In the past decades, the spatial patterns of microbial biodiversity were widely investigated on the regional, continental and global scale. Growing evidence indicates that most microbial taxa display biogeographic patterns that are similar to macroorganisms.
However, our understanding of the fundamental processes that underlie microbial biogeographic patterns remains limited. The distance-decay relationship is one of the most well-known biodiversity patterns observed in communities from all domains of life.
It is sensitive to critical ecological processes and thus often considered as a powerful tool for testing mechanistic ecological theories.
The distance-decay patterns have been observed for free-living microorganisms across a range of habitats at various taxonomic resolutions. Generally, two mechanisms could give rise to this pattern, that is, deterministic processes based on Niche Theory and stochastic processes based on Neutral Theory.
Vellend (2010) proposed a new community ecology theory to explain the biodiversity patterns. In his conceptual synthesis, most mechanisms that contribute to patterns in the composition and diversity of species can be categorized into four classes of processes: selection, dispersal, drift and speciation.
This conceptual model relates many of the existing theories and models in community ecology to each of the four processes alone or their combinations.
Based on this conceptual framework, Dr. WANG Xiaobo, a microbial ecologists in the Institute of Applied Ecology of the Chinese Academy of Sciences, conducted a 4,000 km transect survey in China’s drylands across four different habitats including alpine grassland, desert, desert grassland and typical grassland.
He collected 545 soil samples in total and compared systematically the differences in the distance-decay curves of bacterial communities (at both the 97 and 99% resolutions), and in the relative importance of underlying factors (environmental variables or geographic distance) contributing to such relationships.
He attempted to reveal a potential association between different bacterial diversity patterns observed and the relative importance of the ecological processes.
The results showed that a significant distance-decay relationship of bacterial communities was found across each habitat, but the slopes and intercepts of the distance-decay relationships varied across different habitat.
Both the β-diversity pattern of bacterial communities and the relative importance of environmental factors versus geographic distance to a distance-decay relationship were habitat specific.
Moreover, the abundance and distribution of dominant bacteria species also show significant difference among habitats. A strong distance-decay relationship was observed in the alpine grassland and it was only affected by strong environmental heterogeneity.
Thus, selection is likely to have dominant roles in driving bacterial β-diversity pattern in the alpine grassland.
In contrast, bacterial community similarity was solely influenced by the geographic distance in the desert which suggests that bacterial dispersal in this area was limited.
Therefore, inherent stochastic processes such as drift and dispersal limitation may have a much greater role in driving bacterial β-diversity pattern in the area. There was no evidence that dispersal limitation strongly influenced the β-diversity of bacterial communities in the desert grassland and typical grassland.
In conclusion, selection may have a prominent role in shaping microbial biogeographic patterns in drylands.
The results entitled “Habitat-Specific Patterns and Drivers of Bacterial β-diversity in China’s Drylands” was online-published in the latest issue of the ISME Journal.
This work was financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the General Program of the National Natural Science Foundation of China.