Effects of UV Exposure and Litter Position on Decomposition in a California Grassland
- 691 Downloads
The importance of photodegradation in surface litter decomposition has recently been recognized in arid and semi-arid terrestrial ecosystems, yet its importance in decomposing dense litter and the mechanisms through which it acts remain unclear. We investigated how ultraviolet (UV) radiation exposure and litter position affected decomposition processes in a California annual grassland. In a split-plot design, we exposed Bromus diandrus litter to two levels of UV radiation (UV pass and UV block) at two aboveground locations (at the top, suspended above the litter layer, and at the bottom of the litter layer) for 1 year. We found that UV radiation increased the litter decay constant by 23% at the top location over 1 year, consistent with the occurrence of photodegradation. Surprisingly, UV radiation also increased the litter decay constant by 30% at the bottom location over 1 year. We speculate that photodegradation indirectly increased microbial decomposition through priming effects. Overall, litter in the top location had a 29% higher decay constant than litter in the bottom location. In terms of litter chemistry, exposure to UV radiation increased loss of hemicellulose by 26%, but not loss of lignin. Litter in the bottom location exhibited greater loss of the cell solubles fraction and greater nitrogen immobilization, but lower loss of hemicellulose than litter in the top location. Our results demonstrate that litter position significantly regulates the contribution of photodegradation to overall decomposition, both through direct (top location) and indirect (bottom location) effects. Therefore, better quantification of both direct and indirect effects of photodegradation can greatly improve understanding of biogeochemical cycling in grasslands.
Keywordsphotodegradation decomposition UV-A UV-B invasive species hemicellulose cellulose lignin litterbag drylands
We thank Dad Roux-Michollet, Keri Opalk, Kenneth Marchus, Matt Mass, Viviane Vincent, Molly Zimmerman, and Heather Christian for their assistance in the field and lab. 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, field facilities, and technical support. This work was supported by the National Science Foundation under DEB-0935984.
- Adair EC, Parton WJ, Del Grosso SJ, Silver WL, Harmon ME, Hall SA, Burke IC, Hart SC. 2008. Simple three-pool model accurately describes patterns of long-term litter decomposition in diverse climates. Glob Chang Biol 14:1–25.Google Scholar
- Anderson JM. 1973. The breakdown and decomposition of sweet chestnut (Castanea sativa Mill.) and beech (Fagus sylvatica L.) leaf litter in two deciduous woodland soils. Oecologia 12:251–74.Google Scholar
- Brandt LA, Bohnet C, King JY. 2009. Photochemically induced carbon dioxide production as a mechanism for carbon loss from plant litter in arid ecosystems. J Geophys Res 114:G02004.Google Scholar
- Burnham KP, Anderson DR. 2002. Model selection and multimodel inference: a practical information-theoretic approach. New York: Springer.Google Scholar
- Hatfield RD, Jung HG, Ralph J, Buxtond DR, Weimeraq PJ. 1994. A comparison of the insoluble residues produced by the Klason lignin and acid detergent lignin procedures. Phytochemistry 65:51–8.Google Scholar
- Rozema J, Tosserams M, Nelissen HJM, Van Heerwaarden L, Broekman RA, Flierman N. 1997. Stratospheric ozone reduction and ecosystem processes: enhanced UV-B radiation affects chemical quality and decomposition of leaves of the dune grassland species Calamagrostis epigeios. Plant Ecol 128:285–94.CrossRefGoogle Scholar
- Rutledge S, Campbell DI, Baldocchi D, Schipper LA. 2010. Photodegradation leads to increased carbon dioxide losses from terrestrial organic matter. Glob Chang Biol 16:3065–74.Google Scholar
- Van Soest PJ. 1963. Use of detergents in the analyses of fibrous feeds. A rapid method for the determination of fiber and lignin. J Assoc Off Anal Chem 46:829–35.Google Scholar
- Van Soest PJ. 1965. Symposium on factors influencing the voluntary intake of herbage by ruminants: voluntary intake in relation to chemical composition and digestibility. J Anim Sci 24:834–43.Google Scholar
- Zar JH. 1999. Biostatistical analysis. Upper Saddle River, NJ: Prentice Hall.Google Scholar