Does light exposure make plant litter more degradable?
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Many field experiments have indicated that litter decomposition in semi-arid areas may be partly or fully controlled by photodegradation. We devised a study to test our hypothesis that light exposure makes plant litter more degradable. Dry, senescent, aboveground plant litter from Miscanthus x giganteus was exposed to light including ultraviolet (UV) radiation for various lengths of time from 0 to 289 days. Weight loss was measured after exposure and appeared to be modest and did not increase with time of exposure. The litter of the longest and shortest exposure time as well as controls were then incubated with soil and moisture for 35 days and CO2 and N2O production were measured. The longest exposed litter degraded much faster than any other treatment during incubation with moisture, about twice as fast as the unexposed control. The shortest exposed however, degraded only slightly faster than the unexposed control. This suggests that increasing litter degradability is a more important mechanism for photodegradation than direct light-induced mass loss. N2O production from decomposition of the exposed litter was high in the beginning, suggesting that nitrogen may be released quickly. The mechanism is probably that light exposure leaves the nitrogen in plant litter easily available to microbial utilisation upon wetting. Such a mechanism might play an important role for nutrient cycling in semi-arid areas.
KeywordsPhotodegradation Decomposition Nitrous oxide 13C
The authors wish to thank Dr. John Clifton-Brown at IGER, UK for supplying the Miscanthus plant material, and Dr. David Burslem at Aberdeen University for supplying soils from a tropical environment. Professor David Robinson at Aberdeen University is acknowledged for helping with light spectrum measurements. This study was funded by the University of Aberdeen. Professor Pete Smith at Aberdeen University is acknowledged for helping to obtain funding.
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