Changes in carbon flux and spectral reflectance of Sphagnum mosses as a result of simulated drought

Sphagnum is an important peat-forming genus, which aids the carbon sequestration of peatlands. Sphagnum is sensitive to drought; however, and it is uncertain how well it can recover from long periods without rainfall. Spectral reflectance can be used to assess Sphagnum desiccation damage, and we also tested whether it can be used to detect recovery. Different rainfall simulations were applied to two species of Sphagnum to assess the impact of drought on carbon function. After 80 days all samples were rewetted to assess recovery. The rainfall simulations included inputs analogous to actual precipitation at the field site (Forsinard Flows reserve, Northern Scotland), potential future changes in rainfall, and extended total drought. During the experiment gross primary productivity and respiration were measured. Photosynthesis decreased after approximately 30 days of continuous drought (i.e., days without rain). Spectral reflectance was measured to assess Sphagnum bleaching. The spectral absorption feature of Sphagnum associated with red light (around 650 nm) was affected by drought and did not recover after rewetting during the experimental period. No significant difference was found between the two Sphagnum species studied with respect to their photosynthesis or respiration, but there was a significant difference in optimum water content and spectral reflectance between the two. The results from this study suggest that Sphagnum carbon function is resilient to quite long drought periods, but once damage has occurred recovery is likely to be difficult. The spectral reflectance of Sphagnum can give useful information in assessing whether significant desiccation damage has occurred.