Microbial succession of nitrate‐reducing bacteria in the rhizosphere of Poa alpina across a glacier foreland in the Central Alps

Abstract

Changes in community structure and activity of the dissimilatory nitrate-reducing community were investigated across a glacier foreland in the Central Alps to gain insight into the successional pattern of this functional group and the driving environmental factors. Bulk soil and rhizosphere soil of Poa alpina was sampled in five replicates in August during the flowering stage and in September after the first snowfalls along a gradient from 25 to 129 years after deglaciation and at a reference site outside the glacier foreland (>2000 years deglaciated). In a laboratory-based assay, nitrate reductase activity was determined colorimetrically after 24 h of anaerobic incubation. In selected rhizosphere soil samples, the community structure of nitrate-reducing microorganisms was analysed by restriction fragment length polymorphism (RFLP) analysis using degenerate primers for the narG gene encoding the active site of the membrane-bound nitrate reductase. Clone libraries of the early (25 years) and late (129 years) succession were constructed and representative clones sequenced. The activity of the nitrate-reducing community increased significantly with age mainly due to higher carbon and nitrate availability in the late succession. The community structure, however, only showed a small shift over the 100 years of soil formation with pH explaining a major part (19%) of the observed variance. Clone library analysis of the early and late succession pointed to a trend of declining diversity with progressing age. Presumably, the pressure of competition on the nitrate reducers was relatively low in the early successional stage due to minor densities of microorganisms compared with the late stage; hence, a higher diversity could persist in this sparse environment. These results suggest that the nitrate reductase activity is regulated by environmental factors other than those shaping the genetic structure of the nitrate-reducing community.

Effect of Earthworm Feeding Guilds on Ingested Dissimilatory Nitrate Reducers and Denitrifiers in the Alimentary Canal of the Earthworm

“…1 and 4A). Mycobacteriumrelated narG sequences have been retrieved from soil (14,49), species of Mycobacterium can reduce nitrate to nitrite (73), and mycobacterial species and other Actinobacteria occur in earthworm guts and casts and might be associated with gut walls (9,23,24,37,69). Furthermore, the percentages of Actinobacteriarelated 16S rRNA genes can be higher in earthworm gut and cast than in soil (24,47) (41), but the nitrate reductase encoded by this operon might also dissimilate nitrate (63,73).…”

“…1, 2A, and 4A). Indeed, narG sequences related to those detected in this study have been retrieved from soil (11,14,20,49). Species of detected genera have been cultured from earthworm gut contents and casts (9,24,28,32,37,69).…”

“…Dissimilatory nitrate reducers also possess nitrate reductases, most of which are encoded by narGHI (45). Thus, denitrifiers and dissimilatory nitrate reducers can be evaluated by analyzing narG (11,14,20,26,46,49), whereas only denitrifiers are targeted by analyzing nosZ (30,52,58,65,66,67,76).…”

Abundances and potential activities of nitrogen cycling microbial communities along a chronosequence of a glacier forefield

“…The pronounced root penetration in the developed soils brings along an enhanced water retention potential resulting in less oxygen diffusion and reduced partial oxygen pressure (Rheinbaben and Trolldenier, 1984;Deiglmayr et al, 2006). In combination with the sevenfold increase of the nitrate concentrations, developed soils (120 and 2000a) provide good conditions for denitrification.…”

Bacterial Communities Involved in Soil Formation and Plant Establishment Triggered by Pyrite Bioweathering on Arctic Moraines

“…Very few works nevertheless analytically described the microbial succession along glacier forefronts. Successions of communities of early colonizers, dominated by Cyanobacteria, followed by typical soil bacterial phylotypes have been described, occurring in a large time interval during glacial regression in several glacier forefronts [8][9][10][11][12].…”