Linking Microbial Community Structure and Function to Seasonal Differences in Soil Moisture and Temperature in a Chihuahuan Desert Grassland

Abstract

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.

Seasonality and resource availability control bacterial and archaeal communities in soils of a temperate beech forest

“…Also Shen et al (2008) and Tourna et al (2008) have found temporal shifts in archaeal abundance, and Stres et al (2008) and Tourna et al (2008) evidenced responsiveness of soil archaea to variations in soil temperature and soil moisture. Seasonal changes in soil climate were further closely linked to short-and medium-term variations in resource availability, which further correlated with the quantity and quality of organic matter entering the soil, as it was also previously suggested (Bell et al, 2009;Cookson et al, 2006;Krave et al, 2002). Consequently, total bacterial communities and individual phyla studied were clearly shaped by supply of DOC, DON and mineral N (that is, ammonia, nitrate), which is in agreement with previously published data (Drenovsky et al, 2004;Zak et al, 2003;Alden et al, 2001).…”

Soil enzyme responses to varying rainfall regimes in Chihuahuan Desert soils

“…Increased water availability following rain events stimulated hydrolytic enzyme activities early in the monsoon season, and as the season ended, enzyme activities decreased back to pre-season levels. Similar pre-and post-monsoon season enzyme activities have been observed elsewhere in the Chihuahuan Desert (Bell et al 2009), but our enzyme measurements associated with individual rain events highlight how variable enzyme activities can be following rain events throughout the monsoon season. Changes in enzyme activities were similar following either large, infrequent or small, frequent precipitation regimes, but ratios between enzyme activities highlighted greater nutrient limitation following large, infrequent rain events.…”

“…Given that dryland systems are sensitive to changes in precipitation (HeislerWhite et al 2009, Thomey et al 2011, Sala et al 2012 it is unclear how availability of soil resources, often made available via extracellular enzymes, will change under future patterns of precipitation. A study by Bell et al (2009) in desert grassland found that EEA was similar at the beginning and end of the summer monsoon season, but enzyme dynamics following individual rain events across the season have not been determined. In this study, we experimentally altered the size and frequency of soil moisture inputs during the summer monsoon in a northern Chihuahuan Desert grassland and monitored extracellular enzyme potentials to examine how rainfall changes potential enzyme activities throughout the season.…”

Soil enzyme activities during the 2011 Texas record drought/heat wave and implications to biogeochemical cycling and organic matter dynamics

“…In the SHP region, increases up to 37% has been found in EAs after only 2-3 rotations of sorghum with cotton (AcostaMartínez et al, 2011) and within two years following conversion from monoculture cotton to high input forage sorghum cropping systems without a change in soil organic C (Cotton et al, 2013). However, little is known about how these ecosensors respond to drought and whether soil type (e.g., differing textures) or management history affects the response under natural conditions in the field as most studies on the effects of drought and warming on soil EAs are conducted under simulated conditions (i.e., Sardans and Peñuelas, 2005;Bell et al, 2009). Under simulated drought conditions, soil EAs have shown a decrease as soil moisture is gradually reduced in native ecosystems in which other dynamics are involved (i.e., changes in plant physiology and biomass) (Sardans and Peñuelas, 2005;Sardans et al, 2008a,b).…”