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 from their environment (carbon, nitrogen, phosphorus, etc.) 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 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 via 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, other studies indicate the level of mixing of wind/water-transported soils with litter is the key factor. Research supported by this NSF grant sought to resolve these competing explanations. A collaborative effort initiated in 2008 involved scientists 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 New Orleans (Paul Barnes). Field experiments in the Chihuahuan and Sonoran Deserts and complimentary controlled environment studies at Loyola University and New Mexico State University were used to ascertain how light energy and soil movement interact to affect decomposition rates in the context of woody plant encroachment into grasslands, a globally extensive vegetation change in drylands. This research has yielded 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. In particular, we have found 1) that sunlight (UV and visible) can be an important driver of decomposition in drylands but this can be ameliorated by soil coverage of litter, 2) soil litter mixing results in the formation of adhering "soil films" that consist of soil particles and microbial products, which in turn, 3) enhances microbial decomposition processes. Thus, decomposition in these drylands is driven by the interaction of these two important factors. Additionally, we have developed new approaches and techniques to characterize the UV environment of surface litter by adopting techniques that have been used to monitor UV exposure in humans. 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 characterize major portions of the US and global land area, and may be significant carbon sinks. Understanding fundamental processes governing carbon storage and nutrient recycling are critical to evaluating and predicting the effects and drivers of global climate change. This work has led to numerous peer reviewed publications and provided training opportunities for undergraduate students, graduate students, and postdocs.
