Influence of Soil Microorganisms on Plant Growth and Fitness

Most terrestrial plants benefit from symbiosis with soil microorganisms. Symbiotic bacteria and fungi have wide-ranging effects on host plants, including improved nutrition, disease resistance, and drought tolerance. Association with Arbuscular Mycorrhizal Fungi (AMF) can enhance growth and protect plants from environmental stressors while they share products of photosynthesis with the resident fungi. Scores of studies indicate that mycorrhizal plants are more resistant to drought stress than their non-mycorrhizal counterparts. Use of microbes as a plant and soil supplement in home gardens represents a sustainable alternative to resource-intensive inputs and may allow for reduced water use. I investigated the effects of commercially-available microbial products and a peat soil amendment on strawberry plants under water stress. In a greenhouse experiment, strawberry plants were grown across factorial treatments of two AMF mixtures, two types of soil, and two water treatments. Inoculated strawberry plants had greater total dry weight biomass and leaf surface area than un-inoculated plants but showed no increases in reproductive tissues. Plants grown in peat-amended soil had improved growth in all measures except number of fruits and flowers. This data shows that modification of urban and suburban soil with peat and soil microorganisms can improve plant biomass. Despite a large body of literature that describes the effects of mycorrhizal colonization on plant resistance to water deficit, reviews of these works are only in narrative form and it is therefore difficult to quantify the magnitude of the effect. In a meta-analysis, we examined the effect of mycorrhizal colonization on growth and yield of plants exposed to water-deficit stress. We found that, in terms of biomass measurements, mycorrhizal plants are more resistant to water stress compared to non-mycorrhizal plants. When variables such as habit, lifecycle, or water stress level are considered, differences in mycorrhizal effect on growth between variables are observed. For example, while growth of both annual and perennial plants is improved by symbiosis, perennials respond more favorably to colonization than annuals. Overall, meta-analysis reveals a quantifiable corroboration of the commonly held view that mycorrhizal symbiosis improves plant\u27s resistance to water-deficit conditions. Efforts to restore native vegetation may benefit from treatment of native seeds and plants with AMF. Invasive plants can alter ecosystems by out-competing native species or changing the physicochemical properties of the local environment. Tamarisk (Tamarix spp.), a shrubby tree native to the Europe, Asia, and Africa, has now invaded 1.6 million acres of land in the western United States. Tamarisk exudes salt from its leaves that accumulates in surrounding soils and can affect the growth of native plant species. Here we examined the effect of AMF on the growth of an array of restoration species native to riparian areas of the southwest US under varied water and salinity regimes. AMF affected only one plant species with regard to root biomass and root:shoot ratio. Infection rates of inoculated plants varied from 0-61% and were limited by high salinity. We also found that salinity and water have strong effects on several native species, and that biomass decreases with increasing salinity or decreasing water