Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Controlled continuous flow delivery system for investigating taste-aroma interactions

A multichannel flavor delivery system, Dynataste, was developed. Controlled amounts of isoamyl acetate (100 ppm) and sucrose (0-3%) solution was administered to experienced and na?ve assessors who used time intensity techniques to record perceived 'fruit' flavor intensity. In-nose volatile delivery was monitored using atmospheric pressure chemical ionization-mass spectrometry. Results indicated that sucrose is a key driver of fruit flavor intensity but that the magnitude of the effect varies between individuals. The combined temporal analysis of chemical stimuli in vivo and sensory data indicate evidence of interactions at a perceptual level. Comparison of experienced and na?ve assessors revealed cross-modal interactions in each group, although a subgroup of experienced assessors was unaffected by changes in sucrose concentration. This raises the question of the selected use of experienced panels in cross modal investigations.     

Dynamics of phosphorus fractions in a savanna Alfisol under continuous cultivation

Abstract. We examined the dynamics of inorganic P (P_i) and organic P (P_o) pools of a savanna Alfisol under continuous cultivation complemented with nitrogen (N) and phosphorus (P) fertilizers with or without cow manure (D), using a modified Hedly fractionation. Continuous cultivation without P fertilizer decreased the concentration of P_i and P_o, pools including the residual P fraction compared with an unfertilized treatment with natural vegetation. Adding P fertilizers alone or in combination with D (P, NPK, D+P, D+NP and D+NPK) increased the concentration of labile P_i pools, but decreased the concentration of P_o, pools and the residual P fraction. The tendency of the residual P fraction to decrease along with P_o pools suggested that the residual P fraction was largely P_o. This is consistent with the correlation between the residual P fraction and total P_o (r=0.74^**) and the residual P fraction and organic carbon content (r=0.47^**). Analysis of the relationships between plant available P, estimated by resin-extractable P, and the more stable P_i and P_o, pools indicated that 85% of the variation in resin-P was atiributable to the hydroxide extractable P_i, (OH-P_i) and HCI-P_i which acted as sinks for fertilizer-P. The contribution of the residual P fraction to resin-P was indirect via bicarbonate-extractable P_o (HCO₃-P_o) and OH-P_o. These results also clarify why attempts to find P extraction methods which correlate well with response to P and to P uptake in the savanna have given inconsistent results.     

Dynamics of mineral nitrogen, water-soluble carbon and potential nitrification in band-steamed arable soil

Steaming of narrow soil bands prior to sowing is a new technique that reduces the need for intra-row weeding in herbicide-free row crops. However, the steam treatment may eliminate both weed seeds and non-target soil organisms, thereby affecting the nutrient cycling in the soil. This study tested the effect of band-steaming on N and C dynamics in a sandy loam soil that was steamed in situ to maximal temperatures of 70–90°C using a prototype band-steamer. Soil samples (0–5 cm depth) were collected during 90 days from band-steamed soil, undisturbed control soil, and control soil treated just mechanically with the band-steamer. In the steamed soil, ammonium concentrations increased from 1.1 to 20.3 μg NH ₄ ⁺ -N g^?1 dry weight during 28 days. This coincided with an immediate and persistent inhibition of potential nitrification (33–61% inhibition during 90 days). Assays of the temperature response of potential nitrification confirmed the temperature sensitivity and showed an optimum temperature of 27.1°C and a temperature coefficient (Q ₁₀) of 1.9. The effects of band-steaming on concentrations of nitrate and water-soluble carbon were divergent and stimulatory, respectively, but generally not statistically significant. Mechanical effects of band-steaming were negligible. The observed ammonium surplus could be of agronomic benefit and should be evaluated in integrated studies of the effects of band-steaming on crop growth and plant N uptake.     

Detection of nitrification in a stagnohumic-gley soil

Summary Three different nitrification assays (short-term nitrifier activity, assimilatory nitrate reductase activity of Lolium perenne, and nitrate accumulation in the absence of plants) were performed either on soil from a naturally acidic stagnohumic-gley or on leaves from L. perenne grown in this soil. Before the investigation the soil was limed and fertilised in a manner consistent with established agricultural pasture improvement strategies. Short-term nitrifier activity was only detected in soils above pH 5.6. However, nitrate reductase activity and nitrate accumulation both showed a near linear increase between soil pH 3.8 and 6.8. These findings are attributed to the nature of the assays, each of which considers a different component of the soil nitrifier population.     

Active methanotrophs suppress nitrification in a humisol

Summary The coexistence of chemoautotrophic nitrifiers and methanotrophs in a cultivated humisol was investigated. Under laboratory conditions which supported the growth and activity of methanotrophs, the nitrifiers were partially or completely inhibited. The inhibition was related to a competition for available oxygen and a high assimilatory requirement for inorganic nitrogen by the Methanotrophs. Dissolved methane concentrations as high as 250 M had no direct effect on the oxidation of ammonium. Simultaneous nitrification and methane oxidation was observed only if relatively high levels of ammonium and oxygen were maintained. Coupled nitrification-assimilatory/dissimilatory nitrate reduction resulted from the high oxygen demand of the actively growing methanotrophs. This study suggests that the potential competitive effects of methanotrophs may influence nitrification by chemoautotrophic nitrifiers in certain environmental systems.     

Archaea and bacteria respectively dominate nitrification in lightly and heavily grazed soil in a grassland system

To investigate the effects of stocking rates on nitrification activity and active nitrifying communities in a typical steppe grazing system, we conducted a laboratory incubation study using soil from a 10-year-old grassland gradient grazing experiment with sheep. A combination of molecular methods, such as DNA-based stable-isotope probing (DNA-SIP), real-time quantitative PCR, and high-throughput sequencing, was used to identify changes of nitrification activity and active nitrifying communities under different stocking rates (0 (SR0), 3 (SR3), 6 (SR6), and 9 (SR9) sheep per ha). The nitrification activity of soils was significantly increased by light grazing (SR3), while it was significantly decreased by heavy grazing (SR9). Nitrososphaera viennensis lineage of ammonia-oxidizing archaea (AOA) functionally predominated over ammonia-oxidizing bacteria (AOB) in nitrification in the SR3 soil, while the Nitrosospira cluster 3 of AOB was the major player in the SR9 soil. Therefore, stocking rates altered the distribution of active nitrifying communities by affecting soil chemical and physical conditions.     

Distribution of bacteria in a continuous-flow nitrification column

Nutrient solution containing (NH₄)₂SO₄ was supplied at a constant rate to Nitrosomonas europaea and Nitrobacter agilis growing in a column packed with glass beads. Conversion of NH₄⁺ to NO₂^? and NO₃^? was incomplete indicating that growth of the bacteria was not nutrient limited. After 7 months the column was dismantled and the arrangement of the bacteria on the beads examined using a scanning electron microscope. Nitrifying bacteria were found only in the upper regions of the column. They occurred most commonly in monolayers, less commonly in layers of about 20 cells and rarely in piles of about 100 cells in depth. Further down the column the glass beads were covered in a layer of slime and no bacteria were seen. This suggests that growth of the nitrifiers was neither controlled by diffusion of metabolites through a microbial film nor limited by competition between the bacteria for space on the surface of the glass beads.     

Autotrophic nitrification in a fertilized acid heath soil

The nature of nitrification in fertilized, acid heath soils was studied. Autotrophic ammoniumand nitrite-oxidizing bacteria were enumerated in non-fertilized and fertilized heath soils. Ammoniumoxidizing bacteria were not detected in the non-fertilized soils, whereas nitrite-oxidizing bacteria were only found in the organic layer. Enrichment of acid heath soils with NPK fertilizer increased the number of autotrophic ammonium- and nitrite-oxidizing bacteria in the organic (F + H) layer as well as in the upper part of the mineral (Ah) layer, although the pH of the soil hardly changed with fertilization. In soil suspensions of the upper mineral layer of fertilized heath soils, nitrification was shown to be autotrophic as nitrification was completely inhibited by the addition of nitrapyrin under both neutral and acid conditions. Stimulation of nitrification by addition of peptone appeared to be due to the increase in pH caused by ammonification of peptone. Under acid conditions, nitrification seemed to be coupled with net nitrogen mineralization. The possible influence of vegetation on nitrification is discussed.     

Abiotic factors regulating nitrification in a Swedish arable soil

Summary The effects of temperature, water potential and ammonium concentrations were studied in field and laboratory experiments on arable soil. The two field experiments used different sampling intervals, one at daily (short-term) and the other at monthly (long-term) intervals. In the short-term field experiment, the numbers and activities of nitrifiers were assessed before and after natural rain or irrigation. The nitrifiers were apparently outcompeted by heterotrophs during the first days after wetting the soil. Potential nitrification was affected only slightly by changes in water potential, whereas the numbers of ammonium and nitrite oxidizers appeared more sensitive to these changes. The numbers of ammonium and nitrite oxidizers correlated strongly during the daily samplings. The potential nitrite-oxidation rates correlated with water potentials whereas the potential ammonium oxidation rates did not. Extractable ammonium decreased in proportion to increasing nitrate concentrations in both the rain-fed and the irrigated plots. In the long-term field experiments, the numbers of ammonium oxidizers correlated with water potentials but not with in situ temperature or with ammonium concentrations. The potential ammonium-oxidation rates correlated with water potentials and with ammonium-oxidizer numbers. The potential nitrite-oxidation rates correlated strongly with the potential ammonium-oxidation rates. The field experiments implied that nitrite oxidizers obtained substrate from ammonium oxidizers but also from nitrate reduction. In laboratory experiments nitrate accumulated at a Q ₁₀ of about 2 and the V _max for nitrification was observed at a water potential of –0.11 MPa (65% of water-holding capacity). The K _m for ammonium oxidation at pH 8.2 was 1.72 mg l^–1 soil water.     

黄土坡面细沟流水动力学特性

我国是土壤侵蚀最严重的国家之一,黄土高原地区的水土流失造成严重的生态环境恶化问题.为探求黄土细沟流的水动力学特性,从水力学及河流运动力学的角度出发,系统研究6种坡度(2.、4.、6.、8.、10.、12.),5种流量(8、16、24、32和40 L/min)组合水槽冲刷试验条件下细沟水流水动力学特征.结果表明:细沟流平均流速与径流流量呈幂函数关系,坡度对其影响较小,其原因同水流强度与床面形态的相互制约有关;黏性底层厚度与坡度、流量均呈现负相关关系;阻力系数与雷诺数无关,说明水流强度增加的同时,床面形态发育愈显著,即水流耗散能量增加愈显著,其值在0.16 ～1.45之间变化.研究结果对细沟水流水动力学的探究具有一定的理论价值,进而对黄土坡面水土流失治理及生态修复均具有一定的指导意义.     

Effectiveness of dicyandiamide as a nitrification inhibitor in biochar-amended soil

Overuse of nitrogen (N) fertilizers may lead to many environmental issues via N leaching into groundwater and agricultural runoff into surface water. Biochar, a sustainable soil amendment agent, has been widely studied because of its potential to retain moisture and nutrients. However, recent studies have shown that biochar has a very limited ability to improve the retention of negatively charged nitrite (NO₂^-) or nitrate (NO₃^-). Although positively charged ammonium (NH₄⁺) can be better held by biochar, it is usually susceptible to nitrification and can be easily transformed into highly mobile NO₂^-and/or NO₃^-. In practice, dicyandiamide (DCD) has been used to inhibit nitrification, preserving N in its relatively immobile form as NH₄⁺. Therefore, it is likely that the effects of DCD and biochar in soils would be synergistic. In this study, the influences of biochar on the effectiveness of DCD as a nitrification inhibitor in a biochar-amended soil were investigated by combining the experimental results of incubation, adsorption isotherm, and column transport with the simulated results of different mathematical models. Biochar was found to stimulate the degradation of DCD, as the maximum degradation rate slightly increased from 1.237 to 1.276 mg kg^-1 d^-1 but the half-saturation coefficient significantly increased from 5.766 to 9.834 mg kg^-1. Considering the fact that the availability of DCD for nitrification inhibition was continuously decreasing because of its degradation, a novel model assuming non-competitive inhibition was developed to simulate nitrification in the presence of a decreasing amount of DCD. Depending on the environmental conditions, if the degradation of DCD and NH₄⁺ in biochar-amended soil is not significant, improved contact due to the mitigated spatial separation between NH₄⁺ and DCD could possibly enhance the effectiveness of DCD.     

Rapid quantification of proanthocyanidins (condensed tannins) with a continuous flow analyzer

Proanthocyanidins (condensed tannins) frequently need to be quantified in large numbers of samples in food, plant, and environmental studies. An automated colorimetric method to quantify proanthocyanidins with sulfuric acid (H(2)SO(4)) was therefore developed for use in a continuous flow analyzer. Assay conditions were optimized using 50% methanol extracts of paper birch, sugar maple, and quaking aspen leaves. Short extraction times and centrifugation of samples prevented proanthocyanidin degradation that otherwise occurred in 50% methanol extracts of aspen leaves. Extraction of birch and maple proanthocyanidins with 50% methanol was comparable to or better than that with 70% acetone. Proanthocyanidin levels in aspen were lower when extracted with aqueous methanol, but relative differences among samples were consistent with those found in aqueous acetone extracts. Results from the automated sulfuric acid assay were highly correlated with those of the conventional BuOH-HCl method for proanthocyanidins and, except for birch, with the Folin--Denis assay for total phenolics. This new technique significantly improves assay processing rate and repeatability compared to conventional colorimetric proanthocyanidin assays.     

Dynamics and availability of phosphorus in the rhizosphere of a temperate silvopastoral system

A field rhizosphere study was carried out over a period of 12 months on a 6-year-old silvopastoral trial in New Zealand. The trial comprised radiata pine (Pinus radiata) with lucerne (Medicago sativa) and perennial ryegrass (Lolium perenne) understoreys. The study was initiated because of the unique interrelationships between roots in silvopastoral systems and a paucity of understanding about the processes involved in phosphorus (P) dynamics in temperate silvopastoral systems. Improving our understanding in this area has important implications for nutrient management in silvopastoral systems. Rhizosphere soils were analysed to determine inorganic (Pi) and organic (Po) P fractions, macroporous resin Pi and Po, phosphatase enzyme activity, microbial biomass carbon and pH. Concentrations of labile Pi were consistently greater and Po lower in tree rhizosphere soil compared to the companion understorey, indicating that radiata pine when grown with a productive understorey mineralised Po to a greater extent than either understorey species. Tree rhizosphere soil from under lucerne and lucerne rhizosphere soil contained the lowest concentrations of total Pi and Po compared with tree under ryegrass and ryegrass rhizosphere soils. This was partly attributed to higher levels of phosphatase enzyme activity in the lucerne rhizosphere soils. The results suggest the combination of lucerne with radiata pine may enhance greater utilisation of soil P, although this requires further investigation. Lower levels of labile Po, and higher levels of labile Pi and phosphatase enzyme activity, were determined in tree and understorey lucerne and ryegrass rhizosphere soils in spring compared with autumn. This data confirmed that overall rates of soil organic P mineralisation are greatest in spring.     

硝化抑制剂/菌剂对设施土壤–蔬菜体系中氮素去向的影响

【目的】明确硝化抑制剂与菌剂单施与配施条件下设施土壤–茄子生产体系中氮的去向,为设施茄子科学施氮提供理论依据。【方法】田间试验采用随机区组设计,设置6个处理：不施氮肥对照(CK)、常规施氮720kg/hm² (FN)、减施30%氮肥(N 504 kg/hm²,RN),减氮30%配施硝化抑制剂(RND)、菌剂(RNB)和同时配施硝化抑制剂与菌剂(RNDB)。研究设施土壤–茄子体系中茄子对氮素的吸收利用、土壤剖面NO₃~–-N累积量、N₂O排放和NH₃挥发的气态损失量及各去向所占比例。【结果】1) RNDB处理产量为112.27 t/hm²,比RND处理显著增加11.0%;可溶性糖含量达0.95%,较RND和RNB处理分别显著提高17.3%和18.8%。2)各处理吸氮量均为果实>茎秆>叶片>根系;RNDB处理的总吸氮量为259.66 kg/hm²,比RN处理显著提高16.1%;氮肥表观利用率最高为20.87%,与RND和...     

Temperature effects on ammonification and nitrification in a tropical soil

Ammonification of soil organic N and nitrification of ammonium-N was studied in Tindall clay loam over a range of temperatures from 20–60 C. Nitrification rates at each temperature were constant throughout the 28 day incubation, whereas most of the ammonification occurred in the first 7 days. The optimum for nitrification was close to 35 C. exhibiting a sharp peak at this temperature at which the potential rate was 4.8 μg N/g day^?1, compared with 0.5 μg N/g day^?1 at 20°C and 0.25 μg N/g day^?1 at 60°C. The optimum temperature for ammonification was approximately 50°C at which the rate was 2.8 μg N/g day^?1 in the first 7 days but only 0.5 μg N/g day^?1 between 14 and 28 days.The temperature responses could be described mathematically with functions of the type log_oN = k × 1/T.The results are discussed in relation to daily patterns of N mineralization in the field where temperatures show diurnal fluctuation.     

Laboratory evaluation of dicyandiamide as a soil nitrification inhibitor

Abstract

Laboratory studies to evaluate dicyandiamide (DCD) as a soil nitrification inhibitor showed that it is considerably more effective than several compounds that have been patented or proposed as fertilizer amendments for retarding nitrification of fertilizer nitrogen (N) in soil, but is considerably less effective than 2‐ethynylpyridine, nitrapyrin (N‐Serve), etridiazole (Dwell), 3‐methylpyrazole‐l‐carboxamide (MPC), or 4‐amino‐l,2,4‐triazole (ATC). Other findings in studies reported were as follows: a) DCD is more effective for inhibiting nitrification of ammonium‐N than of urea‐N; b) the effectiveness of DCD as a nitrification inhibitor is markedly affected by soil temperature and soil type and is limited by the susceptibility of DCD to leaching; c) DCD has very little, if any, effect on urea hydrolysis, denitrification, or seed germination in soil; d) products of DCD decomposition in soil (guanylurea and guanidine) have little, if any, effect on nitrification compared with DCD; e) in the absence of leaching, the persistence of the inhibitory effect of DCD on nitrification decreases with increase in soil temperature from 10 to 30°C, but the inhibitory effect of 50 μg DCD g^‐1 soil is substantial even after incubation of DCD‐treated soils at 20 or 30°C for 24 weeks.     

Overland flow systems for treatment of landfill leachates—Potential nitrification and structure of the ammonia-oxidising bacterial community during a growing season

Overland flow systems are useful for treating landfill leachates, because they provide favourable conditions for nitrification and they are easy to maintain. However, little is known about the microbial communities in such systems or the nitrification capacity of those microorganisms. In this study, seasonal variations in potential nitrification and in community composition of nitrifying bacteria were investigated in two overland flow areas receiving leachate from landfills at Korslöt and Hagby, Sweden. Samples were collected in the settling ponds sediment and at two depths in the overland flow areas (the macrophyte litter layer and the rhizosphere) in May, August and November 2003. A short-term incubation method was used to measure potential oxidation of ammonia and nitrite (designated PAO and PNO). The ammonia-oxidising bacterial (AOB) community was investigated using a 16S rRNA gene approach that included PCR amplification and analysis of PCR products by denaturing gradient gel electrophoresis (DGGE), followed by nucleotide sequencing and phylogenetic analysis.PAO was determined in the range 5-2700 (NO₂⁻+NO₃⁻)-N g⁻¹ dw d⁻¹ and PNO in the range 60-2000 μg NO₂⁻-N g⁻¹ dw d⁻¹. At Korslöt, PAO and PNO showed similar temporal variation in the different ecosystems, whereas no such relationship was noticed at Hagby. Considering both sites, there was no obvious change in the composition of the AOB community over the growing season. However, the composition did differ between the ecosystems: Nitrosomonas-like sequences were more common in the ponds, and in the litter layers they were found as often as Nitrosospira-like sequences, whereas Nitrosospira-like sequences were more common in the rhizospheres. Altogether, we found nine different AOB sequences, five Nitrosomonas-like and four Nitrosospira-like, which belonged to clusters 0, 2, 3b, 6a, 6b and 7. There was no apparent relationship between the number of AOB populations and the PAO in different soil layers and sediments.     

Nanoclay polymer composites loaded with urea and nitrification inhibitors for controlling nitrification in soil

Nanoclay polymer composites (NCPCs) were synthesized with partially neutralized acrylic acid and bentonites and loaded with urea and nitrification inhibitors (NIs) to act as a slow release carrier of nitrogen (N). The resulting product was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD of NCPCs revealed that the bentonite layers were completely exfoliated and dispersed in the composite after the polymerization. The water absorbency of pure polymer (Acrylic acid + Acrylamide) was 197.53 g g^?1 and 137.75 g g^?1 by nanocomposite (8% nanobentonite) in distilled water. The nitrification inhibition ability of these NCPCs was evaluated by incubation study for 60 days in laboratory at 28°C and 50% water-holding capacity. The Schiff base -NCPCs were most effective at inhibiting nitrification (30–87%) compared to dicyandiamide and Neem oil. A column study was performed to know the movement of NH₄-N and NO₃-N at three different depths. Result showed that the Schiff base -NCPC decreased nitrate movement by 78.5% at the depth of 5 cm in soil column. The slow release of nitrogen and good water retention capacity confirmed that these NCPCs can be viably exploited for application in agriculture.     

A novel amended nitrification inhibitor confers an enhanced suppression role in the nitrification of ammonium in soil

Journal of Soils and Sediments - Nitrification inhibitor plays an important regulatory role in inhibiting the nitrification of ammonium in soils. However, most of nitrification inhibitors lack the...