Atrazine movement in soil: Comparison of field observations and PRZM simulations

The predictive capability of the pesticide root zone model (PRZM) was investigated for herbicide atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] in corn production under no‐till (NT) and conventional‐till (CT) management practices. Simulation values of atrazine residues obtained using our site‐specific soil and environmental data were compared with the actual values measured in soil samples taken from the root zones of the NT and CT plots during three growing seasons: 1986, 1987, and 1988. The mean concentration of atrazine in soil at each sampling time and depth after application, for each tillage treatment plot (NT or CT), was estimated based on the type of distribution (i.e., normal or lognormal). Overall, the PRZMs simulated concentrations for the top 10 cm of soil compared well with the atrazine residues measured in the CT plots, but overestimated measurements in NT plots. For example, in 1986 the mean atrazine concentration measured in soil samples taken 6 d after application from the top 10 cm of CT plots was 548 μg/kg (S.E. 198 μg/kg), and the PRZM predicted value was 690 μg/kg. In contrast, the mean atrazine concentration for the same soil depth increment in NT plots was 385 μg/kg (S.E. 154 μg/kg), with a PRZM predicted value of 674 μg/kg. Although the PRZM prediction was closer to the measured mean for atrazine concentrations in the top 10 cm of the CT system, the model did not transport atrazine to the lower soil depths, as the actual values have indicated in all 3 years. The results of this model comparison, especially for the lower soil depths (20 to 30 cm) in the NT practice, indicated that the PRZM model does not account for the preferential transport of, and, consequently, underestimates the atrazine residue levels in the lower soil profile under NT management systems.     

Chemical properties of soils amended with compost of urban waste

The influence of urban waste compost on soil fertility was tested by an experiment performed under laboratory conditions in which two soils treated with compost were incubated at a constant moisture for 12 months at 25°C and 35°C. Separately, some soil-compost samples were treated with atrazine at the rate of 40 ppm. Analyses of total and available elements and the characteristics of extracted humus were carried out during the experiment. The initial increase of most of the analytical parameters tested, caused by the addition of compost, was maintained till the end of the experiment. Negligible differences were noted between soils incubated with and without atrazine.     

Analysis of Pesticides in Soil Using Dispersive Solid Phase Extraction Coupled to GC-MS

A multi-residue method using dispersive solid phase extraction and gas chromatography with mass spectrometric detection has been developed for determination of trace levels of 103 pesticides, including organophosphate, organochlorine, carbamate, and pyrethroid compounds in agricultural soil. Dispersive solid phase extraction using 10 mL of acetonitrile for 3 min of extraction time showed satisfactory extraction efficiency. Recoveries of pesticides from fortified agricultural soil samples ranged from 65% to 117% for three different fortified levels of 50, 100, and 500 μg/kg and relative standard deviations of the recoveries are below 19%. Detection and quantification limits ranged from 1 to 13 μg/kg and from 3 to 38 μg/kg, respectively. The proposed method was less time-consuming, safer, and easy to use for routine analysis.     

Determination of zeranol and its metabolites in bovine muscle and liver by a chemiluminescence enzyme immunoassay: compared to an ultraperformance liquid chromatography tandem mass spectroscopy method

A chemiluminescent enzyme immunoassay (CLEIA) was compared to an ultraperformance liquid chromatography tandem mass spectroscopy (UPLC‐MS/MS) procedure for the analysis of zeranol and its metabolites in bovine tissue samples. Apparent recoveries from fortified samples by both methods were comparable at 0.5–4.0 µg/kg and a significant correlation was obtained. For CLEIA analysis, hapten mimicking the analyte was first synthesized and conjugated with the carrier protein bovine serum albumin as the immunogen to produce monoclonal antibody. The obtained antibody showed extensive cross‐reactivity toward zeranol metabolites (zearalanone). The limit of detection of CLEIA and UPLC‐MS/MS was 0.05 µg/kg and 0.5 µg/kg, respectively. Recoveries of both methods for fortified samples were higher than 75.0% with the coefficient of variation less than 15%. These results indicated that the combination of screening with CLEIA and confirmation with UPLC‐MS/MS for zeranol and its metabolites would be a reliable method for a large number of bovine samples. Copyright © 2013 John Wiley & Sons, Ltd.     

黄土旱塬区土壤水分状况与作物生长、降水的关系

土壤水分研究是统筹农业生产和生态环境建设的关键环节.本研究结合4年田间定位试验,通过对黄土高原南部长武旱塬冬小麦和春玉米2012—2015年土壤水分状况的研究,分析农田土壤干层形成情况、土壤水分对作物生长的影响、降水对土壤水库的影响以及作物对土壤水分状况的影响.结果表明: 降水年型是冬小麦地土壤干层形成的主导因素,年内降水分布不均是春玉米地土壤干层形成的主导因素.长武旱塬区冬小麦和春玉米一年一季的种植制度不会导致永久性干层的产生;相较于春玉米,冬小麦根系生长习性更符合黄土旱塬区土壤水分循环特征,黄土旱塬区土壤水分有效性可保证作物产量稳定;降水作用下,冬小麦土壤水库充、放水过程呈现收获期、休闲期和苗期连续充水、缓慢消耗期和大量消耗期连续失水相互交替的特点.0～300和300～600 cm土层土壤水库不一致性现象明显,以最大根深作为野外监测试验中土壤含水量的取样深度时,由于深层土壤水库负反馈作用,不同降水年型下,休闲期和苗期的蒸散均会被高估,缓慢消耗期和大量消耗期的蒸散均会被低估.冬小麦田间过渡层存在的范围为140～360 cm;作物生长的时间跨度影响土壤水库效应的发挥,土壤水库对冬小麦供水表现为年际间的调节作用,土壤水库对春玉米供水表现为季节间的调节作用.     

Enhancement of Atrazine Removal by Free and Immobilized Arthrobacter Sp. HB-5 in Soil and Wastewater

In an attempt to remove atrazine in situ, high-efficiency atrazine–degrading Arthrobacter sp. strain HB-5 (HB-5) and HB-5 immobilized on sodium alginate were introduced into two atrazine-polluted soils that are representative of soils in North China. Soil and wastewater with and without (controls) HB-5 or immobilized HB-5 were incubated at 25°C after the addition of atrazine. Soil samples were collected after 0 d, 1 d, 3 d, 5 d, 7 d, 10 d, and 13 d, and wastewater samples were collected after 0 d, 1 d, 3 d, 7 d, 14 d, 21 d, and 28 d. The residual atrazine was extracted from each sample and detected using gas chromatography. The half-life of the atrazine in the in soil samples was less than 3 d, and less than 7 d in the wastewater samples, treated with HB-5 or with immobilized HB-5. The immobilized HB-5 appears to exhibit better self-protection than the free bacteria at different pHs, and its ability to degrade atrazine was less affected by different conditions. Thus, in practice, immobilized HB-5 is better suited to incubations longer than 7 days because of its good adaptability. Both HB-5 and immobilized HB-5 exhibited better degradation of atrazine under conditions similar to the optimal living conditions of HB-5 than under other conditions. A small part of atrazine was removed by adsorption of organic matters, too. This study demonstrates the usefulness of these microorganisms in the bioremediation of soil and water systems polluted with triazine herbicides.     

Comprehensive utilization of activated sludge for the preparation of hydrolytic enzymes,polyhydroxyalkanoates, and water-retaining organic fertilizer

The urban wastewater treatment industry produces a large amount of excess activated sludge which is mainly composed of microbial biomass and costly to be disposed. In this research, a comprehensive utilization of activated sludge was developed by sequentially extracting hydrolytic enzymes and polyhydroxyalkanoates (PHAs), and the residue was used to prepare water-retaining organic fertilizer. The sludge was extracted with fourfold H₂O-containing 1% Triton X-100 with the yield of 66.7% protease activity. The enzyme solution was precipitated in 80% acetone and vacuum dried at 40°C at the dried enzyme yield of 2.4?g/kg wet sludge. The enzyme product contains collagenase, lipase, amylase, and cellulase activities, which are good compound enzymes to feed. The PHAs were extracted with 30% sodium hypoclorite:chloroform (1:3). The PHA solution was decolored and dried, and pure white PHAs were obtained at the yield of 70.1?g/kg wet sludge. The residue was used to prepare water-retaining organic fertilizer at the optimal condition. The fertilizer absorbs 131.3-fold distilled water and had good performance in water retention and can effectively slow down the loss of soil moisture when added into soil. This work provides a simple and practical approach for comprehensive utilizing activated sludge with significant economic benefits.     

Effect of mustard green manure and dried plant residue on chickpea wilt (Fusarium oxysporum f.sp. ciceris)

Pot experiments were carried out in the green house at Amhara Regional Agriculture Research Institute (ARARI) Bahirdar, Ethiopia, to evaluate the potential of Brassica carinata cultivars, namely Holleta-l, S-67 and Yellow Dodola in 2007 and 2008. The effect of B. carinata (Ethiopian mustard) cultivars Holleta-1, S-67 and Yellow Dodola as green manure and Holleta-1 as dried plant residue on chickpea fusarium wilt (Fusarium oxysporum f.sp. ciceris) was studied. Six rates of green manure and dried plant residue (0, 20, 40, 60, 80 and 100 g) each per kg of pathogen-infested soil were used in the experiments. Infested soil without B. carinata cultivars amendment as a control and susceptible check variety JG-62 without amendment was used in the experiments. In the experiments, the treatments were arranged in randomised complete block design in three replications and repeated twice. Data on seedling emergence, wilt incidence, fresh weight and dry weight were collected. The amendments of infested soil with B. carinata cultivars green manure and dried plant residue reduced the incidence of chickpea fusarium wilt. The incorporation of the green manure Holleta-1, S-67 and Yellow Dodola at 20–100 g/kg of infested soil was effective in reducing wilt incidences on chickpea. However, the incorporation of Yellow Dodola at 80 and 100 g green manure per kg of infested soil were the best combination in reducing significantly wilt incidence. The application of the dried plant residue at 20–100 g/kg of infested soil was effective in reducing wilt incidences on chickpea. However when applied dried plant residue at 60, 80 and 100 g green manure per kg of infested soil were better in reducing wilt incidence as compared to 20 and 40 g/kg of infested soil. The three cultivars green manure incorporated at different level of doses affected the influence of fusarium wilt on the fresh and dry weight respectively. The use of Holleta-1 green manure at 20–100 g/kg of infested soil significantly reduced disease incidence in the range of 20.0–33.3%. Green manure amendment S-67 significantly reduced disease incidence in the range of 20.0–46.6%. Yellow Dodola reduce disease incidence with 26.7–60%. The dried plant residue incorporated at different level influence fusarium wilt. The application of Holleta-1 dried plant residue at 20–100 g/kg of infested soil reduced disease incidence in the range 20.0–26.7%. The results imply the potential of using B. carinata green manure and dried plant residue as cultural management components in chickpea fusarium wilt disease management.     

Bioremediation of a petroleum‐contaminated cryic soil: Effects of phosphorus,nitrogen, and temperature

Bioremediation has been shown to be an effective means of treating petroleum‐contaminated soils in cold areas, although the conditions required to maximize bioremediation in cold region (cryic) soils are not well documented. A laboratory study was conducted to investigate the effects of nitrogen and phosphorus levels and temperature on petroleum bioremediation. A cryic entisol contaminated with diesel fuel was treated with nitrogen (0, 400, 800, or 1200 mg/kg of soil) and phosphorus (0, 60, 120, or 180 mg/kg of soil) and incubated at two temperatures (10 and 20°C). At 10°C, bioremediation rates were not affected by fertility treatments. At 20°C, reaction rates were increased by the addition of P, but unaffected by N. Regardless of fertility regime, the rate of diesel loss was much greater in soil incubated at 20°C than in soil incubated at 10°C.     

土壤水分变化对玉米苗期吸收积累镉的影响

采用土壤盆栽试验研究不同土壤水分含量对玉米苗期吸收积累 Cd的影响。试验结果表明 ,玉米生物量及其吸收 Cd量在玉米不同的生长时期差异较大。2 2 d收获时 ,玉米地上部和地下部生物量均随着田间持水量 (35 %～ 85 % )的增加而提高 ;而 16 d收获时 ,玉米生物量在田间持水量为 35 %和 85 %时比在其它水分时低许多。 16 d和 2 2 d收获时 ,玉米地上部 Cd含量在田间持水量 5 5 %时分别达到最大值 ,5 5 .4 1mg/ kg和 39.33mg/ kg;而在田间持水量 85 %时分别达最小值 ,2 7.97mg/ kg和 2 3.5 2 m g/kg。在玉米根系的影响下 ,土壤溶液 Cd含量基本上随着玉米的不断生长而降低。田间持水量为 6 5 %时的土壤溶液 Cd含量比田间持水量为 75 %和 85 %时大。玉米总吸 Cd量与水分蒸腾量之间呈极显著的线性正相关关系     

Enhancing cell survival of atrazine degrading Rhodococcus erythropolis NI86/21 cells encapsulated in alginate beads

AIMS: To develop a method to produce beads with encapsulated Rhodococcus erythropolis NI86/21 with high cell density, extended shelf life, ease of handling and good atrazine degradation capabilities in both liquid and in agricultural soil. METHODS AND RESULTS: Our findings show that the supplementary recovery step in nutrient broth media shortly after cell encapsulation facilitates cell survival in both wet and dry beads upon extended storage at 4 degrees C. Air drying has little or no impact on encapsulated R. erythropolis cell's ability to degrade atrazine in liquid or soil. Bead storage for periods extending up to 12 months at 4 degrees C did not affect the capacity of R. erythropolis encapsulated cells to degrade atrazine in either BMN or nonsterile soil extracts. Bentonite-amended beads formulated with 1% skim milk and exposed to the supplementary growth step, outperformed all other bead formats. These beads provided adequate numbers of vigorous R. erythropolis cells in either liquid or soil media to degrade atrazine. CONCLUSIONS: Supplementary growth in nutrient broth media immediately following cell encapsulation greatly enhances R. erythropolis cells survival in both wet and dry beads upon extended storage at 4 degrees C. Wet and dried beads have similar capacity for atrazine degradation, and their usefulness and appeal in agronomic practise will only be known after bioassay evaluation and successful demonstration at field scale using incurred residues. SIGNIFICANCE AND IMPACT OF THE STUDY: R. erythropolis NI86/21 encapsulated cells have the potential to reduce residual atrazine in soil, thereby minimizing the likelihood of off-site transport to ground or river water and reduce the loss of crops because of phytotoxicity of residual herbicide. Owing to their ease of handling, storage and possible compatibilities with pre-existing mechanical equipment, dried bead formats are ideally suited for agricultural and remediational applications.     

Use of exogenous specialised bacteria in the biological detoxification of a dump site‐polychlorobiphenyl‐contaminated soil in slurry phase conditions

The possibility of biologically detoxifying a contaminated soil from an Italian dump site containing about 1500 mg/kg (in dry soil) of polychlorinated biphenyls was studied in the laboratory in this work. The soil, which contained indigenous aerobic bacteria capable of growing on biphenyl or on monochlorobenzoic acids at concentration of about 300 CFU per g of air‐dried soil, was amended with inorganic nutrients, saturated with water and treated in aerobic 3‐L batch slurry reactors (soil suspension at 20% w/v). Either Pseudomonas sp. CPE1 strain, capable of cometabolising low‐chlorinated biphenyls into chlorobenzoic acids, or a bacterial co‐culture capable of aerobically dechlorinating polychlorobiphenyls constituted by this bacterium and the two chlorobenzoic acid degrading bacteria Pseudomonas sp. CPE2 strain and Alcaligenes sp. CPE3 strain, were used as inocula (final concentration of about 10⁸ CFU/mL for each bacterium), in the absence and in the presence of biphenyl (4 g/kg of air dried soil). Significant soil polychlorobiphenyl depletions were observed in all the reactors after 119 days of treatment. The soil inoculation with the sole CPE1 was found to slightly enhance the polychlorobiphenyl depletions (about 20%) and the soil detoxification; the effect was higher in the presence of biphenyl. The use of the polychlorobiphenyl mineralising bacterial co‐culture as inoculum resulted in a strong enhancement of the depletions of both the soil polychlorobiphenyls (from 50 to 65%) and of the original soil ecotoxicity. The bacterial biomass inoculated was found to implant into the soil; the higher specialised biomass availability thus reached in the inoculated soil was probably responsible of a more extensive biodegradation of polychlorobiphenyls and therefore of the higher detoxification yields observed in the inoculated reactors. The soil ecotoxicity, measured through two different soil contact assays, i.e., the Lepidium sativum germination test and the Collembola mortality test, was often found to decrease proportionally with the soil polychlorobiphenyl concentration. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 240–249, 1999.     

土壤水分对返青期断根冬小麦补偿效应的影响

通过盆栽试验研究了不同土壤水分条件下返青期断根冬小麦的补偿效应.结果表明,断根小麦的早期生长受到抑制,叶面积在返青 拔节期间显著下降,到开花期能恢复至对照水平.高水分条件下断根小麦拔节期的叶绿素荧光参数包括表观光合电子传递速率、实际光化量子产量、光化学淬灭系数、非光化学淬灭值均显著大于对照,开花后单茎干物质积累为0.81 g,显著大于对照（0.56 g）,花后干物质积累系数比对照提高了38.79%,断根小麦根量虽有所下降但差异不显著;低水分条件下断根小麦的叶绿素荧光参数和花后干物质积累与对照之间没有显著差异,但断根小麦的根系生物量（7.83 g·pot^-1）显著小于对照（9.77 g·pot^-1）.土壤水分对断根小麦的地上生物量和籽粒产量的补偿效应没有显著影响.断根处理的冬小麦在两种土壤水分条件下均显著降低了耗水量,在整个生育期,高水分条件下冬小麦断根处理可节水2 000 ml左右,水分利用效率为1.97 g·kg ^-1,显著大于对照的1.70 g·kg ^-1;低水分条件下也可节水1 500 ml左右,水分利用效率虽有所提高,但未达到显著性差异.     

Combining supercritical fluid extraction of soil herbicides with enzyme immunoassay analysis

Supercritical fluid extraction (SFE) of soil herbicides followed by enzyme immunoassay analysis (EIA) is explained in a step-by-step process. Extracted herbicides, include 2,4-D, simazine, atrazine, and alachlor. The herbicide, trifluralin was not successfully analyzed by EIA because of crossreacting metabolites. Problems with SFE, including uneven packing of cells, leaks, uneven flow and clogging, can largely be eliminated as the method parameters are optimized. It was necessary to add modifiers including methanol or acetone to the SF CO₂ to increase the solubility of the analytes. Detection limits of 2.5 ng/g soil for atrazine and alachlor and 15 ng/g soil for simazine and 2,4-D without concentration of the sample were achieved. Recoveries above 80% and relative standard deviations (RSDs) less than 15% for 2,4-D simazine, atrazine and alachlor were achieved. Atrazine and alachlor recoveries were above 90% with RSDs below 10%. Forty soil samples could be extracted and analyzed in an 8-h day.     

Resistance to metamitron in Chenopodium album from sugar beet. a tale of the (un)expected?

Metamitron is a key herbicide in modern low rate weed control programs in sugar beet. Fat hen (Chenopodium album, CHEAL) is a common, highly competitive, weed in sugar beet and one of the targets of metamitron. Recently, unsatisfactory control of fat hen has been reported in several sugar beet fields situated in various regions in Belgium. Weather conditions as well as the mere fact of using low rate systems have been blamed for these poor performances. To address the question "Is the recently recorded poor control of C. album due to decreased sensitivity to metamitron", greenhouse bioassays were carried out. A first experiment was conducted applying metamitron (0, 350, 700 and 1,400 g ai/ha) postemergence to three "suspected" C. album populations originating from sugar beet fields with unsatisfactory control by standard metamitron based treatment schemes ('Ligne', 'Outgaarden' and 'Boutersem I' respectively) and to one sensitive population originating from an untreated garden site ('Gent'). In a second experiment seven population, five "suspected" fat hen populations from sugar beet fields ('Boutersem I', 'Boutersem II', 'Postel', 'Vissenaken' and 'Kortessem' respectively), one sensitive reference population 'Herbiseed' and one atrazine-resistant reference population 'ME.85.01', were submitted to metamitron (0, 1, 2 and 4 mg ai/kg air-dry soil) and atrazine (1.5 mg ai/kg air-dry soil) preplant incorporated. All "suspected" C. album populations displayed a significantly lower sensitivity to metamitron compared to the sensitive populations ('Gent' and 'Herbiseed') that never had been exposed to this herbicide. As target site cross-resistance of atrazine-resistant C. album, selected by atrazine in maize, to metamitron has been known for a long time, cross-resistance of C. album populations in sugar beet grown on fields with "maize - atrazine" containing rotations might be expected to appear. The outcome of the experiment with atrazine preplant incorporated was the confirmation of resistance in all "suspected" populations ('Boutersem I', 'Boutersem II', 'Postel', 'Vissenaken' and 'Kortessem'). However, some "suspected" populations came from fields with no background of cropping with maize and use of atrazine. So, the question remains whether these triazine-resistant C. album had been imported, e.g. with slurry, or the rather unexpected possibility that metamitron itself did select for metamitron-resistant biotypes bearing cross-resistance to atrazine, had become reality.     

The Growth,physiological and biochemical response of foxtail millet to atrazine herbicide

Foxtail millet (Pennisetum glaucum L.) is a vital crop that is planted as food and fodder crop around the globe. There is only limited information is present for abiotic stresses on the physiological responses to atrazine. A field experiment was conducted to investigate the effects of different atrazine dosages on the growth, fluorescence and physiological parameters i.e., malonaldehyde (MDA) and reactive oxygen species (ROS) (H₂O₂ and O₂) in the leaves to know the extent of atrazine on oxidative damage of foxtail millet. Our experiment consisted of 0, 2.5, 12.5, 22.5 and 32.5 (mg/kg) of labeled atrazine doses on 2 foxtaill millet varieties. High doses of atrazine significantly enhanced ROS and MDA synthesis in the plant leaves. Enzymes activities like ascorbate peroxidase (APX) and peroxidase (POD) activities enhanced, while catalase (CAD) and superoxide dismutase (SOD) activities reduced with increasing atrazine concentrations. Finally atrazine doses at 32.5 mg/kg reduced chlorophyll contents, while chlorophyll (a/b) ratio also enhanced. Biomass, plant height, chlorophyll fluorescence parameters, minimal and maximal fluorescence (Fo, Fm), maximum and actual quantum yield, photochemical quenching coefficient, and electron transport rate are decreased with increasing atrazine doses.     

Cellulose and lignin degradation in forest soils: Response to moisture,temperature, and acidity

The concentration of lignin in plant tissue is a major factor controlling organic matter degradation rates in forest ecosystems. Microbial biomass and lignin and cellulose decomposition were measured for six weeks in forest soil microcosms in order to determine the influence of pH, moisture, and temperature on organic matter decomposition. Microbial biomass was determined by chloroform fumigation; lignin and cellulose decomposition were measured radiometrically. The experiment was designed as a Latin square with soils of pH of 4.5, 5.5, and 6.5 adjusted to 20, 40, or 60% moisture content, and incubated at temperatures of 4, 12, or 24°C. Microbial biomass and lignin and cellulose decomposition were not significantly affected by soil acidity. Microbial biomass was greater at higher soil moisture contents. Lignin and cellulose decomposition significantly increased at higher soil temperatures and moisture contents. Soil moisture was more important in affecting microbial biomass than either soil temperature or soil pH.     

陕西洛川旱塬苹果园地深层土壤水分和养分特征

测定了陕西洛川旱塬11、15、20、25和43龄苹果园地0～1500 cm土层土壤湿度和0～300 cm土层土壤有机质、全氮、全磷、全钾、速效氮、速效磷、速效钾含量,分析了测定深度范围内土壤干燥化情况、各养分指标丰缺状况及其随种植年限和土层深度的变化特征.结果表明： 11、15、20、25和43龄苹果园地0～1500 cm土层土壤湿度依次为18.6%、13.7%、170％、11.5%和13.1%,随树龄增加果园土壤湿度总体呈降低趋势,有补灌果园土壤尚未发生干燥化,而旱作果园均发生了轻度或中度干燥化,0～300 cm土层土壤湿度高于麦田.0～300 cm土层土壤有机质、全氮和碱解氮含量分别小于10 g·kg^-1、0.75 g·kg^-1和50 mg·kg^-1,均处于亏缺状态;速效磷含量介于3.30～6.42 mg·kg^-1,总体表现为浅层适宜、深层亏缺状态,速效钾含量介于78.09～98.31 mg·kg^-1,尚未亏缺.果园0～100 cm土层有机质和氮、磷、钾含量均高于100～300 cm土层.随果树种植年限增加,土壤有机质、全氮、碱解氮含量及土壤养分指数（SNI）均表现为先增加后降低趋势;除全钾外,随土层深度增加,各养分含量在0～100 cm土层范围内快速降低,之后维持相对稳定.土壤有机质、全氮、碱解氮、全磷、速效磷和速效钾含量之间呈极显著正相关,而全钾与其他6个养分指标之间的相关性不显著.     

瓦屋山扁刺栲-中华木荷常绿阔叶次生林土壤有机碳组分特征

次生林在全球碳循环中占有重要地位,为了研究中国中亚热带次生林土壤有机碳组分特征,以四川瓦屋山中山段扁刺栲-中华木荷常绿阔叶次生林为对象,通过挖取土壤剖面分层(0—10、10—40、40—70 cm和70—100 cm)取样方式,研究土壤各有机碳组分特征。结果表明:土壤有机碳、微生物生物量碳、可浸提溶解性有机碳和易氧化碳含量均随土层深度增加而减小,0—10 cm土层有机碳含量为121.89 g/kg,高于已报道的亚热带其他常绿阔叶林和四川各类森林;0—10 cm层微生物生物量碳含量为1931.82 mg/kg,可浸提溶解性有机碳含量为697.42 mg/kg,易氧化碳含量为20.98 g/kg,高于已报道的许多相似天然林和人工林活性碳含量。土壤有机碳储量为154.87 t/hm2,在四川省各类森林中处于中等水平。研究表明瓦屋山扁刺栲-中华木荷常绿阔叶次生林活性碳含量较大,微生物活动和养分流动较为活跃,凋落物层转化为土壤碳的潜力较大,这类生态系统可能会在区域碳循环过程中扮演更为重要的角色。     

After more than a decade of soil moisture deficit,tropical rainforest trees maintain photosynthetic capacity,despite increased leaf respiration

Determining climate change feedbacks from tropical rainforests requires an understanding of how carbon gain through photosynthesis and loss through respiration will be altered. One of the key changes that tropical rainforests may experience under future climate change scenarios is reduced soil moisture availability. In this study we examine if and how both leaf photosynthesis and leaf dark respiration acclimate following more than 12 years of experimental soil moisture deficit, via a through‐fall exclusion experiment (TFE) in an eastern Amazonian rainforest. We find that experimentally drought‐stressed trees and taxa maintain the same maximum leaf photosynthetic capacity as trees in corresponding control forest, independent of their susceptibility to drought‐induced mortality. We hypothesize that photosynthetic capacity is maintained across all treatments and taxa to take advantage of short‐lived periods of high moisture availability, when stomatal conductance (g_s) and photosynthesis can increase rapidly, potentially compensating for reduced assimilate supply at other times. Average leaf dark respiration (R_d) was elevated in the TFE‐treated forest trees relative to the control by 28.2 ± 2.8% (mean ± one standard error). This mean R_d value was dominated by a 48.5 ± 3.6% increase in the R_d of drought‐sensitive taxa, and likely reflects the need for additional metabolic support required for stress‐related repair, and hydraulic or osmotic maintenance processes. Following soil moisture deficit that is maintained for several years, our data suggest that changes in respiration drive greater shifts in the canopy carbon balance, than changes in photosynthetic capacity.