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FIGURE 7.4 Variation in Acidobacteria (A) taxon richness and (B) phylogenetic diversity across the elevation gradient at four different taxonomic resolutions. Taxonomic richness is the total number of taxa (phylotypes) and phylogenetic diversity is the minimum total branch length connecting all taxa in the community and the root. Richness and phylogenetic diversity are best modeled as linearly decreasing with elevation at all taxonomic resolutions (Akaike information criteria). Slopes of the taxon richness patterns: 99%, −0.006982*; 97%, −0.005158*; 94%, −0.001939; 90%, −0.002364*. Slopes of the phylogenetic diversity pattern: 99%, −0.0007653*; 97%, −0.0004603*; 94%, −0.0002757*; 90%, −0.0001679. Asterisks indicate that the decrease in diversity with elevation is significant (P < 0.05) based on linear regression analysis.

FIGURE 7.4 Variation in Acidobacteria (A) taxon richness and (B) phylogenetic diversity across the elevation gradient at four different taxonomic resolutions. Taxonomic richness is the total number of taxa (phylotypes) and phylogenetic diversity is the minimum total branch length connecting all taxa in the community and the root. Richness and phylogenetic diversity are best modeled as linearly decreasing with elevation at all taxonomic resolutions (Akaike information criteria). Slopes of the taxon richness patterns: 99%, −0.006982*; 97%, −0.005158*; 94%, −0.001939; 90%, −0.002364*. Slopes of the phylogenetic diversity pattern: 99%, −0.0007653*; 97%, −0.0004603*; 94%, −0.0002757*; 90%, −0.0001679. Asterisks indicate that the decrease in diversity with elevation is significant (P < 0.05) based on linear regression analysis.

the angiosperm phylogenic tree topology was constructed by using the widely accepted supertree approach (Webb and Donoghue, 2005), and branch lengths were assigned based on estimates of the minimum age of internal nodes (see Materials and Methods). Comparative analyses using molecular approaches alone for both plants and microbes would improve our confidence in such phylogenetic comparisons. Such approaches will be facilitated in the future by increased accessibility to molecular data.

Microorganisms (especially prokaryotes) are very diverse in soils (Torsvik et al., 1990; Janssen, 2006). On par with most microbial diversity studies, it is likely that we sampled the most abundant taxa in each soil core along the elevational gradient. Sampling effort (i.e., the proportion of a community that is sampled) is known to significantly influence taxonomic biodiversity patterns (Plotkin et al., 2002; Woodcock et al., 2006; Green and Plotkin, 2007; Morlon et al., 2008). To our knowledge the influence of sampling effort on phylogenetic biodiversity patterns has not been explored. For example, estimators are available to predict the taxon richness (Hughes et al., 2001) and taxon similarity (Chao et al.,



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