Effects of UV photodegradation on subsequent microbial decomposition of Bromus diandrus litter
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Photodegradation acts as a direct contributor to litter decomposition in arid and semi-arid ecosystems. However, its indirect effects are unclear. Does photodegradation condition litter for subsequent microbial decomposition?
We conditioned litter of Bromus diandrus with ambient or reduced ultraviolet (UV) radiation and three periods of exposure (summer, summer-winter, and 1 year) in a California annual grassland. We then investigated how field UV exposure affected subsequent microbial decomposition of litter using a controlled laboratory incubation.
Surprisingly, microbial decomposition was decreased by UV radiation when the exposure occurred during summer but was unaffected by UV treatment for exposure longer than summer. Litter lignin concentrations did not explain these results, as they were not affected by UV radiation for any of the exposure periods. However, for the summer period exposure, UV radiation was associated with decreased litter N concentration, which corresponded with lowered subsequent microbial activity.
Our results suggest a new mechanism through which photodegradation interacts with litter microbial decomposition: photodegradation may decrease microbial decomposition through inhibition of microbial N immobilization. Our results imply that solar radiation can interact with litter N cycling dynamics to influence litter decomposition processes.
KeywordsPhoto-oxidation Photo-mineralization Dryland Grass Invasive species Drought
We thank Dad Roux-Michollet, Keri Opalk, and Ken Marchus for their assistance in the field and laboratory. We thank Oliver Chadwick and Carla D’Antonio for their valuable comments on the experimental design and on this manuscript. We thank Kate McCurdy, Eric Massey, and the University of California’s Sedgwick Reserve for providing the study site. We thank Alfonso Escudero and anonymous reviewers for comments that improved the manuscript. This work was supported by the National Science Foundation under DEB-0935984 and DEB-1406501. RDS was supported by the McNair Scholars Program.
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