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University of Vermont ScholarWorks @ UVM Graduate College Dissertations and Theses Dissertations and Theses 2008 Influence of Altered Temperature and Precipitation on Desert Microfauna and Their Role in Mediating Soil Nutrient Availability Brian Darby University of Vermont Follow this and additional works at: https://scholarworks.uvm.edu/graddis Recommended Citation Darby, Brian, "Influence of Altered Temperature and Precipitation on Desert Microfauna and Their Role in Mediating Soil Nutrient Availability" (2008). Graduate College Dissertations and Theses. 64. https://scholarworks.uvm.edu/graddis/64 This Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks @ UVM. It has been accepted for inclusion in Graduate College Dissertations and Theses by an authorized administrator of ScholarWorks @ UVM. For more information, please contact [email protected]. INFLUENCE OF ALTERED TEMPERATURE AND PRECIPITATION ON DESERT MICROFAUNA AND THEIR ROLE IN MEDIATING SOIL NUTRIENT AVAILABILITY A Dissertation Presented by Brian J. Darby to The Faculty of the Graduate College of The University of Vermont In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Specializing in Plant and Soil Science October, 2008 Accepted by the Faculty of the Graduate College, The University of Vermont, in partial fulfillment of the requirements for the degree of Doctor of Philosophy, specializing in Plant and Soil Science. Dissertation Examination Committee: dvisor ~leksandiaDrizo, Ph.D. Donald S. Ross. PbD. ~hom&0. Powers, Ph-D. Chairperson Vice President for Research and Dean of the Graduate College Date: May 13, 2008 Abstract Arid-land deserts comprise up to 30% of global land surface area and experience degradation by anthropogenic land use demands. Sixteen of the 19 climate models used by the International Panel on Climate Change predict increased temperature and prolonged periods of drought for much of the arid southwest US. Soil microfauna consume organic-bound nitrogen and excrete soluble inorganic and dissolved organic nitrogen that is available for plant uptake or as substrate for microbial saprotrophs. However, the growth and activity of nematodes and protozoa is restricted to periods of adequate temperature and moisture. The objective of this dissertation research project is to determine the possible effects of predicted climate changes on cool desert soil nematodes and protozoa and their role in nitrogen cycling. Climate changes are predicted to affect nematodes more adversely than protozoa. Nematodes are thought to contribute more to nitrogen cycling through dissolved organics while protozoa are thought to contribute relatively more to nitrogen cycling through inorganic nitrogen. A shift in community composition favoring amoebae over nematodes could shift the relative balance of organic and inorganic pools of soil nitrogen. Soil microfauna are not readily observed in their soil habitat, so extraction and enumeration techniques are adapted and tested for the desert microfaunal communitites. Desert soil nematodes and protozoa participate in energy channels deriving from vascular and non-vascular primary producers as well as bacterial and fungal saprotrophs. Environmental conditions influence the prey that are available to nematodes and protozoa and, thus, indirectly affect the relative composition of microfaunal feeding groups. Environmental conditions also directly affect microfauna. Not only are nematodes affected more negatively by adverse abiotic stress than amoebae, many species of bacterivorous nematodes appear to be susceptible to unique combination of the major abiotic stresses experienced in the desert. Findings from a two-year field experiment treated with elevated temperature and summer precipitation are consistent with lab and field mesocosm experiments, but highlight the uncertainly inherent in predicting long-term trends with brief experiments. In comparison with temperature and precipitation, long-term elevated carbon-dioxide enrichment was not shown to affect the abundance of desert soil microfauna directly but did affect the distribution of protozoa and the composition of nematodes indirectly through altered plant water use patterns. Continued work is needed to devise experimental systems that quantify the relative role of microfaunal functional groups in nutrient cycling. Acknowledgements Many thanks go to my advisor, Dr. Deborah Neher, whose enduring patience and encouragement motivated me through this project. You balanced enthusiasm with diligence and helped me to understand the process of learning. I thank my committee members for offering their time and expertise to my growth as a student and scientist: Dr. Brian Beckage, Dr. Jayne Belnap, Dr. Aleksandra Drizo, Dr. Tom Powers, and Dr. Don Ross. I also thank the fellow lab members who have supplied helpful conversations and assistance in the lab. This dissertation research is supported by a grant from the Department of Energy, Program for Ecosystem Research, awarded to Jayne Belnap (USGS, Moab, Utah), Cheryl Kuske (Los Alamos National Laboratory, New Mexico), and Deborah Neher (University of Vermont, Burlington, VT). The research would not have been possible without the hard work and expertise of the USGS field crew in Moab, UT, and I especially appreciate the assistance of Dr. David Housman as a valuable point of contact for many years. Awards from the Soil Ecology Society, University of Vermont Graduate Student Association and College of Arts and Sciences, Dow Agrosciences, Soil Science Society of America, and International Society of Protistologists made travel to conferences possible. Finally, I thank the dear friends I‟ve made in Vermont, the fellow graduate students who have helped me to enjoy the time, my extended family, grandparents, and siblings, and to my Mom and Dad, Carl and Donna, for their interest, encouragement and example. ii Table of Contents Acknowledgements ............................................................................................. ii List of Tables ..................................................................................................... vi List of Figures ................................................................................................... vii Chapter 1. Introduction ........................................................................................1 Desert Soil Environment ..................................................................................1 Desert Soil Microfauna ....................................................................................2 Abiotic Stress ...................................................................................................3 Nitrogen Transformations ................................................................................5 From Principles to Predictions..........................................................................8 References ..................................................................................................... 10 Chapter 2. General Methodology........................................................................ 18 Methods ......................................................................................................... 20 Protozoa Extraction .................................................................................... 20 Nematode Extraction .................................................................................. 21 Auxiliary Experiments ................................................................................ 24 Results ........................................................................................................... 26 Discussion ...................................................................................................... 27 Protozoa Methods ....................................................................................... 27 Nematode Methods..................................................................................... 28 References ..................................................................................................... 30 Chapter 3. Energy Pathways in the Desert Soil Food Web .................................. 40 Methods ......................................................................................................... 42 Plant Experiment ........................................................................................ 42 Crust Removal Experiment ......................................................................... 43 Analysis ..................................................................................................... 44 Results ........................................................................................................... 47 Plant Experiment ........................................................................................ 47 iii Crust Removal Experiment ......................................................................... 48 Discussion ...................................................................................................... 49 References. .................................................................................................... 52 Chapter 4. Environmental Stress as a Determinant of Soil Microfaunal Composition .................................................................................................. 63 Methods ........................................................................................................

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