03037nas a2200205   4500008004100000245014400041210006900185300001300254490000700267520228400274653002402558653001502582653000902597653001102606653002902617653002302646100001902669700001702688856012602705       2007                        eng d00aSeven years of enhanced water availability influences the physiological, structural and functional attributes of a soil microbial community0 aSeven years of enhanced water availability influences the physio  a535 -5450 v353 aWater availability is known to influence many aspects of microbial growth and physiology, but less is known about how complex soil microbial communities respond to changing water status. To understand how long-term enhancement of soil water availability (without flooding) influences microbial communities, we measured the seasonal dynamics of several community-level traits following >7 years of irrigation in a drought-prone tallgrass prairie soil. From late May to mid-September, water was supplied to the irrigated treatments based on calculated plant water demand. Phospholipid fatty acids (PLFA) were used to assess changes in microbial community structure and physiology. To assess the community-level physiological profile, microbial utilization of BIOLOG substrates was determined. After incubation for 2 days, the distribution of added 13C-glucose in microbial and respired pools was used as an index of substrate utilization efficiency. We also measured the relative contribution of fungi and bacteria to soil microbial biomass via substrate-induced respiration (SIR). Multivariate analysis of mol% PLFA and BIOLOG substrate utilization indicated that both water availability and sampling time influenced both the physiological and structural characteristics of the soil microbial community. Specific change in biomarker PLFA revealed a decreased ratio of cyclopropyl to ω7-precursors due to water addition, suggesting community-level stresses were reduced. Over the growing season, continuously greater water availability resulted in a 53% greater ratio of fungal to bacterial biomass using SIR, and a 65% increase in fungal PLFA. The number of substrates utilized by the cultivable microbial community tended to be greater in continuously wetted soil, especially during periods of low rainfall. While water dynamics appeared to be associated with some of the shifts in microbial community activity, structural and functional changes in the community appeared to be more closely linked to the cumulative effects of water regime on ecosystem properties. Seasonality strongly influenced microbial communities. The environmental factors associated with seasonal change need to be more closely probed to better understand the drivers of community structure and function.10aMicrobial community10aphysiology10aPLFA10aStress10aSubstrate use efficiency10aWater availability1 aWilliams, M.A.1 aRice, C., W.  uhttp://knz.lternet.edu/content/seven-years-enhanced-water-availability-influences-physiological-structural-and-functional