1:00 pm - 2:00 pm
Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Deyu Mu. This seminar is open to the general public to attend via Zoom.
Thesis Topic: Selected Aspects of Plant Responses to Elevated pH, Salinity and Drought: Implications for Oil Sands Revegetation
Seminar Abstract: Elevated salinity, high pH, and drought are among the most challenging environmental factors affecting the growth and survival of plants in oil sands reclamation areas. In my thesis research, I focused on the selected aspects of these environmental stresses to better understand their potential impacts on plants. Three research studies were carried out as part of this thesis project.
In Study 1, I examined the processes of salt and water redistribution as well as physiological responses of trembling aspen (Populus tremuloides) plants subjected to heterogeneous distribution of NaCl in soil and soil water gradients. A vertical split-root growth setup was used to study the effects of soil salinity and water content gradients on plants under controlled-environment conditions. Trembling aspen seedlings were first subjected to drought treatment and then, 30 and 60 mM NaCl was applied to the lower part of the root system. I found that plant roots could transport water from deeper, moister, parts of the soil into the upper, drier, areas through the process known as the hydraulic lift. The water released to the dry soil through hydraulic lift increased the soil water content by about 13%. The salinity and drought caused decreases in net photosynthetic rates, transpiration rates, chlorophyll concentrations, and stem water potentials. Moreover, Na+ accumulated in the lower part of the root system and no detectable Na+ was released with hydraulically lifted water to the soil. It was concluded that the trembling aspen could supply water from the deeper soil layers with elevated salinity without contributing to salt redistribition in the soil. This process could also benefit neighbouring shallow-rooted plants in reclamation areas during the periods of drought.
In Study 2, I focused on the responses of sweet yellow clover (Agropyrum trachycaulum) and slender wheatgrass (Melilotus officinalis) to NaCl when their roots were exposed to high pH in the lower soil layer. A vertical split-root setup was used to induce the salinity and pH stress in the lower soil layer in a controlled-environment study. The growth of slender wheatgrass was sharply inhibited when only 10% of the root system was exposed to NaCl and (or) high pH, but it was relatively less affected in yellow sweet clover. The NaCl and high pH treatments triggered a series of different physiological responses and lowered leaf photosynthetic rates, decreased transpiration rates, and reduced stem water potentials, which contributed to growth reductions when only a relatively small part of the root system was exposed to NaCl and (or) high pH. Compared with high pH, NaCl was the main factor responsible for the decreased root distribution in slender wheatgrass. However, root growth in sweet yellow clover was stimulated by high (7.7-8.3) soil pH. The combined NaCl and pH were more harmful to wheatgrass and clover plants than the NaCl and pH stresses alone. More importantly, in wheatgrass, salt stress inhibited root distribution in the deeper soil profile with elevated NaCl level, while, in sweet yellow clover, high pH stimulated root distribution in the deeper high pH soil layer.
In Study 3, I investigated the diversity of ericoid mycorrhizal (ERM) fungi in the roots of velvetleaf blueberry (Vaccinium myrtilloides) seedlings from the northeastern Alberta, and their role in drought resistance of upland and lowland populations. The ERM fungi enhanced the growth and survival of plants subjected to drought stress and increased net photosynthetic rates, transpiration rates and shoot water potentials. Of the examined ericoid mycorrhizal fungi, Pezicula ericae was the most effective in enhancing growth and physiological parameters of plants. I concluded that inoculation of velvetleaf blueberries plants with Pezicula ericae prior to planting could be an effective method to improve the establishment and growth of velvetleaf blueberry in oil sands reclamation areas and other sites exposed to harsh environmental conditions.