The role of soil chemistry and parent material in determining microbial community composition and activity in temperate coniferous forests

Background/Question/Methods

Parent material is one of the state factors that controls soil development, and microsite soil chemical environment may be a key factor shaping microbial community structure and diversity. We assessed the influence of parent material and small-scale soil microsite chemistry on microbial community composition.

Study site 1 is a Picea abies (Norway spruce) forest in the Czech Republic, with constant climate, topography, and vegetation, but with sharp transitions in parent material. Previous studies shave shown that the forests on soils derived from each parent material are growth limited by different nutrients: Mg for granite, K and P for serpentinite, and N for amphibolite. In the organic and mineral horizons we assessed the total soil microbial community (bacteria and fungi), the fungal hyphal community (in-growth mesh bags), and the ectomycorrhizal community (root-tips), using 454 pyrosequencing and sanger sequencing of the ITS (fungi) and 16S (bacteria) regions.

Study site 2 is a Pinus muricata (bishop pine) forest in coastal California. We measured fungal community composition and structure across 2 parent materials (sandstone and granite) as well as across very fine spatial scales. On 1 cm³samples we assessed microsite soil chemistry (%C, %N, pH, exchangeable Ca, Mg, K, Na) and used t-RFLP in conjunction with molecular cloning and sanger-sequencing to assay fungal community composition.

Results/Conclusions

At both sites parent material exerted the strongest influence on microbial community composition. At the California site, within a particular parent material, base cations, soil horizon, and % carbon were all strongly associated with microbial community composition. On smaller spatial scales (<1m), % carbon and depth were most strongly associated with community composition. At the Czech sites bacterial growth (leucine incorporation) was significantly higher on the moderate pH and more productive amphibolite soil, while fungal growth (acetate incorporation) was significantly higher on the sepentinite derived soil.

Ectomycorrhizal communities were significantly different between mineral soil and organic horizon, as well as between different parent materials. Ectomycorrhizal communities were more different between mineral soils on different parent materials than they were between organic horizons. Ectomycorrhizal biomass, both hyphal and on roots, was significantly higher (>3 X) on the serpentine soils and significantly lower on the granite derived soil.

This research demonstrates that soil chemistry, strongly influenced by parent material, is significantly associated with soil microbial community composition, but forest nutritional status may also play a role in determining broader patterns in microbial biomass and community structure.