Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/1999
Publication Date: 7/1/2000
Citation: LIU,X., LINDEMANN,W.C., WHITFORD,W.G., STEINER,R.L. MICROBIAL DIVERSITY AND ACTIVITY OF DISTURBED SOIL IN THE NORTHERN CHIHUAHUAN DESERT. BIOLOGY AND FERTILITY OF SOILS. 2000. V. 32(3). P. 243-249. Interpretive Summary: This study focused on a measure of microbial diversity as an indicator of environmental stress in desert grasslands. Stresses imposed included intensive grazing during summer and winter, winter drought and summer drought (elimination of seasonal rainfall by rain-out shelters) and fire. The measure of microbial diversity was the capacity of different species of microbes to utilize specific organic substrates. In addition, a suite of enzymes associated with microbial activity was measured. Maximum diversity and activity occurred during summer in plots subjected to winter drought (using 'rain-out') shelters. This pattern of microbial diversity and activity occurs because drought kills soil microflora (bacteria and fungi) and the dead microbial biomass is a readily available substrate for drought-resistant microflora. Summer drought reduced microbial diversity as did fire. Seasonal patterns of microbial diversity and activity were similar in stressed and unstressed plots with diversity highest in summer, intermediate in winter and lowest in spring. Microbial activity was higher in summer and lower in winter. The seasonal patterns generally reflected soil moisture but were modified by the different stresses. This study provides evidence that biolag (organic substrate) plates provide a rapid and repeatable technique for assessing the effects of environmental stress on soil microbial communities.
Technical Abstract: The effects of intense grazing, seasonal drought, and fire on soil microbial diversity (substrate utilization) and activity in a northern Chihuahuan Desert grassland were measured in summer 1997, winter 2998, and spring 1998. Intense livestock grazing was initiated in winter 1995, burning occurred in August 1994, and drought stresses were imposed from October 1994 to June 1997. Microbial diversity was inferred from the carbon substrate utilization patterns in both gram (+) and gram (-) Biolog plates. Microbial activity was estimated by the activity of selected enzymes. Neither microbial diversity nor activity was affected by grazing. The interaction of intense grazing and stress subtreatments only occurred in spring for one set of diversity measurements. The maximum microbial diversity and activity occurred in the winter-drought-stress subplots in summer and spring. Burning reduced microbial diversity and most enzyme activities as compared to the control in summer and spring. Microbial diversity was also lower in summer-drought-stress subplots than in the control in summer and spring. Microbial diversity was highest in summer, intermediate in winter, and lowest in spring. Microbial activity was generally higher in summer and lower in winter. It was concluded that substrate availability was the most important factor affecting the diversity and activity of soil microorganisms within a season. Soil moisture was not the factor causing differences in microbial diversity and activity among the stress treatments, but it was a predictor for some microbial responses under a particular stress.