The influence of arbuscular mycorrhiza on the water relations of trees

• Main Author: Dunsiger, Zoe
• Published: University of Edinburgh 2001
• Subjects: 634.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649813

This study increases the body of knowledge on the drought response of plant-fungal associations. Hybrid black popular <i>Populus </i>x <i>canadensis</i>, a species commonly seen in shelter belts and small plantations, is tested on its drought response to mycorrhizal colonisation. It also suggests an alternative mechanism for the alteration of plant water relations by arbuscular mycorrhiza. The concept of chemical signalling compounds which control plant response to stress, including drought stress, is topical. This study aims to extend the concept of the plant-fungus symbiosis. The ability of the fungal hyphae to act as an integral part of the root system is tested in its contribution to signalling of drought stress to the host shoot. The response of mycorrhizal poplar to gradients in water availability was tested in two ways. First the effect of changing water availability over time, as drying and wetting cycles, was examined. Second, gradients in water availability across the root-fungal system were considered. The response of poplar to drought stress was tested when inoculated with one of four species of mycorrhizal fungi. These were <i>Glomus intraradices</i>, <i>Glomus mosseae</i>, <i>Gigaspora rosea </i>and <i>Gigaspora margarita</i>. There was no consistent improvement in plant response to drying. However there were variations in plant response over time, and with severity of drought conditions, particularly by plants colonised with <i>G. intraradices </i>and <i>Gi. rosea</i>. Changes in the host plant nutrient status were also found. The concept of hyphal to plant shoot signalling of drought was tested with poplar inoculated with <i>G. intraradices</i>, grown in a specially designed microcosm. Fungal hyphae were able to grow into a separate volume of soil from which plant roots were excluded. The soil water availability around plant roots and adjacent hyphae was altered independently. The plant response in terms of gas exchange was monitored under conditions of varying water availability in each section of the root-hyphal system. In general there were no consistent alterations in plant gas exchange with changing water availability. However during one experiment possible evidence for short-term hyphal signalling to host plants was noticed. This method is suggested as a new concept for further experimentation in plant-fungal water relations.