Climate Change and Canada's Forests
In addition to changing temperatures, which have already been observed in Canada, weather and climate patterns are also expected to shift. This means some regions, those in which drought has, historically, been rare, may begin to experience drought conditions at higher frequencies. Trees that have not adapted to these conditions may be unable to cope with the climatic shift and we may begin to see large-scale die-off. Additionally, forests used for timber harvest will need to adjust so that survival and growth rate of newly planted trees is not affected by uncertain future conditions.
In order to maintain these forests, which are a particularly important national resource, new management strategies must be devised to help forests adjust to increased occurrence of drought. One potential strategy is to seek out populations, within a particular species, that are more tolerant of drought conditions, without sacrificing efficient growth. By locating these populations we can begin using a drought-resistant seed stock in areas that are expected to fall victim to drought in the future. We are particularly interested in White Spruce (Picea glauca), which is an important species for the forestry sector in Alberta. We will be using seedlings from populations across the country, paired with long term growth trials, to examine the variability of drought tolerance.
In order to maintain these forests, which are a particularly important national resource, new management strategies must be devised to help forests adjust to increased occurrence of drought. One potential strategy is to seek out populations, within a particular species, that are more tolerant of drought conditions, without sacrificing efficient growth. By locating these populations we can begin using a drought-resistant seed stock in areas that are expected to fall victim to drought in the future. We are particularly interested in White Spruce (Picea glauca), which is an important species for the forestry sector in Alberta. We will be using seedlings from populations across the country, paired with long term growth trials, to examine the variability of drought tolerance.
Measuring Drought Stress
In order to measure drought stress from a physiological perspective we will be utilizing measurements of chlorophyll fluorescence in White Spruce needles. Chlorophyll fluorescence has been established as an accurate measurement of photosystem II efficiency, and will help us to identify the extent of the stress placed on seedlings (Maxwell 2000).
When light hits the surface of a leaf, and the chlorophyll molecules within it, three things can happen:
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Figure 1. Illustration showing the potential pathways that solar energy may take in a leaf.
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Drought affects chlorophyll fluorescence through a chain of physiological events that eventually lead to a decrease in oxidation and electron transfer rates (Goltsev, 2012), thereby decreasing photosynthetic efficiency (Figure 2). This decrease in photosynthetic efficiency is observable through changes in chlorophyll fluorescence. We are able to do live fluorescence measurements with a handheld fluorometer, which uses small pulses of light to induce photosynthesis as well as fluorescence (Figure 3).
Figure 2. Drought affects photosynthetic efficiency through a chain of events.
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Figure 3. A handheld fluorometer used for measuring chlorophyll fluorescence in the field. It uses a technique called pulse amplitude modulated fluorometry, or PAM, to send tiny pulses of light to the leaf and measure the responding fluorescence.
Image from ICT International |
Questions and Hypotheses
We will use these seedlings, grown together in controlled conditions, to answer the following questions:
We expect that those populations from southern latitudes, as well as those from montane areas, will shower greater tolerance to drought because these species have historically experience drought more frequently than northern or coastal regions. Previous studies using White Spruce have found that slower-growing individuals tend to be more drought tolerant (Bigras 2005). We can use this, after examining long term growth data, to determine which species exhibit highest growth rates and drought tolerance. It has also been found that, though more tolerant Picea glauca populations exist, it is also likely that variation within populations is higher than between them (Liepe 2015). This could mean that we may find that it is more beneficial to choose more tolerant individuals for breeding and planting, rather than finding tolerant populations.
We will use these seedlings, grown together in controlled conditions, to answer the following questions:
- Are some populations of White Spruce more drought-tolerant?
- Does drought tolerance come at the cost of growth and survival rates?
- What physiological mechanisms give some species greater drought tolerance than others?
We expect that those populations from southern latitudes, as well as those from montane areas, will shower greater tolerance to drought because these species have historically experience drought more frequently than northern or coastal regions. Previous studies using White Spruce have found that slower-growing individuals tend to be more drought tolerant (Bigras 2005). We can use this, after examining long term growth data, to determine which species exhibit highest growth rates and drought tolerance. It has also been found that, though more tolerant Picea glauca populations exist, it is also likely that variation within populations is higher than between them (Liepe 2015). This could mean that we may find that it is more beneficial to choose more tolerant individuals for breeding and planting, rather than finding tolerant populations.
References.
Bigras, F. J. “Photosynthetic response of white spruce families to drought stress.” New Forests, vol. 29, no. 2, 2005, pp. 135–148.
Goltsev, Vasilij, et al. “Drought-Induced modifications of photosynthetic electron transport in intact leaves: Analysis and use of neural networks as a tool for a rapid non-Invasive estimation.” Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 1817, no. 8, 2012, pp. 1490–1498.
Liepe, Katharina J., et al. “Adaptation of lodgepole pine and interior spruce to climate: implications for reforestation in a warming world.” Evolutionary Applications, vol. 9, no. 2, 2016, pp. 409–419.
Maxwell, Kate, and Giles N. Johnson. “Chlorophyll fluorescence—a practical guide.” Journal of Experimental Botany, vol. 51, no. 345, 2000, pp. 659–668.
Bigras, F. J. “Photosynthetic response of white spruce families to drought stress.” New Forests, vol. 29, no. 2, 2005, pp. 135–148.
Goltsev, Vasilij, et al. “Drought-Induced modifications of photosynthetic electron transport in intact leaves: Analysis and use of neural networks as a tool for a rapid non-Invasive estimation.” Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 1817, no. 8, 2012, pp. 1490–1498.
Liepe, Katharina J., et al. “Adaptation of lodgepole pine and interior spruce to climate: implications for reforestation in a warming world.” Evolutionary Applications, vol. 9, no. 2, 2016, pp. 409–419.
Maxwell, Kate, and Giles N. Johnson. “Chlorophyll fluorescence—a practical guide.” Journal of Experimental Botany, vol. 51, no. 345, 2000, pp. 659–668.