Foliar litter chemistry mediates susceptibility to UV degradation in two dominant species from a semi-arid ecosystem
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Abiotic processes such as photodegradation play important roles in litter decomposition in semi-arid ecosystems. However, little is known about whether UV degradation responds similarly to factors controlling biotic decomposition rates, such as soil moisture and plant litter chemistry. Here, we evaluated the relative importance of UV degradation versus biotic decomposition in contrasting precipitation regimes for two species.
We manipulated ultraviolet (UV) radiation under two rainfall treatments (ambient and added precipitation) and measured decomposition rates of leaf litter from two abundant species in a southern California coastal sage scrub ecosystem: a native shrub (Salvia mellifera) and an exotic annual grass (Avena fatua).
The influence of UV radiation exposure on decomposition did not vary with rainfall treatment, and UV radiation exposure only increased litter mass loss of the A. fatua litter, not S. mellifera. This pattern was driven by accelerated loss of hemicellulose and cellulose litter fractions when the exotic grass litter was exposed to UV radiation. The greatest influence of UV radiation was observed after 18 months.
The sensitivity of hemicellulose and cellulose litter fractions to UV radiation suggests that shifting plant species composition which results in altered litter chemistry could change ecosystem sensitivity to UV photodegradation.
KeywordsAvena fatua Coastal sage scrub Drylands Invasion Lignin Photodegradation Precipitation variability Salvia mellifera
We thank Rachel Abbott, Andrew Heath, Christopher Kopp, Yang Lin, and Elizabeth Premo for help in maintaining the field experiment and Sharon Booth, Laurel Brigham, Kirk Hutchison, and Prisca Ratsimbazafy for their data processing assistance. We thank Yang Lin for help with logistical design and shelter transportation. This material is based upon work supported by a National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144086 and a National Science Foundation Division of Environmental Biology grant (DEB-1154082). UV manipulation shelters were funded by NSF Ecosystem Science (DEB-0542935, DEB-0935984). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Grants from the California Native Plant Society and the University of California Institute for the Study of Ecological Effects of Climate Impacts also helped support this research.
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