Forest soil organic matter delta 13C along a altitudinal transect on northern slope of Changbai Mountains under effects of simulated warming

The litters, bulk soils, and soil particle-size fractions were sampled from three typical natural forests, i.e., broadleaf Korean pine (Pinus koraiensis) mixed forest (PB, altitude 740 m), spruce-fir (Picea asperata-Abies nephrolepis) forest (SF, altitude 1350 m), and Erman's birch (Betula ermanii) forest (EB, altitude 1996 m), on the northern slope of Changbai Mountains to analyze their organic matter delta13C values, and the intact soil cores (20 cm depth) from EB (high altitude) were relocated to PB and SF (low altitudes) for a year to study the responses of the delta13C values to simulated warming. It was shown that the litters had a significantly lower delta13C value than the soils, and the delta13C values of the litters and soils increased downward through the litter- and soil layers in all the three typical forest types. Soil particle-size fractions had an increased delta13C value with decreasing particle size fractions. The delta13C value of the litters was in the order of SF (-28.3 per thousand) >PB (-29.0 per thousand) >EB (-29.6 per thousand), while that of the soils was in the order of EB (-25.5 per thousand) >PB (-25.8 per thousand) >SF (-26.2 per thousand). Over one-year soil warming (an increment of 0.7 degrees C - 2.9 degrees C) , the delta13C values of the bulk soils and soil particle-size fractions all presented a decreasing trend, and the decrement of the delta13C value was larger in <2 microm (0.48 per thousand) and 2-63 microm fractions (0.47 per thousand) than in >63 microm fraction (0.33 per thousand). The results suggested that climate warming could have great effects on the older organic carbon associated with fine soil particle-size fractions.     

有机物添加下太岳山油松林土壤微生物元素组成的稳态分析

在山西太岳山地区,向油松林土壤中分别添加生物炭、玉米秸秆、蒙古栎叶、油松叶、木屑等5种有机物,测定各处理的土壤养分、酶及微生物生物量等指标,研究外源有机物添加下土壤酶化学计量特征及微生物元素组成的内稳性。结果表明: 添加木屑显著增加了土壤N(17.1%)、P(37.6%)含量,显著增加了微生物生物量碳(118.0%)、氮(41.0%)、磷(176.6%)。C、N、P获取酶(β-1,4-葡萄糖苷酶、β-1,4-N-乙酰氨基葡萄糖苷酶、亮氨酸氨基肽酶、酸性磷酸酶)活性总体上随添加有机物C/N值(生物炭<蒙古栎叶<油松叶<玉米秸秆<木屑)的增加而增加,其化学计量变化受土壤养分状态及微生物生物量的调控。酶活性相对比例及矢量特性表明,研究区微生物生长受到P的限制,且添加有机物没有缓解P的制约作用。微生物生物量碳、氮及化学计量比C∶N、C:P、N∶P属于绝对稳态型,而微生物生物量磷处于非稳态。微生物通过改变酶的分配策略保持微生物体元素及比例的相对稳定,仅有微生物生物量磷对土壤养分变化表现出不稳定性,可能因为P是研究区微生物生长的限制性元素。     

Organic matter and soil biota of upland wetlands in Taylor Valley,Antarctica

In January 2001, we surveyed streams and ponds above 300 m a.s.l. in Taylor Valley, South Victoria Land, Antarctica. One pond was examined in detail. Organic materials covered nearly 100% of the adjacent soil to 5–20 m from the shore, with intermittent patches to 80 m. Organic matter averaged 257 g C/m², and totaled 1,388 kg organic C on the soil around the pond. Soil-moisture content (0.56–12.41%) decreased with distance from shore, whereas pH (7.8–10.8) increased with distance. Electrical conductivity was lowest in the soils <10 m from the pond (416±94 µS/cm). Mineral soil organic C and total N concentrations were greatest between 10 and 30 m from the edge of the pond (1.21±0.37 and 0.13±0.05 mg/g soil, respectively). Soil invertebrates were present in only 50% of samples and included tardigrades, rotifers, and two nematodes, Scottnema lindsayae and Plectus antarcticus. A non-parametric, discriminant function analysis based on soil moisture, soil organic carbon, and electrical conductivity correctly predicted 87.0% of sites that had invertebrates and 70.8% of sites for which invertebrates were absent. Tardigrades, rotifers, and P. antarcticus were found only in the wettest soils nearest the pond whereas S. lindsayae was restricted to drier soils further from shore. Other ponds and streams also showed substantial accumulations of organic matter, suggesting that upland wetlands serve as resource islands in these polar deserts that provide a source of organic matter to nearby soils.     

人为干扰下子午岭次生林土壤生态因子动态变化

对黄土高原陕西子午岭次生林区不同人为扰动条件下林地土壤容重、有机质、团聚体和微生物等进行了研究.结果表明,人为干扰(砍伐与开垦)对土壤生态因子影响较大,随干扰程度加剧,土壤理化性质变差,土壤有机质由2.2%下降到0.8%.土壤稳定性团聚体减少30%;微生物数量由1×10⁹个·g^-1干土下降到8×10⁷个·g^-1干土,土壤退化严重.在同一干扰类型的土壤剖面上,土壤有机质和土壤微生物随土层深度的增加分别减少了50%和90%,并且在不同干扰强度下变化幅度略有差异.土壤容重由表层的0.9 g·cm^-3增加到1.21 g·cm^-3,呈增大趋势.同一干扰类型土壤理化性质在沟缘线上下存在一定差别,沟缘线以下样地表现出较好的土壤理化性质和较高的微生物量.     

喀斯特峰丛洼地土壤有机质的空间变化及其对干扰的响应

通过网格(10 m×10 m)取样,运用地统计学方法研究了喀斯特峰丛洼地4类典型干扰区表层土壤（0～20 cm）有机质的空间变异、分布,及其生态学过程和机制.结果表明:随着干扰强度降低,植被由农作物(Ⅰ)—人工林(Ⅱ)—次生林(Ⅲ)—原生林(Ⅳ)顺向演替,土壤有机质逐步提高,且达到了显著水平(P＜0.05).4类干扰区均具有良好的空间自相关性,不同干扰区空间变异特征不同,除Ⅲ类干扰区土壤有机质半变异函数优化符合指数模型外,其他3类干扰区均符合高斯模型;Ⅰ类区土壤有机质的空间自相关呈中等程度,C₀/(C₀+C)值达26.5%,其他3类干扰区C₀/(C₀+C)值在9.0%～22.6%,呈强烈的空间相关性;由于人类干扰强烈,Ⅰ和Ⅱ类区呈低能量匀质状态,变程及空间自相关范围较大,Ⅳ类区植被覆盖率较高,变程也较大;Ⅲ类区干扰强度中等,植被类型多且分布不均,变程最小;Ⅱ和Ⅳ类区的分维数（D）值较小,土壤有机质的空间依赖性较强;而Ⅰ和Ⅲ类区D值较大, 土壤有机质空间分布的随机变异较大;Ⅰ和Ⅱ类区土壤有机质呈单峰分布,Ⅲ类区土壤有机质呈凹型分布,Ⅳ类区呈凸型分布.减少干扰是喀斯特峰丛洼地脆弱生态系统土壤质量改善、植被迅速恢复及生态重建的重要保障.     

废弃盐田复垦利用后土壤盐分与有机质含量空间变异特征

针对目前莱州湾南岸废弃盐田复垦过程中存在的土壤盐碱、瘠薄等障碍问题,以该区两个典型复垦地块为研究对象,综合运用经典统计学和地质统计学的克立格法,研究不同复垦年限下各层土壤盐分和表层土壤有机质的空间变异性,对二者进行相关性分析,并绘制了各土层盐分和表层土壤有机质含量的空间分布图。结果表明:两个区域各层土壤含盐量较高,均超过1g/kg;受复垦年限、土地平整水平和施肥等人为复垦措施影响,二区土壤含盐量明显低于一区;两个区域土壤有机质含量普遍较低,其中一区为4.37g/kg,二区为3.66g/kg;两个区域各层土壤含盐量和表层土壤有机质变异系数在32.79%—83.83%之间,在水平方向上呈中等变异强度;相关性分析结果表明各层土壤含盐量与有机质含量均呈极显著负相关;各土层土壤含盐量和有机质含量的块基比均小于25%,表明二者具有强烈的空间相关性;空间自相关距离最小为440m,超过采样间距(最小为160m),表明采样间距设置合理;Kriging插值结果表明两个区域土壤含盐量和有机质含量呈条带状分布;一区土壤含盐量以中部为高值区逐渐向南北部降低,二区土壤含盐量则以东南部最低,逐渐向西北部高值区过渡;一区土壤有机质含量表现为中部低南北部较高,二区则为东南部最高,中北部含量较低。研究结果为后期高含盐量的水盐运移模拟研究提供初步论证,也为盐田复垦区盐渍土的合理分区,改良利用和科学管理提供了技术支撑。     

The structure and biogeochemical activity of the phototrophic communities from the Bol'sherechenskii alkaline hot spring

Microbial communities growing in the bed of the alkaline, sulfide hot spring Bol'sherechenskii (the Baikal rift area) were studied over many years (1986-2001). The effluent water temperature ranged from 72 to 74 degrees C, pH was from 9.25 to 9.8, and sulfide content was from 12 to 13.4 mg/ml. Simultaneous effects of several extreme factors restrict the spread of phototrophic microorganisms. Visible microbial fouling appears with a decrease in the temperature to 62 degrees C and in the sulfide content to 5.9 mg/l. Cyanobacteria predominated in all biological zones of the microbial mat. The filamentous cyanobacteria of the genus Phormidium are the major mat-forming organisms, whereas unicellular cyanobacteria and the filamentous green bacterium Chloroflexus aurantiacus are minor components of the phototrophic communities. No cyanobacteria of the species Mastigocladus laminosus, typical of neutral and subacid springs, were identified. Seventeen species of both anoxygenic phototrophic bacteria and cyanobacteria were isolated from the microbial mats, most of which exhibited optimum growth at 20 to 45 degrees C. The anoxygenic phototrophs were neutrophiles with pH optimum at about 7. The cyanobacteria were the most adapted to the alkaline conditions in the spring. Their optimum growth was observed at pH 8.5-9.0. As determined by the in situ radioisotope method, the optimal growth and decomposition rates were observed at 40-32 degrees C, which is 10 to 15 degrees C lower than the same parameter in the sulfide-deficient Octopus Spring (Yellowstone, United States). The maximum chlorophyll a concentration was 555 mg/m2 at 40 degrees C. Total rate of photosynthesis in the mats reached 1.3 g C/m2 per day. The maximum rate of dark fixation of carbon dioxide in the microbial mats was 0.806 g C/m2 per day. The maximum rate of sulfate reduction comprised 0.367 g S/m2 per day at 40 degrees C. The rate of methanogenesis did not exceed 1.188 micrograms C/m2 per day. The role of methanogenesis in the terminal decomposition of the organic matter was insignificant. Methane formation consumed 100 times less organic matter than sulfate reduction.     

深挖垦复对锥栗重要农艺性状及土壤理化性质的影响

为探索锥栗林地高效的土壤管理方式,提升我国锥栗栽培管理技术水平,进而提高其产量、品质以及经济效益。该研究采用全垦和环垦两种方式对锥栗林地进行连续4年的深挖垦复,通过测定垦复前后土壤理化性质变化以及锥栗树体生长、叶片表型和生理特征、结果性状、产量及品质等重要农艺性状,统计数据并进行对比分析。结果表明:(1)深挖垦复对锥栗林地土壤理化性质改善效果显著,两种垦复方式土壤容重较垦复前降低31.21%及以上(0～30 cm处),土壤含水率、土壤孔隙度、有机质含量以及各种大量元素含量较垦复前和对照均有不同程度的增加,土壤肥力及其保水保肥能力显著增强。(2)环垦区土壤有机质含量、有效磷含量以及交换性镁含量高于全垦区,其土壤有机质含量较垦复前增加40.59%,远高于全垦增加幅度(17.76%),从土壤保肥能力的角度来看,环垦效果优于全垦。(3)土壤肥力的提升增强了其对锥栗叶片的供肥能力,使得叶片含水率、叶绿素含量以及各种矿质元素含量显著增加,从而提升其光合作用能力。(4)深挖垦复对锥栗树体生长、结实能力、产量及品质同样具有显著的提升效果,其中全垦和环垦区单位面积产量分别是对照的1.75倍和1.33倍,且栗苞总重、单果质量、出籽率、可溶性糖含量以及磷、钾元素含量显著高于对照,而空苞率显著低于对照。综上,深挖垦复是改良林地土壤和提高锥栗生产力的有效举措。     

Ash in composting of source-separated catering waste

Our earlier experiments in small composters (220 l) indicated the favourable effect of ash from co-incineration of sorted dry waste on the composting of catering waste. The aim of this new study was to clarify further, at a scale of 10 m3, the feasibility of using similar ash as an additive in composting. Source-separated catering waste was mixed with bulking agent (peat and wood chips) and fuel ash from a small (4 MW) district heating power plant. Three compost mixes (CM) were obtained: CM I with 0%, CM II with 10% and CM III with 20 wt.% of fuel ash. These three different mixes were composted in a 10-m3 drum composter as three parallel experiments for 2 weeks each, from January to April 2000. After drum composting, masses were placed according to mixing proportions in separate curing piles. The catering waste fed to the drum was cold, sometimes icy. Even then the temperature rapidly increased to over 50 degrees C. In CM III, the temperature rose as high as 80 degrees C, and after the first week of composting the temperature was about 20 degrees C higher in the CMs II and III than in the CM I. It also improved the oxygen concentrations at the feeding end of the drum and obviously prevented the formation of H2S. No odour problems arose during the composting. Addition of ash increased the heavy metal contents of the composting masses, but the compost was suitable for cultivation or green area construction. Ash clearly decreased the loss of total nitrogen in a time span of 2 years. The lower amounts of nitrogen mean that the amounts applied per hectare can be greater than for normal composts. Measured by mineralization, the breaking down of the organic matter was more rapid in the CM III than in the CM I. Humic acid increased steadily during first 12 months composting, from the initial 39 mg/g organic matter to 115 and 137 mg/g in CMs II and III. Measured by temperature, mineralization and humification the addition of ash appeared to boost the composting. Ash had also other beneficial effects on composting it improved the availability of oxygen in compost mass during the drum composting phase and reduced the formation of odorous gases, especially H2S.     

Common Mesophilic Anaerobes, Including Clostridium botulinum and Clostridium tetani, in 21 Soil Specimens

A relatively rich medium was markedly superior to a dilute medium for the isolation of anaerobic bacteria from soil. The obligate anaerobes isolated from 21 soil samples were all clostridia and the counts ranged from 2.7 X 10-2 to 3.3 X 10-6 per g. The organisms most frequently isolated were Clostridium subterminate, C. sordelii, C. sporogenes, C. indolis, C. bifermentans, C. mangenoti, and C. perfringens. Seventeen other species were also recognized but almost one-third of the isolates could not be identified with any known species of Clostridium. C. botulinum type A was demonstrated in six soil samples, and type B in one. These soils were neutral to alkaline in reaction (average pH 7.9) and low in organic matter content (1.4%). The association of C. botulinum types A and B with neutral to alkaline soils was statistically significant (P = 0.001) as was their association with soils low in organic matter (P = 0.005). C. botulinum types E and F were found in one soil sample, pH 4.5, with organic matter 13.7%. C. tetani was isolated from two soil samples, both of intermediate pH value and higher than average organic matter content.     

Experimental wood addition in streams: effects on organic matter storage and breakdown

1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before–after/control–impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2‐ to 70‐fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m² in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a non‐significant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale.     

Soil enzyme activities and organic matter composition in a turfgrass chronosequence

Highly managed turfgrass systems accumulate considerable soil organic C, which supports a diverse and robust soil microbial community. Degradation of this soil organic C is mediated by a suite of soil enzymes. The relationship between these enzyme activities and the quality of soil organic C is central to understanding the dynamics of soil organic matter. We examined the activities of several soil enzymes involved in microbial C acquisition, including β-glucosidase, N-acetyl-β-glucosaminidase, cellulase, chitinase, and phenol oxidase, and characterized the chemical composition of soil organic matter using Fourier transform infrared spectroscopy (FTIR) in a turfgrass chronosequence (1–95 years old) and adjacent native pines. Non-metric multidimensional scaling analysis showed that the chemical composition of soil organic matter varied with turf age and land use (turf versus pines). Using the polysaccharide peak (1,060 cm⁻¹) as a reference, both aliphatic (2,930 cm⁻¹) and carboxylic (1,650 and 1,380 cm⁻¹) compounds increased with turf age, indicating that soil organic matter became more recalcitrant. Soil enzyme activities per unit soil mass increased with turf age and were correlated to soil C content. Most soil enzyme activities in native pines were similar to those in young turf, but the cellulase activity was similar to or greater than the activity in old turfgrass systems. On a soil C basis, however, the activities of N-acetyl-β-glucosaminidase and cellulase decreased with turf age; this reduction was correlated to the relative changes in the chemical composition of soil organic matter. We observed that the chemical composition of soil organic matter was significantly correlated with the enzyme activity profile when expressed per unit microbial biomass C, but not per unit soil organic C. Our results suggest that chemical composition of soil organic matter changes with turf age and this change partially determines the relative abundance of C-degrading soil enzymes, likely through the influence on microbial community composition.     

不同干扰程度下土壤有机质空间最优插值法研究

选择最优空间插值方法对明确不同干扰程度下干旱区土壤有机质空间分布规律具有重要意义。通过对新疆阜康市土壤采样分析,分别运用普通克里格法(Ordinary Kriging, OK)、反距离权重法(inverse distance weight, IDW)、径向基函数法(radial basis function, RBF)、局部多项式法(local polynomial, LPI)4种插值方法,描述不同人为干扰程度下干旱区土壤有机质空间分布特征,以探讨其最优空间插值方法。结果表明:①随干扰程度增加,土壤有机质含量降低,空间变异性由弱到中等,变异系数由9.27%增加至28.7%;同时,土壤有机质空间自相关性逐渐降低,从无人为干扰区、人为干扰区到重度人为干扰区分别呈强烈、中等、弱相关关系,即干扰程度越强受随机因素作用越大。②虽然4种方法的插值精度均随干扰程度的增强而降低。但OK法在空间结构性较强的无人为干扰区插值效果最好,R~2为0.625;在人为干扰区及重度人为干扰区RBF法的插值精度均最高,R~2分别为0.562和0.434。该结果为寻找适合于不同干扰程度下干旱区土壤有机质的空间插值方法提供一定的科学参考。     

Storage and turnover of carbon in grassland soils along an elevation gradient in the Swiss Alps

Amount, composition, and rate of turnover of soil organic carbon (SOC) in mountainous cold regions is largely unknown, making predictions of future responses of this carbon (C) to changing environmental conditions uncertain. We hypothesized increasing amounts and declining turnover times of soil organic matter (SOM) under permanent grassland with increasing elevation and decreasing temperature. Samples from an irrigated transect in the Swiss Alps (880 to 2200 m elevation, mean annual temperatures +8.9 to +0.9 °C) were analyzed. Soil C stocks ranged from 49 to 96 t C ha⁻¹ (0–20 cm) and were not related to elevation, though the highest site stored least C. Particulate organic carbon (POC) increased significantly with elevation and accounted for > 80% of the total soil C at 2200 m (0–5 cm). Mean residence times (MRTs) of POC computed by means of radiocarbon dating were in the order of years to decades and were positively related to elevation in the topsoil. At higher elevations, the estimated total C flux through the soil profile mainly depended on this fraction. MRT of mineral-associated matter ranged from decades to centuries and was not systematically related to elevation, but positively related to the soil mineral surface area and it increased with soil depth. Turnover rates from simulations with the soil C model RothC exceeded those from ¹⁴C measurements by a factor of 1.7–3.3 which suggests that C dynamics at these sites is overestimated by the model. Size of model pools and amount of C in soil fractions were only weakly correlated, thereby challenging previously postulated hypotheses concerning the correspondence of pools and fractions for grasslands at higher elevations.     

A Cross-System Comparison of Bacterial and Fungal Biomass in Detritus Pools of Headwater Streams

The absolute amount of microbial biomass and relative contribution of fungi and bacteria are expected to vary among types of organic matter (OM) within a stream and will vary among streams because of differences in organic matter quality and quantity. Common types of benthic detritus [leaves, small wood, and fine benthic organic matter (FBOM)] were sampled in 9 small (1st-3rd order) streams selected to represent a range of important controlling factors such as surrounding vegetation, detritus standing stocks, and water chemistry. Direct counts of bacteria and measurements of ergosterol (a fungal sterol) were used to describe variation in bacterial and fungal biomass. There were significant differences in bacterial abundance among types of organic matter with higher densities per unit mass of organic matter on fine particles relative to either leaves or wood surfaces. In contrast, ergosterol concentrations were significantly greater on leaves and wood, confirming the predominance of fungal biomass in these larger size classes. In general, bacterial abundance per unit organic matter was less variable than fungal biomass, suggesting bacteria will be a more predictable component of stream microbial communities. For 7 of the 9 streams, the standing stock of fine benthic organic matter was large enough that habitat-weighted reach-scale bacterial biomass was equal to or greater than fungal biomass. The quantities of leaves and small wood varied among streams such that the relative contribution of reach-scale fungal biomass ranged from 10% to as much as 90% of microbial biomass. Ergosterol concentrations were positively associated with substrate C:N ratio while bacterial abundance was negatively correlated with C:N. Both these relationships are confounded by particle size, i.e., leaves and wood had higher C:N than fine benthic organic matter. There was a weak positive relationship between bacterial abundance and streamwater soluble reactive phosphorus concentration, but no apparent pattern between either bacteria or fungi and streamwater dissolved inorganic nitrogen. The variation in microbial biomass per unit organic matter and the relative abundance of different types of organic matter contributed equally to driving differences in total microbial biomass at the reach scale.     

Influence of soil variables on in situ plasmid transfer from Escherichia coli to Rhizobium fredii.

A model system was established to determine whether intergeneric plasmid transfer occurs in soil and how various soil variables affect the rate of plasmid transfer. The donor bacterium, Escherichia coli HB101 carrying plasmid pBLK1-2 (pRK2073::Tn5), and the recipient bacterium, Rhizobium fredii USDA 201, were inoculated into a sterile Adelphia fine-sandy-loam soil. Transconjugants were enumerated by direct plating on antibiotic-amended HM [N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid; 2-(N-morpholino) ethanesulfonic acid] salts medium. Randomly chosen transconjugants were verified by serological typing and Southern hybridization with a Tn5 gene probe. The maximum transfer frequency was observed after 5 days of incubation (1.8 x 10(-4) per recipient). The influences of clay (0 to 50% addition), organic matter (0 to 15% addition), soil pH (4.3 to 7.25), soil moisture (2 to 40%), and soil incubation temperature (5 to 40 degrees C) on plasmid transfer were examined. Maximum transfer frequencies were noted at a clay addition of 15%, an organic matter addition of 5%, a soil pH of 7.25, a soil moisture content of 8%, and a soil incubation temperature of 28 degrees C. These results indicate that intergeneric plasmid transfer may occur in soil and that soil variables may significantly affect the rate of transfer.     

Influence of soil variables on in situ plasmid transfer from Escherichia coli to Rhizobium fredii

A model system was established to determine whether intergeneric plasmid transfer occurs in soil and how various soil variables affect the rate of plasmid transfer. The donor bacterium, Escherichia coli HB101 carrying plasmid pBLK1-2 (pRK2073::Tn5), and the recipient bacterium, Rhizobium fredii USDA 201, were inoculated into a sterile Adelphia fine-sandy-loam soil. Transconjugants were enumerated by direct plating on antibiotic-amended HM [N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid; 2-(N-morpholino) ethanesulfonic acid] salts medium. Randomly chosen transconjugants were verified by serological typing and Southern hybridization with a Tn5 gene probe. The maximum transfer frequency was observed after 5 days of incubation (1.8 x 10(-4) per recipient). The influences of clay (0 to 50% addition), organic matter (0 to 15% addition), soil pH (4.3 to 7.25), soil moisture (2 to 40%), and soil incubation temperature (5 to 40 degrees C) on plasmid transfer were examined. Maximum transfer frequencies were noted at a clay addition of 15%, an organic matter addition of 5%, a soil pH of 7.25, a soil moisture content of 8%, and a soil incubation temperature of 28 degrees C. These results indicate that intergeneric plasmid transfer may occur in soil and that soil variables may significantly affect the rate of transfer.     

玛纳斯河流域扇缘带不同植被类型下土壤物理性质

对生长在玛纳斯河流域扇缘带上的柽柳、盐穗木、白刺、猪毛菜4种植被类型下的土壤物理性质进行了研究.结果表明:在水平方向上,1m剖面内柽柳土壤pH值、全盐含量、土壤容重最小,分别为8.75、0.97g/kg和1.42g/cm3;土壤有机质、含水率、总孔隙度、毛管孔隙度均最大,分别为9.04 g/kg、16.67％、45.57％和36.18％,表明柽柳能够显著降低土壤盐分,改善土壤结构.沿垂直剖面,4种植被类型在表层0-20 cm土壤盐分均达到最高,出现盐分“表聚”现象而形成“盐霜”;随着土层深度增加,含水率和土壤容重均呈显著性升高,土壤有机质、田间持水量、总孔隙度、毛管孔隙度和非毛管孔隙度均呈显著性降低(P＜0.05).相关性分析显示,土壤有机质是引起其他土壤物理性质变化的主要原因.相比空裸地,4种植被覆盖类型1 m剖面内土壤有机质、总孔隙度和毛管孔隙度均呈显著性提高,土壤容重显著性降低,有机质分别提高了162.94％、82.94％、85.59％和27.94％,总孔隙度分别提高了44.90％、20.83％、36.06％和15.80％,毛管孔隙度分别提高了58.27％、30.71％、43.48％和25.72％,土壤容重分别降低了18.86％、10.86％、17.14％和7.43％,表明干旱荒漠区盐碱土上生长的不同盐生植物能够显著改善土壤质量.     

Soil nitrogen dynamics along a gradient of long-term soil development in a Hawaiian wet montane rainforest

I analyzed the rates of net N mineralization and nitrification of soils from seven sites in a Hawaiian wet montane forest. The sites differ in age, ranging from 400 to 4,100,000 yr, but are comparable in other variables (all at 1200 miasl with 4000 mm or more mean annual rainfall), and the chronosequence simulated a development of soils from basaltic lava. Soils were incubated for 20 days at 17.5 °C, which is nearly equivalent to a mean field air temperature of the sites, and at an elevated temperature of 25.5 °C under three treatments: 1) field-wet without amendments, 2) air dried to a permanent wilting point, and 3) fertilized with phosphate (NaH₂PO₄) at the rate of 50 g P per g dry soil. Both mineralization and nitrification rates varied significantly among the sites at the field temperature (p<.00001). Fractions of the mineralized organic matter (indexed by the N produced per g organic C) increased sharply from the youngest to the 5000-yr site before declining abruptly to a near constant value from the 9000 to the 1,400,000-yr sites. Total organic C in the top soils (<15 cm deep) increased almost linearly with age across the sites. Consequently, net NH₄- and NO₃-N produced on an area basis (g m^-2 20 d^-1) increased sharply from 0.2 in the youngest site to 1.2 in the 5000-yr site, then both became depressed once but steadily increased again. The fraction of organic matter mineralized, and the net N turnover rates were outstandingly high in the oldest site where a large amount of organic matter was observed; the topsoil organic matter which was used in this analysis appeared to be highly labile, whereas the subsurface organic matter could be relatively recalcitrant. As suggested by earlier workers, the initial increase in N turnover seemed to correspond to the increasing quantity of N in the soils through atmospheric deposition and biological fixation. The later decline in fraction of organic matter mineralized seemed to relate to increasing soil C/N ratios, increasingly recalcitrant organic matter, and poorer soil drainage with age. The elevated temperature treatment produced significantly higher amounts of N mineralization, except for the youngest site where N was most limiting, and for two sites where soil waterlogging might be severe. P fertilization invariably resulted in slower N turnovers, suggesting that soil microbes responded to added P causing N immobilization. The youngest site did not significantly respond to added P. The magnitude of immobilization was higher in older than in younger soils, suggesting that P more strongly limits microbial populations in the older soils.