Date of Award

9-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Food Science

First Advisor

Dr. Elke Neumann

Second Advisor

Dr Firas Abu Elsamen

Third Advisor

Dr. Khaled Abbas El Tarabily

Abstract

Sudan grass (Sorghum x drummondii) is commonly grown for the production of animal fodder in the UAE. Cyperus conglomeratus (locally termed 'Thenda') is a sedge native to the UAE, and one of the very few plants that colonize soils of shifting desert dunes. The native plant is grazed by camels, and may thus have a potential for animal feed production. While Sudan grass is a mycotrophic plant that normally lives in symbiosis with arbuscular mycorrhizal fungi for facilitation of nutrient uptake, C. conglomeratus is a non-host to these root symbionts. In the deseli sedges rhizosheaths comprising of dense coats of root hairs and entangled soil particles seem to constitute an alternative strategy to support nutrient acquisition. One objective of this study was to compare nutrient uptake from soils of the UAE between Sudan grass and C. conglomeratus. Another aim was to investigate how removal of biomass and presence of soil salinity, alone or in combination, would affect the development and functioning of arbuscular mycorrhizal symbioses in Sudan grass grown on a sandy soil of the UAE. In a field experiment, Sudan grass and C. conglomeratus were either sole cropped or intercropped under two different irrigation regimes. After 7 months of cultivation, C. conglomeratus plants had produced more biomass, and had taken up larger quantities of nutritional elements compared with Sudan grass, even though these plants had received smaller amounts of fertilizers. Neither Sudan grass nor C. conglomeratus growth differed depending on whether plants were sole- or intercropped. This may suggest that the two plant species under investigation utilized different pools of nutritional elements, and thus competed only little for nutrient uptake. There was no effect of the water supply level on the growth of intercropped or sole cropped plants, possibly because the water supply level was in a sufficient range even for the plots of the lower water supply treatment. Results of a pot experiment where Sudan grass and C. conglomeratus were grown with approximately half of their root systems sharing the same soil volume, confirm the hypothesis that the two plant species under investigation do not compete for the same pools of phosphate (P). However, C. conglomeratus growth and nutrient uptake was negatively affected by the presence of a mycorrhiza fungal colonized root system. This confirms the results of the previous pot experiments that reported a direct negative effect of mycorrhizal root systems on the growth of the neighboring non-hosts. The majority of agricultural soils in the UAE are prone to salinization. It was hypothesized that on saline soil, arbuscular mycorrhiza fungal root colonization and plant mechanisms of adaptation to a saline environment would compete for photoassimilates. Such competitive effects would aggravate upon removal of photosynthetic tissues, and lead to a decline in the development and functioning of mycorrhizae. The null or alternative hypothesis, results indicated that neither salinity nor severe leaf pruning, alone or in combination, had an effect on the relative contribution of arbuscular mycorrhiza fungal symbiosis to plant growth and nutrient uptake. There was also no effect of leaf removal or salinity on the extent by which roots were colonized by endomycorrhizal fungi at the time of harvest. These results suggest that contributions of arbuscular mycorrhiza fungal root colonization to plant performance are relatively robust, and may persist under a wide range of environmental conditions and agricultural practices. Future studies should further shed light into mechanisms by which C. conglomeratus mobilizes nutritional elements. As the plant seems to have a great potential to increase nutrient utilization efficiency in agricultural systems of the UAE, its value for animal feed production should be further assessed. Given the superiority of C. conglomeratus over Sudan grass in terms of growth and nutrient uptake, it seems unlikely that introduced mycotrophic grasses have the potential to outcompete native dune sedges when released into UAE plant ecosystems.

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