Soil Microbial Community Response to Drought and Precipitation Variability in the Chihuahuan Desert |
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Authors: | Jeb S Clark James H Campbell Heath Grizzle Veronica Acosta-Martìnez John C Zak |
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Institution: | (1) Department of Biological Sciences, Texas Tech University, P.O. Box 43131, Lubbock, TX 79409-3131, USA;(2) Department of Pediatrics, Division of Pediatric Nephrology, University of Mississippi Medical Center, Research Wing, Room R127, 2500 North State Street, Jackson, MS 39216-4505, USA;(3) Clean Air Laboratory, 228 Midway Lane, Suite B, Oak Ridge, TN 37830, USA;(4) Plant Stress and Water Conservation Lab, USDA-ARS, 3810 4th Street, Lubbock, TX 79415, USA |
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Abstract: | Increases in the magnitude and variability of precipitation events have been predicted for the Chihuahuan Desert region of
West Texas. As patterns of moisture inputs and amounts change, soil microbial communities will respond to these alterations
in soil moisture windows. In this study, we examined the soil microbial community structure within three vegetation zones
along the Pine Canyon Watershed, an elevation and vegetation gradient in Big Bend National Park, Chihuahuan Desert. Soil samples
at each site were obtained in mid-winter (January) and in mid-summer (August) for 2 years to capture a component of the variability
in soil temperature and moisture that can occur seasonally and between years along this watershed. Precipitation patterns
and amounts differed substantially between years with a drought characterizing most of the second year. Soils were collected
during the drought period and following a large rainfall event and compared to soil samples collected during a relatively
average season. Structural changes within microbial community in response to site, season, and precipitation patterns were
evaluated using fatty acid methyl ester (FAME) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE)
analyses. Fungal FAME amounts differed significantly across seasons and sites and greatly outweighed the quantity of bacterial
and actinomycete FAME levels for all sites and seasons. The highest fungal FAME levels were obtained in the low desert scrub
site and not from the high elevation oak–pine forests. Total bacterial and actinomycete FAME levels did not differ significantly
across season and year within any of the three locations along the watershed. Total bacterial and actinomycete FAME levels
in the low elevation desert-shrub and grassland sites were slightly higher in the winter than in the summer. Microbial community
structure at the high elevation oak–pine forest site was strongly correlated with levels of NH4
+–N, % soil moisture, and amounts of soil organic matter irrespective of season. Microbial community structure at the low elevation
desert scrub and sotol grasslands sites was most strongly related to soil pH with bacterial and actinobacterial FAME levels
accounting for site differences along the gradient. DGGE band counts of amplified soil bacterial DNA were found to differ
significantly across sites and season with the highest band counts found in the mid-elevation grassland site. The least number
of bands was observed in the high elevation oak–pine forest following the large summer-rain event that occurred after a prolonged
drought. Microbial responses to changes in precipitation frequency and amount due to climate change will differ among vegetation
zones along this Chihuahuan Desert watershed gradient. Soil bacterial communities at the mid-elevation grasslands site are
the most vulnerable to changes in precipitation frequency and timing, while fungal community structure is most vulnerable
in the low desert scrub site. The differential susceptibility of the microbial communities to changes in precipitation amounts
along the elevation gradient reflects the interactive effects of the soil moisture window duration following a precipitation
event and differences in soil heat loads. Amounts and types of carbon inputs may not be as important in regulating microbial
structure among vegetation zones within in an arid environment as is the seasonal pattern of soil moisture and the soil heat
load profile that characterizes the location. |
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