Submitted to: Microbial Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/25/2009
Publication Date: 11/1/2009
Citation: Bell, C.W., Acosta Martinez, V., McIntyre, N.E., Cox, S., Tissue, D.T., Zak, J.C. 2009. Linking microbial community structure and function to seasonal differences in soil moisture and temperature in a Chihuahuan Desert Grassland. Microbial Ecology. 58(4):827-842. Interpretive Summary: Global climate models (GCM) predict an increase in temperature and precipitation variability across arid regions in the Southwest region of USA within the next century, which will result in less frequent rain events of greater magnitude. This research examined the soil microbial component, biogeochemical cycling, and other soil responses in a field simulation of GCM predictions of a 25% increased seasonal rainfall applications over a 7-year period (2002-2008) in order to determine long-term soil responses to climate change in the Chihuahuan desert sotol grassland at Big Bend National Park. According to our study, the GCM predictions of higher soil temperature and increased variability in precipitation magnitudes and frequencies in arid ecosystems will cause significant changes in soil microbial community of the desert evaluated within 3 yrs of climate changes. If future climate patterns predictions occur, declines in primary production as a result of lower soil microbial community function and shifts in structural dynamics may occur in this system with potential to limit the whole ecosystem functioning.
Technical Abstract: Global climate models (GCM) predict increased temperature and precipitation variability across arid regions across the Southwest region of USA within the next century, which will result in less frequent rain events of greater magnitude. While many studies have addressed the short-term impacts of precipitation - pulse variability in arid ecosystems on soil microbial and biogeochemical response patterns, few efforts have directly assessed their shifts over more than a couple of years. We conducted a field simulation study of GCM predictions of a 25% increase in seasonal rainfall over a 7-year period (2002-2008) to determine long-term soil responses to climate change in the Chihuahuan desert sotol grassland at Big Bend National Park (BBNP). We hypothesized that over time, these minor but realistic increases in moisture additions would produce a measurable accumulative change in soil microbial, biogeochemical cycling, and other soil properties. The soil microbial community structure was evaluated using bacterial (gram-negative, gram-positive, and actinomycetes) and fungal (saprophytic fungi and arbuscular mycorrhiza) fatty acid methyl ester (FAME) markers. Microbial community functional responses to precipitation were characterized via carbon substrate utilization patterns (BIOLOG) and enzymatic activities involved in nutrient cycling. Over time, cumulative changes in soil microbial, biogeochemical, and other soil properties were detected with 25% higher moisture than normal based on climate change predictions. Microbial community structural responses emerged during the third year of this study, as the relative abundances of saprophytic fungi, AM fungi, and G- bacteria were higher with increased watering in the SW plots. The activities of ß-glucosidase and phosphodiesterase were also elevated, which are involved in key processes such as cellulose degradation and phosphorus cycling, respectively. Our results strongly suggested that long-term, increased precipitation applications will alter soil microbial community dynamics and will reduce microbial community functionality in this desert grassland at BBNP.