Soil nitrogen patterns induced by colonization of Polygonum cuspidatum on Mt. Fuji

Summary The spatial pattern of soil nitrogen was analyzed for a patchy vegetation formed by the colonization of Polygonum cuspidatum in a volcanic desert on Mt. Fuji. Soils were sampled radially from the bare ground to the center of the patch, and analyses were done for bulk density, water content, soil acidity, organic matter, organic nitrogen, and ammonium and nitrate nitrogen. The soils matured with succession from the bare ground through P. cuspidatum to Miscanthus oligostachyus and Aster ageratoides sites: bulk density decreased, and water content, organic matter, organic nitrogen, and ammonium nitrogen increased. Nitrate nitrogen showed the highest values at the P. cuspidatum site. Application of principal component analysis to the soil data discriminated two component factors which control the variation of soil characteristics: the first factor is related to soil formation and the second factor to nitrogen mineralization and nitrification. The effect of soil formation on nitrogen mineralization and nitrification was analyzed with a first-order kinetic model. The decreasing trends with soil formation in the ratios of mineral to organic nitrogen and of nitrate to ammonium nitrogen could be accounted for by the higher activity of immobilization by microorganisms and uptake by plants in the more mature ecosystem.     

Effects of arbuscular mycorrhizal fungi and soil developmental stages on herbaceous plants growing in the early stage of primary succession on Mount Fuji

A pot culture experiment was conducted to examine the effects of arbuscular mycorrhizal (AM) fungi and soil developmental stages on the growth and nutrient absorption of pioneer plants growing in the early stage of primary succession on Mt. Fuji. Four herbaceous plants, Polygonum cuspidatum (Polygonaceae), Miscanthus oligostachyus (Gramineae), Aster ageratoides var. ovatus (Compositae), and Hedysarum vicioides (Leguminosae), were grown from seed in soils collected from two different successional stages, bare ground and an herbaceous plant community. Spores of indigenous AM fungi collected from the herbaceous plant community were used as inoculum. The initial colonizer P. cuspidatum showed very low levels of AM colonization (<0.4%), whereas the average AM colonization levels of M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides were within the range of 13–49%. AM fungi had positive effects on the growth and N acquisition of the leguminous species (H. vicioides) irrespective of soil developmental stages. In contrast, AM colonization did not increase the plant dry weight and N content of the non-leguminous species (P. cuspidatum, M. oligostachyus, and A. ageratoides var. ovatus) in both soil developmental stages. A positive effect of AM colonization on P content was observed in M. oligostachyus, A. ageratoides var. ovatus, and H. vicioides only in soil collected from the herbaceous plant community. P. cuspidatum showed no or a negative response to AM colonization in all cases. These results suggest that the effect of AM fungi on plant growth depends more on the plant species than soil developmental stages in the early stage of primary succession in this volcanic area.     

The effect of harvesting intensity on the fate of applied 15N-ammonium to the organic horizons of a coniferous forest in N. Wales

¹⁵N-ammonium sulphate equivalent to 0.5 kg N/ha was added as a tracer to lysimeters containing the organic horizons of an acid forest soil. The effect of logging debris (brash), vegetation and second rotationPicea sitchensis seedlings on the amount of the¹⁵N found in various soil, vegetation and leachate pools was followed over a period of 60 days. Transformation of¹⁵N-ammonium to nitrate occurred within 24 hours. Although total nitrate leachate losses were high, tracer-derived nitrate represented only 0.4%–4.2% of the applied¹⁵N-ammonium. The atom % excess of the KCI-extractable organic-N pool was initially lower than for the inorganic species but due to the large pool size, consistently represented 3–6% of the applied¹⁵N-ammonium. The similarity of the atom % excess of the ammonium and nitrate pools indicated an autotrophic nitrification pathway.A significant proportion of the¹⁵N-ammonium passed through the microbial biomass which contained between 16 and 48% of the¹⁵N-ammonium 2 days after addition of the¹⁵N-ammonium. This nitrogen was in a readily available form or short-term pool for the first two weeks (with no change in the overall biomass pool), after which the nitrogen appeared to become transformed into more stable compounds representing a long-term pool. Total recovery of the¹⁵N was between 68% and 99% for the different treatments. The presence of brash reduced microbial immobilisation of the¹⁵N-ammonium and total retention in the organic matter. This is suggested to be a consequence of greater nitrification and denitrificatiion rate in organic horizons beneath a brash covering due to different microclimatic conditions.     

Nitrate reduction and nitrate content in ash trees (Fraxinus excelsior L.): distribution between compartments,site comparison and seasonal variation

Summary Nitrate reductase activity (NRA), nitrate content and biomass components of leaflets, leaf stalks, old stem, current-year stem and roots of ash trees (Fraxinus excelsior L.) growing in their natural habitats were investigated. In addition, NRA, total nitrogen and nitrate concentration were analyzed in the leaves and roots of ash trees from four different field sites. The highest NRA per gram biomass and also per total compartment biomass was found in the leaflets, even though root biomass was much higher than total leaflet biomass. The highest nitrate concentrations were found in the leaf stalks. Correlations between nitrate availability in the soil and NRA in leaves were not significant due to high variability of the actual soil nitrate concentrations. The seasonal variation in foliar NRA, nitrate concentration and total nitrogen concentration is much smaller in F. excelsior than reported for herbaceous species and is mainly caused by changes in the actual soil nitrate availability and by senescence of the leaves.     

Effect of nodulation on the nitrate assimilation in vegetative soybean plants

Summary Nitrate assimilation in the first trifoliate leaf of vegetative soybean plants (Glycine max L. Merr, cv Hodgson) was studied in relation to nodulation. Nodulated and non-nodulated plants were grown in a nitrate medium (4 mM). As a control nodulated plants were grown in a nutrient medium without combined nitrogen. This study included measurements of the acetylene reduction activity of the whole plant and of thein vitro nitrate reductase, glutamine synthetase and glutamate dehydrogenase activities in the first leaf and of the nitrate concentration. Nitrate accumulation and nitrate reductase activity were depressed in nodulated plants; root growth was decreased in the presence of nitrate. The relationships between nitrate assimilation and nodulation are discussed.     

INHIBITION OF NITRIFICATION BY CLIMAX ECOSYSTEMS. II. ADDITIONAL EVIDENCE AND POSSIBLE ROLE OF TANNINS

The same nine plots were used in this study as in our previous study on inhibition of nitrification (Rice and Pancholy, 1972). These consisted of three stands representing two stages of old field succession and the climax in each of three vegetation types in Oklahoma: tall grass prairie, post oak-blackjack oak forest, and oak-pine forest. Soil samples were analyzed three times during the growing season of 1972 for exchangeable ammonium nitrogen, nitrate, and numbers of Nitrosomonas and Nitrobacter. Results were similar to those obtained during the entire year of 1971. The amount of ammonium nitrogen was lowest in the first successional stage, intermediate in the intermediate successional stage, and highest in the climax. The amount of nitrate was highest in the first successional stage, intermediate in the intermediate successional stage, and lowest in the climax. The numbers of nitrifiers were highest in the first successional stage usually and decreased to a very low number in the climax. These data furnish additional evidence that the nitrifiers are inhibited in the climax so that ammonium nitrogen is not oxidized to nitrate as readily in the climax as in the successional stages. This would aid in the conservation of nitrogen and energy in the climax ecosystem. Some inhibition of nitrification occurred in the intermediate stage of succession also. Previous studies of tannins indicated that these are inhibitory to nitrification, so all important plant species in the intermediate successional stage and the climax were analyzed for total tannin content. A method for extracting and quantifying condensed tannins from soils was developed and the amounts of tannins were determined in each 15-cm level down to 60 cm in the same two plots in each vegetation type. Gallic and ellagic acids, which result from the digestion of hydrolyzable tannins in oak species, were also extracted and quantified in the climax oak-pine forest. All the important herbaceous species, including the grasses, were found to have considerable amounts of condensed tannins. The highest amounts of tannins occurred in the oaks and pine, however. Condensed tannins, hydrolyzable tannins, ellagic acid, gallic acid, digallic acid, and commercial tannic acid (hydrolyzable tannin), in very small concentrations, were all found to completely inhibit nitrification by Nitrosomonas in soil suspensions for 3 weeks, the duration of the tests. Slightly larger concentrations were required to inhibit nitrification by Nitrobacter under similar conditions. The concentrations of tannins, gallic acid, and ellagic acid found in the soil of the research plots were several times higher than the minimum concentrations necessary to completely inhibit nitrification. The inhibition of nitrification was always greater in the climax stand than in the intermediate successional stage in each vegetation type, and the concentration of tannins in the top 15 cm of soil was always higher in the climax stand than in the intermediate successional stage. Moreover, the amounts of tannins calculated to be added to each plot each year are much less than the amounts found in the soil, indicating that the tannins accumulate over a period of time. Thus, it appears that the tannins and tannin derivatives may play a continuous and rather prominent role in the inhibition of nitrification by vegetation.     

Nitrification potentials in early successional black locust and in mixed hardwood forest stands in the southern Appalachians,USA

Soil nitrogen mineralisation and nitrification potentials, and soil solution chemistry were measured in black locust (Robinia pseudo-acacia L.), in pine-mixed hardwood stands on an early successional watershed (WS6), and in an older growth oak-hickory forest located on an adjacent, mixed hardwood watershed (WS14) at Coweeta Hydrologic laboratory, in the southern Appalachian mountains, U.S.A. Nitrification potentials were higher in black locust and pine-mixed hardwood early successional stands than in the oak-hickory forest of the older growth watershed. Ammonification rates were the main factor controlling nitrification in the early successional stands. There was no evidence of inhibition of nitrification in soils from the older growth oak-hickory forest site.Within the early successional watershed, black locust sites had net mineralisation and nitrification rates at least twice as high as those in the pine mixed-hardwood stands. Concentrations of exchangeable nitrate in the soil of black locust stands were higher than in pine-mixed hardwoods at 0–15 cm in March and they were also higher at 0–15, 16–30 and 31–45 cm depth in the black locust dominated sites in July. Soil solution nitrate concentrations were higher under black locust than under pine-mixed hardwoods. Areas dominated by the nitrogen fixing black locust had greater nitrogen mineralisation and nitrification rates, resulting in higher potential for leaching losses of nitrate from the soil column in the early successional watershed.     

The roles of nitrate and ammonium in the regulation of the development of nitrate reductase in Chlamydomonas reinhardii

The regulation of the development of nitrate reductase (NR) activity in Chlamydomonas reinhardii has been compared in a wild-type strain and in a mutant (nit-A) which possesses a modified nitrate reductase enzyme that is non-functional in vivo. The modified enzyme cannot use NAD(P)H as an electron donor for nitrate reduction and it differs from wild-type enzyme in that NR activity is not inactivated in vitro by incubation with NAD(P)H and small quantities of cyanide; it is inactivated when reduced benzyl viologen or flavin mononucleotide is present. After short periods of nitrogen starvation mutant organisms contain much higher levels of terminal-NR activity than do similarly treated wild-type ones. Despite the inability of the mutant to utilize nitrate, no nitrate or nitrite was found in nitrogen-starved cultures; it is therefore concluded that the appearance of NR activity is not a consequence of nitrification. After prolonged nitrogen starvation (22 h) the NR level in the mutant is low. It increases rapidly if nitrate is then added and this increase in activity does not occur in the presence of ammonium, tungstate or cycloheximide. Disappearance of preformed NR activity is stimulated by addition of tungstate and even more by addition of ammonium. The results are interpreted as evidence for a continuous turnover of NR in cells of the mutant with ammonium both stimulating NR breakdown and stopping NR synthesis. Nitrate protects the enzyme from breakdown. Reversible inactivation of NR activity is thought to play an insignificant rôle in the mutant.Abbreviations NR nitrate reductase - BV benzyl viologen     

复合菌剂调控连作当归根围土壤养分及对产量的影响

【背景】连作可引起微生物群落结构失调,导致土壤环境恶化、养分循环不畅、当归[Angelica sinensis (Oliv.) Diels]产量降低,通过现代微生物技术改良土壤、消减连作障碍势在必行。【目的】于大田条件下,研究施用复合菌剂对当归根围土壤酶活、速效养分及产量的影响,明确增产机制,改进增产措施。【方法】利用溶磷圈法检测不同菌株溶磷活性、乙炔还原法检测固氮活性、试剂盒法检测过氧化物酶和硝化能力;复合菌剂T1[荧光假单胞菌(Pseudomonas fluorescens)CBS5、产碱假单胞菌(Pseudomonas alcaligenes) CBS7、嗜冷假单胞菌(Pseudomonas extremaustralis)CBSB、生枝动胶菌(Zoogloea ramigera) CBS4]和T2 (荧光假单胞菌CBS5、产碱假单胞菌CBS7、嗜冷假单胞菌CBSB)及对照CK (无菌马铃薯葡萄糖肉汤培养基)分别处理连作当归,分光光度法测定根围土壤及根中养分循环、转化相关酶活,氮、磷、钾速效养分含量;常规方法测产量;统计软件进行相关数据方差分析和主成分分析。【结果】产碱假单胞菌C...     

Seasonal and annual variation in nitrogen mineralization and nitrification along an elevational gradient in New Mexico

Patterns and amounts of nitrogen loss from disturbed ecosystems vary widely. The mineralization of organic nitrogen to ammonium and then nitrification to nitrate are important processes regulating nitrogen cycling rates and nitrogen losses. Nitrification is a significant process because of the production of the nitrate anion which is easily leached or denitrified. Most studies of these processes do not evaluate their seasonal and yearly variations. This study demonstrates that marked seasonal and yearly variations can occur in these processes in different ecosystems and suggests that nitrogen loss or other system properties correlated with one arbitrarily selected collection can be misleading. Spruce-fir and ponderosa pine ecosystems demonstrated little actual orpotential nitrification. Aspen and mixed conifer ecosystems demonstrated distinct seasonal patterns with increased rates of mineralization and nitrification during spring and summer months and a precipitous decline in both rates coincident with autumn foliage litterfall.The relative availability of soil nitrogen along with the amount of nitrogen circulating annually in litterfall prior to disturbance are useful predictors of the potential for nitrate production and loss following disturbance. However, other controls, including regulation by organic compounds, appear important in determining seasonal and annual variation in actual nitrification rates.     

Nitrification and nitrate reductase activity along a secondary successional gradient

The control of nitrification was studied in a secondary successional gradient on Nantucket Island, MA. It was hypothesized that 1) variability in nitrification along the gradient is controlled by litter primary and secondary chemistry, and 2) differences in nitrate availability along the gradient are reflected in potential nitrate assimilation rates in plant tissue. Nitrification varied significantly (p<0.05) by successional stage in all study sites, generally increasing with successional age. The ratio of nitrification to total N mineralization did not vary significantly between successional stages, suggesting substrate limitation of nitrification. Litter terpenoid resin concentration was a significant predictor (p<0.05) of nitrification rate, but soil %C, %N, and water content also contributed significantly to a stepwise regression model predicting nitrification. Nitrate reductase activity (NRA), an index of potential nitrate assimilation, was measured in an assay species (Schizachyrium scoparium). Although there was no significant correlation with nitrification, NRA was significantly (p<0.05) negatively correlated with soil ammonium concentration along the successional gradient at one site, suggesting that plants preferentially utilized ammonium in this system.     

Soil nitrogen turnover in proximal and distal stem areas of European beech trees

In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in the top 15 cm soil in proximal (defined as 1 m² around beech stems) and distal stem areas. Laboratory incubations and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification, and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal and distal areas. In the in situ incubations the average ratio of nitrification/ammonification was 0.85 in proximal and 0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m^-2 90 day^-1 in both areas. Mineralized nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification. Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the high nitrogen input by stemflow rather than to soil nitrogen turnover. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fluctuations in nitrate reductase activity,and nitrate and organic nitrogen concentrations of succulent plants under different nitrogen and water regimes

The CAM (Crassulacean acid metabolism) succulent species Kalanchoe daigremontiana, K. tubiflora and Crassula argentea, and the succulent C₃ species Peperomia obtusifolia, were cultivated in pure culture in open-air conditions under two different regimes of nitrogen and water supply. At specified intervals during the course of vegetative growth, biomass, nitrate reductase activity (NRA), nitrate concentration, and organic nitrogen concentration of whole plants were measured. After 100 days of cultivation the leaf conductance of Crassula and Peperomia was measured at intervals for the duration of a day. Behaviour of all four species was strongly influenced by the cultivation regime. This was apparent in terms of productivity and variable flucturations in NRA, nitrate concentration, and organic nitrogen concentration during the vegetative period. Increase in biomass was mostly connected with a decrease in all other investigated parameters, especially under conditions of water and/or nitrogen deficiency. The typical reaction of the CAM species Crassula to limited netrogen but adequate soil water was to reduce leaf conductance during light, whereas the C₃ plant Peperomia increased conductance in comparison with plants having a nitrogen suppy. The NRA of all plant species was reduced by both soil nitrate deficiency and drought. The succulent plant species, which are specially adapted to drought, neither took up nor used nitrate when water was limited. This was particularly the case for the CAM species, but less so for the C₃ Peperomia, which showed very high concentrations of nitrate and organic nitrogen, but low NRA and biomass gain. A formula was derived to express the nitrogen use efficiency (NUE) of the species, i.e. the ability of a plant to use nitrogen over a specific period of growth. NUE was shown to increase with age for the crassulacean species but to decrease for the C₃ Peperomia. Furthermore, NUE varied with the different nutrient levels in a species-specific manner, with high values for NUE not necessarily coupled to high productivity, and with NUE of the C₃ species generally higher than that of CAM species.     

Identification of an assimilatory nitrate reductase in mutants of Paracoccus denitrificans GB17 deficient in nitrate respiration

A Paracoccus denitrificans strain (M6Ω) unable to use nitrate as a terminal electron acceptor was constructed by insertional inactivation of the periplasmic and membrane-bound nitrate reductases. The mutant strain was able to grow aerobically with nitrate as the sole nitrogen source. It also grew anaerobically with nitrate as sole nitrogen source when nitrous oxide was provided as a respiratory electron acceptor. These growth characteristics are attributed to the presence of a third, assimilatory nitrate reductase. Nitrate reductase activity was detectable in intact cells and soluble fractions using nonphysiological electron donors. The enzyme activity was not detectable when ammonium was included in the growth medium. The results provide an unequivocal demonstration that P. denitrificans can express an assimilatory nitrate reductase in addition to the well-characterised periplasmic and membrane-bound nitrate reductases. Received: 12 August 1996 / Accepted: 29 October 1996     

Possible positive-feedback mechanisms: plants change abiotic soil parameters in wet calcareous dune slacks

In this paper the results are presented from a mesocosm study of the effects of typical dune slack plants on the soil solution nutrient contents. In dune slack succession, early successional species often show radial oxygen loss (ROL) whereas their successor species do not show ROL. ROL has impact on abiotic soil parameters and therefore, affect the competitiveness of both species. Mesocosms with Littorella uniflora and Carex nigra, used as respectively a ROL and a non-ROL species, showed remarkable differences in soil solution parameters. Special attention was given to nitrogen, as it is the limiting resource in dune slack succession. Mesocosms with L. uniflora showed a higher nitrate content in the soil than mesocosms with C. nigra and the control. Moreover, estimating the nitrogen balance, a significantly higher fraction of nitrogen was missing in L. uniflora (57%) than in C. nigra (5%). The enhanced nitrogen loss in mesocosms with L. uniflora could act as a positive-feedback mechanism for early successional stages that slows down the vegetation development in early stages of dune slack succession towards the more-productive later stages. The mechanism could even lead to alternative stable states in dune slack succession.     

Assessment of Nitrification Potential in Ground Water Using Short Term, Single-Well Injection Experiments

Nitrification was measured within a sand and gravel aquifer on Cape Cod, MA, using a series of single-well injection tests. The aquifer contained a wastewater-derived contaminant plume, the core of which was anoxic and contained ammonium. The study was conducted near the downgradient end of the ammonium zone, which was characterized by inversely trending vertical gradients of oxygen (270 to 0 μM) and ammonium (19 to 625 μM) and appeared to be a potentially active zone for nitrification. The tests were conducted by injecting a tracer solution (ambient ground water + added constituents) into selected locations within the gradients using multilevel samplers. After injection, the tracers moved by natural ground water flow and were sampled with time from the injection port. Rates of nitrification were determined from changes in nitrate and nitrite concentration relative to bromide. Initial tests were conducted with ¹⁵N-enriched ammonium; subsequent tests examined the effect of adding ammonium, nitrite, or oxygen above background concentrations and of adding difluoromethane, a nitrification inhibitor. In situ net nitrate production exceeded net nitrite production by 3- to 6- fold and production rates of both decreased in the presence of difluoromethane. Nitrification rates were 0.02–0.28 μmol (L aquifer)⁻¹ h⁻¹ with in situ oxygen concentrations and up to 0.81 μmol (L aquifer)⁻¹ h⁻¹ with non-limiting substrate concentrations. Geochemical considerations indicate that the rates derived from single-well injection tests yielded overestimates of in situ rates, possibly because the injections promoted small-scale mixing within a transport-limited reaction zone. Nonetheless, these tests were useful for characterizing ground water nitrification in situ and for comparing potential rates of activity when the tracer cloud included non-limiting ammonium and oxygen concentrations.     

Some chemical and physical factors affecting the rate and dunamics of nitrification in urine-affected soil

The effects of urinary chloride and nitrogen concentration and osmotic pressure on the nitrification of ammonium in a calcareous soil treated with cow urine were examined. Urinary chloride concentrations of up to 7.4 g L^–1 had no effect on the rate of nitrification, as determined by the accumulation of soil nitrate. Osmotic stress, generated using a mixed salt solution, had an inhibitory effect on nitrification at soil osmotic pressures lower than or equal to –1.0 PMa. Nitrification was completely inhibited at a soil osmotic pressure of –2.6 MPa. Accumulation of nitrate after a lag phase of 18 days was noted in the –2.0 MPa soil osmotic pressure treatment, indicating some degree of adaptation or osmo-regulation within the nitrifying population at this stress level. High urine-N concentrations resulted in considerable nitrite accumulations and reduced nitrification activity through the effect of free ammonia. It is concluded that in most temperate grassland soils at near-neutral pH, urinary chloride and nitrogen are unlikely to reduce nitrification rates, except where urine-N concentrations exceed 16 g N L^–1. Inhibition due to osmotic stress will be directly related to soil moisture status and may be particularly severe in dry, light-textured soils.     

元素硫和双氰胺对蔬菜地土壤硝态氮淋失的影响

采用温室盆栽淋洗试验,以NH₄HCO₃为氮肥源,研究了元素硫(S₀)和双氰胺（DCD）对种葱和不种作物土壤NO₃^--N淋失量和NO₃^--N、NH₄⁺-N浓度的影响.结果表明,在12周试验期间,与对照相比,S₀+DCD和S₀处理NO₃^--N淋失量分别低83%～86%和83%;NH₄⁺-N淋失量分别高16.8～21.0 mg·盆^-1和20.4～25.0 mg·盆^-1;而同期无机氮（NO₃^--N、NH₄⁺-N）淋失量则低60%.试验结束后,,S₀+DCD和S₀处理土壤无机氮含量分别比对照高79.9%～85.4%和74.9%～82.6%,以NH₄⁺-N为主.S₀+DCD处理无机氮淋失量比S₀和DCD处理分别低4.6%～14.4%和15.4%～30.1%;试验结束后土壤无机氮分别高6.1%和16.8～36.0%.在Na₂S₂O₃+DCD、Na₂S₂O₃和DCD处理中也发现类似结果.可见S₀施入土壤具有与DCD同样的氨稳定和硝化抑制作用.S₀与DCD配合施用可使DCD的硝化抑制性增强,其作用机理是S₀氧化中间体S₂O₃^2-、S₄O₆^2-,具有抑制硝化和DCD降解作用,延缓DCD硝化抑制效果.S0与DCD配合施用可用于延缓太湖流域蔬菜地土壤NH₄⁺-N向NO₃^--N转化,减少氮向水体迁移风险.     

Root-induced changes in radial oxygen loss, rhizosphere oxygen profile, and nitrification of two rice cultivars in Chinese red soil regions

Aims

To evaluate the external and internal morphological differences of roots that might influence rice root radial oxygen loss (ROL) and the corresponding rhizosphere nitrification activity, growth characteristics and nitrogen nutrition of rice.

Methods

The root ROL and rhizosphere oxygen profile were determined using a miniaturised Clark-type oxygen microelectrode system, and the rhizosphere nitrification activity was studied with a short-term nitrification activity assay.

Results

The rice biomass, nitrogen accumulation and nitrogen use efficiency (NUE) of ZH (high yield) were significantly higher than those of HS (low yield). The root biomass, number, diameter and porosity of ZH were also much greater than those of HS. The inner and surface oxygen concentrations of the root of ZH were significantly higher than those of HS. The order of paddy soil oxygen penetration depth was ZH?>?HS?>?CK, and the order of the oxygen concentrations detected in the water layer and rhizosphere soil was the same. The rhizosphere nitrification activity and nitrate concentration of ZH were significantly higher than those of HS.

Conclusions

More porous and thicker roots improved the individual root ROL, and more adventitious root numbers enhanced the entire plant ROL and correspondingly improved the rhizosphere nitrification activity, which might influence the growth and nitrogen nutrition of rice.