high-throughput-fluorometric-measurement-potential-soil-extracellular

High-throughput Fluorometric Measurement of Potential Soil Extracellular Enzyme Activities

Microbes in soils and other environments produce extracellular enzymes to depolymerize and hydrolyze organic macromolecules so that they can be ...

Colorado State University

Plant productivity in deserts may be more directly responsive to soil water availability than to precipitation. However, measurement of soil moisture alone may not be enough to elucidate plant responses to precipitation pulses, as edaphic factors may influence productivity when soil moisture is adequate. The first objective of the study was to determine the responses of the aboveground annual net primary productivity (ANPP) of three perennial species (from different functional groups) in a Chihuahuan Desert grassland to variation in natural precipitation (annual and seasonal) and a 25% increase in seasonal precipitation (supplemental watering in summer and winter). Secondly, ANPP responses to other key environmental and soil parameters were explored during dry, average, and wet years over a 5-yr period. ANPP predictors for each species were dynamic. High ANPP in Dasylirion leiophyllum was positively associated with higher soil NH(4)-N and frequent larger precipitation events, while that in Bouteloua curtipendula was positively correlated with frequent small summer precipitation events with short inter-pulse periods and supplemental winter water. Opuntia phaeacantha was responsive to small precipitation events with short inter-pulse periods. Although several studies have shown ANPP increases with increases in precipitation and soil moisture in desert systems, this was not observed here as a universal predictor of ANPP, particularly in dry years.

Precipitation timing and magnitude differentially affect aboveground annual net primary productivity in three perennial species in a Chihuahuan Desert grassland.

Global and regional climate models predict higher air temperature and less frequent, but larger precipitation events in arid regions within the next century. While many studies have addressed the impact of variable climate in arid ecosystems on plant growth and physiological responses, fewer studies have addressed soil microbial community responses to seasonal shifts in precipitation and temperature in arid ecosystems. This study examined the impact of a wet (2004), average (2005), and dry (2006) year on subsequent responses of soil microbial community structure, function, and linkages, as well as soil edaphic and nutrient characteristics in a mid-elevation desert grassland in the Chihuahuan Desert. Microbial community structure was classified as bacterial (Gram-negative, Gram-positive, and actinomycetes) and fungal (saprophytic fungi and arbuscular mycorrhiza) categories using (fatty acid methyl ester) techniques. Carbon substrate use and enzymic activity was used to characterize microbial community function annually and seasonally (summer and winter). The relationship between saprophytic fungal community structure and function remained consistent across season independent of the magnitude or frequency of precipitation within any given year. Carbon utilization by fungi in the cooler winter exceeded use in the warmer summer each year suggesting that soil temperature, rather than soil moisture, strongly influenced fungal carbon use and structure and function dynamics. The structure/function relationship for AM fungi and soil bacteria notably changed across season. Moreover, the abundance of Gram-positive bacteria was lower in the winter compared to Gram-negative bacteria. Bacterial carbon use, however, was highest in the summer and lower during the winter. Enzyme activities did not respond to either annual or seasonal differences in the magnitude or timing of precipitation. Specific structural components of the soil microbiota community became uncoupled from total microbial function during different seasons. This change in the microbial structure/function relationship suggests that different components of the soil microbial community may provide similar ecosystem function, but differ in response to seasonal temperature and precipitation. As soil microbes encounter increased soil temperatures and altered precipitation amounts and timing that are predicted for this region, the ability of the soil microbial community to maintain functional resilience across the year may be reduced in this Chihuahuan Desert ecosystem.

Linking microbial community structure and function to seasonal differences in soil moisture and temperature in a Chihuahuan desert grassland.

Soil microbial communities in Chihuahuan Desert grasslands generally experience highly variable spatiotemporal rainfall patterns. Changes in precipitation regimes can affect belowground ecosystem processes such as decomposition and nutrient cycling by altering soil microbial community structure and function. The objective of this study was to determine if increased seasonal precipitation frequency and magnitude over a seven-year period would generate a persistent shift in microbial community characteristics and soil nutrient availability. We supplemented natural rainfall with large events (one/winter and three/summer) to simulate increased precipitation based on climate model predictions for this region. We observed a two year delay in microbial responses to supplemental precipitation treatments. In Years 3-5, higher microbial biomass, arbuscular mycorrhizae abundance, and soil enzyme C and P acquisition activities were observed in the supplemental water plots even during extended drought periods. In Years 5-7, available soil P was consistently lower in the watered plots compared to control plots. Shifts in soil P corresponded to higher fungal abundances, microbial C utilization activity, and soil pH. This study demonstrated that 25% shifts in seasonal rainfall can significantly influence soil microbial and nutrient properties, which in turn may have long-term effects on nutrient cycling and plant P uptake in this desert grassland. This article is protected by copyright. All rights reserved.

Article	Year
Precipitation timing and magnitude differentially affect aboveground annual net primary productivity in three perennial species in a Chihuahuan Desert grassland. The New phytologist\| PubMed ID: 19076724	2009
Linking microbial community structure and function to seasonal differences in soil moisture and temperature in a Chihuahuan desert grassland. Microbial ecology\| PubMed ID: 19466479	2009
Soil microbial and nutrient responses to seven years of seasonally altered precipitation in a Chihuahuan Desert grassland. Global change biology\| PubMed ID: 24115607	2013

Colin W. Bell

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