How do soil temperature fluctuations affect water content? Winter Ecology Course CU Mountain Research Station Spring 2015 Evan Franklin

Soil Temperature + Water ●Water in the winter season is a major limiting nutrient for many organisms, particularly in an arid alpine environment. Snowpack plays a major role in hydrating an alpine plant community. ●Plants can uptake water at the leaves and stem, however, root water uptake is their primary means of hydration. Marchand found mixed results for leaf water uptake below the snowpack (Marchand 1996). ●Desiccation or winter burn occurs as a result of solar evaporative demand and low soil moisture uptake, and is a major problem for juvenile evergreens (Kozlowski 1987), (Brady 2008). ●Root water uptake is primarily a function of soil temperature (Brady 2008). ●A majority of root water uptake occurs in upper portion of soil profile (Brady 2008).

Questions ●How does soil temperature influence a plant’s available water in winter? ●How do soil temperatures fluctuate on a diel cycle and across the landscape in the winter?

Experiment Design ●Took temperature measurements at surface and 20 cm depth at 7 AM and 3 PM. ●Collected soil samples for gravimetric water content analysis. ●Recorded snow depth, depth of frozen ground, and locational attributes such as slope and aspect.

Identifying Field Sites ●I identified 4 locations with a variable solar exposure and snowpack levels near the Mountain Research Station. Two sites were visited in the morning, two sites visited in the afternoon. ● At each location, I walked a transect and took two record sets and samples for each of the following categories: snow-covered + open, snow-covered + shady, exposed + open, exposed + shady

Results Interaction P-value:

Results Soil was generally saturated, often in excess of 20% by mass. Daily temperature fluctuations were minimized under snowpack, regardless of solar exposure. Bare ground saw wide temperature fluctuations and experienced widest variability. Soil below 20 cm depth saw stable temperatures, regardless of snow/sun exposure.

Results ●Gravimetric analysis proved insufficient Errors? -Collection problems -Saturated soils -Differences in texture, porosity, compaction -Ice

Discussion ●Bare ground undergoes wider fluctuations. Solar exposure less important. ●Ground tended to be relatively saturated. Water at low temperatures drains less quickly soil water not limited under these conditions (Johnsson and Lundin 1991). ●Plant’s water governed by internal processes rather than availability in winter.

Conclusion ●Plant’s available water is typically high under snowpack or nearby in the winter. ●Actual soil water content varies as function of soil physical properties and structure. ●Temperature is a limit of biological and physical processes in winter. ●Snowpack is a good soil insulator. Questions?

References Brady, Nyle C., and Ray R. Weil. "Soil Aeration and Temperature." The Nature and Properties of Soils. Upper Saddle River, NJ: Pearson Prentice Hall, Print. Johnsson, Holger, and Lars-Christer Lundin. "Surface Runoff and Soil Water Percolation as Affected by Snow and Soil Frost." Journal of Hydrology (1991): Web. 18 Feb Kozlowski, T. T. "SOIL MOISTURE AND ABSORPTION OF WATER BY TREE ROOTS." Journal of Arborculture, 2 Feb Web. 09 Feb Marchand, Peter J. "Plants and the Winter Environment." Life in the Cold: An Introduction to Winter Ecology. 3rd ed. Hanover, NH: U of New England, Print. Running, Steven W., and C. Patrick Reid. “Soil Temperature Influences on Root Resistance of Pinus Contorta Seedlings.” Plant Physiology 65.4 (1980): 635–640. Web.