Thesis (MSc)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Arbuscular mycorrhizal (AM) C-costs in grapevines were investigated. Since both
dormant vines and AM colonisation rely on stored C for initial growth, AM colonisation
costs would therefore compete with plant growth for available C reserves. The aims of
this study were to assess the host C economy during AM development and the subsequent
C-costs of N and P uptake, as well as the effects of C costs on host growth. This was
evaluated in two separate experiments; one assessing the symbiotic influence on the C
costs of fungal establishment and nutritional benefits, whilst the other one evaluated the
effects of the symbiosis on host growth and nutrient productivities.
This study has shown that AM acts as a C sink, competing with the host for available C.
Past work on the AM sink effect has focused mainly on the movement of photosynthetic
C below ground to support the AM fungus. This however, does not take into account the
effect that stored C will have on the C economy of the plant and symbiosis. The role of
stored C becomes even more crucial when working with deciduous plants that rely on
stored C for new growth at start of a growing season. It has been reported that stored C in
AM plants is remobilized at the start of a growing season and then the C reserves are
refilled towards the end of the season, when the plants enter dormancy.
The initial costs of AM fungal colonisation were borne by the above-ground C reserves,
at the expense of new growth in host plants. These costs were offset once the plateau
phase was reached, and the depleted reserves started to refill. Once established, the active
symbiosis imposed a considerable below ground C sink on host reserves. In spite of these costs, the improved P nutrition of AM roots was achieved with a more efficient C-use.
This concurs with other findings, that of the belowground C allocated to AM roots, a
greater part is used by AM respiration and a smaller part for P uptake. The C costs of the
AM fungal phase of rapid development can be seen as negative to root growth and shoot
development. These negative effects may continue for a period of time, even during the
plateau phase of fungal development. Once the AM symbiosis is fully established, the
host growth and development is then improved to a greater extent than in non-AM plants.
From this study it can be concluded that AM growth directly competes with host
development, but the symbionts revert to a beneficial partnership once it is fully
established. / AFRIKAANSE OPSOMMING: Die C koste van arbuskulêre mikorisa (AM) in wingerdstokke is ondersoek. Beide
rustende wingerdstokke en AM koloniseering is afhanklik van gestoorde C vir
aanvanklike groei. AM kolonisering sou dus met plantgroei kompeteer vir
beskikbare C reserwes. Die doelstellings van hierdie ondersoek was eerstens om
die C-ekonomie van die gasheer tydens AM ontwikkeling en die gevolglike Ckostes
van N en P opname te bepaal en tweedens sowel as die invloed van C
veranderings op gasheergroei vas te stel. Hierdie is in twee afsonderlike
eksperimente ondersoek: een om die simbiotiese invloed op die C-kostes van
swam-vestiging en voedingsvoordele te bepaal, terwyl die ander die uitwerking
van simbiose op gasheergroei en voedings doeltreffenheid evalueer het.
Die ondersoek het bewys dat AM, as ‘n C-sink, kompeteer met die gasheer vir
beskikbare C. Vorige werk oor die AM sink-effek het hoofsaaklik gefokus op die
afwaartse beweging van fotosintetiese C om die AM-swam ondergronds te
ondersteun. Die werk neem egter nie in ag wat die effek van gestoorde C op die
C-ekonomie van die plant en simbiose sou wees nie. Die rol van gestoorde C is
selfs nog meer belangrik wanneer met bladwisselende plante gewerk word, omdat
sulke plante op gestoorde-C vir nuwe groei aan die begin van die groeiseisoen
staatmaak. Dit is op rekord dat gestoorde C in bladwisselende plante by aanvang
van die groeiseisoen gemobiliseer word en dat die C-reserwes teen die einde van
die seisoen wanneer die plante rustyd nader, weer hervul word. Die aanvanklike kostes van AM kolonisering is deur die bogronds C-reserwes, ten
koste van nuwe groei van die gasheerplante, gedra. Hierdie kostes herstel sodra
die plato-fase bereik is, waar die uitgeputte reserwes begin hervul het.
As die aktiewe simbiose eers gevestig is, sal dit as ‘n onderg P-voeding van AM
wortels verkry wordrondse C-sink vir gasheer optree.Hierdie C verbruik word
egter as doeltreffend beskou aangesien verbeterde. Dit is bekend dat ‘n groter deel
van die ondergrondse C geallokeer word aan AM-wortels, deur middel van AM
respirasie en P-opname. Die C-kostes van die AM-fungus tydens die fase van
vinnige ontwikkeling, kan ‘n negatiewe effek op wortel- en lootontwikkeling hê.
Hierdie negatiewe uitwerking kan vir ‘n tydperk voortdeur, selfs gedurende die
plato-fase van fungi-ontwikkeling. Sodra die AM-simbiose volledig gevestig is,
word gasheergroei en ontwikkeling tot ‘n groter mate verbeter as in plante sonder
AM-fungi. Hierdie ondersoek het bewys dat AM groei direk met
gasheerontwikkeling kompeteer, maar dat die simbiose ‘n voordelige vennootskap
vorm sodra dit volledig gevestig is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16393 |
| Date | 04 1900 |
| Creators | Mortimer, Peter Edward |
| Contributors | Valentine, A.J., Archer, E., University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 86 leaves : ill. |
| Rights | University of Stellenbosch |
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