Moore, Daniel J., Robert S. Nowak, and Cheryl L. Nowak. “Photosynthetic Acclimation to Temperature and Drought in the Endemic Chelan Rockmat, Petrophytum cinerascens (Rosaceae).” American Midland Naturalist 139 (1998): 374-382. (reviewed by Martin Anderson)
Summary:
The purpose of this study was to assess the photosynthetic ability of Petrophytum cinerascens under changing growth temperatures. P. cinerascens is a plant endemic to the steep rocky outcropping and sandy soils around the Columbia River in eastern Washington. Being restricted to a small area and found nowhere else, P. cinerascens has evolved to meet the conditions of its environment. This study focuses on P. cinerascens to see if given a different set day and night temperature conditions, as would be seen under global warming projections, would affect the photosynthetic productivity, growth, and survival of the plant.
The authors collected six samples of P. cinerascens from different parts of its habitat, created six clones of each sample, and cultivated them in a controlled environment for some months. The authors looked at three different temperature models and two watering cycles during this study. Two clones of each plant were places in a 30/16 (normal growth range), 34/20, or 38/24 day/night temperature (in degrees Celsius) model. One of the two clones was on a regular water cycle (3 times a week to soil saturation) and the other on a drought cycle (2 times a week to soil saturation). These groupings (12 plants total per group) were placed in identical growth chambers with uniform humidity and artificial solar radiation for 81 days before their rates of photosynthesis and nitrogen content (indicative of growth) were measured.
The authors found that although the plants had survived in each chamber the plants in the warmer two chambers were not able to adapt their photosynthetic processes to function at higher temperatures. This was confirmed by looking at the maximum rates of carbon dioxide uptake by each plant under controlled conditions where the measurement chamber was heated and then cooled to various temperatures between 20 C and 46 C. Each plant demonstrated a near identical maximum uptake at around 28 C with the plants exposed to the two hotter conditions having a reduced uptake compared to the 30/16 model. The plants under regular water cycles demonstrated a 68 % decrease in photosynthetic activity at the highest temperatures compared with 23% for the drought cycle plants. Nitrogen content was non-significant for the purposes of this experiment.
The authors conclude that P. cinerascens would not survive well under global warming conditions (34/20 and 38/24) due to decreased ability to photosynthesize, and as such would make a good indicator of climate change.
Critique:
The authors of this paper are careful in their analysis, methods, and very clear in their intent. The study conclusion may not be profound in its contents but the message is one of importance on a global scale. It may not really be a problem in the grand scheme if a single endemic plant become extinct due to global warming, but think what may happen when an entire forest cannot adapt to a changing climate. That would have profound consequences not only on the forest but all the animals and natural process (snow melt cycles, precipitation, the carbon cycle, etc.) dependent on the forest. This would cause still further problems to the surrounding areas (on the order of hundreds or thousands of mile around) and perhaps perpetuate further still.
It is important to remember that this study was very limited in scope but the implications of what it is saying have global consequences. The natural history of a place is not made only of the geology and the climate, but also the more transient organisms which shape the landscape and help create the climate. These things are interconnected, so that changing one thing ultimately has a significant effect on all of the others.
This article would be useful for a researcher looking at the effects of global warming, Columbia River plants, or plant adaptation. This paper consists of 9 pages, 4 graphs, 1 table, and 22 references
Robert D. Clark Honors College, University of Oregon
HC 441: Science Colloquium, Columbia River Ecology
Fall term, 2005
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