Local community assembly mechanisms shape soil bacterial β diversity patterns along a latitudinal gradient

Biodiversity patterns across geographical gradients could result from regional species pool and local community assembly mechanisms. However, little has been done to separate the effects of local ecological mechanisms from variation in the regional species pools on bacterial diversity patterns. In this study, we compare assembly mechanisms of soil bacterial communities in 660 plots from 11 regions along a latitudinal gradient in eastern China with highly divergent species pools. Our results show that β diversity does not co-vary with γ diversity, and local community assembly mechanisms appear to explain variation in β diversity patterns after correcting for variation in regional species pools. The variation in environmental conditions along the latitudinal gradient accounts for the variation in β diversity through mediating the strength of heterogeneous selection. In conclusion, our study clearly illustrates the importance of local community assembly processes in shaping geographical patterns of soil bacterial β diversity.


Statistics
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For hierarchical and complex designs, identification of the appropriate level for tests and full reporting of outcomes Estimates of effect sizes (e.g. Cohen's d, Pearson's r), indicating how they were calculated Our web collection on statistics for biologists contains articles on many of the points above.

Software and code
Policy information about availability of computer code Data collection Soil bacterial communities were sequenced using Illumina Miseq system with Reagent Kit v2 2 × 250 bp.

Data analysis
The raw sequences were sorted based on unique sample tags and then were trimmed using QIIME Pipeline (http://qiime.org/tutorials/ tutorial.html). Analyses were performed in R project 3.6.1 and The R code supporting the findings presented here is available at https:// github.com/YTHHN/R-code.
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Data
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Study description
The study was conducted in natural forest communities along the North-South Transact of eastern China, which spans 3,700 km from north to south with latitude ranging from 53º27ʹN to 18º43ʹN and longitude ranging from 108º53ʹE to 122º20ʹE. Soil bacterial communities was investigated in 660 plots from 11 regions (60 plots at each region along the latitudinal gradient in North-South Transect of eastern China.

Research sample
Our research samples are soil bacterial communities.

Sampling strategy
We had 60 replicates per region. We based this on previous studies ( Timing and spatial scale Sampling occurred during June and July (summer) in 2015, from the south to the north along the latitudinal gradient in eastern China. We ensure all the samples are completed in summer.
Soil samples were collected from all 660 plots using a uniform sampling protocol. Each sample was a composite of six individual soil cores (2.5 cm diameter × 10 cm depth) randomly collected from the horizon within each plot.

Data exclusions
No data were excluded.

Reproducibility
Sequencing methods taken in this study are widely adopted.

Randomization
In each region, 60 plots were randomly selected. In each region, 60 plots were established randomly in a typical forest without anthropogenic or natural disturbance.

Blinding
Blinding was not relevant to this study because it did not involve a treatment group.
Did the study involve field work?

Yes No
Field work, collection and transport

Field conditions
The mean annual temperature (MAT) of the transect ranges from −4.4 to 20.9°C. The mean annual precipitation (MAP) is approximatelyabout 482~ 2,449 mm.