Decomposition in Drylands: Soil Erosion and UV Interactions
Death is an integral part of the cycle of life. In ecosystems, plants acquire inorganic compounds from their environment (carbon, nitrogen, phosphorus, etc.) and build them into complex organic compounds that nourish animals either directly (e,g,, herbivores than consume plants) or indirectly (carnivores that consume herbivores). Eventually, all plants and animals in the ecosystem die. What is the fate of the nutrients they have accumulated during their life-time? These nutrients are released back to the environment vial the process of ‘decomposition'. Decomposition, the breakdown of dead plant and animal material, is a fundamental ecosystem process that affects long-term soil fertility and carbon storage. Most of what is known about decomposition is from studies in high rainfall areas, but this knowledge does not translate well to dryland ecosystems. Some recent studies suggest solar ultra-violet radiation is a major driver of decomposition in drylands; however, o
ther studies indicate the level of mixing of wind/water-transported soils with litter is the key factor.
Many interacting drivers potentially influence decomposition. We propose to extend research on traditional decomposition drivers to include erosion-based drivers, and test the notion that development of the litter/soil matrix is a key but overlooked component of dryland decomposition. We hypothesize this matrix is controlled by wind/water transport of soil which, in turn, is controlled by vegetation structure. We further hypothesize that as the litter/soil matrix develops, key biotic (microbial activity) and abiotic forces (moisture, UV photodegradation) are mediated.
A $1.1M grant from the National Science Foundation, entitled "Decomposition in drylands: Soil erosion and UV interactions", seeks to resolve these competing explanations. The new project starting in September 2008, will be a collaborative effort involving scientists in the School of Natural Resources and the Environment at the University of Arizona (Steve Archer and Dave Breshears) , New Mexico State University (Heather Throop), the University of Kentucky (Rebecca McCulley) and Loyola University (Paul Barnes). Field experiments at the Santa Rita Experimental Range and complimentary controlled environment studies will be used to ascertain how light energy-soil movement interact to affect decomposition rates in the context of woody plant encroachment into grasslands, a globally extensive vegetation change in drylands. The research is expected to yield new insights into processes that affect soil fertility and carbon storage in drylands by combining the disciplines of plant community ecology, ecosystem science and earth science in a n
ovel framework. The findings will be relevant nationally and internationally, as dryland ecosystems characterize major portions of the US and global land area, and may be significant carbon sinks. The study will provide training opportunities for four graduate students and numerous undergraduates.
Progress to date:
Conferences:
Abbene ML, Barnes PW, Throop HL, Archer S. 2008. Interactive effects of UV radiation and soil coverage on leaf litter decomposition in velvet mesquite (Prosopis velutina). In Ecological Society of America Annual Meetings. Milwaukee, WI
Throop, H. L., and S. Archer. 2008. Shrub encroachment, land management and litter decomposition. 5th Annual Research Insights in Semiarid Ecosystems (RISE) Symposium, Tucson, AZ.
Throop, H., S. Archer, P. W. Barnes, M. L. Abbene, D. Hewin, and G. Okin. 2008. Addressing the dryland decomposition conundrum by integrating vegetation structure, soil transport and UV photodegradation. LTER Cross-Site Comparison Symposium, Albuquerque, NM.
Funding: NSF Ecosystems Program, Collaborative Research: Decomposition in drylands: Soil erosion and UV interactions
Publications:
Throop, H. L., and S. Archer. 2007. Interrelationships among shrub encroachment, land management and leaf litter decomposition in a semi-desert grassland. Ecological Applications 17:1809-1823.
Throop, HL, SR Archer. 2008. Resolving the dryland decomposition conundrum: some new perspectives on potential drivers. Progress in Botany: 70:171-194.
Breshears, D. D., J. J. Whicker, J. P. Field, C. B. Zou, and C. D. Allen. 2009. A conceptual framework for dryland aeolian sediment transport along the grassland-forest continuum: effects of woody plant canopy cover and disturbance. Special Issue on Wind Erosion Measurements. Geomorphology: 105: 28-38.
Key Collaborators:
Jeannie McLain (USDA-ARS, US Arid-Land Agricultural Research Center, Maricopa, AZ)
Curtis Monger (New Mexico State University)
Thom Rahn (Los Alamos National Laboratory)
Jeff Whicker (Los Alamos National Laboratory)
Greg Okin (University of California, Los Angeles)
