The effect of arbuscular mycorrhizal fungi on water relations of sorghum (Sorghum bicolor L. cv.Tegemeo)
In this thesis, the hypothesis was tested that AMF (Glomus mosseae, Scutellospora calospora and Gigaspora margarita), thought to differ functionally, will produce different effects on water relations when inoculated onto sorghum. To overcome inherent differences between nonmycorrhizal (NM) and mycorrhizal (M) plants, a split-root system (SRS) was devised. In this approach, the plant root system was equally divided between two compartments one of which was subsequently inoculated with AMF, allowing NM and M roots on the same plant to be compared. Initially, water loss from NM and M (inoculated with G. mosseae) compartments of the SRS was measured. Roots in the M compartment had 73% of root length colonized (RLC) by G. mosseae. The water holding capacity (WHC) of the substrate was enhanced in the M compartment, and this was maintained through the drought period. G. mosseae increased root length (RL), number of root tips, root surface area and root volume. However, there was no difference in the rate of water loss between the M and NM sides of the SRS. The next experiment examined the possibility that different species of AMF might alter water loss in sorghum plants differently. Above ground, inoculation with S. calospora produced bigger plants than the other two isolates. Below ground, %RLC also differed between isolates. There was no significant difference in total RL (adding both sides) between plants, but there were differences in the number of root tips, root surface area, root volume and root branching degree. When NM and M compartments of the SRS for each AMF isolate were contrasted, roots colonized by S. calospora and G. margarita had greater RL, number of root tips and root surface area, whereas roots colonized by G. mosseae had more root tips and a different degree of branching. Once again, G. mosseae increased the WHC of the substrate, but G. margarita did so only at the last harvest. There was no effect of S. calospora on WHC. However, there were no significant differences in water loss either per LA (with one exception) or per RL between the NM and M sides of the SRS with any AMF isolate. This leads to the conclusion that while AMF affected the WHC of the substrate used in these experiments, they did not affect rates of transpirational water loss from that substrate.