Bacterial immobilization and remineralization of N at different growth rates and N concentrations

Abstract

An experiment was designed to resolve two largely unaddressed questions about the turnover of N in soils. One is the influence of microbial growth rate on mobilization and remineralization of cellular N. The other is to what extent heterotrophic immobilization of NO(3)(-) is controlled by the soil concentration of NH(4)(+). Bacteria were extracted from a deciduous forest soil and inoculated into an aqueous medium. Various N pool dilution/enrichment experiments were carried out to: (1) calculate the gross N immobilization and remineralization rates; (2) investigate their dependence on NH(4)(+)and NO(3)(-) concentrations; (3) establish the microbial preference for NH(4)(+)and NO(3)(-) depending on the NH(4)(+)/NO(3)(-) concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and NH(4)(+) concentrations. There was a positive correlation between NH(4)(+) immobilization and remineralization rates, and intracellular recycling of N seemed to be an efficient way for bacteria to withstand low inorganic N concentrations. Thus, extensive remineralization of microbial N is likely to occur only when environmental conditions promote high growth rates. The results support previous observations of high NO(3)(-) immobilization rates, especially at low NH(4)(+) concentrations, but NO(3)(-) was also immobilized at high NH(4) concentrations. The latter can be understood if part of the microbial community has a preference for NO(3)(-) over NH(4)(+).

Plant community controls on short‐term ecosystem nitrogen retention

“…However, caution is needed when interpreting these results: plant communities dominated by fast‐growing, resource‐exploitative species and their associated microbial communities might rapidly take up available N, but high rates of nutrient cycling also mean that N is remineralized (Bengtson & Bengtsson, 2005) and potentially lost quickly from ecosystems. We did not measure this process, but it can be relevant at longer timescales.…”

Microbial communities and primary succession in high altitude mountain environments

“…The authors explained that this observation was maybe due to nitrate immobilization by root or by microorganisms, rather than nitrification activities. Nitrifying microorganisms could be inhibited by heterotrophic bacteria in N-poor environments such as the glacier foreland (Bengtson and Bengtsson 2005), while nitrogen fixation and ammonification could guarantee the ammonium amount in these soils.…”

High Diversity of Diazotrophs in the Forefield of a Receding Alpine Glacier

“…In fact, Verhagen et al [83] and Bengtson and Bengtsson [8] reported that nitrifying bacteria are outcompeted by heterotrophic bacteria in ammoniumpoor environments. In contrast, microbial nitrogen fixation and ammonification may explain the sustainability of the ammonium pool.…”