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Carex humilis - a caespitose clonal plant: ramet demography, ring formation, and community interactions

Wikberg, Sofie LU (2002)
Abstract (Swedish)
Popular Abstract in Swedish

Carex humilis - en ringbildande klonväxt



Växter som kan föröka sig asexuellt kallas klonväxter. Det genetiska individet (geneten) består då av flera självständiga plantor (rameter). Exempel på klonväxter är hallon, jordgubbe, kvickrot, potatis, tulpan och vitsippa. Den här avhandlingen handlar om ett centraleuropeiskt klonalt halvgräs, som heter Carex humilis på latin men som saknar svenskt namn. Hos Carex humilis sitter rameterna väldigt tätt tillsammans och bildar en cirkel, vars diameter ökar successivt då fler rameter produceras. Efter en tid minskar antalet rameter i mitten av cirkeln och geneten får då formen av en ring. Eftersom ringarna kan bli upp till en meter i... (More)
Popular Abstract in Swedish

Carex humilis - en ringbildande klonväxt



Växter som kan föröka sig asexuellt kallas klonväxter. Det genetiska individet (geneten) består då av flera självständiga plantor (rameter). Exempel på klonväxter är hallon, jordgubbe, kvickrot, potatis, tulpan och vitsippa. Den här avhandlingen handlar om ett centraleuropeiskt klonalt halvgräs, som heter Carex humilis på latin men som saknar svenskt namn. Hos Carex humilis sitter rameterna väldigt tätt tillsammans och bildar en cirkel, vars diameter ökar successivt då fler rameter produceras. Efter en tid minskar antalet rameter i mitten av cirkeln och geneten får då formen av en ring. Eftersom ringarna kan bli upp till en meter i diameter och vara 10-20 cm breda handlar det om ganska stora strukturer som kan påverka sin egen miljö.



Från 1993 till 1998 studerade jag Carex humilis på Hexenberg, 300 meter över havet, 60 km öster om Wien, Österrike. I avhandlingen har jag först beskrivit rameternas livscykel och sedan analyserat deras demografi, det vill säga hur många nya rameter som produceras och hur många som dör. På så vis kan jag förklara hur ringarna bildas. Demografin ger däremot inget svar på varför ringarna bildas. Det skulle till exempel kunna bero på miljöfaktorer och jag beskriver därför också hur miljön runt ringarna varierar och hur andra växter förhåller sig till Carex humilis.



I studien visade det sig att blommande rameter dog utan att producera några nya rameter. Inte heller producerade de några frön som kunde gro och ge upphov till nya geneter eftersom fröna antingen var infekterade av sotsvamp eller åts upp av fluglarver. Nya rameter producerades istället av de rameter som inte blommade. Bland dessa producerade stora rameter både fler och större nya rameter, jämfört med små rameter. Hur tätt rameterna stod påverkade inte hur många nya rameter som producerades. Vissa år ökade det totala antalet Carex humilis-rameter och andra år minskade det. Totalt sett ökade antalet rameter under tidsperioden. Rameterna i ringens ytterkant producerade fler nya rameter än de längre in mot mitten. Främst berodde detta på att rameterna i ytterkanten var större. Kombinerat med att de flesta rameterna bildade nya rameter på den sidan som vette mot ringens ytterkant, så gjorde detta att antalet rameter ökade i ringarnas ytterkant medan antalet rameter minskade längre in mot mitten.



Marken under ringarna innehöll mer kväve och fosfor och hade högre vattenhalt än marken utanför ringarna. Anledningen till att antalet rameter inuti ringarna minskade var därför knappast brist på dessa ämnen. Inte heller kunde det bero på konkurrens från andra växter eftersom de flesta andra växter var ovanligare inuti ringarna än utanför. Brist på något annat näringsämne, ackumulering av någon giftig substans eller påverkan av microorganismer kan istället vara förklaringen till att Carex humilis bildar ringar. (Less)
Abstract
Carex humilis forms rings of densely aggregated ramets in dry grassland vegetation in Central Europe. In the thesis I conclude that ramet demography is important both for analyzing fitness in clonal plants and for understanding how C. humilis rings are formed. I studied the ramet demography of C. humilis from 1993-1998 at the Hexenberg mountain, 300 m.a.s., 60 km east of Vienna, Austria. In total, the size of the ramet population increased during the study period but there was considerable variation in ramet population growth rate between years. Flowering ramets of C. humilis did not produce any offspring ramets, and at the study location, the seeds were either infected by smut of infested by insect larvae. The size of vegetative parent... (More)
Carex humilis forms rings of densely aggregated ramets in dry grassland vegetation in Central Europe. In the thesis I conclude that ramet demography is important both for analyzing fitness in clonal plants and for understanding how C. humilis rings are formed. I studied the ramet demography of C. humilis from 1993-1998 at the Hexenberg mountain, 300 m.a.s., 60 km east of Vienna, Austria. In total, the size of the ramet population increased during the study period but there was considerable variation in ramet population growth rate between years. Flowering ramets of C. humilis did not produce any offspring ramets, and at the study location, the seeds were either infected by smut of infested by insect larvae. The size of vegetative parent ramets positively correlated to both number and size of offspring ramets, i.e. larger parent ramets produced both more and larger offspring ramets.



The ramet population growth rate was higher in the periphery of rings than in the interior, mainly due to the ramets being larger in the periphery. Because of this, of the ramet population size in the periphery of rings increased, whereas the ramet population size in the interior decreased. However, the ramet density in the interior was lower than would be predicted from the population growth rate alone, and I conclude that the difference is due to the centrifugal dispersal of ramets. A simulation model showed that ramet populations with lower maximum population growth rate, or with more peripheral dispersal, formed rings, whereas populations with higher maximum growth rates or less peripheral dispersal formed filled circles. A size structured matrix model showed that although there was variance in the production of all size classes, both between years as well as between periphery and interior, it was only the variance in the production of larger ramets that was important for the variance in the asymptotic population growth rate.



Compared to the surrounding vegetation, the cover of most other plants was reduced inside C. humilis rings. In addition, the soil under C. humilis rings contained more moisture, nitrogen and phosphorus than the surrounding soil. Hence, the reason behind the lower population growth rate in the interior of rings was neither competition from other plants, nor depletion of any of the soil resources measured. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • PhD Oborny, Beata, Department of Plant Taxonomy and Ecology, Lorand Eotvos University, Budapest, Hungary
organization
publishing date
type
Thesis
publication status
published
subject
keywords
ramet density, Plant ecology, Växtekologi, ramet population dynamics, aggregated ramets, intravaginal, phalanx type, LTRE, matrix model, fitness, dry grassland, hollow crown, fairy ring, central die back
pages
117 pages
publisher
Sofie Wikberg, Plant Ecology, Ecology building, SE-223 62 Lund, Sweden,
defense location
Blå Hallen, Ecology Building, Sölveg 37 Lund, Sweden
defense date
2002-05-03 10:15
external identifiers
  • other:ISRN: SE-LUNBDS/NBBE-02/1066+117pp
ISBN
91-7105-170-8
language
English
LU publication?
yes
id
141101b9-9ae3-455f-b75e-adf40781baf6 (old id 464568)
date added to LUP
2007-09-07 11:42:51
date last changed
2016-09-19 08:45:10
@phdthesis{141101b9-9ae3-455f-b75e-adf40781baf6,
  abstract     = {Carex humilis forms rings of densely aggregated ramets in dry grassland vegetation in Central Europe. In the thesis I conclude that ramet demography is important both for analyzing fitness in clonal plants and for understanding how C. humilis rings are formed. I studied the ramet demography of C. humilis from 1993-1998 at the Hexenberg mountain, 300 m.a.s., 60 km east of Vienna, Austria. In total, the size of the ramet population increased during the study period but there was considerable variation in ramet population growth rate between years. Flowering ramets of C. humilis did not produce any offspring ramets, and at the study location, the seeds were either infected by smut of infested by insect larvae. The size of vegetative parent ramets positively correlated to both number and size of offspring ramets, i.e. larger parent ramets produced both more and larger offspring ramets.<br/><br>
<br/><br>
The ramet population growth rate was higher in the periphery of rings than in the interior, mainly due to the ramets being larger in the periphery. Because of this, of the ramet population size in the periphery of rings increased, whereas the ramet population size in the interior decreased. However, the ramet density in the interior was lower than would be predicted from the population growth rate alone, and I conclude that the difference is due to the centrifugal dispersal of ramets. A simulation model showed that ramet populations with lower maximum population growth rate, or with more peripheral dispersal, formed rings, whereas populations with higher maximum growth rates or less peripheral dispersal formed filled circles. A size structured matrix model showed that although there was variance in the production of all size classes, both between years as well as between periphery and interior, it was only the variance in the production of larger ramets that was important for the variance in the asymptotic population growth rate.<br/><br>
<br/><br>
Compared to the surrounding vegetation, the cover of most other plants was reduced inside C. humilis rings. In addition, the soil under C. humilis rings contained more moisture, nitrogen and phosphorus than the surrounding soil. Hence, the reason behind the lower population growth rate in the interior of rings was neither competition from other plants, nor depletion of any of the soil resources measured.},
  author       = {Wikberg, Sofie},
  isbn         = {91-7105-170-8},
  keyword      = {ramet density,Plant ecology,Växtekologi,ramet population dynamics,aggregated ramets,intravaginal,phalanx type,LTRE,matrix model,fitness,dry grassland,hollow crown,fairy ring,central die back},
  language     = {eng},
  pages        = {117},
  publisher    = {Sofie Wikberg, Plant Ecology, Ecology building, SE-223 62 Lund, Sweden,},
  school       = {Lund University},
  title        = {Carex humilis - a caespitose clonal plant: ramet demography, ring formation, and community interactions},
  year         = {2002},
}