Hypolithic community shifts occur as a result of liquid water availability along environmental gradients in China's hot and cold hyperarid deserts

Abstract

Hypolithic cyanobacterial communities occur in hot and cold hyperarid environments but the physical factors determining their diversity are not well understood. Here we report hypolithic diversity and colonization of a common quartz substrate at several hyperarid locations in the ancient deserts of north-western China, that experience varying mean annual temperature, rainfall and concomitant availability of liquid water in soil. Microscopy and enrichment culture resulted only in Chroococcidiopsis morphotypes which were ubiquitous, but community phylogenetic analysis revealed considerable cyanobacterial and heterotrophic bacterial diversity. Species Richness and Shannon's Diversity Index displayed a significant positive linear correlation with availability of liquid water but not temperature or rainfall alone. Several taxonomic groups occurred only in specific climatically defined locations, while for Chroococcidiopsis, Deinococcus and Phormidium location specific lineages within these genera were also evident. Multivariate analysis was used to illustrate pronounced community shifts due to liquid water availability, although these did not significantly affect the predicted functional relationships within any given assemblage in either hot or cold, wet or dry hyperarid deserts. This study clearly demonstrates that availability of liquid water, rather than temperature or rainfall per se is the key determinant of hypolithic diversity in hyperarid locations, and furthermore that functionally similar yet taxonomically distinct communities occur, characterized by the presence of taxa that are specific to defined levels of aridity.

Stochastic and deterministic processes interact in the assembly of desert microbial communities on a global scale

“…An implicit consequence of the classical view is that extremophilic communities could be expected to converge toward an average stable and low diversity community. Despite this, recent molecular evidence has indicated that hypolithic communities may harbor significant phylogenetic diversity among bacterial phyla (Warren-Rhodes et al, 2006;Pointing et al, 2007Pointing et al, , 2009Bahl et al, 2011). Our data demonstrate that patterns generally interpreted as indicative of the presence of niche partitioning and non-neutral processes (for example, convergence due to relatively homogeneous environments) vary on a global biogeographical scale (continent) and also between phototrophic and heterotrophic bacteria within a given community.…”

“…Certainly, this is partly due to the fact that we introduced the environmental effect using a relatively broad approximation (climate categories based upon long-term mean annual temperature and precipitation), which ignored any unmeasured local environmental drivers that may be involved in determining community structure (for example, see Tracy et al, 2010). However, given previous studies on these communities that showed hypoliths develop independently of the surrounding soil (Warren-Rhodes et al, 2006; Pointing et al, 2007Pointing et al, , 2009Tracy et al, 2010) owing to the specific microclimatic conditions of rocks, and that climate and continent were independent of spatial patterns observed, it is likely that a large amount of this variation is due to environmental (for example, see Dornelas et al, 2006;Pointing et al, 2009) and/or demographic stochasticity (sensu Hubbell, 2001 andTilman, 2004).…”

“…Hypolithic communities are thought to develop as a result of marginal gains in niche favorability in terms of moisture availability and possible thermal buffering (Schlesinger et al, 2003;Warren-Rhodes et al, 2006;Tracy et al, 2010), although micro-niche variability may occur between individual rocks (Tracy et al, 2010). Several studies have indicated that hypolithic communities comprise relatively simple communities dominated by cyanobacteria, with a heterotrophic component largely represented by the Acidobacteria, Actinobacteria, Bacteriodetes and proteobacterial phyla (Schlesinger et al, 2003;Warren-Rhodes et al, 2006Pointing et al, 2007Pointing et al, , 2009Wood et al, 2008;Wong et al, 2010). These studies have indicated that the Archaea and eukaryal microorganisms are either absent or present with low abundance.…”

“…These studies have indicated that the Archaea and eukaryal microorganisms are either absent or present with low abundance. The lithic communities formed by bacteria in hyperarid deserts thus provide ecologists with a tractable global-scale model system for testing theories of community assembly, comprising relatively few phyla that are readily identified as producers or consumers (Warren-Rhodes et al, 2006;Pointing et al, 2007Pointing et al, , 2009 Therefore, it offers the opportunity to analyze a natural community with a very limited (basically two) number of trophic levels and without the potentially confounding effect of higher taxa such as protistans and metazoans. This allowed us to focus on both the entire community and/or part of it.…”

Microbial Diversity in Soil, Sand Dune and Rock Substrates of the Thar Monsoon Desert, India

“…Despite this a major gap in our understanding remains concerning the spatial distribution of desert microorganisms. Some studies on lithic communities have indicated the role of macro-climatic drivers such as mean annual precipitation including fog [13][14][15]. The influence of local scale processes has also been demonstrated, such as spatial self-organisation [15] and biological interactions [16,17].…”