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Phenology and Source-Sink Dynamics of Carbohydrates in Relation to Management of Perennial Weeds: Cirsium arvense (L.) Scop and Tussilago farfara L

Nkurunziza, Libère (2010) Phenology and Source-Sink Dynamics of Carbohydrates in Relation to Management of Perennial Weeds: Cirsium arvense (L.) Scop and Tussilago farfara L. PhD thesis, University of Copenhagen, Agriculture and Ecology. .

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Summary

Perennial weed infestations are putting severe constraints on organic and conventional farming. Cirsium arvense (L.) Scop. and Tussilago farfara L. have high vegetative regeneration capacity from underground organs. These organs can reach deep soil layers, which prevent them from being easily uprooted. In our research, we primarily addressed the importance of the source-sink dynamics of carbohydrates at different phenological stages and related results to eventual management strategies.
Experimental work was carried out under greenhouse and/or growth chamber conditions. The first study spanned from roots/rhizomes planting to shoot establishment. The second study began after establishment and included the rosette to the flowering stages. The third study was about the storage of carbohydrates in the underground parts. And finally, a fourth study aimed at unraveling the effect of drought on new shoots of these perennials.
To determine the depletion of carbohydrate storage associated with shoot development, we destructively sampled roots of C. arvense and rhizomes of T. farfara from which nonstructural carbohydrates were measured using HPLC. We found that fructan was highest at the planting time, but it decreased by releasing fructose as shooting growth progressed. However, before the released fructose was depleted, carbohydrates were reloaded by photo-assimilates. This was demonstrated by 14C labelling to track the commencement of the basipetal translocation of photo-assimilates. The conclusion was that appreciable basipetal translocation starts at 6 and 8 fully developed leaves for T. farfara and C. arvense, respectively. This falls between 500 and 600 degree days or around 21 to 23 days after emergence under our experimental conditions.
After shoot establishment we measured the maximum net photosynthesis of disturbed and undisturbed clones over a period of 3 weeks, from the rosette stage to the flowering stage. Maximum net photosynthesis decreased over time, but there were no differences between disturbed and undisturbed clones. Our conclusion was that the physiological integration found in other clonal species seems to be absent in C. arvense and T. farfara, suggesting that shoots are autonomous.
To understand carbohydrate storage, juvenile and mature plants were grown at different temperatures. The results showed that the polymerization of fructans was associated with low temperatures for C. arvense but not for T. farfara. Polymerization of fructans in roots/rhizomes was not significantly different between juvenile and mature plants. Only the dry weight of shoots from juvenile plants reflected the differences found in carbohydrate content. The conclusion is that the continuous growth of underground propagules facilitates the survival of these two perennials and thus complicates their control.
Gradient soil water content during the establishment period of shoots of C. arvense, T. farfara and Elytrigia repens showed that E. repens is more tolerant to water stress than broadleaf T. farfara and C. arvense. T. farfara is more prone to water stress compared to C. arvense if we consider the relationship between the soil water content and shoot biomass. This susceptibility might give an opportunity window for managing broadleaf perennial weeds.

Summary translation

Flerårige ukrudt medfører alvorlige begrænsninger for planteproduktionen i økologisk og konventionelt landbrug. Cirsium arvense (L.) Scop og Tussilago farfara L. har høj vegetative regenereringsevne fra de underjordiske organer. Disse organer kan nå dybe jordlag, der forhindrer dem i at blive trukket op og udtørret på jordoverfladen. I vores forskning undersøgte vi primært betydningen af ”source-sink” dynamik for kulhydrater i forskellige fænologiske faser og relaterede resultaterne til mulige bekæmpelsesstrategier. Det eksperimentelle arbejde blev udført i drivhus, og / eller i vækstkammer.
Den første undersøgelse spændte fra plantning af rødder/rhizomer til skudetablering. Den anden undersøgelse blev indledt efter etableringen af rosetstadiet og indtil blomstring. Den tredje undersøgelse drejede sig om oplagring af kulhydrater i de underjordiske dele, og den fjerde undersøgelse studerede virkningen af tørke på nye skud af disse flerårige arter.
For at bestemme nedbrydningen af kulhydrat i forbindelse med dannelse af nye skud, brugte vi en destruktiv prøveudtagning af rødder fra C. arvense og jordstængler fra T. farfara og målte opløselige kulhydrater ved hjælp af HPLC. Fruktaner var højest ved plantningen, men faldt ved at frigive fruktose under skuddannelsen. Men før den frigivne fruktose var udtømt, begyndte oplagringen igen af fotosyntesens kulhydrater. Dette blev påvist med 14C mærkning. Konklusionen var, at basipetal transport begynder ved 6 og 8 fuldt udviklet blade for henholdsvis T. farfara og C. arvense. Dette falder mellem 500 og 600 graddage eller omkring 21 til 23 dage efter ny skuddannelse.
Efter etablering målte vi den maksimale nettofotosyntese af forstyrret og uforstyrret kloner over en periode på 3 uger, fra roset- til blomstringsstadiet. Fotosyntesens nettoeffekt faldt over tid, men der var ingen forskel mellem forstyrret og uforstyrret kloner. Med andre ord den fysiologiske integration som findes i andre flerårige arter med underjordiske vegetative organer synes at være fraværende i C. arvense og T. farfara, og det tyder på, at skuddene er autonome.
Unge og ældre vegetative planter dyrket ved forskellige temperaturer viste, at størrelsen af fruktanreserven var forbundet med lave temperaturer for C. arvense, men ikke for T. farfara. Størrelserne af fruktankoncentrationen i rødder/rhizomer var ikke signifikant forskellig mellem unge og ældre planter. Kun tørvægten af unge planter afspejlede forskelle i kulhydratindholdet. Konklusionen er, at den fortsatte vækst af rødder og/eller rhizomer letter overlevelse af disse to flerårige arter og dermed komplicerer deres bekæmpelse.
Gradienter i jordens vandindhold under etableringsperioden af C. arvense, T. farfara og Elytrigia repens viste, at E. repens er mere tolerant overfor vandstress end de bredbladede T. farfara og C. arvense. T. farfara er mere tilbøjelige til at lide af vandstress i forhold til C. arvense, hvis vi ser på forholdet mellem jordens vandindhold og biomasseproduktion. Denne følsomhed kan give en mulighed for at rammer ukrudtet når det er mest tørkestresset.

EPrint Type:Thesis
Subjects: Farming Systems
Food systems
Research affiliation: Denmark > DARCOF III (2005-2010) > WEEDS - Control of weeds in organic cropping
Deposited By: Nkurunziza, Libère
ID Code:18240
Deposited On:01 Feb 2011 14:20
Last Modified:23 May 2013 08:49
Document Language:English
Status:Published

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