| Summary: | Arbuscular mycorrhizal fungi form a root symbiosis with most plants and are known to benefit plants in a variety of ways. These organisms could be valuable in agricultural settings, leading to increased crop production and quality. For instance, the economically important Vitis vinifera is a highly mycorrhizal plant, dependent on the fungi for tolerating harsh growing conditions. Deficit irrigation is a viticultural practice that enables V. vinifera to be grown in arid climates where water resources are scarce, but how this management practice affects soil communities is not understood. There are three parts to this thesis. In the first experiment, I studied the abundance of different soil organisms to determine if irrigation frequency affects soil communities in general. The two frequencies of irrigation resulted in soil moisture levels that were either constant or fluctuated in a three-day cycle. I found that the biomass of fungi increased with fluctuating moisture, but in general the animal groups were most abundant in constantly moist soils. Secondly, I focused solely on the response of AM fungal communities. These did not respond to irrigation frequency. Instead, results of this experiment indicated there was an environmental effect as the fungal communities differed between the blocks. Both plant physiology and soil chemistry were identified as contributing to observed variation. Arbuscular colonization increased in the fluctuating soil moisture treatment compared with constant soil moisture, indicating a possible functional change in AM fungi due to irrigation frequency. In the final experiment I determined whether grapevines had distinct AM fungal communities compared to plants in co-occurring communities in the adjacent interrows. I found support for my prediction that the vinerow and interrow plant communities supported different AM fungal communities. Overall, this thesis indicates that management practices do affect soil communities, either in abundance, composition, or function. This could be due to changes in soil moisture, chemistry, or indirectly through changes in plant eco-physiology. It also provides
reasoning that more research is needed to enhance our understanding how AM fungal communities function in this agricultural setting.
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