The effect of arbuscular mycorrhizal colonisation on the C economy, growth and nutrition of young grapevines

[摘要] ENGLISH ABSTRACT: Arbuscular mycorrhizal (AM) C-costs in grapevines were investigated. Since bothdormant vines and AM colonisation rely on stored C for initial growth, AM colonisationcosts would therefore compete with plant growth for available C reserves. The aims ofthis study were to assess the host C economy during AM development and the subsequentC-costs of N and P uptake, as well as the effects of C costs on host growth. This wasevaluated in two separate experiments; one assessing the symbiotic influence on the Ccosts of fungal establishment and nutritional benefits, whilst the other one evaluated theeffects 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 photosyntheticC below ground to support the AM fungus. This however, does not take into account theeffect that stored C will have on the C economy of the plant and symbiosis. The role ofstored C becomes even more crucial when working with deciduous plants that rely onstored C for new growth at start of a growing season. It has been reported that stored C inAM plants is remobilized at the start of a growing season and then the C reserves arerefilled 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 plateauphase was reached, and the depleted reserves started to refill. Once established, the activesymbiosis 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, agreater part is used by AM respiration and a smaller part for P uptake. The C costs of theAM fungal phase of rapid development can be seen as negative to root growth and shootdevelopment. These negative effects may continue for a period of time, even during theplateau phase of fungal development. Once the AM symbiosis is fully established, thehost 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 hostdevelopment, but the symbionts revert to a beneficial partnership once it is fullyestablished.

[发布机构] Stellenbosch University