On the ecology of varieties of Sonchus arvensis L. Pegtel, Dirk Michiel

On the ecology of varieties of Sonchus arvensis L.
Pegtel, Dirk Michiel
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Publication date:
1976
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Pegtel, D. M. (1976). On the ecology of varieties of Sonchus arvensis L. s.n.
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SUMMARY
The perennialsowthistle(SonchusarvensisL.) - a geophyticcomposite- is found
throughoutthe temperatureregionsof the world. From the middle of the 1gth
hasoccurredfrom the originalareaof distributionin Europeand
centurydispersal
Asia.
Western
In The Netherlands
two varietiescan be distinguished.
Both showdistinctdistribupatterns.
tion
The coastaltype, var.maritimus
G. F. W. Mey.,hasrelativelynarrow.
long and irregularlyindented,prickly leaveswith a waxy surface.This variety
occurspredominantlyon the outer coastaldunes.
Leaves
of the arabletype, var. arvensis,are mesophyticin appearance.
They are
shorterand broaderthan thoseof the coastaltype. The arabletype may be found
in a numberof different habitats,alwayson fertile soilsand principallyon arable
l a n dT
. h et w o v a r i e t i ehsa v et h e s a m ec h r o m o s o mneu m b e r , 2 n = 5 4 .
Proofthat the leaf morphologicaldifferencesbetweenthe two varietiesaregenetiwhen they are
callydeterminedis providedby the fact that theseremainunchanged
grownfrom achenes
underidenticalconditions.
This study aimsto find out by what mean(s)the varietiesareadaptedto their partiresponsible
for their distributionpatcularhabitatsand to trace the mechanisms
terns.
Previous
literatureindicatesthat coastalsanddunesare chemicallylessfertilethan
arableland. Chemicalanalysisof outer dune soil of the West Frisian lslandof
confirms that nitrogenand plant availablephosphatelevelsare
Schiermonnikoog
low. The questionthus arisesas to whetherand by what meanthe inadequateNfor the presence
and P- suppliesof the dunesis responsible
of the coastal,and the
of the arabletype.
absence
germiAchenes
of both varietiessown in the outer dune areaof Schiermonnikoog
137
natesuccessfully.
However,eventuallyall seedlings
of the arabletype die and only a
fractionof the coastaltype seedlings
survive.Thesesurvivalsshow a slow rate of
growth.Persisting
coastaltype plantsgrow from relativelylargeand heavyachenes.
Development
to floweringtakesabout 3 to 4 years.Desiccation
appearsto be the
ultimatecauseof seedlinq
death.
Seedlings
of the arabletype raisedunder favourableconditionsfail to establish
themselves
when plantedon the dune site of Schiermonnikoog.
On the other hand
many of the individualsof the coastaltype developinto floweringand achene
bearingplants.Dressings
of superphosphate
showno effectson the growthof either
the coastalor the arabletype. Applicationof nitrogenousfertilizermakeno differenceto the growth of the arabletype. When administeredto the coastaltype,
groMh improvesconsiderablyand developmentwas noticeablvaccelerated.
Combineddressings
of N- and P-fertilizers
resultin greatlystimulatedgrowthand developmentof both types to such an extent that their life-cyclecan be completed
duringthe yearof planting.
Whengrown on balancednutrient solutionswell suppliedwith mineralsthe dry
matterproductionper unit time provesto be largerfor the arabletype than for the
coastaltype, This higherrate growth of the arabletype is largelyexplainedby the
storageof total water soluble carbohydratesin thickened roots. The total dry
vveightof structuralmaterial,i.e.the dry matterof both rootsand shootsminusthe
v\rater
solublecarbohydrates.
is alsohigherin the arablethan in the coastaltype.
The coastaltype producesrelativelyfew thickenedroots. The ratio shoot: total
root dry weightis lower in the arabletype than in the coastaltype. The opposite
holdsfor the ratio shoot:thin root dry weight.The ability to generate
an extensive
fibrousroot systemappears
to be one reasonwhy the coastaltype can surviveon Nand P-deficient
dunesano.
Chemicalanalysisdemonstrates
the thickenedroots of the arabletype to be outstandingin their relativelyhigh content of organicnitrogenand possiblyorganic
phosphate
as well. Varietaldifferences
in mineralcontentsof other plant partshave
not beenascertained.
The higher Norg. and possibly Porg.contentsmentioned,allied to a largerdry
matterproductionof the arabletype, is indicativeof the comparativelyhigh nutrient demandsof this varietv.
On non-fertilized
coastaldune sandsthesedemandscannotbe met by the spatially
restrictedroot systemof this type. The limited nutrient suppliesof the dunesand
can be exploitedmore eff iciently by the root systemof the coastaltype, but even
for this varietythe N-supplies
are inadequate
for optimalgrowthand development.
138
Seedlings
of neithervarietyhavebeenfound on arableland.Despitethis, sowingof
both varietiesat the inlandexperimentalgardenof Harenshow goodgermination.
T h i s i n d i c a t etsh a t e s t a b l i s h m efnr to m a c h e n eiss p o s s i b l el f. l e f t u n d i s t u r b esde e d s l a n t st h a t f l o w e ra n d b e a ra c h e n eisn t h e
l i n g sg r o ww e l la n dd e v e l o pi n t o v i g o r o u p
secondyearaftersowingdue to the relativelylatedateof sowing.
grow well and developinto vigorousplantsthat flower
lf left undisturbedseedlings
in the secondyearaftersowing.
andbearachenes
vegetatively
from piecesof thickenedroot. PropaBothvarietiescan be propagated
gationfrom similarsizedroot fragmentsof the two types carriedout in spring
resultsin a much more vigorousshoot growth in the arabletype. This is probably
dueto the largeramountsof total watersolublecarbohydrates
found in the thickenedrootsof the arabletype. Perunit weightof storedtotal watersolublecarbohyfrom root buds is the samefor
drates.the shoot dry weightof plantsregenerated
both types.The rate of sproutingis lower in the autumn than in the spring.The
differences
seasonal
are more pronouncedfor the arabletype than for the coastal
type.The numberof budsper unit lengthof thickenedrootsshowsneithervarietal
differences
nor differences
dependingon season.
ystablished
F o l l o w i n gm e c h a n i c adle f o l i a t i o ni n s p r i n ga n d s u m m e ro f p r e v i o u s l e
plantsregrowthof the arabletype is more vigorousthan of the coastalone. This
in total amountsof storedwatersoluble
alsois thoughtto be due to the differences
carbohydrates
in the two varieties.After mid-summerregrowthafter defoliationis
no longerpossible
at the prevailingtemperatures.
The aboveresultsillustratethe relativelylow capacityof the coastaltype to overc o m em e c h a n i c adli s t u r b a n c essu c h a s w o u l d o c c u ro n a g r i c u l t u r al al n d .F u r t h e r more,previouslyestablished
coastaltype plantsdisappearcompletelyafter being
grownamongagriculturalcrops for three years.Neither the density and surface
coverage
of the crop plant. nor the speciesgrown (e.9.oatsor potatoes)are the
significant
factors.The arabletype is not eradicated
by the agriculturaloperations,
but its growthis diminishedby the competingcrop.
Differences
in the distributionpatternsof the two varietiesmust haveoriginatedin
habitat-adapted
selection.In the coastalsanddunesselectionfor:
(i) the extensiveroot systemthat is capableof exploitingthe soil nitrogenand
plantavailable
phosphatesupplymosteffectively;
( i i ) t h er e l a t i v e llyo w n i t r o g e nd e m a n d ;
{iii) the rateof growthand developmentkeepingpacewith the nitrogensupply;
139
(ivl the comparatively
smallrestrictionin the rateof shootgrowthfrom root buds
i n e a r l ys p r i n g .
On arablelandand on fertilesitesselectionfor:
(i) the rate of dry matter productionthat is efficient enoughto competewith
that of (cultivated)plants;
(ii) the more frequentformationof thickenedrootswith a relativelyhighcontent
carbohydrates;
of non-structural
(iii) the substantiallimitationduring low springtemperatures
of the rateatwhich
shootsgrow from root buds; thus preventingprematuresproutingas a safegrowingconditions;
guardagainstadverse
(iv) the easewith which, in spring and summer,regenerationfrom fragments
of thickenedrootstakesplaceand defoliatedplantsdevelopnew shoots.
betweenthe types might resultin hybrid populationsthat cannot
Cross-pollination
on the basisof leaf morphologyfrom populationsof the arable
be distinguished
type. Thesehybrids are also likely to resemblethe arabletype physiologically.
to provewhetheror not uncontrolledhybridizationoccurs.
Thereis no evidence
140