John Zak

Research Interests

Our core research activities have focused on elucidating the diversity and structure of soil bacterial and fungal communities and their subsequent roles in regulating the functioning of natural and managed arid ecosystems.  Our research efforts incorporate traditional culture based techniques for assessing species richness of fungi and bacteria linked to novel techniques such as 445 Pyrosequencing, from enzyme analyses, to functional diversity assessments using carbon based substrates.  Our lab developed the Fungilog and Nitrolog techniques that evaluate patterns of fungal carbon and nitrogen use at the community level.  We also participate in collaborative efforts to understand the ecological dynamics of aquatic bacteria as these dynamics pertain to antibiotic resistance.  Several of these efforts are linked with projects to bring field research opportunities to minority community college students in Dallas and in Waco.

Arid Ecosystems and Climate Change

For the past 17 years my students and I have conducted a series of collaborative research efforts at Big Bend National Park (BBNP) in the Chihuahuan Desert with colleagues from Texas Tech, UC Santa Cruz, Arizona State, the USGS, Colorado State University, and Washington State University to understand the role of climate variability in structuring soil microbial and nutrient dynamics as they are linked to plant ecophysiology, and plant community diversity.  In 1993 we initiated the Pine canyon Watershed Program at BBNP to understand the spatial and temporal variations in ecosystem process, microbial biodiversity and nutrient dynamics.  Our project was part of the larger Referenced Watershed Program that had been developed in the National Parks by the USGS to examine the impacts of climate change and anthropogenic impacts on environmental resources in the National Parks.  From these initial efforts we expanded our research to examine the impacts of changes in precipitation magnitude and frequency on soil microbial and nutrient dynamics, plant diversity and plant ecophysiology within the sotol grasslands in Pine Canyon.  This research is one component of a larger effort to understand the impacts of Global Climate Change in the functioning of arid ecosystems across the southwestern U.S.  In addition, we have been funded by the National Parks Service to examine the interactive impacts of water and atmospheric nitrogen deposition on mid-elevation grasslands and high elevation forests.  Our efforts at Big Bend are part of a larger network, PrecipNet, which is a collaborative effort among six colleagues to examine and coordinate precipitation impact research in arid ecosystems across the western United States.  We are currently also involved in evaluating the roles of Daily Temperature Varaibility  (DTR) on soil microbial and nutrient dynamics at BBNP and in determining the success of reclamation efforts using debris dams to reestablish degraded low elevation grasslands in BBNP.

Agriculture

Our agricultural research addresses how management decision in a semi-arid environment impact soil microbial diversity and activity.  The goals of this research are to determine if and how microbial diversity and activity are linked to productivity.  We are exploring how we can manage the soil microflora in such a manner to reduce energy inputs into the system.  Our agricultural related research is being conducted with colleagues at the USDA Plant Stress and Waters Use lab her in Lubbock.

Aquatic Microbiology

In conjunction with several colleagues in Biological Sciences we have examined the complex dynamics that determine bacterial community dynamics and abundances of playa lakes within the city of Lubbock.  These lakes created from run-off from streets are used for flood control and also for recreational fishing by residents across the areas.  Given the water sources, we have explored the seasonal dynamics of coliform bacteria and of Aeromonas species.  As an emerging pathogen, we have discovered that Aeromonas can become multiple-drug resistant and have examined the mechanism that contribute to the pathogenicity of this bacterium.  We continue to explore the environmental conditions that promote lateral gene exchange in this bacterium.

Selected Publications

• Robertson, T.R., J.C. Zak and D.T. Tissue. 2010. Precipitation magnitude and timing differentially affect species richness and plant density in the sotol grassland of the Chihuahuan Desert. Oecologia.162: 185-197.
• Acosta-Martínez V., C. W. Bell, B. E. L. Morris, J. C. Zak, and V. G. Allen. 2009.  Long-term soil microbial community and enzyme responses to integrated cropping-livestock systems in a semi-arid region. Agriculture, Ecosystems and Environment 137:231-240.
• Bell, C.W., V. Acosta-Martinez, N. McIntyre, S. Cox, D. Tissue, and J.C. Zak. 2009. Linking microbial community structure and function to seasonal differences in soil moisture and temperature in Chihuahuan Desert grassland. Microbial Ecology 58:827-842.
• Campbell, J. J. Clark, and J. Zak. 2009. PCR-DGGE Comparison of bacterial Community Structure in Fresh and Archived Soils Samples along a Chihuahuan Desert Elevational Gradient. Microbial Ecology. (Published first on-line)
• Clark, J.S., J. H. Campbell, H. Grizzle, V. Acosta-Martinez, and J. C. Zak. 2009. Soil Microbial Community Response to Drought and Precipitation Variability in the Chihuahuan Desert. Microbial Ecology. 57: 248-260.
• Humpheries, J, S. Cox and J. Zak. 2009. Characterization of the Structural and Functional Diversity of Indigenous Soil Microbial Communities in Smelter-Impacted and Non-Impacted Soils. Environmental Toxicology and Chemistry.
• Patrick, L., K. Ogle, C.W. Bell, J. Zak and D. Tissue. 2009. Physiological responses of two contrasting desert plant species to precipitation variability are differentially regulated by soil moisture and nitrogen dynamics. Global Change Biology 15: 1214-1229.
• Robertson, T.R., J.C.  Zak and D.T. Tissue. 2009. Precipitation timing and magnitude differentially affect aboveground annual net primary productivity in three perennial species in a Chihuahuan Desert grassland. New Phytologist 181:230-242.
• Anderson, J.A.H., M.J. Hooper, J.C. Zak, and S. Cox. 2008. Molecular and Functional Assessment of Bacterial Community Convergence in Metal-Amended Soils. Microbial Ecology. (Published first on-line).
• Bell, C. W., N. McIntyre, S. Cox, D. Tissue and  J. Zak . 2008. Soil Microbial Responses to Temporal Variations of Moisture and Temperature in Chihuahuan Desert Grassland. Microbial Ecology 56: 153-167.
• Huddleston, J.R., J. C. Zak and R.M. Jeter. 2007. Sampling bias created by ampicillin in isolation media for Aeromonas. Can J. Micro. 53: 39-44.
• Patrick, L., J. Cable, D. Potts, D. Ignace, G. Barron-Gafford, A. Griffith, H. Alpert, N. van Gestel, T. Robertson, T. Huxman, J. Zak, M. Loik, and D. Tissue. 2007. Effects of an increase in summer precipitation on leaf, soil, and ecosystem fluxes of CO2 and H20 in a sotol grassland in Big Bend National Park, TX. Oecologia 151:704-718.