Photo-exposure affects subsequent peat litter decomposition

Exposure to sunshine is known to play a role in litter decomposition in some semi-arid areas. The aim of this study was to find out if it also plays a role in higher latitude environments in peat litter decomposition and could contribute to an explanation to the patchy nature of peat litter decomposition. Peat litter from 5 microenvironments (top of slope, bottom of slope, ridge, ryam and hollow) and put out and exposed to the sun or shaded over a summer in Western Siberia, 26 km west of the town of Khanty-Mansiysk. Afterwards the peat litter was incubated in the laboratory - at field capacity or submerged in peat water - and CO2 and methane emission measured. Chemical composition of exposed and control peat litter was also investigated using stepwise extraction. The results indicate that exposure to sunlight does increase subsequent decomposition rate in most peat litters when incubated at field capacity, but the difference between the treatments levelled off at the end of the 2 weeks incubation in most peat litter types. The total extra carbon loss was calculated to be up to about 2 mg Cm-2 over a season. When incubated submerged previous photo-exposure had less effect on CO2 evolution then when incubated at field capacity. No methane emission was recorded in any treatment. Some differences in chemical composition between exposed and shaded peat litters were found that could help explain the differences in subsequent decomposition rate. The results indicate that photodegradation could play a role in peat litter decomposition at higher latitudes when peat is disturbed and exposed to sunshine. However, the effect of photo exposure in these areas is much smaller than observed in semi-arid areas at lower latitudes.