Low Pore Connectivity Increases Bacterial Diversity in Soil

Abstract

One of soil microbiology's most intriguing puzzles is how so many different bacterial species can coexist in small volumes of soil when competition theory predicts that less competitive species should decline and eventually disappear. We provide evidence supporting the theory that low pore connectivity caused by low water potential (and therefore low water content) increases the diversity of a complex bacterial community in soil. We altered the pore connectivity of a soil by decreasing water potential and increasing the content of silt-and clay-sized particles. Two textures were created, without altering the chemical properties or mineral composition of the soil, by adding silt-and clay-sized particles of quartz to a quartz-based sandy soil at rates of 0% (sand) or 10% (silt؉clay). Both textures were incubated at several water potentials, and the effect on the active bacterial communities was measured using terminal restriction fragment length polymorphism (TRFLP) of bacterial 16S rRNA. Bacterial richness and diversity increased as water potential decreased and soil became drier (P < 0.012), but they were not affected by texture (P > 0.553). Bacterial diversity increased at water potentials of <2.5 kPa in sand and <4.0 kPa in silt؉clay, equivalent to <56% water-filled pore space (WFPS) in both textures. The bacterial community structure in soil was affected by both water potential and texture (P < 0.001) and was correlated with WFPS (sum of squared correlations [␦ 2 ] ‫؍‬ 0.88, P < 0.001). These findings suggest that low pore connectivity is commonly experienced by soil bacteria under field conditions and that the theory of pore connectivity may provide a fundamental principle to explain the high diversity of bacteria in soil.

Conservation tillage increases soil bacterial diversity in the dryland of northern China

“…3b) correlated with the relative abundances of the dominant bacterial phyla (class) including the Acidobacteria, Firmicutes, Actinobacteria, Chloroflexi, and Alphaproteobacteria. These results partially support the notion that soil texture is the strongest factor in structuring bacterial communities (Bach et al 2010;Carson et al 2010). Our study suggests that the soil texture fraction is the principal factor that plays an important role in determining soil nutrient status and moisture (Davinic et al 2012;Li et al 2014) and contributes to the differences in soil bacterial composition between conservation (chisel plow and zero tillage) and convention (plow) tillage.…”

“…This observation can be explained by similarities in the soil texture and moisture between the zero and chisel plow tillage. The soil texture and moisture are principle factors affecting soil pore connectivity, which leads to changes in bacterial diversity, and are significantly related to the Shannon (P = 0.03) and Simpson (P = 0.01) indices (Carson et al 2010). The zero tillage, which caused less soil disturbance than the chisel plow tillage did, could provide a suitable environment for multiplying soil bacteria.…”

Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota

“…protozoan predation) in finetextured soils than in coarse-textured soils (Rutherford & Juma 1992). Recent results show that low pore connectivity may even contribute to high bacterial diversity in soil (Carson et al 2010).…”

Soil Health and Related Ecosystem Services in Organic Agriculture

“…Near edge X-ray fine structure spectroscopy and scanning transmission X-ray microscopy have potential to provide new opportunities for three-dimensional investigation of molecules in soil (Schmidt et al, 2011). There are also opportunities for clarification of "recalcitrant" vs "protected" organic matter (Dungait et al, 2012b), and for identifying the roles of different microbial communities in connected and disconnected soil pores (Carson et al, 2010).…”