Comparison of symbiotic effectiveness of Rhizobium sp. with positive hydrogen-uptake activity compared with negative mutants in relation to nitrogen fixation in mungbean (Vigna radiata L.)

H₂ uptake activity was well distributed in Rhizobium sp. strains isolated from nodules of mung-bean (Vigna radiata L.). Two effective strains, RMP1 und RMP2, exhibiting significantly higher H₂ uptake activity were subjected to mutagenesis with nitrosoguanidine. The respective mutation frequencies were 0.18 and 0.19%. Three Hup^- mutants each of RMP1 und RMP2 were compared with the wild-type parent strains under pot culture experiments to evaluate the significance of the H₂ uptake system in biological N₂ fixation. Nodulation capabilities, plant growth characteristics, and the chlorophyll content of the leaves were significantly reduced in the plants treated with Hup^- mutants. Nitrogenase activity in Hup^- nodules was reduced by 8–41%. Similarly, N accumulation was also reduced singificantly.     

Demonstration of two different H2-oxidizing activities in soil using an H2 consumption and a tritium exchange assay

H₂-oxidizing activities were assayed in slurries of four soils by measuring the consumption of H₂ and the exchange of ³H₂ with H₂O at increasing mixing ratios of H₂ or ³H₂. Both H₂ consumption and ³H₂ exchange were abolished by autoclaving or the addition of formaldehyde. The rates of H₂ consumption and ³H₂ exchange were proportional to the quantity of soil used. Both activities increased with increasing concentrations of H₂ or ³H₂ and displayed biphasic kinetics, demonstrating the existence of two different H₂-oxidizing activities, one with a relatively low K _m and V _max, and a second with a relatively high K _m und V _max. The first type of activity was characteristic of abiontic soil hydrogenases, and the second of aerobic H₂-oxidizing bacteria. In contrast to H₂ consumption, which required the presence of either O₂ or ferricyanide, ³H₂ exchange operated equally well without an external electron acceptor. The ³H₂ exchange assay may thus be particularly useful for enrichment of soil hydrogenases which have not yet been isolated and for which no natural electron acceptor is known.     

土著AMF与氮形态对辣椒||菜豆间作系统植株氮利用及其影响因素研究

近年来设施辣椒连作障碍日益突出,其中氮肥的大量不合理施用和高残留是限制辣椒高产、优质栽培的主要因素之一。研究土著丛枝菌根真菌(arbuscular mycorrhizal fungi, AMF)与间作体系强化蔬菜对不同形态氮(N)的利用并结合土壤菌丝密度、N形态及酶活性的反馈作用,可为设施土壤N素的高效利用和降低土壤N残留提供依据。本研究采用盆栽试验,设置辣椒||菜豆间作和各自单作种植模式,不同AMF处理[不接种(NM)、接种土著AMF]和不同形态N处理[不施N(N0)、无机氮(碳酸氢铵120mg·kg~(-1),ION)和有机氮(谷氨酰胺120 mg·kg~(-1),ON)],探讨了设施条件下接种土著AMF、施用不同形态N与间作对辣椒、菜豆根围土壤菌根建成、酶活性及N利用的影响。结果表明,与NM相比,接种土著AMF使设施辣椒、菜豆植株生物量及N吸收量显著增加(除菜豆单作-ON处理),显著降低土壤NH_4~+-N、NO_3~--N含量。无论施用何种形态N,均显著增加辣椒、菜豆植株生物量(除菜豆单作-AMF处理)及N吸收量,表现为ONION。与单作-ON-AMF处理相比,间作-ON-AMF处理下的辣椒N吸收量显著增加39.9%、菜豆N吸收量显著增加93.0%。对N利用影响因子的分析结果表明,间作协同接种土著AMF较大程度上增加了土壤有机质含量及蛋白酶、脲酶、硝酸还原酶活性。相关性分析显示,辣椒、菜豆植株N吸收量与AMF侵染率呈极显著正相关关系,而土壤NH_4~+-N和NO_3~--N含量则与AMF侵染率呈现一定的负相关关系。此外,土壤蛋白酶、脲酶和硝酸还原酶活性与辣椒、菜豆植株N吸收量呈正相关关系。可见,所有复合处理中,以间作体系接种土著AMF与施用适量有机氮的组合明显促进了设施辣椒、菜豆生长和N素利用。     

低硒土壤中75Se的形态转化

用⁷⁵SeO₂水溶液分别按0.131ppm和1.631ppm比例处理暗棕色森林土。用这种土壤盆栽的小麦含Se分别为0.023ppm和0.493ppm。小麦收获之后,对土壤残留的⁷⁵Se用不同的提取剂连续进行化学分级,⁷⁵Se的各种形态按其占土壤总Se的百分比大小排序为:同位素交换态Se>NH₄OH可提态Se>HNO₃可提态Se>HCl可提态硒>水溶态Se>K₂SO₄可提态硒。土壤残留⁷⁵Se主要以NaHSeO₃同位素交换态存在,其量占土壤总硒28%,NH₄OH可提态Se次之,占20%;水溶态Se较少,仅6-7%。以SeO₃^-2形式加入土壤的⁷⁵Se被土壤紧密吸附。     

Hydrogen oxidation activities in soil as influenced by pH,temperature, moisture,and season

Summary Hydrogen oxidation in soil was measured at low (1 ppmv) and high (300 ppmv) H₂ concentrations to distinguish between the activities of abiontic soil hydrogenases and Knallgas bacteria, respectively. The two activities also showed distinctly different pH optima, temperature optima, and apparent activation energies. The pH optima for the soil hydrogenase activities were similar to the soil pH in situ, i.e., pH 8 in an slightly alkaline garden soil (pH 7.3) and pH 5 in an acidic cambisol (pH 4.6–5.4). Most probable number determinations in the alkaline acidic soils showed that Knallgas bacterial populations grew preferentially in neutral or acidic media, respectively. However, H₂ oxidation activity by Knallgas bacteria in the acidic soil showed two distinct pH optima, one at pH 4 and a second at pH 6.4–7.0. The soil hydrogenase activities exhibited temperature optima at 35–40°C, whereas the Knallgas bacteria had optima at 50–60°C. The apparent activation energies of the soil hydrogenases were lower (11–23kJ mol^-1) than those of the Knallgas bacteria (51–145 kJ mol^-1). Most of the soil hydrogenase activity was located in the upper 10 cm of the acidic cambisol and changed with season. The seasonal activity changes were correlated with changes in soil moisture and soil pH.     

Enhanced denitrification in plots of N2-fixing faba beans compared to plots of a non-fixing legume and non-legumes

Denitrification rates were studied using the C₂H₂ inhibition technique in a 2-year field experiment within plots of nodulated and non-nodulated faba beans, ryegrass, and cabbage. Denitrification rates ranged from 14.40 to 0.02 ng N₂O–N g^–1 soil dry weight h^–1. Mean denitrification increased fourfold in plots of N₂–fixing Vicia faba compared to non-nodulated V. faba mutant F48, Lolium perenne, and Brassica oleracea. The results with and without C₂H₂ treatment indicate that in the field the major part of this enhanced denitrification led to the endproduct N₂ rather than to the ozone-degrading N₂O. Higher denitrification rates of plots with N₂–fixing plants in September seemed to be caused by an increase in soil NO _inf3 ^sup- of about 20 kg ha^–1 found between July and August. Soil NO _inf3 ^sup- and soil moisture explained 67% of the variation in denitrification rates of the different soil samples over the growing seasons in the 2 years. Soil moisture explained 44% of the variation for soil planted with N₂–fixing plants and 62% for soil planted with non-fixing plants. Positive exponential relationships were obtained between denitrification rates and soil nitrate (r=0.71) and soil moisture (r=0.82).     

Soil microbial biomass phosphorus as an indicator of phosphorus availability in a Gleyic Andosol

Abstract

The relationship between plant phosphorus (P) uptake and soil microbial biomass phosphorus (biomass P) or available phosphorus (Truog P) was estimated in a Gleyic Andosol in Sapporo, Hokkaido, in a 4-year field trial (2004–2007). Every year, the soil was treated in duplicate (each plot 36?m²) or triplicate (each plot 24?m²) with chemical fertilizer, cow manure compost or sewage sludge compost, and then kidney beans (Phaseolus vulgaris) were planted. Pooled data of the shoot content of P at harvest over the 4?years was significantly correlated with biomass P determined 1?month after the application of fertilizer (P?<?0.01). A multivariate analysis revealed that the grain yield was significantly positively correlated with the shoot content of P (P?<?0.01) and significantly negatively correlated with the shoot content of calcium (P?<?0.05), but not correlated with the shoot content of either nitrogen or potassium. These results suggest that P is the most limiting element to affect the productivity of kidney bean plants in this trial and that biomass P is an important P source that explains the differences in P availability among soil amendments. Biomass P is a better indicator of P availability for kidney beans grown in Gleyic Andosols compared with Truog P, which is widely used in Japan.     

农茬口对土壤特性及熟地当归育苗的调控效应

利用高寒草甸生荒地进行当归育苗的传统方式造成严重的水土流失。为了探讨农茬口调控土壤特性继而影响后茬当归育苗的效应,在道地产区甘肃省卓尼县熟地培育农作物茬口后进行当归育苗,测定育苗期土壤特性、成苗数和产量。结果表明,农茬口对后茬当归育苗田土壤特性具有显著影响,与休耕茬田比较,马铃薯、油菜、蚕豆茬田土壤电导率极显著降低, pH显著提高,青稞茬田土壤pH和电导率均降低,农茬口极显著提高了后茬土壤阳离子含量,降低了阴离子含量。各茬口土壤K~+含量依次为青稞蚕豆油菜马铃薯休耕, Na~+含量为马铃薯青稞蚕豆油菜和休耕, Cl~-含量为休耕马铃薯青稞油菜蚕豆。随土层加深,紧实度增加,孔隙度减少,含水量随土层和茬口而异。0～15 cm土层的土质疏松且含水量高则有利于保苗。当归成苗数和苗产量与土壤电导率、Cl~-含量均呈显著负相关;苗产量与pH、K~+含量呈显著正相关,与5～10 cm土层容重呈显著负相关;苗数与0～5 cm土层总孔隙度呈显著正相关。各茬口育成苗产量排序与综合评价指数顺序一致,综合评价指数依次为蚕豆(0.986)油菜(0.682)青稞(0.668)马铃薯(0.297)休耕(0.159)。因此,优异的茬口特性可优化当归幼苗赖以生存的农田土壤环境,改善土壤性质,富集营养,促生保苗,蚕豆茬口更为优异。     

Equilibria of weak acids and organic Al complexes explain activity of H+ and Al3+ in a salt extract of exchangeable cations

Two sequential extractions with unbuffered 0.1 m BaCl₂ were done to study the release of salt-exchangeable H⁺ and Al from mineral horizons of five Podzols and a Cambisol. Released Al was found to have a charge close to 3+ in all horizons and in both extractions. This finding was supported by the near-equality of the titrated exchangeable acidity (EA_T) and the sum of exchangeable acids (EA = H_e + 3Al_e, calculated from the pH and Al concentration of the extract). The ratio between EA of the second and the first extraction was over 0.50 in the Bs2 and C horizons and smaller in the other horizons. H⁺ was assumed to be in equilibrium with weak acid groups, and the modified Henderson–Hasselbach equation, pK_HH = pH ? n log (α/(1 ? α)), was used to explain pH of the extract. The degree of dissociation (α) was calculated as the ratio between effective and potential cation exchange capacity. Value of the empirical constant n was found to be near unity in most horizons. When the monoprotic acid dissociation was assumed in all horizons, pK_HH had the same value in both extractions. For Al³⁺, two equilibrium models were evaluated, describing (i) complexation reactions of Al³⁺ with soil organic matter, and (ii) equilibrium with Al(OH)₃. Apparent equilibrium constants were written as (i) pK_o = xpH ? pAl³⁺, and (ii) log Q_gibbs= log Al³⁺ ? 3log H^+. The two extractions gave an average reaction stoichiometry x close to 2 in all horizons. Results suggest that an equilibrium with organic Al complexes can be used to express dissolved Al³⁺, aluminium being apparently bound to bidentate sites. The value of log Q_gibbs was below the solubility of gibbsite (log K_gibbs = 8.04) in many horizons. In addition, log Q_gibbs of the second extraction was greater than that of the first extraction in all horizons except the C horizon. This indicates that equilibrium with Al(OH)₃ cannot explain dissolved Al³⁺ in the soils. We propose that the models of pK_HH and pK_o can be used to simulate exchangeable H⁺ and Al³⁺ in soil acidification models.     

Nitrogen fixation by biological soil crusts and heterotrophic bacteria in an intact Mojave Desert ecosystem with elevated CO2 and added soil carbon

Fixation of N by biological soil crusts and free-living heterotrophic soil microbes provides a significant proportion of ecosystem N in arid lands. To gain a better understanding of how elevated CO₂ may affect N₂-fixation in aridland ecosystems, we measured C₂H₂ reduction as a proxy for nitrogenase activity in biological soil crusts for 2 yr, and in soils either with or without dextrose-C additions for 1 yr, in an intact Mojave Desert ecosystem exposed to elevated CO₂. We also measured crust and soil δ¹⁵N and total N to assess changes in N sources, and δ¹³C of crusts to determine a functional shift in crust species, with elevated CO₂. The mean rate of C₂H₂ reduction by biological soil crusts was 76.9±5.6 μmol C₂H₄ m⁻² h⁻¹. There was no significant CO₂ effect, but crusts from plant interspaces showed high variability in nitrogenase activity with elevated CO₂. Additions of dextrose-C had a positive effect on rates of C₂H₂ reduction in soil. There was no elevated CO₂ effect on soil nitrogenase activity. Plant cover affected soil response to C addition, with the largest response in plant interspaces. The mean rate of C₂H₂ reduction in soils either with or without C additions were 8.5±3.6 μmol C₂H₄ m⁻² h⁻¹ and 4.8±2.1 μmol m⁻² h⁻¹, respectively. Crust and soil δ¹⁵N and δ¹³C values were not affected by CO₂ treatment, but did show an effect of cover type. Crust and soil samples in plant interspaces had the lowest values for both measurements. Analysis of soil and crust [N] and δ¹⁵N data with the Rayleigh distillation model suggests that any plant community changes with elevated CO₂ and concomitant changes in litter composition likely will overwhelm any physiological changes in N₂-fixation.     

Use of NaCN to increase the growth of N2-fixing bacteria in a model spermosphere mimicked by sucrose and amino acids leached by seeds

In order to study the establishment of a spermosphere, the C₂H₂ reduction activity of N₂-fixing bacteria isolated from river sand was examined in a simulated spermosphere in the river sand which contained sucrose, an amino acid mixture, and CN^- released from plant seeds. The sand incubated with 10^-10 to 10^-9 mol CN^- 30 g sand^-1 exhibited higher C₂H₂ reduction activity than that without CN^-. The change in the most probable number of N₂ fixers with increasing quantities of CN^- roughly corresponded to that in C₂H₂ reduction activity. However, the most probable number of non-N₂-fixing bacteria decreased except for CN^--tolerant ones. Both C₂H₂ reduction activity and proliferation of the N₂ fixers isolated on a modified Burk's medium were almost similar to those in the bacteria in the sand. In contrast, the proliferation of some nonfixers decreased with an increasing CN^- concentration. C₂H₂ reduction activity of N₂ fixers cultured in combination with non-fixers exhibited a clear peak at 10^-7 M CN^- as for C₂H₂ reduction activity in the sand. We therefore speculate that cyanide evolved from seeds during a pregermination period may suppress the growth of general bacteria, but may promote the proliferation of N₂ fixers, thus contributing to the establishment of a spermosphere.     

不同植被对红壤养分含量及吸附-解吸 性能的影响

植被类型和生长状况, 对土壤养分和土壤对 H2PO4- 的吸附-解吸及对 K +的缓冲特性均具有较大影响。 草灌 乔植被下土壤中氮磷钾等养分的含量均较高, 白茅植被下土壤有机质含量较高(21.16g/ kg), 无植被处理下土壤有 机质和养分含量均较低。 3 种类型植被下, 土壤对 H2PO4-吸附的 b 值以无植被>白茅>草灌乔, 不同 H2PO4- 吸附 范围内的解吸率以草灌乔相对较高, 而无植被处理下则相对较低 ;对 K +缓冲的 Q/ I 曲线参数比较, Δk0 值以草灌 乔>白茅>无植被, AR0 值为白茅>无植被>草灌乔, PBCk 值为无植被>白茅>草灌乔。     

Degradation of 14C-Zinc Ammonium Acetate in Soils as Influenced by Soil Types,Soil Sterilization,and Carriers

Zinc ammonium acetate (ZAA), typically applied to soils in anhydrous ammonia as a carrier, has been used to improve corn (Zea maysL.) productivity. This study aimed to determine the fate of ZAA in soils as influenced by soil type (sandy, silt, and clay loam), sterilization (sterile and non-sterile), and two carriers (H₂O and NH₄OH). A 16 d laboratory incubation experiment with ¹⁴C-ZAA showed that total recovery of carbon-14 (¹⁴C) from ¹⁴CO₂ trap and soil extraction by CaCl₂ ranged from 72% to 94% in the first 8 d for sterilized soils. However, < 17% ¹⁴C was found in non-sterilized soils. Most ¹⁴C recovered in sterilized soil was associated with soil extraction, and relatively little was found in the CO₂ traps. All sterilized soils provided similar ¹⁴C recoveries except the sandy loam. Slightly more ¹⁴C was extracted from the soil when NH₄OH was the ZAA carrier rather than water. Conversely, recovery of ¹⁴CO₂ continued to increase during the 16 d incubation, but started faster when water was the ZAA carrier. Microbial activity appeared to be instrumental in the assimilation and disappearance of ZAA.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

高氮和NO2-对中亚热带森林土壤N2O和NO产生的影响

利用15N同位素标记方法,研究在两种水分条件即60％和90％ WHC下,添加硝酸盐(NH4NO3,N 300 mg kg-1)和亚硝酸盐(NaNO2,N 1 mg kg-1)对中亚热带天然森林土壤N2O和NO产生过程及途径的影响.结果表明,在含水量为60％ WHC的情况下,高氮输入显著抑制了N2O和NO的产生(p＜0.01);但当含水量增为90％ WHC后,实验9h内抑制N2O产生,之后转为促进.所有未灭菌处理在添加NO2-后高氮抑制均立即解除并大量产生N2O和NO,与对照成显著差异(p＜0.01),在60％ WHC条件下,这种情况维持时间较短(21 h),但如果含水量高(90％ WHC)这种情况会持续很长时间(2周以上),说明水分有效性的提高和外源NO2-在高氮抑制解除中起到重要作用.本实验中N2O主要来源于土壤反硝化过程,而且加入未标记NO2-后导致杂合的N2O(14N15NO)分子在实验21 h内迅速增加,表明这种森林土壤的反硝化过程可能主要是通过真菌的“共脱氮”来实现,其贡献率可多达80％以上.Spearman秩相关分析表明未灭菌土壤NO的产生速率与N2O产生速率成显著正相关性(p＜0.05),土壤含水量越低二者相关性越高.灭菌土壤添加NO2-能较未灭菌土壤产生更多的NO,但却几乎不产生N2O,表明酸性土壤的化学反硝化对NO的贡献要大于N2O.     

Competition and persistence of Rhizobium tropici and Rhizobium etli in tropical soil during successive bean (Phaseolus vulgaris L.) cultures

Strains of Rhizobium tropici IIB, CIAT899 and F98.5, both showing good N₂ fixation, and a R. etli strain W16.3SB were introduced into a field which had no history of bean culture. Plant dilution estimates showed that in the presence of its host (Phaseolus vulgaris cv. Carioca) during the cropping seasons and the subsequent fallow summer periods, the bean rhizobial populations increased from less than 30 to 10³ g^–1 dry soil after 1 year and to 10⁴ g^–1 dry soil after 2 years. In the 1st year crop, the inoculated strains occupied most of the nodules, which resulted in a higher nodulation and C₂H₂ reduction activity. Without reinoculation for the second and third crops, however, little R. tropici IIB was recovered from the nodules and the bean population consisted mainly of R. etli, R. leguminosarum bv. phaseoli, and R. tropici IIA. Reinoculation with our superior R. tropici IIB strains before the second crop resulted in R. tropici IIB occupying the main part of the nodules and a positive effect on nodulation and C₂H₂ reduction activity, but reintroduction of the inoculant strain in the third season did not have any effect.     

Nitrogen yield and nitrogen fixation of winter faba beans

Introducing autumn-sown legumes into Central European farming systems could be beneficial for addressing two challenges for European agriculture, i.e., the substantial deficit of protein sources for livestock and expected changes in agroclimatic conditions. Therefore, a two-year field experiment was conucted under Pannonian climate conditions in eastern Austria to assess nitrogen (N) yield and N fixation of several winter faba bean varieties from different European countries as compared to a spring faba bean. Winter wheat was used as a reference crop for estimating atmospheric N fixation. Winter faba beans were susceptible to frost damage especially in the harder of the two winters. Winter faba bean varieties could not achieve a higher grain yield and a higher grain N yield than the spring faba bean but had a higher grain N concentration (except for one variety). Grain yield and grain N yield of faba beans were severely impaired by drought in one year (with a mean of varieties of 8.3 g N m^?2, winter wheat: 6.4 g N m^?2); in the other year, grain N yield of faba beans considerably surpassed that of winter wheat (with a mean of varieties of 21.5 g N m^?2, winter wheat: 8.8 g N m^?2). After harvest, faba beans left higher nitrate residues in the soil, especially in the subsoil, and higher amounts of N in above-ground residues compared to winter wheat. Faba beans showed high N fixation under optimum conditions (with a mean of varieties of 21.9 g N m^?2) whereas drought considerably impaired N fixation (with a mean of varieties of 6.3 g N m^?2; with no differences between autumn- and spring-sown faba beans). In conclusion, growing winter faba bean varieties in eastern Austria did not result in higher grain yield, grain N yield, and N fixation compared to growing a spring faba bean.     

SO42-和Cl-对稻田土壤养分及其吸附解吸特性的影响

利用长期定位试验 ,比较了长期施用含SO₄^2-和Cl^- 化肥 22年后稻田土壤的 pH值、养分状况及其吸附解吸特性。结果表明 ,长期施用含SO₄^2-化肥 ,土壤有机质、速效氮和速效钾的含量较高 ,但全量氮磷钾的含量较低 ;长期施用含Cl^- 化肥 ,土壤全量氮磷钾和速效磷的含量较高 ,但pH值相对较低。长期施用含上述二种阴离子的化肥后 ,土壤对H₂PO₄^-的最大吸附量均较大 ,且在Cl^- 处理下土壤对H₂PO₄^-吸附的结合能较大 ,而SO₄^2-处理下土壤在同等吸附量时对H₂PO₄^-的解吸量相应较多。长期施用含SO₄^2-的化肥亦使土壤对钾素的供应强度较大 (ΔK0的绝对值较大 )、缓冲能力增强 (AR0值较高 ) ,而长期施用含Cl^- 的化肥时则与SO₄^2-相反     

NaCl对真盐生植物囊果碱蓬硝态氮吸收亲和力系统的影响

采用营养液培养方法,研究了真盐生植物囊果碱蓬(Suaeda physophora Pall.) 在不同盐度和氮水平中预处理21 d后硝态氮的吸收动力学特征。结果表明,氮饥饿后,囊果碱蓬对NO-3吸收符合离子吸收动力学模型,其吸收动力学参数表现为NO-3预处理浓度增加后,高亲和力系统中Vmax增大,Km值增加,但增加的幅度不一致。经过低氮高盐预处理的囊果碱蓬高亲和力系统增加的幅度比经过高氮高盐预处理的囊果碱蓬高亲和力系统增加的幅度大; 对于低亲和力系统,NaCl长期胁迫对高氮预培养的囊果碱蓬的低亲和力系统吸收速率有抑制作用,而对低氮预培养的囊果碱蓬的低亲和力系统吸收速率有促进作用。结果说明,真盐生植物囊果碱蓬长期生长在低氮高盐条件下,为了适应特殊的环境条件,形成了耐盐的硝态氮吸收系统。     

有机修饰(土娄)土对CrO42-吸附特征的初步研究

以CTMAB（十六烷基三甲基溴化铵）单一修饰和CTMAB＋SDS（十二烷基磺酸钠）混合修饰塿土耕层、粘化层土样，从修饰比例、土层、温度角度探讨了有机修饰塿土对CrO4^2-的平衡吸附特征。结果表明，各供试土样中CrO4^2-平衡吸附量均随CrO4^2-平衡浓度增高而增大，有机修饰土对CrO4^2-的吸附等温线呈现L型等温线形式，原土土样的吸附等温线基本上类似于S型吸附等温线形式，两层次各土样对CrO4^2-的吸附量呈现100CB〉120CS〉50CB〉CK的顺序（100，120，50分别表示修饰比例为100，100＋20，50；CB为CTMAB修饰；cs为CTMAB＋SDS修饰；CK为未修饰原土）；随着平衡浓度的增大，耕层原土对CrO4^2-的吸附能力增加较快而粘化层原土增加较慢，塿土粘化层修饰土样对CrO4^2-的平衡吸附量均高于塿土耕层土样，但修饰比例增高导致两层次土样对CrO4^2-吸附亲和力的差异减小；未修饰原土对CrO4^2-吸附呈现增温效应，粘化层CK土样增温效应高于耕层CK土样，表明增温促进粘粒矿物对CrO4^2-的专性吸附。随平衡浓度的增大，修饰土样CrO4^2-吸附温度效应比值均变化不大，耕层各修饰土样对CrO4^2-吸附呈现增温负效应，而粘化层修饰土样对CrO4^2-吸附的温度效应则与修饰剂和修饰比例有关。