Aims: The aim of the present study was to design and test a method allowing the detection and quantification of methanogenic consortia in organic-rich rocks to determine the potential of methane biotransformation. Methods and Results: Methanogen numbers in the rock are often below the detection levels of quantification methods. Biostimulation was tested as a means to specifically increase bacterial and archaeal numbers above the detection levels in microcosms. Biostimulation reveals the presence of active heterotrophic and syntrophic bacterial consortia, methane accumulation and methanogens in one of four rock samples. Syntrophs and heterotrophs were dominated by Firmicutes, whereas archaeal diversity was limited to methanogens. Methane-producing microcosms were characterized by a higher Firmicutes diversity. Conclusions: Biostimulation is a reliable tool for detection of methanogenic consortia in organic-rich rocks. For routine and large scale experimentation, methane accumulation monitoring after biostimulation appears as the most time, work and cost efficient approach to detect the presence of active methanogenic consortia. Significance and Impact of the Study: We report for the first time the presence of live methanogenic consortia in organic-rich shales and their ability to mineralize the rock into methane. This approach will be instrumental to quantify the potential of these rocks to produce methane as a novel energy source.
Summary
Some temperate tree species are associated with very low soil nitrification rates, with important implications for forest N dynamics, presumably due to their potential for biological nitrification inhibition (BNI). However, evidence for BNI in forest ecosystems is scarce so far and the nitrifier groups controlled by BNI‐tree species have not been identified. Here, we evaluated how some tree species can control soil nitrification by providing direct evidence of BNI and identifying the nitrifier group(s) affected. First, by comparing 28 year‐old monocultures of several tree species, we showed that nitrification rates correlated strongly with the abundance of the nitrite oxidizers Nitrobacter (50‐ to 1000‐fold changes between tree monocultures) and only weakly with the abundance of ammonia oxidizing archaea (AOA). Second, using reciprocal transplantation of soil cores between low and high nitrification stands, we demonstrated that nitrification changed 16 months after transplantation and was correlated with changes in the abundance of Nitrobacter, not AOA. Third, extracts of litter or soil collected from the low nitrification stands of Picea abies and Abies nordmanniana inhibited the growth of Nitrobacter hamburgensis X14. Our results provide for the first time direct evidence of BNI by tree species directly affecting the abundance of Nitrobacter.
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