Bremer et al. 2009

Bremer C, Braker G, Matthies D, Beierkuhnlein C, Conrad R. 2009. Plant presence and species combination, but not diversity, influence denitrifier activity and the composition of nirk-type denitrifier communities in grassland soil. FEMS Microbiology and Ecology 70: 377-387.

These authors ran a manipulative, common-garden experiment to examine interactions between surface-plant community and soil denitrifier community diversities. The major finding of this paper, as described in the title, is that denitrifier community diversity is influenced by the species of plants in the system, but not how many species are there.

I saw 2 major problems with this paper that calls their major finding into question at least in my mind. First, the single greatest effect on denitrifier community composition found here was the very distinct community in the control, no-plant plots. These authors never acknowledge that zero plants is a point on their spectrum of species diversity; they state their range of plant community species richness was 2 to 8, but it was actually 0 to 8, with a strong effect of the 0 community. They do not analyze their data in this way that I can see, so I do not know if this 0-community effect does or does not reverse their conclusion that plant species diversity does not influence denitrifier diversity.

Second, the single most distinct with-plants community that was included in analysis is probably an outlier and should be excluded, because the plant community was 2 species of grasses (rather than mixed grass / forb), which also had the highest productivity in one of the study years. Furthermore that year was a high-temperature drought year across much of Europe including the study site. This probably-outlier result is acknowledged by these authors as having some of these problems, but their discussion of the probable role of greater niche-space in the soil under the more-diverse-but-same-species-richness plots does not suggest they have considered the confounding effects.

Despite the suspect results, this paper provides a useful overview, especially in the introduction and large parts of the discussion sections of denitrifier communities in soils and their probable interactions with plant communities.