Nathan Lauer | ALES Graduate Seminar

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 Nathan Lauer. This seminar is open to the general public to attend.
Thesis Topic: Effects of Elevated Root Zone pH and NaCl on the Stress Response and Recovery of Selected Boreal Forest Tree Seedlings

PhD with Dr. Janusz Zwiazek.

Seminar Abstract:

Surface mining for bitumen in the Athabasca oil sands region of northern Alberta involves razing all vegetation and soil from native boreal forest land. Reclamation is challenging because the extraction process leaves soils in some areas with high pH, salinity, and Na levels that are un-naturally high. Furthermore, soil Na levels are heterogeneous and transient in the soil. In my first thesis study, I subjected trembling aspen (Populus tremuloides), green alder (Alnus crispa), tamarack (Larix laricina), and white spruce (Picea glauca) to three levels of pH (5, 7, 9) and three levels of NaCl treatment (0, 30, 60 mM) in a factorial design for a total of 9 treatments in liquid culture for 50 days. Trembling aspen exhibited tolerance at pH 5 & 7 with 30 mM NaCl. but showed significant decreases in total dry weight, chlorophyll concentration, photosynthesis, and transpirationhigh mortality at pH 5 & 7 60 mM NaCl and all pH 9 treatments. Green alder was sensitive to elevated root zone pH and NaCl where moderate increases caused significant physiological decline but high levels of root zone pH and NaCl caused 100% mortality. Tamarack exhibited declines in total dry weight, chlorophyll concentration, photosynthesis, and transpiration as root zone pH and NaCl increased, but very little mortality. White spruce showed no mortality or changes in total dry weight from elevated root zone pH and NaCl; however, elevated NaCl caused significant declines in photosynthesis and transpiration rates. All species showed decreases in foliar nitrogen, total dry weight, chlorophyll concentrations, net photosynthesis, and transpiration rates as a result of increased stress. In the second study, supplementation with 4x N caused a partial recovery of net photosynthesis and transpiration rates in trembling aspen exposed to elevated root zone NaCl but had no effect on seedlings exposed to elevated root zone pH. White spruce seedlings exposed to elevated root zone pH and NaCl exhibited decreases in Pn. Supplementation with 4x N had no effects on Pn for seedlings exposed to elevated root zone NaCl but caused further declines in Pn for seedlings exposed to elevated root zone pH. In the third study, I investigated the processes of recovery from NaCl stress by subjecting trembling aspen, tamarack, and white spruce seedlings grown in soil to 0, 50, or 100 mM NaCl for 60 days and then allowed to recover from stress for another 60 days. Most seedlings treated with 50 mM NaCl showed a return to non-stressed levels of total dry weight, foliar chlorophyll concentration, photosynthesis, and transpiration rates after 30 days of recovery. Recovery after 60 days from 100 mM NaCl treatment varied between species. Some trembling aspen seedlings completely defoliated during the stress period and re-flushed during the recovery period. After 60 days of recovery, the new leaves exhibited higher levels of chlorophyll concentration, net photosynthesis, and transpiration rates compared to untreated controls. Following 60 days of recovery from 100 mM NaCl treatment, the dry weight, chlorophyll concentration, and net photosynthesis values in tamarack were lower compared with control seedlings, whereas white spruce showed no changes in any of the measured parameters. In the fourth study, NaCl stress was applied to trembling aspen, tamarack, and white spruce seedlings that were first subjected to non-lethal NaCl stress followed by overwintering. Plants of all three species exhibited some form of salt injury from NaCl treatment in the first year. Aspen and tamarack seedlings treated with 50 mM NaCl in year one exhibited lower total dry weights compared to non-treated control in year one. Both species exhibited elevated foliar K in response to NaCl treatment in year two. Tamarack seedlings exposed to NaCl in year one exhibited increases in photosynthesis and water use efficiency when exposed to NaCl in year two compared to control seedlings that were not treated with NaCl in year one. For white spruce, NaCl treatment in year two had virtually no effect on total dry weight, chlorophyll concentration, photosynthesis, or transpiration of seedlings. The information generated from this work can be used to improve land reclamation efforts in northern Alberta.