Environmental selection overturns the decay relationship of soil prokaryotic community over geographic distance across grassland biotas

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    Evaluation Summary:

    This study, which is of interest to students of microbial biogeography, explores the distance-decay relationship for soil prokaryotic communities in alpine and temperate grasslands. Although the experimental scale and conclusions are fairly substantial, there are concerns about the methods, as well as several concerns related to the inferences and presented results.

    (This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)

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Abstract

Though being fundamental to global diversity distribution, little is known about the geographic pattern of soil microorganisms across different biotas on a large scale. Here, we investigated soil prokaryotic communities from Chinese northern grasslands on a scale up to 4000 km in both alpine and temperate biotas. Prokaryotic similarities increased over geographic distance after tipping points of 1760–1920 km, generating a significant U-shape pattern. Such pattern was likely due to decreased disparities in environmental heterogeneity over geographic distance when across biotas, supported by three lines of evidences: (1) prokaryotic similarities still decreased with the environmental distance, (2) environmental selection dominated prokaryotic assembly, and (3) short-term environmental heterogeneity followed the U-shape pattern spatially, especially attributed to dissolved nutrients. In sum, these results demonstrate that environmental selection overwhelmed the geographic ‘distance’ effect when across biotas, overturning the previously well-accepted geographic pattern for microbes on a large scale.

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  1. Evaluation Summary:

    This study, which is of interest to students of microbial biogeography, explores the distance-decay relationship for soil prokaryotic communities in alpine and temperate grasslands. Although the experimental scale and conclusions are fairly substantial, there are concerns about the methods, as well as several concerns related to the inferences and presented results.

    (This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)

  2. Reviewer #1 (Public Review):

    This study explored the distance-decay relationship for soil prokaryotic communities in alpine and temperate grasslands. With large amounts of natural samples (258 soils) across 4000 km distances, this survey on soils and microbial communities is pretty massive and extensive. Their results showed that in contrast to traditional linear relationship within the same biome, a significant U-shape pattern was found across both two grassland types. More interestingly, further analysis showed homogeneous selection process instead of geographic distance effects may contribute to the soil prokaryotic community patterns, mainly attributed to dissolved nutrients. It subverted the popular standpoint that microbial distribution pattern as same as macroorganisms had clear distance-decay relationship. The habitat environments, especially the soil dissolved nutrients, could be more important on shaping microbial distributions on large scale.

  3. Reviewer #2 (Public Review):

    In this manuscript, Zhang et al. collected 258 topsoil and subsoil samples from northern Chinese grasslands on a scale up to 4,000 km. They found that prokaryotic communities in those samples did not follow the common distance-decay relationship, which (they believed) was caused by homogeneous environmental selection. In general, it is a well-versed manuscript. It presents an excellent sampling campaign that generates a large number of precious soil samples. Lack of distance-decay relationship is an interesting observation, but it has been observed in other large-scale biogeographic studies (e.g., References 90 and 91). This study took samples throughout a transect from northeastern China to southwestern China. Both ends of the transect are cold climates, which explains the U shape of distance-decay relationship. This is rare since such transects are difficult to find in other places of the world. Therefore, the U shape pattern is an exception to large-scale biogeographic patterns. I like most of the results here and applaud the tremendous efforts to collect samples since China is a vast country, but I disagree with the authors that their results have challenged any tenet of the microbial biogeographic field.