Can drought frequency be tracked by stable carbon isotopes in Sphagnum soluble sugars?

As the climate changes due to human activity, precipitation patterns are being altered, leading to increasing severity of droughts in some areas. To understand if intra-seasonal weather patterns are changing, the periodicity of droughts needs to be measured. This study explores the use of stable carbon isotopes (¹³C) in soluble sugars from Sphagnum moss to record bioavailable water over a timescale of weeks. Two different species, S. magellanicum and S. fallax, were exposed to wet and dry conditions over three months in a growth room. The stable isotope composition (δ¹³C) of bulk tissue and soluble sugars was measured. For bulk tissue, a three-way ANOVA test was performed to test the significance of wet treatment, species, and time. In both species, plants grown under the wet treatment were isotopically heavier and the difference was significant (p<0.001). There was also a significant difference between the δ¹³C signal of the two species, with S. magellanicum being isotopically heavier than S. fallax (p<0.001). Also, there was a significant increase in the δ¹³C value of all the plants over time (p<0.001) with greater increases in plants from the wet treatments indicating higher concentrations of ¹³C. In the wet treatment, neither species showed stable δ¹³C values after three months indicating a longer response time.  The δ¹³C in the soluble sugars is expected follow similar patterns with respect to species and wet treatments. However, the δ¹³C in soluble sugars is expected to change and stabilize much more rapidly than that of the bulk tissue, providing a signal that reflects changing water conditions over two to three week increments, rather than over the three months observed in bulk tissue. The δ¹³C of Sphagnum bulk tissue, which is stored in peat deposits allows for reconstructions of past climates and records long term climate change. Less is known about ways to record the intra-seasonal shifts in weather patterns caused by climate change. The δ¹³C of Sphagnum soluble sugars may allow for efficient and accurate measurement of these shifts.