覆盖模式及小麦根系对土壤微生物区系的影响

采用平皿分离培养法研究了5种栽培模式和小麦根系对土壤细菌、真菌及放线菌数量的影响。连续2年的定位测定结果表明:覆膜有利于土壤微生物数量增加。5种栽培模式中,小麦根区、根外土壤细菌数量均以覆膜模式下最高,分别为116.8×106cfu·g-1和86.7×106cfu·g-1;土壤真菌和放线菌数量均以垄沟覆膜(垄上覆膜、垄沟播种)模式下最高,分别为3.0×103cfu·g-1、1.4×103cfu·g-1和18.9×105cfu·g-1、19.7×105cfu·g-1。不同模式下小麦根系对土壤细菌和真菌数量影响较大,表现为根区高于根外;而根系对放线菌影响较小,只有补灌和覆膜2种模式为根区高于根外。多重比较结果显示,覆膜与其他模式之间细菌数量差异极显著,根区土壤细菌和真菌数量与根外存在显著差异。覆盖和根系能大幅度增加根区细菌、真菌和放线菌的数量,强化小麦根区根外细菌和真菌的数量差异。     

Soil chemistry versus environmental controls on production of CH4 and CO2 in northern peatlands

Rates of organic carbon mineralization (to CO₂ and CH₄) vary widely in peat soil. We transplanted four peat soils with different chemical composition into six sites with different environmental conditions to help resolve the debate about control of organic carbon mineralization by resource availability (e.g. carbon and nutrient chemistry) versus environmental conditions (e.g. temperature, moisture, pH). The four peat soils were derived from Sphagnum (bog moss). Two transplant sites were in mid‐boreal Alberta, Canada, two were in low‐boreal Ontario, Canada, and two were in the temperate United States. After 3 years in the field, CH₄ production varied significantly as a function of peat type, transplant site, and the type–site interaction. All four peat soils had very small rates of CH₄ production (< 20 nmol g^?1 day^?1) after transplant into two sites, presumably caused by acid site conditions (pH < 4.0). One peat soil had small CH₄ production rates regardless of transplant site. A canonical discriminant analysis revealed that large rates of CH₄ production (4000 nmol g^?1 day^?1) correlated with large holocellulose content, a large concentration of p‐hydroxyl phenolic compounds in the Klason lignin, and small concentrations of N, Ca and Mn in peat. Significant variation in rates of CO₂ production correlated positively with holocellulose content and negatively with N concentrations, regardless of transplant site. The temperature response for CO₂ production varied as a function of climate, being greater for peat formed in a cold climate, but did not apply to transplanted peat. Although we succeeded in elucidating some aspects of peat chemistry controlling production of CH₄ and CO₂ in Sphagnum‐derived peat soils, we also revealed idiosyncratic combinations of peat chemistry and site conditions that will complicate forecasting rates of peat carbon mineralization into the future.     

Microbial activity and functional composition among northern peatland ecosystems

The extent to which complex interrelationships between plants and microorganisms influence organic matter dynamics is critical to our understanding of global C cycles in changing environments. We examined the hypothesis that patterns of soil microbial activity and functional composition differ among vegetation types in northern peatland ecosystems. Microbial characteristics were compared among peatlands differing in plant growth form (tree, shrub/moss, sedge) in two regions (New York State and West Virginia). Microbial activity (basal respiration) was greater in surface (0-15 cm) than subsurface (15-30 cm) peat and from sites dominated by shrubs and Sphagnum moss (3.9±0.65 μg C g⁻¹ h⁻¹) compared to forested (1.8±0.20 μg C g⁻¹ h⁻¹) or sedge-dominated sites (1.9±0.38 μg C g⁻¹ h⁻¹). Microbial activity was not related to decomposability of peat organic matter among vegetation types, and activity was unexpectedly higher in sites with lower peat pH and higher water table level. Substrate-induced respiration (SIR) did not show a clear pattern among vegetation types, but was greater in surface than subsurface peat. Microbial responsiveness to added glucose was very low. The ratio of basal respiration to SIR varied between 0.39 and 0.72 and, like activity, was highest in shrub/Sphagnum sites. Microbial substrate utilization patterns (assayed with BIOLOG^® GN plates) also differed between shrub/Sphagnum sites and forest or sedge sites, suggesting that C fluxes were mediated by different assemblages of microorganisms in shrub/Sphagnum peatlands. Principal component (PC) scores indicated more utilization of N-containing compounds and carboxylic acids, and less utilization of carbohydrates by microbial communities in shrub/Sphagnum sites. PC scores were much more variable both within and among vegetation types for sites in West Virginia than in New York State, and a greater diversity of C sources were utilized in WV (57±3) than NYS (47±2) peat. Our results suggest a link between microbial respiratory activity and microbial functional composition as they vary among these peatland vegetation types.     

中国西北干旱土壤中固定二氧化碳的RuBisCO基因丰度及其多样性研究

Arid soils where water and nutrients are scarce occupy over 30% of the Earth's total surface. However, the microbial autotrophy in the harsh environments remains largely unexplored. In this study, the abundance and diversity of autotrophic bacteria were investigated, by quantifying and profiling the large subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase(Ru Bis CO) form I(cbb L) responsible for CO2 fixation, in the arid soils under three typical plant types(Haloxylon ammodendron, Cleistogenes chinensis,and Reaumuria soongorica) in Northwest China. The bacterial communities in the soils were also characterized using the 16 S r RNA gene. Abundance of red-like autotrophic bacteria ranged from 3.94 × 105 to 1.51 × 106 copies g-1dry soil and those of green-like autotrophic bacteria ranged from 1.15 × 106 to 2.08 × 106 copies g-1dry soil. Abundance of both red- and green-like autotrophic bacteria did not significantly differ among the soils under different plant types. The autotrophic bacteria identified with the cbb L gene primer were mainly affiliated with Alphaproteobacteria, Betaproteobacteria and an uncultured bacterial group, which were not detected in the 16 S r RNA library. In addition, 25.9% and 8.1% of the 16 S r RNA genes were affiliated with Cyanobacteria in the soils under H. ammodendron and R. soongorica, respectively. However, no Cyanobacteria-affiliated cbb L genes were detected in the same soils. The results suggested that microbial autotrophic CO2 fixation might be significant in the carbon cycling of arid soils, which warrants further exploration.     

恶臭假单胞菌P861(Gus)在油菜根部定殖的生态研究

本研究采用Gus 基因标记技术和常规方法跟踪考察了恶臭假单胞菌P861(Gus) 在缩影系统油菜根圈的定殖情况,以及缩影系统内土壤类型、土壤含水量对根部定殖的影响。土壤含水量分别为60% FC和75% FC时,P861(Gus) 在砂姜黑土中的定殖水平高于50% FC的,不但能散布至种子下8cm 以内的根段部位,且定殖水平分别为7.5×10²和2.8×10³cfu·g^-1。在灰潮土缩影中,P861(Gus) 在油菜根圈的定殖动态表现为在油菜播种后3 ～6 天,定殖密度可达最高水平(5.5×10⁶cfu·g^-1) ,然后急速下降,最后保持在一个相对稳定的较低水平(7.6×10²cfu·g^-1) 。P861(Gus) 在不同根段部位的定殖密度并无从上到下逐渐递减的规律。     

Winter Time Concentrations and Size Distribution of Bioaerosols in Different Residential Settings in the UK

The total concentration and size distribution of bioaerosols in three different types of housing (single room in shared accommodation [type I], single bedroom flat in three-storey building [type II] and two- or three-bedroom detached houses [type III]) was assessed during the winter. This research was an extension of a previous study carried out in the summer. The measurement campaign was undertaken in winter 2008 and 30 houses were sampled. Samples were taken from kitchens, living rooms, corridors (only in housing type I) and outdoors with an Anderson 6 stage viable impactor. In housing type I, the total geometric mean concentration was highest in the corridor for both bacteria and fungi (3,171 and 1,281?CFU/m³, respectively). In type II residences, both culturable bacteria and fungi were greatest in the living rooms (3,487 and 833?CFU/m³, respectively). The living rooms in type III residences had largest number of culturable bacteria (1,361?CFU/m³) while fungi were highest in kitchens (280?CFU/m³). The concentrations of culturable bacteria and fungi were greater in mouldy houses than non-mouldy houses. A considerable variation was seen in the size distribution of culturable bacteria in type I residences compared to types II and III. For all housing types more than half of culturable bacterial and fungal aerosol were respirable (<4.7???m) and so have the potential to penetrate into lower respiratory system. Considerable variation in concentration and size distribution within different housing types in the same geographical region highlights the impact of differences in design, construction, use and management of residential built environment on bioaerosols levels and consequent varied risk of population exposure to airborne biological agents.     

Characterization of cultivable methanotrophs from paddy soils and rice roots

Abstract

Characterization of methanotrophs isolated from paddy soils and rice (Oryza sativa) roots was investigated in the present study. The number of methanotrophs in root homogenates of the rice cultivar Mutsuhomare was 4.9 × 10⁷ most-probable-number (MPN) g^?1 dry roots, in Yumeakari it was 2.0 × 10⁸ MPN g^?1 dry roots and in Kirara it was 4.6 × 10⁷ MPN g^?1 dry roots. Although bacterial cells were observed infrequently on the surface and in the interiors of roots before incubation, a large number of colonies, measuring 0.5–5 mm in diameter, were observed on the sterilized roots after incubation on nitrate mineral agar plates under methane in air. In particular, a large number of colonies were observed at the emergence sites of lateral roots and root hairs. Strains MD5-1 and M1 were isolated from the roots of Mutsuhomare and strain R62 was isolated from the root homogenate of Yumeakari. All isolates were catalase-positive and oxidase-positive, Gram-negative, straight-rod-shaped and curved-rod-shaped bacteria, and formed exospores. The isolates were able to fix nitrogen and grew in the absence of copper. In addition, all were found to be positive for naphthalene-oxidizing activities (corresponding to soluble methane mono-oxygenase activities). Strains MD5-1, M1 and R62 were closely related to Methylosinus sporium. Methanotrophic strains W3-6, SD3-5 and 2-19, isolated previously from paddy field soils, were classified into Methylosinus (W3-6) and Methylocystis (SD3-5 and 2-19) type II methanotrophs. Isolates from the rice roots (MD5-1, R62 and M1) grew logarithmically when casamino acid was used as the nitrogen source; however, the growth of these strains was reduced on the nitrate medium. These strains preferred amino acids over inorganic nitrogen as a nitrogen source for growth.     

"秸秆降解生防菌强化技术"对黄瓜连作土壤微生物区系的影响

"秸秆降解生防菌强化技术"(BS)近年在我国北方冬季温室栽培中广泛使用, 具改良土壤、减轻病害、改善品质、提高产量等多方面的效果。为探讨应用该技术后对黄瓜连作土壤中微生物区系的影响, 本研究采用平板培养计数与末端标记限制性片段长度多态性(T-RFLP)分析相结合的方法, 检测了黄瓜连作土壤中真菌、细菌、放线菌以及生防菌和病原菌的数量动态。结果表明, BS处理土壤后, 在连作第2茬时, 土壤中真菌群体总量比第1茬显著减少; 细菌总量比第1茬显著增加。细菌与真菌数量比值(B/F值)在连作两茬时明显升高, 土壤表现为"细菌型"; 连茬土壤中两种生防菌的含量保持相对稳定; 枯萎病原菌数量在连作两茬时与其他处理和对照相比有所降低, 但不显著; 处理后土壤细菌多样性在第2茬时显著升高, 并能促进TRF139等有益菌群增殖, 抑制TRF341和TRF501等有害菌群增殖。BS处理土壤能明显提高连作黄瓜的产量并降低根结线虫的病情指数, 在第3茬时产量比对照增加25.9%, 病情指数比对照减少71.4%。生防菌与秸秆配合使用对黄瓜连作土壤微生物的数量和群落结构影响显著, 在一定的连作茬数内能够保证生防菌有效定殖, 抑制病原菌数量增长, 提高土壤微生物多样性, 使土壤微环境达到相对健康的状态。     

猪粪沼液防治辣椒疫病机理研究--沼液中铵与腐殖酸的作用

为探明猪粪沼液对作物土传病害的防治效果与机制,设纯化肥处理为对照,采用盆栽试验比较了猪粪沼液(ADP1)、外源添加铵沼液(ADP2)、除铵沼液(ADP3)、除腐殖酸沼液(ADP4)施用对辣椒疫病的防治效果。结果表明,猪粪沼液(ADP1)可以显著降低辣椒疫病的发病率(防效40.8%),去除沼液中的铵或腐殖酸后,对辣椒疫病的防治效果显著下降,其发病率与病原菌对照(PC)无显著差异。定量PCR检测结果表明,ADP2处理土壤疫霉数量最少(2.51×103copies.g 1),ADP3、ADP4沼液处理的辣椒根际疫霉数量较多,分别为8.19×103copies.g 1、1.38×104copies.g 1;土壤中辣椒疫霉菌的数量低于9.54×103copies.g 1时,辣椒疫病发病率与土壤中病原菌数量有较好的对应关系。不同沼液处理对细菌、真菌和放线菌数量的影响不同。病原菌存在下,ADP1处理的细菌、真菌、放线菌数量均最多,ADP2处理的真菌数量最少。孢子萌发试验表明,随着铵和腐殖酸处理浓度的增加,对疫霉菌游动孢子萌发的抑制率均逐渐增大。浓度为500 mg.L 1、1 000 mg.L 1、1 500 mg.L 1NH4+对疫霉菌孢子萌发的抑制率分别为77.6%、81.8%、95.4%。用浓度为25 mg(C).L 1、50 mg(C).L 1、75 mg(C).L 1、150mg(C).L 1的猪粪沼液腐殖酸处理疫霉菌游动孢子6 h,游动孢子萌发率分别比无菌水对照下降了27.8%、54.5%、70.0%、87.5%。研究表明铵和腐殖酸可能是沼液的主要抑菌因子,沼液作为土传病害抑制剂具有一定的应用前景。     

Mycoflora Distribution in Dry‐Milled Fractions of Corn in Argentina

Corn samples and different commercial dry‐milled fractions collected from an industrial mill in Argentina were surveyed for fungal contamination. The percentage of Fusarium isolates in whole corn kernels among all fungi recovered was 2.0–97.0%; in corn grits, it was 2.6–50.0%. Maximum levels in the other fractions were 5.2 × 10⁵ colony forming units per gram (CFU/g) in germ and bran, 5.0 × 10³ CFU/g in C flour, and 2.7 × 10³ CFU/g in corn meal. The high initial contamination from whole corn is reflected in germ and bran, which is destined for animal consumption, but not in corn meal. F. verticillioides and Aspergillus flavus were the most frequent species in the whole corn kernel, but F. verticillioides was prevalent in all the other industrial fractions. Other potentially toxigenic fungi that were isolated included Aspergillus parasiticus, Alternaria alternata, Penicillium citrinum, and P. funiculosum. In this first report about mold contamination in corn industrial dry‐milled fractions in Argentina, the high fungal contamination level observed in the stored corn could indicate the necessity to improve the hybrid quality and the storage conditions to diminish the risk of mycotoxin occurrence.     

Diversity of anammox bacteria and abundance of functional genes for nitrogen cycling in the rhizosphere of submerged macrophytes in a freshwater lake in summer

Purpose

Submerged plants make an important contribution to nitrogen cycling in lakes including in the rhizosphere microenvironment through microbial activities. The main objective of this study was to investigate the abundance of functional genes for nitrogen cycling and the ecological relationship between these genes in the rhizosphere sediment of a freshwater lake in summer.

Materials and methods

Sediment from the rhizosphere of four submerged macrophytes (Ceratophyllum demersum, Hydrilla verticillata, Potamogeton maackianus, and Vallisneria spiralis) was sampled in Lake Liangzi, China, in summer. The anammox bacteria community structure and abundance of five functional genes for nitrogen cycling, ammonia monooxygenase (amoA) of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), anammox 16S rRNA, and nitrite reductase genes (nirK and nirS) in the sampled sediment, were determined.

Results and discussion

A total of 100 anammox gene sequences were grouped into eight operational taxonomic units (OTUs) and genus Ca. Kuenenia was the dominant species in Lake Liangzi in summer. Quantitative polymerase chain reaction (qPCR) revealed that gene copies of AOA amoA (2.42?×?10⁶ copies g^?1) were more than one order of magnitude higher than those of AOB amoA (1.98?×?10⁵ copies g^?1). The nirS gene (4.13?×?10⁸ copies g^?1) was more abundant than the nirK gene (7.28?×?10⁷ copies g^?1). There was no significant difference in the abundance of the AOB amoA gene among the rhizosphere of the four macrophytes. Redundancy analysis (RDA) showed a positive correlation between the abundance of the anammox 16S rRNA gene, AOA amoA and AOB amoA, which suggested two of these microbes may have provided a substrate for anammox bacteria in summer.

Conclusions

The diversity of anammox in the rhizosphere of submerged macrophytes of the freshwater lake in summer was very low, but the plant species could affect the abundance of most nitrogen circulating bacteria, especially for anammox bacteria. Anammox 16S rRNA gene was positively correlated with four other functional genes, indicating that all four genes had significant effects on anammox bacteria.

     

Composting of Tropical Toxic Weed Lantana camera L. Biomass and Its Suitability for Agronomic Applications

ABSTRACT

Lantana camara is an evergreen, which is the most notorious toxic weed of the terrestrial ecosystem. It is native to subtropical and tropical America, but a few taxa are indigenous to tropical Asia and Africa. An enormous quantity of green foliage is produced by this weed, which cannot be used as livestock feed due to its toxic properties. Management through utilization seems the only sustainable option for this problem. In this study, the composting of Lantana biomass was done and changes in chemical characteristics of waste biomass were measured. The composting caused decreases in pH, organic carbon, C:N ratio _totK and _totC by 2.0-, 1.25-, 1.66-, and 19-fold, respectively, but increases in electrical conductivity (EC), ash content, _totN, _totP, _totZn, and _totMg of 2.0-, 1.11-, 3.36-, 1.76-, 1.28-, and 1.70-fold, respectively. The C/N ratio (20.1) and soil respiration rate (47.12–66.20 mg CO₂-C/100 g) suggested the compost maturity at 52 days. The high bacterial (38.67 CFU × 10^?7 g^?1), fungal (30.0 CFU × 10^?3 g^?1), and actinomycetes (32.0 CFU × 10^?5 g^?1) population in composted material suggested the suitability of compost for agronomic purposes. Phytotoxity measured through compost:water extract and compost pot trial suggested the germination index (GI) in the ranges of 52.3%–122.3% and 74.5%–166.9%, respectively. The high ranges of chlorophyll, protein, and carotenoids in seedling than control suggested the non-toxicity of ready materials. Results suggested that composting can be a potential technology to manage Lantana biomass for sustainable land fertility management programs.     

Polycyclic aromatic hydrocarbons (PAHs) in peat and plants from selected peat‐bogs in the north‐east of Poland

The concentrations of polycyclic aromatic hydrocarbons (PAHs) were analyzed in samples of peat and of two plant species (Pinus sylvestris and Ledum palustre) overgrowing peat‐bogs in the north‐east of Poland. Peat samples were collected from different depths according to the stratigraphic profile of the peat bogs. The total concentrations of the 16 anthropogenic PAHs (15 from the US EPA list and benzo[e]pyrene) in all peat samples were between 70 and 439 ng g^—1. The concentration for the same compounds in pine needles (Pinus sylvestris) and Dutch Myrthe leaves (Ledum palustre) varied between 194 and 1039 ng g^—1. A noticeably high fluorene concentration in Dutch Myrthe leaves was found at some sites. In all peat samples 3‐ring compounds were predominant (55 to 319 ng g^—1). There were less 4‐ring PAHs (15 to 110 ng g^—1) and the least common PAHs were 5‐ring and 6‐ring compounds (0 to 81 ng g^—1 for both groups). In some peat samples, the perylene concentration largely exceeds of the total concentration of all the other PAHs investigated. The high content of perylene in bottom layers could result from the processes of perylene sorption from water during peat‐bog formation or from biogenic formation of perylene.     

东北地区四种农作物根际磷细菌的分布

从小麦、水稻、玉米,大豆根际土壤中磷细菌数量及其群落结构、多样性和相似性等几个方面,对东北地区代表性农作物根际磷细菌生态分布规律进行了系统研究.结果表明,4种作物根际土壤中分布大量解磷菌和溶磷菌,其中解磷菌达到2.15～6.68×105cfu·g-1、溶磷菌达到0.7～3.9×104cfu·g-1,解磷菌数量多于溶磷菌;作物根际土壤有效磷含量与磷细菌数量问无直接相关性;东北地区农作物根际磷细菌种群结构复杂,小麦、玉米、水稻、大豆根际土壤解磷菌分别涉及9个、11个、13个、12个菌属,溶磷菌分别涉及9个、8个、9个、7个菌属:4种主要农作物根际土壤中分布的磷细菌具有较高的多样性指数,且一般来说根际土壤中解磷菌多样性更高;作物根际磷细菌组成相似性系数在0.50～1.00之间,总体处于较高水平,且溶磷菌的相似性系数高于解磷菌.     

Effect of biofertilizers application on the growth of Eucalyptus grandis seedlings under greenhouse conditions

Abstract

To investigate the effect of biofertilizers on the growth and yield of Eucalyptus grandis seedlings, greenhouse experiments were performed applying fertilizers based on agricultural byproducts, inoculated with nitrogen-fixing bacteria of the genera Azotobacter spp and Azospirillum spp. For the biofertilizers formulation, a nitrogen-fixing bacteria consortium was inoculated, and the experimental design was a 2?×?2 × 2 factorial arrangement, the factors were nitrogen source (NS: chicken manure), source of carbon (CS: eucalyptus leaf litter) and source of micronutrients (RS: rhizospheric soil) with two dose levels, inoculated with a consortium of Azotobacter spp and Azospirillum spp. The optimal time production of the best biofertilizers was 30?days, with the highest density of Azospirillum (9.23 × 10⁶ CFU·g^?1) and Azotobacter (19.3 × 10⁶ CFU·g^?1), and total nitrogen contents in the range of 2.15-5.64%, released into the biofertilizers with chicken manure and bioaugmented with the bacterium consortium. The treatment with the highest dose of biofertilizer, 500?g, showed the most significant effect on seedling development, increasing growth, stimulating rooting and the highest increase in leaf number. The results show that biofertilizers contributed to Eucalyptus grandis crop yield, and biofertilizers are proposed as an alternative for implementing sustainable soil management in the forest sector.     

Distribution of Fusarium Molds and Fumonisins in Dry-Milled Corn Fractions

The distribution of Fusarium molds and fumonisins was determined in commercial and experimental dry-milled corn fractions. Fusarium infection of the commercial whole corn samples ranged from 10 to 28%; F. moniliforme was the predominant species. Fusarium counts in corn fractions were <100 colony-forming units (CFU)/g in flaking grits, <100 - 6.4 × 10⁴ CFU/g in bran, <100 − 1.6 × 10⁴ CFU/g in germ, and <100 − 2.7 × 10³ CFU/g in flour. Fumonisin concentrations were ≤0.1 μg/g in flaking grits, 0.2–1.1 μg/g in flour, 0.1–2.0 μg/g in germ, and 1.5–3.2 μg/g in bran. Yellow, blue, and white dent corns naturally contaminated with varying levels of fumonisins (25.4, 3.9, and 0.3 μg of fumonisin B₁ per gram) and Fusarium molds (3.9 × 10⁶, 8.0 × 10⁵, and 2.6 × 10⁴ CFU/g) were experimentally dry milled with a horizontal drum degermer. Number 5 grits contained significantly lower Fusarium counts and fumonisin concentrations than the whole kernel corn. Fusarium counts and fumonisins increased as grit size decreased, and high Fusarium counts and fumonisin concentrations were found in germ, bran, and fines.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.     

Effect of boron and sulfur interaction on some important biological indices in an inceptisol

In most soil ecosystems, soil biological activity and associated processes are concentrated in the rhizosphere soil and is influenced by the external application of plant nutrients. The impacts of boron and sulfur on soil biological properties were evaluated in an Aeric Haplaquept (pH 5.7) growing rapeseed (Brassica campestris L.) as a test crop. Application of boron (B) at 2 mg kg^?1 in combination with sulfur (S) at 30 mg kg^?1 (B₂S₃₀) resulted in highest available Boron and sulfur of 0.239 and 15.4 mg kg^?1, respectively and registered 62.5% and 71.3% increase over control (B₀S₀) at 60 days of crop growth compared to individual applications. The microbial populations viz. phosphate solubilizing microorganisms (PSM) and nitrogen fixing bacteria (NFB) were the highest of 52.63 and 85.87 × 10⁵ g^?1 soil, respectively, CFU in B₂S₃₀ treatment at 60 days and adjudged as the best treatment combination for enhancement of soil biological indices and seed yield.     

Laboratory mesocosm studies of Fe,Al, Mn,Ca, and Mg dynamics in wetlands exposed to synthetic acid coal mine drainage

To evaluate the potential for constructed wetlands to treat acid coal mine drainage, six model wetland mesocosms (each 2.4 m × 15 cm) were filled with Sphagnum peat (15 cm deep), planted either with cattails (Typha latifolia) and living Sphagnum, living Sphagnum only, or left as bare peat (2 mesocosms per treatment). The model wetlands were exposed to synthetic acid coal mine drainage (pH 3.5, concentrations of Fe²⁺, Al³⁺, Mn^2*, Ca²⁺, and Mg²⁺ of 78.8, 10.0, 5.2, 12.0, and 4.5 mg L^?1, respectively) at a rate of 90 mL min^?1, 6 hr d^?1, 5 d wk^?1, over a 16 week period. Chemical analysis of peat at periodic intervals indicated that the model wetlands were net sources of Al³⁺, Mn²⁺ Ca²⁺ and Mg²⁺, but net sinks for Fe²⁺. Type of vegetation had no significant effect on Fe²⁺ retention; of the 204 g of Fe²⁺ added to the model wetland systems, 162 g were retained. Formation of Fe oxides accounted for 73 to 86% of the Fee' retention, with exchangeable Fe contributing 0.2 to 1.2%, organically bound Fe contributing 4 to 19%, and residual Fe contributing 7 to 15% of total Fee' retention. Fe retention was greatest at the inflow ends of the model wetlands where Fe retention appeared to reach saturation at a final Fe concentration in the peat of 235 mg g^?1. At the rate of application of the synthetic acid mine drainage, we estimated that the model wetland systems would have reached complete Fe saturation after 157 days. We suggest that the mesocosm approach could be useful in generating site-specific data that can be applied to the formulation of cost-benefit analyses that can compare a proposed wetland treatment system with alternative conventional chemical methods for treating acid mine drainage.     

Genetic tagging of Azotobacter chroococcum for colonization on wheat (Triticum aestivum) and cotton (Gossypium sp.) roots

Abstract

Azotobacter chroococcum strains E12, HT57 were genetically tagged with lac Z, gfp to study the colonization behaviour on wheat (Triticum aestivum) and cotton (Gossypium sp.) in soil under controlled conditions. 10³ – 10⁴ cfu g^?1 soil of HT57 lac Z were found to colonize roots of both cotton and wheat crops whereas 1.7 × 10⁴ – 7.2 × 10⁴ cfu g^?1 soil of E12 gfp was colonizing wheat roots and 1.6 × 10⁴ – 9.3 × 10⁴ cfu g^?1 soil of E12 gfp colonized cotton roots respectively. Tagged strains colonized mostly on root tips compared to basal roots in both the crops.