Soil Coverage Reduces Photodegradation and Promotes the Development of Soil-Microbial Films on Dryland Leaf Litter
- 569 Downloads
Litter decomposition is a central focus of ecosystem science because of its importance to biogeochemical pools and cycling, but predicting dryland decomposition dynamics is problematic. Some studies indicate photodegradation by ultraviolet (UV) radiation can be a significant driver of dryland decomposition, whereas others suggest soil–litter mixing controls decomposition. To test the influence of soil coverage on UV photodegradation of litter, we conducted a controlled environment experiment with shrub (Prosopis velutina) leaf litter experiencing two UV levels and three levels of coverage with dry sterile soil. Under these conditions, decomposition over 224 days was enhanced by UV, but increasing soil coverage strongly and linearly diminished these effects. In a complementary study, we placed P. glandulosa leaf litter in different habitats in the field and quantified litter surface coverage by soil films. After 180 days, nearly half of the surface area of litter placed under shrub canopies was covered by a tightly adhering film composed of soil particles and fungal hyphae; coverage was less in grassy zones between shrubs. We propose a conceptual model for the shifting importance of photodegradation and microbial decomposition over time, and conclude that (1) soil deposition can ameliorate the direct effects of UV photodegradation in drylands and (2) predictions of C losses based solely on UV effects will overestimate the importance of this process in the C cycle. An improved understanding of how development of the soil–litter matrix mediates the shift from abiotic (photodegradation) to biotic (microbial) drivers is necessary to predict how ongoing changes in land cover and climate will influence biogeochemistry in globally extensive drylands.
Keywordscarbon cycle decomposition dryland mesquite Prosopis photodegradation soil erosion soil–litter mixing ultraviolet radiation
We appreciate the assistance of V. del Bianco, A. Dickhute, M. Tobler and J. Fitzgerald. P. Cooke provided advice and assisted with microscopy. Financial assistance was provided by the US National Science Foundation [DEB 0815897 (Loyola University), DEB 0815808 (New Mexico State University), and DEB 0816162 (University of Arizona)], the Loyola University J.H. Mullahy Endowment for Environmental Biology, and the Jornada Basin LTER (DEB 0618210).
- Caldwell MM. 1971. Solar UV irradiation and the growth and development of higher plants. Photophysiology 6:131–77.Google Scholar
- Couteaux MM, Bottner P, Berg B. 1995. Litter decomposition, climate and litter quality. Trends Ecol Evol 10:363–7.Google Scholar
- Lee H, Rahn T, Throop H. 2012. An accounting of C-based trace gas release during abiotic plant litter degradation. Glob Change Biol. doi: 10.1111/j.1365-2486.2011.02579.x.
- Okin GS, Gillette DA. 2001. Distribution of vegetation in wind-dominated landscapes: implications for wind erosion modeling and landscape processes. J Geogr Res 106:9673–84.Google Scholar
- Pancotto VA, Sala OE, Robson TM, Caldwell MM, Scopel AL. 2005. Direct and indirect effects of solar ultraviolet-B radiation on long-term decomposition. Glob Change Biol 11:1982–9.Google Scholar
- Rozema J, Tosserams M, Nelissen HJM, Vanheerwaarden 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 128:284–94.Google Scholar
- Rutledge S, Campbell DI, Baldocchi D, Schipper L. 2010. Photodegradation leads to increased carbon dioxide losses from terrestrial organic matter. Glob Change Biol 16:3065–74.Google Scholar
- Wainwright J. 2006. Climate and climatological variations in the Jornada Basin. In: Havstad K, Huenneke LF, Schlesinger W, Eds. Structure and function of a Chihuahuan Desert ecosystem. New York: Oxford. p 44–80.Google Scholar