Response of Atmospheric Methane Consumption by Maine Forest Soils to Exogenous Aluminum Salts

Abstract

Atmospheric methane consumption by Maine forest soils was inhibited by additions of environmentally relevant levels of aluminum. Aluminum chloride was more inhibitory than nitrate or sulfate salts, but its effect was comparable to that of a chelated form of aluminum. Inhibition could be explained in part by the lower soil pH values which resulted from aluminum addition. However, significantly greater inhibition by aluminum than by mineral acids at equivalent soil pH values indicated that inhibition also resulted from direct effects of aluminum per se. The extent of inhibition by exogenous aluminum increased with increasing methane concentration for soils incubated in vitro. At methane concentrations of >10 ppm, inhibition could be observed when aluminum chloride was added at concentrations as low as 10 nmol g (fresh weight) of soil ؊1. These results suggest that widespread acidification of soils and aluminum mobilization due to acid precipitation may exacerbate inhibition of atmospheric methane consumption due to changes in other parameters and increase the contribution of methane to global warming.A number of factors adversely affect atmospheric methane consumption by soils. Ammonium is one of the most important of these (6,8,13,14,20,30,31,37,49), but other factors include water stress (47), terpenes (3), salts (1,21,27,32), and land use (22,23,25,28). Soil pH has also been documented as a potentially important limiting factor, with both acidic (pH Ͻ4) and alkaline (pH Ͼ7) regimes inhibiting activity (2, 12, 22; J. Benstead and G. M. King, unpublished results). Although some evidence supports a role in methane consumption for acid-tolerant or moderately acidophilic methanotrophs in peats (12), the acid-tolerant peat isolates described to date have not been shown to consume atmospheric methane, and acid-tolerant methanotrophs have not been documented for soils.In contrast to the impact of pH in peats, the effects of pH on methanotrophic activity in acidic soils may be compounded by solubilization of aluminosilicates, which constitute a major fraction of the mineral horizons where atmospheric methane consumption occurs most actively. Although the chemistry of aluminum is well understood (36) and its toxic effects on multicellular organisms are known in some detail (15,17,(34)(35)(36)52), the response of microbes to aluminum is not well documented (42).Several studies have examined the effects of aluminum on cyanobacteria and fungi and documented a range of responses (10,(41)(42)(43). Physiological studies with bacteria have emphasized well-known strains, such as Escherichia coli, Staphylococcus aureus, Bacillus megaterium, and Pseudomonas fluorescens (4,11,19,42,44). A broader range of studies have focused on rhizobia and documented toxicity in cultures and in bacteriumlegume symbioses (7,8,18,24,26,33,38,39,43,50,51). However, the effects of aluminum on microbes or microbial processes in a more general ecological context have not been adequately assessed.Nonetheless, dissolved aluminum concentrations can reach ...

Vertical distribution and interaction of ethylene and methane in temperate volcanic forest soils

“…1c). The results indicated that low Al concentrations in the upper soil layers supported a larger consumption of CH 4 and C 2 H 4 in forest surface soils, due to Al toxic effect on methanotrophs ( Nanba and King, 2000;Tamai et al, 2003Tamai et al, , 2007. More interestingly, it was observed that maximum Al concentrations occurred in subsurface soil rather than in surface soil layers under spruce and birch (P ≤ 0.05) (Table 1), which paralleled the maxima of the CH 4 and C 2 H 4 consumption activity in forest soils at various depths (Fig.…”

Distribution of Atmospheric Methane Oxidation and Methanotrophic Communities on Hawaiian Volcanic Deposits and Soils

“…Although not intended to be synoptic, results from pmoA analyses are consistent with other studies 14,27,33,39) that reveal a limited number of taxa, often including novel lineages. Notably, the extent of diversity for facultative lithotrophs and CO-oxidizing bacteria in Hawaiian volcanic deposits appears much greater than that for methanotrophs 11,31) . Again, this suggests a limited role for methanotrophs in developing Hawaiian ecosystems.…”

Toxicity of Al to Desulfovibrio desulfuricans

“…Despite the general agreement that Al toxicity derives from its replacement of divalent metal complexes, chiefly Mg and Ca, in cells or cell membranes, there is less agreement about whether the effect is generic to all forms of soluble Al. Stable organic complexes of Al (e.g., oxalate or citrate) seem to mitigate the toxic effects on methanotroph activity (25) and root growth (13). However, citrate complexes also seem to be the mechanism by which soluble Al crosses the blood-brain barrier (46).…”