The effect of vesicular-arbuscular mycorrhiza on the growth of two indigenous grass species Themeda triandra and Trachypogon spicatus grown on coalmine spoil topsoil.
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Date
1997
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Abstract
The main project was an assessment of the effect that colonization by five different
Vesicular-arbuscular mycorrhiza (VAM) cultures have on the growth of the indigenous-grasses
Themeda triandra and Trachypogon spicatus, when grown on coalmine topsoil.
With unamended topsoil, VAM showed the ability to significantly increase the growth of
the grasses compared to non-VAM control plants. The amount of effect varied with the VAM
inoculum culture type, with a VAM culture originally from the Cape Flats being the most
effective. In a second trial, soil fertilized with nitrogen, potassium and low concentrations of
phosphate (P) was used. Again VAM displayed the ability to improve grass plant growth. The
increase in P caused the Large spore inoculum to become the most effective. This indicated that
different VAM cultures are inhibited to different degrees by an increase in phosphate fertilization.
The low level of VAM infection, in both trials, seemed to preclude most of the VAM associated nutrient uptake control.
Varying reports have been published on the effect of fertilization on VAM infection and
colonization. In an attempt to further elucidate the role of fertilizer in VAM inhibition,
rhizosphere soil from a long term fertility trial near Witbank, S.A. was sampled. Amcoal
environmental services fertilized forty-two plots with varying concentrations of nitrogen,
potassium, phosphate and lime to assess the growth of a variety of grasses. The trial had been
maintained for ten years before sampling was completed for this project. Samples from each plot
were taken from the rhizosphere soil of the most prominent grass (Digitaria eriantha). VAM
spores were extracted from all the samples and five different types of spores were identified and
counted for each sample. By comparing spore counts from each plot, the effect that the fertilizer
regime had on the VAM on that plot could be assessed.
Variation in the concentrations of nitrogen (N) and potassium had no significant effect on
VAM colonization. Very low concentrations of N could not be assessed as all plots had been
initially top dressed with nitrogen fertilizer. Phosphate (P) fertilizer concentration had a marked
effect on spore concentrations. There was a significant increase in spore concentration as P levels
were increased from zero P fertilization to 80kgs P/ha. Further increase in P to ≥ 60kgs P/ha
resulted in a significant decrease in spore concentrations. From this it would appear that a low
level of soil P is needed to give maximum VAM colonization and further increase in soil P causes
VAM inhibition. Lime ameliorated the VAM inhibition caused by high concentrations of P.
Increase in P caused spore concentrations of low abundance propagules (LAP) too decreased
more rapidly than high abundance propagules (HAP). In high P soils VAM with LAP would
eventually be eliminated from the system resulting in a decrease in VAM diversity.
A project was attempted to use the recently developed Randomly Amplified Polymorphic
DNA in conjunction with the Polymerase Chain Reaction (RAPD PCR) techniques to identify different VAM families. The technique causes the amplification of segments of DNA which can
be visualized by gel electrophoresis and staining. Band patterns formed can be related to the VAM
of origin and hence used in identification of that VAM. An attempt was made to amplify DNA
from a single spore in this manner which would, in conjunction with morphological observations,
make identification of VAM easier and more accurate. Problems with either releasing the DNA
from the spores, or substances in the spore inhibiting the PCR reaction made obtaining band
patterns difficult. After many PCR attempts, varying extraction methods and PCR conditions, no repeatable results could be obtained and work on this project was discontinued.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1997.
Keywords
Themeda triandra., Vesicular-arbuscular mycorrhizas., Plant-fungus relationships., Revegetation., Soil stabilization., Andropogoneae., Theses--Botany.