The effect of vine root age and ground cover on arbuscular mycorrhizal fungi

by | Apr 26, 2019 | South Africa Wine Scan

The aim of this study was to determine how the symbioses between arbuscular mycorrhizal (AM) fungi and vines change as absorptive roots are produced and die-off over a season. Additionally, researchers also investigated whether the microbial communities supported by different ground covers, affected the symbioses.

AM fungi have a mutually beneficial relationship with plants where it colonises plant roots. The AM fungi provides nutritional and plant protective benefits to its host in turn for sugars from photosynthesis. In perennial woody hosts, the absorptive roots on which these fungi grow, changes over the course of a season as they are produced and eventually become less functional and senesce towards the end of the season. This could affect the symbioses between plant and fungi. Very little research has been done on fine roots during the process of senescence.

Grapevine rootstocks (101-14 Mgt) were grown in soil inoculum collected from a field trial, in a greenhouse. The groundcover treatments represented a range of vineyard practices:

    • Exotic grass mix with sprinkler irrigation (EG),
    • Exotic grass mix plus legumes with occasional sprinkler irrigation (EGL),
    • Native grass mix with no sprinkler irrigation (NG) and
    • Native grass mix plus forbs with occasional sprinkler irrigation (NGF).
  • The different combinations of vegetation and irrigation regimes could induce different soil environments and in turn lead to the establishment of different microbial communities.
  • Five replicates of each treatment were done and vines were harvested after eight months.
  • Root systems were sub-sampled – young (light colour) and old roots (dark colour) as well as first and second order roots, were separated.
  • Researchers determined the AM fungi colonisation, total % root length colonised, proportion arbuscules, and proportion intra-radical storage organs (ISOs) produced by fungi. The AM fungal community composition was determined by DNA extraction and Illumina metabarcoding.

Total AM fungal colonisation was higher in older roots than younger roots – this is counter-intuitive as one would expect the fungal colonisation to become limited as the metabolic activity of the host decreases.

  • There was no difference in total colonisation between the different ground covers and no interaction between ground cover and root age.
  • Fungal structures varied between root ages- Arbuscules were more present in young roots while there were more vescicles/spore structures on older roots.
  • Fungal communities varied between different ground covers, but not between young and old roots within the same ground cover treatment.
  • Arbuscules were more frequently found in the NGF treatment than all other treatments. This could mean that no vegetation cover potentially also affects the symbiotic function between fungi and perennial crops.

The observations from this research indicate that aging roots may lead to changes in the functional behaviour of the AM fungi symbiosis. Further research is required to determine the mechanisms responsible for these shifts in AM functioning. A better understanding of these mechanisms can help growers improve their vineyard floor management practices to benefit optimally from the symbiotic relationship between AM fungi and vines.

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