Variation in Microbial Community Composition and Culturability in the Rhizosphere of Leucanthemopsis alpina (L.) Heywood and Adjacent Bare Soil Along an Alpine Chronosequence

Abstract

We compared the size, culturability, diversity, and dominant species similarity of the bacterial communities of Leucanthemopsis alpina (L.) Heywood rhizosphere and adjacent bare soil (interspace) along a chronosequence of soil development time (5, 50, and 70 years) in the forefield of the Dammaglacier (Switzerland). We found no evidence that the size of the bacterial community was significantly affected by either soil age or the presence of L. alpina. In contrast, the proportion of the bacterial community that could be cultured on nonselective agars, and which was taken as an indication of the proportion of r-selected populations, was significantly higher in the 50- and 70-year-old soils than in the 5-year-old soil, and was also significantly higher in the rhizosphere of L. alpina at all time points. RDA indicated significant correlations between the increased culturability of the bacterial community over time and increasing concentrations of labile N, and between the increased culturability in the rhizosphere and increased concentrations of labile C and N. HaeIII-amplified ribosomal DNA (rDNA) restriction analysis of a library of 120 clones of 16S rDNA revealed 85 distinct phylotypes. Hurlbert's probability of interspecific encounter (PIE) values derived from this library ranged from 0.95 to 1.0, indicating a very high genetic diversity. There was no significant difference in the PIE values of rhizosphere and interspace communities. Detrended correspondence analysis (DCA) of 16S ribosomal RNA (rRNA) denaturing gradient gel electrophoresis (DGGE) community profiles clearly distinguished the rhizosphere from the interspace community in the 5-year-old soils and also clearly distinguished between these communities and the rhizosphere and interspace communities of the 50- and 70-year-old soils. However, 16S rRNA DGGE revealed little difference between rhizosphere and interspace communities in the 50- and 70-year-old soils. The relative similarity of the 16S rRNA profiles strongly reflected labile carbon and nitrogen availability. Overall, our results suggest that improved C and N availability in the rhizosphere of L. alpina increases the size of r-selected bacterial species populations, but that the influence of L. alpina depends on soil age, being maximal in the youngest soils and minimal in the oldest. The reduced influence of L. alpina in the older soils may reflect a feedback between improved nutrient availability and reduced rhizodeposition.

Abundances and potential activities of nitrogen cycling microbial communities along a chronosequence of a glacier forefield

“…Moreover, initial sites are often dominated by microbes belonging to the r-strategists being able to respond quickly to changing environmental conditions, whereas with continuing succession a shift to k-strategists occurs that rather pursue the strategy of maintenance . In contrast to these studies, some reports found no significant correlation between soil age and diversity (Edwards et al, 2006) or increasing diversity (Tscherko et al, 2003;Nemergut et al, 2007).…”

“…Sampling took place along the forefield of the Damma glacier (46138 0 20 0 'N and 8128 0 00 0 'E) in canton Uri, Switzerland (Figure 1; Edwards et al, 2006). The forefield is characterized by gneiss as bedrock and silty sandy soil texture (Lazzaro et al, 2009).…”

The role of microorganisms at different stages of ecosystem development for soil formation

“…In parallel, functional groups leading to N losses like nitrifying or denitrifying microbes were reduced in the rhizosphere, which is in line with the assumption that plants are able to actively influence their rhizosphere community (Singh et al, 2004) by changing their exudation pattern or by actively excreting substances like tannins, polyphenolic substances or monoterpenes (Briones et al, 2003;Kowalchuk and Stephen, 2001;Ward et al, 1997;Cocking, 2003). In this regard, Edwards et al (2006) detected changes in the exudation pattern of L. alpina along the forefield of the Damma Glacier mainly attributed to a strong reduction of oxalic and citric acid concentrations. In general, it seems that indeed microbial activity and abundance is much higher in the rhizosphere of pioneering plants compared to the bulk soil, but the community composition is strongly driven by the bulk soil community, whereas at developed sites the plant determines the microbial community in the rhizosphere (Duc et al, 2009;Miniaci et al, 2007).…”

“…The phenomenon of enhanced microbial activity and abundance in the rhizosphere of plants is known as the "rhizosphere effect" (Butler et al, 2003;Hartmann et al, 2008). Regarding the Damma Glacier the rhizosphere effect is generally more pronounced at initial sites compared to developed ones (Töwe et al, 2010;Edwards et al, 2006). This observation seems to be a general effect independent of plant species, bedrock material or climatic conditions.…”

Drop-Size Soda Lakes: Transient Microbial Habitats on a Salt-Secreting Desert Tree

“…Microbial biodiversity estimates in plant environments have been carried out to a much more limited extent. Recent reports describe a high diversity in rhizosphere environments (Stafford et al 2005;Edwards et al 2006), with no attempt to estimate the total number of OTUs. In fact, very little use has been made to date of culture-independent methods for the study of phyllosphere bacterial populations and their diversity.…”