Decomposition, the breakdown of dead plant and animal material, is a fundamental process that affects soil fertility and ecosystem 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 has a major influence on decomposition in drylands; however, other studies indicate the level of mixing of wind/water-transported soils with litter is the key factor. This project seeks to resolve these competing explanations through a series of laboratory studies and field experiments in Arizona designed to measure interactions among these factors. These linkages will be assessed in the context of woody plant encroachment into grasslands, a globally extensive vegetation change in drylands.
This investigation will 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 novel 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. In addition to dissemination in the scientific community, results will be communicated to land management personnel and organizations through outreach programs. The study will provide training opportunities for four graduate and numerous undergraduate students. The collaborating institutions (University of Arizona, New Mexico State University, University of Kentucky and Loyola University) have substantial minority enrollments, and efforts will be made to recruit students from underrepresented groups.
Death is an integral part of the cycle of life. In ecosystems, plants acquire inorganic compounds (carbon, nitrogen, phosphorus, etc.) from their environment and build them into complex organic compounds that nourish animals either directly (e.g., herbivores that consume plants) or indirectly (carnivores that consume herbivores). Eventually, all plants and animals die. What is the fate of the nutrients they have accumulated during their life-time? These nutrients are released back to the environment through a process called ‘decomposition.’ Decomposition, the breakdown of dead plant and animal material, is a fundamental ecosystem processes that is crucial to determining the long-term fertility of a location and providing the ecosystem service of nutrient retention and 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 plant litter decomposition in drylands; however, other studies indicate the level of mixing of wind and water-transported soils with litter is the key factor. This NSF grant supported research aimed at resolving these contrasting results. We developed a collaborative effort, initiated in 2008, involving scientists from the University of Arizona (Steve Archer and Dave Breshears), New Mexico State University (Heather Throop), Loyola University (Paul Barnes), and the University of Kentucky (Rebecca McCulley), to further explore the controls on dryland plant litter decomposition. Field experiments in the Sonoran Desert of Arizona and the Chihuahuan Desert of New Mexico, and complimentary controlled environment studies at Loyola University and New Mexico State University were used to ascertain how light energy and soil movement and deposition interacted to affect microbial colonization of litter and subsequent decomposition. We also evaluated the effect of woody plant encroachment into grasslands, a globally extensive vegetation change in drylands, on ultra-violet radiation regimes, litter chemistry and decomposition, and soil movement and deposition. By combining the scientific disciplines of plant community ecology, ecosystem science, and earth science in a novel framework, this research has yielded new insights into processes that affect nutrient cycling and retention in drylands. Specifically, we have found: 1) that sunlight (ultra-violet and visible) can be an important driver of decomposition in drylands, but its effect can be ameliorated by soil coverage of the litter; 2) soil-litter mixing results in the formation of adhering "soil films" that consist of soil particles and microbial products, which in turn, enhances microbial decomposition processes; and 3) drylands are dynamic ecosystems, experiencing significant spatial and temporal variability in soil movement processes, which in turn, create substantial spatial and temporal variability in decomposition. Decomposition in these systems is clearly driven by the interaction of ultra-violet radiation, the type of litter being decomposed and resident microbial community, and by soil-litter mixing. Additionally, we developed new approaches and techniques to characterize the ultra-violet environment of surface litter by adopting techniques that have been used to monitor ultra-violet exposure in humans. Woody plant encroachment into grasslands significantly alters the ultra-violet radiation regime experienced at the soil surface. These findings, and others, have contributed new insights into the processes controlling decomposition in drylands (grasslands, savannas, and deserts) and are relevant nationally and internationally, as these ecosystems comprise major portions of the US and global land area. Understanding fundamental processes governing long-term nutrient storage and release are critical to predicting potential feedbacks between these ecosystems and global climate change. This research also provided advanced scientific training opportunities for high school, undergraduate, and graduate students, high school teachers, and international scientific collaborators.
