Side Effects of Nitrification Inhibitors on Non Target Microbial Processes in Soils (original) (raw)
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Evaluation of the side effects of nitrification inhibiting agrochemicals in soils
Selected bioassays were used to assess the side effects of agricultural chemicals on microbial activities under laboratory conditions using loamy clay, loam, sandy soil and the nitrification inhibitors (NI) 3,4dimethyl pyrazole phosphate (DMPP), 4-Chlor-methyl pyrazole (ClMP) and dicyandiamide (DCD). The NI influence with concentrations from 1-1000 times the recommended application rate was assessed on the general microbial activity. Also, the dehydrogenase (DHA) and the dimethyl sulfoxide reductase activity (DRA) on the nitrogenase activity (NA) was evaluated. The potential denitrification capacity (PDC), representing nitrogen cycle, specific to soil microbial processes was examined in incubation experiments in the presence of DMPP, ClMP and DCD. DHA was estimated spectrophotometrically and DRA, PDC and NA gas was quantified using gas chromatography. The morphological changes of a nitrifying bacterial consortium in presence of the recommended DMPP field application rate and at 10 times higher concentration were observed under a transmission electron microscopy. The inhibition in the presence of increasing NI concentrations was calculated as no effect level (NOEL), effective dose ED 10 (10% inhibition) and ED 50 (50% inhibition). Dose response curves expressing the inhibition effectiveness was most distinct in sandy soils. Most NI sensitive reacted PDC>DRA>DHA>NA and ClMP added to the three differently structured test soils influenced non-target microbial processes activity at a higher level. Our results clearly showed that the evaluation of agrochemical side effects with soil enzymes exhibited as reliable, sensitive, reproducible and suitable method to investigate soil microbial activity interferences.
2020
ABSTRACTNitrification inhibitors (NIs) applied to soil reduce nitrogen fertilizer losses from agricultural ecosystems. Currently available NIs appear to selectively inhibit ammonia-oxidizing bacteria (AOB), while their impact on other groups of nitrifiers is limited. Ethoxyquin (EQ), a preservative shown to inhibit ammonia-oxidizers (AO) in soil, is rapidly transformed to 2,6-dihydro-2,2,4-trimethyl-6-quinone imine (QI) and 2,4-dimethyl-6-ethoxy-quinoline (EQNL). We compared the inhibitory potential of EQ and its derivatives in vitro with other established NIs that have been applied in an agricultural setting (dicyandiamide (DCD), nitrapyrin (NP), 3,4-dimethylpyrazole phosphate (DMPP)) by evaluating their impact on the activity and growth of five soil-derived strains (two AOB (Nitrosomonas europaea, Nitrosospira multiformis), two ammonia-oxidizing archaea (AOA) (“Candidatus Nitrosocosmicus franklandus”, “Candidatus Nitrosotalea sinensis”), and one nitrite-oxidizing bacterium (NOB) (...
Frontiers in Microbiology, 2020
Nitrification inhibitors (NIs) applied to soil reduce nitrogen fertilizer losses from agro-ecosystems. NIs that are currently registered for use in agriculture appear to selectively inhibit ammonia-oxidizing bacteria (AOB), while their impact on other nitrifiers is limited or unknown. Ethoxyquin (EQ), a fruit preservative shown to inhibit ammonia-oxidizers (AO) in soil, is rapidly transformed to 2,6-dihydro-2,2,4-trimethyl-6-quinone imine (QI), and 2,4-dimethyl-6-ethoxy-quinoline (EQNL). We compared the inhibitory potential of EQ and its derivatives with that of dicyandiamide (DCD), nitrapyrin (NP), and 3,4-dimethylpyrazole-phosphate (DMPP), NIs that have been used in agricultural settings. The effect of each compound on the growth of AOB (Nitrosomonas europaea, Nitrosospira multiformis), ammonia-oxidizing archaea (AOA; "Candidatus Nitrosocosmicus franklandus," "Candidatus Nitrosotalea sinensis"), and a nitrite-oxidizing bacterium (NOB; Nitrobacter sp. NHB1), all being soil isolates, were determined in liquid culture over a range of concentrations by measuring nitrite production or consumption and qPCR of amoA and nxrB genes, respectively. The degradation of NIs in the liquid cultures was also determined. In all cultures, EQ was transformed to the short-lived QI (major derivative) and the persistent EQNL (minor derivative). They all showed significantly higher inhibition activity of AOA compared to AOB and NOB isolates. QI was the most potent AOA inhibitor (EC 50 = 0.3-0.7 µM) compared to EQ (EC 50 = 1-1.4 µM) and EQNL (EC 50 = 26.6-129.5 µM). The formation and concentration of QI in EQ-amended cultures correlated with the inhibition patterns for all isolates suggesting that it was primarily responsible for inhibition after application of EQ. DCD and DMPP showed greater inhibition of AOB compared to AOA or NOB,
FEMS Microbiology Reviews, 2020
ABSTRACTNitrification is the microbial conversion of reduced forms of nitrogen (N) to nitrate (NO3−), and in fertilized soils it can lead to substantial N losses via NO3− leaching or nitrous oxide (N2O) production. To limit such problems, synthetic nitrification inhibitors have been applied but their performance differs between soils. In recent years, there has been an increasing interest in the occurrence of biological nitrification inhibition (BNI), a natural phenomenon according to which certain plants can inhibit nitrification through the release of active compounds in root exudates. Here, we synthesize the current state of research but also unravel knowledge gaps in the field. The nitrification process is discussed considering recent discoveries in genomics, biochemistry and ecology of nitrifiers. Secondly, we focus on the ‘where’ and ‘how’ of BNI. The N transformations and their interconnections as they occur in, and are affected by, the rhizosphere, are also discussed. The NH...
Toxicity of Nitrification Inhibitors on Dehydrogenase Activity in Soils
International Journal on …, 2011
The objective of this research was to determine the effects of nitrification inhibitors (NIs) such as 3,4-dimethylpyrazolephosphate=DMPP, 4-Chlor-methylpyrazole phosphate=ClMPP and dicyandiamide, (DCD) which might be expected to inhibit microbial activity, on dehydrogenase activity (DRA) in three different soils in laboratory conditions. Dehydrogenase activity was assayed via reduction of 2-p-Iodophenyl-3-p-nitrophenyl-5-phenyltetrazoliumchloride (INT). The toxicity and dose response curve of three NIs were quantified under laboratory conditions using a loamy clay, a sandy loam and a sandy soil. The quantitative determination of DHA was carried out spectrophotometrically. In all experiments, the influence of 5-1000 times the base concentration was examined. To evaluate the rate of inhibition with the increasing NI concentrations, dose response curves were presented and no observable effect level =NOEL, as well as effective dose ED 10 and ED 50 (10% and 50% inhibition) were calculated. The NOEL for common microbial activity such as DHA was about 30-70 times higher than base concentration in all investigated soils. ClMPP exhibited the strongest influence on the non target microbial processes in the three soils if it compare to DMPP and DCD. The NOEL,ED 10 and ED 50 values higher in clay than in loamy or sandy soil. The NIs were generally most effective in sandy soils. The three NIs considered at the present state of knowledge as environmentally safe in use.
Biology and Fertility of Soils, 2017
Microcosms were set up to evaluate the effect of nitrification inhibitors (DCD, c-PTiO, and NaClO 3) on the abundance and expression of ammonia-oxidizing bacteria (AOB) and archaea (AOA), as well as the nitrite-oxidizing bacteria (NOB) Nitrospira and Nitrobacter. Both DCD and NaClO 3 inhibited the net nitrification rate, while c-PTiO had no significant effects, and NaClO 3 had a much greater inhibitory effect (> 60%) in all soils than DCD. No significant changes in total microbial abundance were observed with DCD and NaClO 3. DCD limited only the growth of AOB; however, NaClO 3 inhibited growth of both AOA and Nitrospira-NOB with no significant effects on AOB and Nitrobacter-NOB. Probably NaClO 3 inhibited both ammonia oxidation and nitrite oxidation. This is the first report to reveal the inhibitory effects of NaClO 3 on a specific nitrification process, helping to clarify the ecological niche of nitrifiers and the potential of nitrification inhibitors applied to soil.