Use of Nitrifier Activity Measurements To Estimate the Efficiency of Viable Nitrifier Counts in Soils and Sediments

Tube‐dwelling invertebrates affect microbial processes by feeding on sediment bacteria, by creating structures with properties different from that of the bulk sediment, by disturbing the benthic boundary layer, and by pumping water through their tubes. We studied the effects of Chironomidae in a flooded soil. Tubes were at least 1.5 cm long and ca. 2 mm in diameter, and extended through the anoxic subsurface soil over most of their length. Larvae had no effect on CH4 flux across the sediment surface either by diffusion or by ebullition. In vitro, CH4 oxidation rates in tubes were significantly (P<0.05) higher than those in surface and subsurface soil. At a mixing ratio of 20 000 ppmv, average CH4 oxidation rates of tubes, surface soil, and bulk soil were 2, 0.4, and 1 μmol g dry wt.−1 h−1, respectively. The number of CH4 oxidizing bacteria determined by the most probable number (MPN) technique was higher in chironomid tubes than in the other soil compartments. CH4 production in tubes was significantly (P<0.05) higher than in the anoxic bulk soil, while no CH4 was produced in the surface soil during 240 h of incubation. We conclude that chironomid tubes are microsites with an intensified microbial activity, where CH4 production and oxidation may be tightly coupled.

Section: Discussionsupporting

confidence: 89%

The effect of chironomid larvae on production, oxidation and fluxes of methane in a flooded rice soil

Kajan

Frenzel

1999

“…However, abundance of nitrite oxidizing bacteria has previously been shown to correlate with ammonia-oxidizing population sizes in rice paddy soils [39]. Potential nitrification activities measured by microsensors and slurry incubations of the surface soil was in the same range as found for surface sediments of shallow waters [40], but considerably lower than rates found for other non-flooded agricultural soils [41], consistent with the lower oxygen penetration in the waterlogged paddy soil. The pronounced population size of ammonia-oxidizing bacteria found in the bulk soil fraction could be explained by the intensive cultivation with extensive soil preparation, which results in frequent mixing of the soil fractions.…”

Section: Discussionmentioning

confidence: 52%

Nitrificationâdenitrification dynamics and community structure of ammonia oxidizing bacteria in a high yield irrigated Philippine rice field

Nicolaisen

Risgaard-Petersen

Revsbech

et al. 2004

Nitrogen is the single most limiting factor for rice production. Detailed knowledge on nitrogen dynamics in rice fields is therefore of major importance for developing sustainable rice production. A combination of state-of-the-art microsensor, stable isotope tracer, and molecular techniques was used to evaluate coupled nitrification-denitrification potentials and community structure of ammonia-oxidizing bacteria in a high yield irrigated rice cropping system in the Philippines, without the use of microcosm incubations. The multiple approaches showed a high degree of concordance among methods and thereby clarified the investigated processes. Numbers and potential activity of ammonia-oxidizing bacteria in the system reflected the availability of substrate in three defined soil factions with a ranking of: surface soil > rhizosphere > bulk soil. No nitrification activity was measured between spit applications of N fertilizer. However, nitrification was induced upon nitrogen amendment in intact soil cores. Despite induction by nitrogen amendment, the loss of nitrogen through coupled nitrification-denitrification was less than 10% of the plant nitrogen uptake. Denaturant gradient gel electrophoresis of amoA fragments revealed no differences in diversity profiles between the soil fractions, and phylogenetic analysis, based on amoA genes retrieved from the rice paddy soil, identified a set of mutually very similar sequences related to Nitrosomonas nitrosa.

“…The potential ammonium-oxidizing activities were determined according to Belser and Mays [14]. 20 g of well-mixed soil were weighed into a 250 ml Erlemeyer; 50 ml 2 mM phosphate buffer (pH 7.5) supplemented with 1 or 2 mM (NH4)2SO4, was added and the suspension was 47 incubated on a rotary shaker at 26°C.…”

Section: Determination Of Potential Ammonium Oxidizing Activitymentioning

confidence: 99%

Repression of nitrification in soils under a climax grassland vegetation

Stienstra

1994

Two hypotheses on repression of nitrification in climax vegetations (i.e. nitrogen immobilization and allelopathy) were investigated. In this study the potential nitrification activities and numbers of ammonium‐oxidizing bacteria were established in a nature reserve with a series of natural grasslands with vegetational different stages of succession of plants species. The pastures had not been fertilized for 3, 7, 20 and 46 years, respectively, and the gradual decrease in availability of nutrients had led to pastures dominated by different grass species. In each field soil parameters, potential nitrification activities (PNA) and numbers of ammonium‐oxidizing bacteria were determined in the root zone of Holcus lanatus as well as in that of a grass species characteristic of the stage of succession. In the rhizosphere of H. lanatus decreasing PNA and numbers of ammonium‐oxidizing bacteria were observed as the period of non fertilization increased. Within each field no significant differences in PNA were observed between the root zones of H. lanatus and those of the dominant grass species. From these results it is concluded that, in these fields, decreasing nitrification was related only to decreasing ammonium availability and not to species composition. No indications were obtained that allelochemicals were involved in the flow nitrification potentials of late stages of succession. The optimum pH of the ammonium‐oxidizing community, measured as PNA, decreased as the period of non fertilization increased. It is suggested that impoverishment of the grassland soil with respect to nitrogen availability selects against ammonium‐oxidizing bacteria with a relatively high pH optimum.