Ambrosia bidentata Micheaux
Missouri roadside, 2003
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A. bidentata
Ill. Plant Information Network,2003
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Dicotyledoneae of Ohio, T. R. Fisher, 1988
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Experimental Study

• Objectives A. Document morphological
  development
• B. Study germination pattern of
  achenes and causes of
  dormancy
• Procerdures Lanceleaf ragweed plants
  collected at various intervals for
  two weeks in late August, 1966
• Seeds collected April, 1967 from
• Three 12x24 surface soil cores
• Photographed 2, 4, and 8 days after
  germination

Univ. of Missouri, Columbia
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A. bidentata (lanceleaf ragweed) Collected
Specimen
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Components of StudyA. bidentata

• Study effects of
• 1. Scarification (sandpaper), steeping and
• GA3 treatments(1,10,100,1000, 10,000 ppm)
• 2. Fruit wall removal
• 3. Stratification
• 4. Inhibitors of germination

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Experimental Results
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Magnification of male floweer
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Morphology of leaf
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Morphology branched stigma
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Maturing Pistillate Flower
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Effects of Soil Storage
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Effects of Dry Storage
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Germination Inhibitor Effects
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Experimental Conclusions

• Ragweed achenes appear to have an after-ripening
  period during which germination will not begin
  until more than 6 weeks have passed.
• Scarification, cracking or removal of seed coat
  did not increase germination. Dormancy is not
• due to impermeable seed coat.
• Leaching with water for 48 hours did not increase
  germination.
• Dry cold storage did not increase ragweed
  germination. Moist soil and fluctuating
  temperatures of the soil were conducive to
  germination.

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Morphological Description

• A. psilostachya (Western ragweed) Perennial
  with creeping rhizomes stems to 1m tall, harsh
  to the touch.
• Pubescence stiff and short, leaves pinnatifid,
  short, petiolate to sessile, staminate involucres
  without tubercles or with very short ones.
  Pistillate flowers without corolla. Rare in Ohio
  found in dry and saline areas
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

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A. PsilostachyaMale heads in Fall these
produce massive amounts of windborne pollen
Univ. of Texas
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Male individual flowers.
Female flowers borne in axils of leaves
Univ. of
Texas
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Dicotyledoneae of Ohio, T. R. Fisher, 1988
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Experimental Studies A. psilostachya (western
ragweed)

• Can a rhizomatous clonal plant species seek
  optimal microhabitats for future growth and
  reproduction?
• Experimental Objectives
• A. Evaluate saline and nonsaline
  microhabitats
• B. Determine magnitude of genetic (clonal)
• variation for habitat preference
• A. G. Salzman, Dept. of Biology, Univ. of Chicago
  (1985)

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Experimental Studies (contd)(western ragweed)

• Procedures Six replicate ramets (stems) of 9
• distinct clones were individually rooted in
  the
• center of low-salinity soil of long narrow
  pots
• (18x46x13cm).
• NACL gradient established on one end of pot
• by washing soil with 1 NACL and flushing the
  remaning soil with tap water.
• Time of evaluation 3 months.

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Experimental StudiesResults

• A value of 0.5 signaled equal placement of shoots
  in both habitats.
• Values lt 5gt indicated respective preference for
  saline vs. nonsaline soil.
• Initiation and development of vegetative shoots
  was strongly toward nonsaline soil (67) of 2730
  shoots initiated

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Habitat Selection in a Clonal Plant Ambrosia
psilostachya Michx.
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Experiment Allelopathic Effects (Western
ragweed)

• Double cropping practices in southern Oklahoma
  It was noted that rye grass established poorly in
  bermudagrass sod following summer forage
  production and where ever stands of western
  ragweed occurred
• Soil moisture and plant nutrition was determined
  to be adequate for the rye
• Hypothesized ragweed allelopathic
  characteristics caused negative rye response.

Dalrymple and Rogers, 1983
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Allelopathic Effects(western ragweed)

• Objective Determine the degree of influence of
  extracts on germination and early seedling growth
  of selected plants.
• Procedures
• Top growth was separated from root growth.
• Fibrous roots removed from rhizomes.
• Plant material oven dried and 10 grams of
  top
• and root material was extracted using 150
  ml.
• distilled water agitated by magnetic stiring
  for 2-hr.

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Allelopathic Effects Results

• Rye seed germination averaged 25 less in
  extracts than in distilled water, thus supporting
• field observation of the negative influence of
  
• western ragweed on rye.
• Dalrymple, R. L. and J. L. Rogers, 1983.
• J. Chemical Ecology, 1983

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Allelopathic Effects Results
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Experiment Effect of Topographic Position
-Plant Species Composition

• Objective Characterize relationship between
• topographic position and vegetation cover of
  upland sites grazed by cattle.
• Study conducted on 2350 ha ranch in eastern
  Nebraska Sandhills.
• Upland prairie dominated by sands range sites
  (mixed mesic Typic Ustipsamments).
• Dunes slope- 5 15, some greater than 20

Schacht et al.,2000 Univ. Of Nebraska
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Effects of Topographic Position

• Four upland topographic positions were
  recognized interdunal valleys, south-facing
  slopes, dune tops, and north facing slopes
• One site per 20 ha spacing
• Transect location selected randomly to run
  parallel with the contour of land at top of
  dunes and valleys along north and south slopes
• Plant species frequency estimated along transect
  with 0.1m2 quadrat at 4 M interval
• (25 quadrats per transect.)

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Topographic Results(western ragweed)

• Total of 89 vascular plant taxa found upland
• Sedges and western ragweed were most common taxa
  occurring over all topographic
• positions
• Mean species richness
• south-facing slope (17.9)
• dune tops (18.6)
• north-facing slope (19.1)
• interdunal position (11.1)
• No significant difference
• Schacht,
  et al., 2000

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Topographic Results
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Experiment Water Relations of Tallgrass
PrairieA. psilostachya

• Objective
• Assess the indirect effects of selective grass
  herbivory by bison on the xylem pressure
  potentials and primary production of ungrazed
• tallgrass prairie forbs.
• Location
• Konza Prairie Research Natural Area
• NE Kansas

Fahnestock and Knapp, 1993
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Water Relations Tallgrass prairie

• Selective grazing behavior by bison results in a
  heterogeneous landscape with grazed patches
  including numerous ungrazed forb species.
• Could water relations or production in ungrazed
  forb species growing in grazed patches be
  affected by selective consumption
• of adjacent grasses?

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Water Relations Tallgrass prairie

• Three speacies compared
• 1. Vernonia baldwinii Torr (ironweed)
• 2. A. psilostachya (western ragweed)
• 3. Aster ericoides (heath aster)
• Factors assessed
• a. water relations
• b. light availability
• c. Patterns of aboveground biomass production

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Water Relations Tallgrass PrairiResults

• Overall, selective grass removal by bison has an
  inconsistent effect on the water relations of
  tallgrass prairie species.
• No consistent seasonal differences in between
  burning treatments, burning treatments were
  combined

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Experimental Conclusions

• No evidence to support hypothesis that grazing
  of the dominant grasses improved water status of
  the remaining forb species.
• Effects of large herebivores on water status of
  of ungrazed forbs may be short term because forbs
  and grasses may exploit different soil water
  resources.
• Transpirational water loss in grazed patches may
  be increased by higher wind speeds at ground
  level, higher radiant heat loads, and higher soil
  temperatures.

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Experimental Conclusions (contd)(Water
Relations)

• Selective grazing of the grasses by bison did ot
  significantly alter seasonal plant water
  relations in the neighboring ungrazed forb
  species, but some biomass measurres in forbs were
  increased.

Fahnestock and Knapp 1993
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Questions?