Structure of a Microbial Community in Soil after Prolonged Addition of Low Levels of Simulated Acid Rain

Abstract

Humus samples were collected 12 growing seasons after the start of a simulated acid rain experiment situated in the subarctic environment. The acid rain was simulated with H2SO4, a combination of H2SO4 and HNO3, and HNO3 at two levels of moderate acidic loads close to the natural anthropogenic pollution levels of southern Scandinavia. The higher levels of acid applications resulted in acidification, as defined by humus chemistry. The concentrations of base cations decreased, while the concentrations of exchangeable H+, Al, and Fe increased. Humus pH decreased from 3.83 to 3.65. Basal respiration decreased with decreasing humus pH, and total microbial biomass, measured by substrate-induced respiration and total amount of phospholipid fatty acids (PLFA), decreased slightly. An altered PLFA pattern indicated a change in the microbial community structure at the higher levels of acid applications. In general, branched fatty acids, typical of gram-positive bacteria, increased in the acid plots. PLFA analysis performed on the bacterial community growing on agar plates also showed that the relative amount of PLFA specific for gram-positive bacteria increased due to the acidification. The changed bacterial community was adapted to the more acidic environment in the acid-treated plots, even though bacterial growth rates, estimated by thymidine and leucine incorporation, decreased with pH. Fungal activity (measured as acetate incorporation into ergosterol) was not affected. This result indicates that bacteria were more affected than fungi by the acidification. The capacity of the bacterial community to utilize 95 different carbon sources was variable and only showed weak correlations to pH. Differences in the toxicities of H2SO4 and HNO3 for the microbial community were not found.

Long-Term Effects of Short-Term Perturbation in a Subalpine Grassland

“…In our study, both the results of the multivariate analysis and the response of individual PLFAs to liming indicated that the effects of the liming treatment were mediated by its effect on soil pH. In the experiment at the Schynige Platte, fatty acids that are typical for low pH (10Me16:0, 10Me17:0) were more abundant in unlimed plots (Frostega˚rd et al 1993, Pennanen et al 1998, Ba˚a˚th and Anderson 2003.…”

“…Experimental manipulation of the soil pH in forests resulted in consistent changes in PLFA patterns, suggesting that pH is a key determinant of soil microbial community composition (Frostega˚rd et al 1993, Ba˚a˚th et al 1995, Pennanen et al 1998, Ba˚a˚th and Anderson 2003. Pennanen et al (1998), in results similar to our study, found that even a small change in soil pH of 0.2 units significantly influenced the composition of the soil microbial community. In our study, both the results of the multivariate analysis and the response of individual PLFAs to liming indicated that the effects of the liming treatment were mediated by its effect on soil pH.…”

Microbial diversity and soil functions

“…Also, the rates of 14 C-leucine or 3 H-thymidine incorporation increased in the presence of the nutrient limiting bacterial growth in soil (Alden et al, 2001). Pennanen et al (1998) and Alden et al (2001) have suggested that by monitoring acetate incorporation in ergosterol, one could determine nutrients that limit fungal growth in soil. Another approach for determining nutrient-limited bacterial growth uses bacteria of a reporter gene (van Overbeek et al, 1997;Jensen & Nybroe, 1999).…”

Pyrosequencing reveals a contrasted bacterial diversity between oak rhizosphere and surrounding soil

“…Distant soil samples characterized by contrasting edaphic characteristics were shown to have few bacterial species in common (Dunbar et al, 1999;Fierer and Jackson, 2006;Acosta-Martinez et al, 2008;Fulthorpe et al, 2008). Similarly, soil characteristics, particularly pH and fertility status, have been shown to correlate with overall bacterial diversity (Pennanen et al, 1998;Oline, 2006;Jones et al, 2009).…”