Abstract
Salinization is recognized as a threat to soil fertility worldwide. A challenge in understanding the effects of salinity on soil microbial communities is the fact that it can be difficult to disentangle the effects of salinity from those of other variables that may co-vary with salinity. Here we use a trait-based approach to identify direct effects of salinity on soil bacterial communities across two salinity gradients. Through dose–response relationships between salinity and bacterial growth, we quantified distributions of the trait salt tolerance within the communities. Community salt tolerance was closely correlated with soil salinity, indicating a strong filtering effect of salinity on the bacterial communities. Accompanying the increases in salt tolerance were consistent shifts in bacterial community composition. We identified specific bacterial taxa that increased in relative abundances with community salt tolerance, which could be used as bioindicators for high community salt tolerance. A strong filtering effect was also observed for pH across the gradients, with pH tolerance of bacterial communities correlated to soil pH. We propose phenotypic trait distributions aggregated at the community level as a useful approach to study the role of environmental factors as filters of microbial community composition.
Highlights
One of the major challenges in the field of microbial ecology is to move beyond descriptive reports of patterns in community composition and find a basis for predicting shifts in bacterial communities in response to environmental changes [1]
Considering that soil salinity can span several orders of magnitude, it should be expected that salinity has a strong effect on bacterial community composition in soil as has been observed in aquatic systems and that soil salinity could be another strong driver of microbial community composition in addition to soil pH
The AG gradient encompassed soil electrical conductivity (EC) ranging from 0.1 to 3 dS m−1 measured in a 1:5 soil:water mixture, while the soil pH along the gradient was between ca. 5.5 and ca. 7.0 for all but one sample, which had a pH > 8 (Fig. S2)
Summary
One of the major challenges in the field of microbial ecology is to move beyond descriptive reports of patterns in community composition and find a basis for predicting shifts in bacterial communities in response to environmental changes [1]. Considering that soil salinity can span several orders of magnitude (from 100 dS m−1 in highly saline soil), it should be expected that salinity has a strong effect on bacterial community composition in soil as has been observed in aquatic systems and that soil salinity could be another strong driver of microbial community composition in addition to soil pH. Studies on the composition of bacterial communities of saline soils found shifts in community composition associated with salinity, as well as a decline in phylogenetic diversity as salinity increased [11,12,13,14]
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