Emery, Neil R.J.

Abstract

Early Responses of Understory Vegetation After One Year of Above Canopy Nitrogen Additions in a Jack Pine Stand in Northern Alberta

Nicole Melong

Nitrogen (N) emissions are expected to increase in western Canada due to oil and gas extraction operations. An increase in N exposure could potentially impact the surrounding boreal forest, which has adapted and thrived under traditionally low N deposition. The majority of N addition studies on forest ecosystems apply N to the forest floor and often exclude the important interaction of the tree canopy. This research consisted of aerial NH₄NO₃ spray applications (5, 10, 15, 20, 25 kg N ha-1yr-1) by helicopter to a jack pine (Pinus banksiana Lamb.) stand in the Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada. The main objective was to assess the impacts of elevated N after one year of treatment on the chemistry of understory vegetation, which included vascular plants, terricolous lichens, epiphytic lichens and a terricolous moss species. Changes in vegetation chemistry are expected to be early signs of stress and possible N saturation. Increased N availability is also thought to decrease plant secondary compound production because of a tradeoff that exists between growth and plant defense compounds when resources become available. Approximately 60% of applied N reached the ground vegetation in throughfall (TF) and stemflow (SF). Nitrate was the dominant form of N in TF in all treated plots and organic N (ON) was the dominant form of N in SF in all plots. The terricolous non-vascular species were the only understory vegetation that responded to the N treatments as N concentration increased with increased treatment. Foliar chemistry of the measured epiphytic lichens, vascular species, and jack pine was unaffected by the N treatments. Based on biomass measurements and N concentration increases, the non-vascular terricolous species appear to be assimilating the majority of TF N after one year. Vegetation from the high treatment plot (25 kg N ha-1yr-1) was compared to a jack pine forest receiving ambient high levels of N (21 kg N ha-1yr-1) due to its proximity to Syncrude mining activities. Nitrogen concentrations in plant tissues did not differ between the two sites; however, other elements and compounds differed significantly (Ca, Mg, Al, Fe). After one year of experimental N application, there were no environmental impacts consistent with the original N saturation hypothesis.

Author Keywords: Athabasca Oil Sands Region, Canopy Interactions, Jack Pine, Nitrogen, Secondary Chemistry, Understory Vegetation

Wild lupine (Lupinus perennis) restoration efforts seek to increase and connect populations, using seeds, to facilitate the recovery of endangered butterflys in Ontario. This study observed plant growth and phytohormone levels of L. albus, L. polyphyllus, and L. perennis through stages of seed development, each with varying strategies in growth and reproductive investment. L. polyphyllus is similar to L. perennis in morphology, acting as similar comparable with L. albus, a well-studied annual, as an outgroup comparator.

Wild lupines showed a lack of sexual reproductive effort as they did not put as much effort into above ground growth, and few in the population reproduces. They also showed cis-zeatin, a weaker cytokinin, throughout development and had higher amounts of abscisic acid at the end of seed maturity, impacting their ability to develop and germinate. These factors contribute to why wild lupines are difficult to restore using seeds, limiting expansion and challenging restoration.

Author Keywords: L. albus, L. perennis, L. polyphyllus, plant physiology, seed development, Wild blue lupine