Growth responses of Sphagnum hollows to a growing season lengthening manipulation in Alaskan Arctic tundra

Abstract

The global increase in surface air temperature has produced an overall lengthening of the growing season by 3-5 days/decade in the Northern Hemisphere during the last 30 years. The direct impact of a longer growing season has not been well documented for Sphagnum moss communities in the Arctic. We hypothesized that an increase in the growing season length may be detrimental to Sphagnum growth as a result of photoinhibition caused by the plants emerging from snow near the seasonal peak of solar irradiance. We conducted an experiment from 1999 to 2002, lengthening the growing season in arctic Alaska, to determine the effects that this simulation of climate change had on the growth of hollows dominated by Sphagnum angustifolium. The lengthened growing season was associated with a decrease in annual moss height increment of 78 and 69 % for 1999 and 2000, respectively. These growth reductions may be related to freeze/thaw episodes and prolonged periods of cold in those years. The growth of individuals exposed to snow removal was also reduced by high global radiation. Overall, snow removal did not significantly affect the seasonal dynamics of growth, but seasonal patterns of growth strongly differed among years. These differences in seasonal dynamics suggest that Sphagnum growth is driven by opportunistic responses to favorable conditions rather than ontogenetic drivers. In addition, we compared environmental variation and growth between control and snow removal plots. Growth of Sphagnum in both treatments was stimulated by warmer soil temperatures and drier conditions. With earlier snowmelt as a result of warmer temperatures, it is likely that S. angustifolium will be subjected to higher levels of radiation and possibly greater photoinhibition which may lead to lower growth rates and significant implications for moss production in tussock tundra.

Temperature-Dependent Oxygen Isotope Fractionation in Plant Cellulose Biosynthesis Revealed by a Global Dataset of Peat Mosses

“…We thus used the T gs , the arithmetic average temperature of the months above 0 • C, as the growth temperature for the whole plant of Sphagnum. In fact, Sphagnum growth during the months of freezing temperature does occur if snow cover was thick and persistent enough to insulate Sphagnum from winter frost (Dorrepaal et al, 2004;Genet et al, 2013), as snow cover shading is not is not a major limiting factor for Sphagnum growth (Clymo and Hayward, 1982;Küttim et al, 2020). That being said, biomass production of Sphagnum during freezing months is much reduced.…”

“…However, the cumulative temperature-such that is defined as growing degree days above zero in bioclimatic studies (Charman et al, 2013)-might be a more accurate measure of the total warmth Sphagnum have experienced. Studies found that Sphagnum productivity at a given site is enhanced during the warmest season (Krebs et al, 2016;Küttim et al, 2020), although a few studies suggested that Sphagnum growth could be limited by summer desiccation stress and photoinhibition (Lindholm, 1990;Dorrepaal et al, 2004;Genet et al, 2013). Certainly, there is a tendency that T gs would underestimate the mass-weighted growth temperature for the whole plant of Sphagnum.…”

Planning for climate change impacts on hydropower in the Far North

“…In the southern-most parts of this region, more precipitation will arrive in liquid form and be available earlier in the season for hydropower generation, rather than stored in the snowpack until spring melt. In the Far North, ET is a relatively small portion of the hydrologic budget and precipitation dominates (Kane et al, 1990), though ET will increase as the growing season continues to lengthen as it has in recent decades (Genet et al, 2013;Olchev and Novenko, 2011;Zeng et al, 2011). Other aspects of the supply side, which include groundwater storage and glacier storage, will be addressed in the next section on regional complexity.…”

Planning for climate change impacts on hydropower in the Far North

“…In the southern-most parts of this region, more precipitation will arrive in liquid form and be available earlier in the season for hydropower generation, rather than stored in the snowpack until spring melt. In the Far North, ET is a relatively small portion of the hydrologic budget and precipitation dominates (Kane et al, 1990), though ET will increase as the growing season continues to lengthen as it has in recent decades (Genet et al, 2013;Olchev and Novenko, 2011;Zeng et al, 2011). Other aspects of the supply side, which include groundwater storage and glacier storage, will be addressed in the next section on regional complexity.…”