氧化石墨烯和五价砷在改性多孔介质中的共迁移特征

砷是农田土壤重金属污染的主要元素之一,在砷污染农田土壤的修复过程中往往忽视纳米颗粒能够使结合态的砷重新释放,导致有效态砷浓度升高,探究土壤中黏土矿物对氧化石墨烯(Graphene Oxide,GO)和五价砷(As(V))在多孔介质中迁移行为的影响,对进一步完善农田土壤砷修复理论以及提高农作物产量、保护人体健康具有重要意义。该研究利用蒙脱石和高岭石改性石英砂,通过砂柱迁移试验系统地研究了GO、As(V)和GO-As(V)在填加0%、10%、30%和50%的蒙脱石和高岭石改性石英砂柱中的迁移行为。研究结果表明,随着高岭石和蒙脱石改性石英砂填加比例的增加,GO和As(V)的迁移能力均呈降低趋势,且GO和As(V)在不同条件下的迁移曲线均存在显著差异(P0.05);GO在50%高岭石和蒙脱石改性石英砂柱中的回收率相对于石英砂柱分别下降了14%和17%,As(V)分别下降了15%和12%;在共迁移试验中,GO和As(V)在石英砂柱中回收率分别上升至99%和100%。分析表明,As(V)在蒙脱石改性石英砂柱中的迁移能力大于高岭石改性石英砂,而GO与之相反;当GO和与As(V)共迁移时,二者在介质中的迁移能力均大于其单独迁移。本研究表明GO、As(V)释放到土壤后,能够加速As(V)的迁移,造成土壤砷污染的扩大化。     

宁夏原州区生态移民村生境景观连接度变化及其驱动因素

[目的]分析生态移民土地利用过程中生境景观连接度变化及其驱动因素,为生态移民的生态风险管理及移民可持续性提供科学依据。[方法]以宁夏原州区"十二五"时期4个生态移民村(丰泽、金轮、和润及泉港)为例,基于2016年高分影像数据,同时参考移民前谷歌地球2010年数据和第二次全国土地调查数据(2010年),经野外GPS校验,通过计算障碍影响指数和生境景观连接度指数,分析生态移民村土地利用生境景观分异。[结果]丰泽村和金轮村的生境景观连接度呈下降态势,和润村和泉港村呈上升态势。4个生态移民村的变化趋势明显,但极高连接度和高连接度比例很小。生态移民村生境景观变化驱动力主要为人为因素,建设用地占用耕地、园地普遍,其中泉港村与和润村建设用地面积年均增长率分别高达27.49%和21.28%,同时金轮村、和润村、泉港村无后备土地资源,生态压力突出。[结论] 4个生态移民村人口密度增大导致建设用地占用耕地明显,生态用地被分割,移民的非农活动比重大造成耕地撂荒,景观破碎化和孤岛化现象明显,生境景观呈现出不稳定状态,生态压力增加。     

Grassland conversion along a climate gradient in northwest China: Implications for soil carbon and nutrients

Soil organic carbon (SOC) stocks and nutrient availability are key indicators of soil quality, and both can be influenced by land-use change. However, it is still unclear whether the impact of land-use change on SOC and nutrient stocks differs between ecoregions. Grasslands near the northeast border of the Qinghai-Tibetan Plateau (QTP) occur across several ecoregions that have recently been subjected to substantial land-use change. Based on long-term land-use history, we conducted a field investigation comparing soil C and nutrient stocks between natural grassland (NGL) and three types of converted grassland (agricultural grassland, AGL; farmland, FL; and abandoned farmland, AFL) in three ecoregions along a climate gradient: alpine meadow, temperate steppe and temperate desert. Compared with NGL, soil C stocks in converted grasslands were 22%–30% lower in the alpine meadow, but 60–82% higher in the temperate steppe and 6%–76% higher in the temperate desert. Converted grasslands also contained higher stocks of available nitrogen and phosphorus than NGL in the temperate steppe and desert. Soils (0–40 cm) in NGL contained 14.8 ± 0.1 kg C m⁻² in alpine meadow, 6.7 ± 0.6 kg C m⁻² in temperate steppe and 1.7 ± 0.3 kg C m⁻² in temperate desert. Together, our results indicate that the responses of soil C and nutrients to grassland conversion differed between ecoregions. Thus, to optimize soil C sequestration rates and overall soil quality, we suggest that land-use policies in this area should take into account local environmental conditions.     

Application and verification of simultaneous determination of cellulose δ13C and δ18O in Picea shrenkiana tree rings from northwestern China using the high-temperature pyrolysis method

Stable isotopes in tree-ring cellulose provide important data in ecological, archaeological, and paleoenvironmental researches, thereby, the demand for stable isotope analyses is increasing rapidly. Simultaneous measurement of cellulose δ¹³C and δ¹⁸O values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement. In this study, we compared the δ¹³C and δ¹⁸O values of tree-ring α-cellulose from Tianshan spruce (Picea schrenkiana) in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements, using the combustion method (at 1050°C) and the high-temperature pyrolysis method (at 1350°C and 1400°C). We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods (separate and simultaneous) produced similar δ¹³C values. The two-point calibrated method improved the results (range and variation) of δ¹³C and δ¹⁸O values. The mean values, standard deviations, and trends of the tree-ring δ¹³C obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration. The simultaneously measured δ¹⁸O from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature. However, they showed similar variations in the time series. The climate responses inferred from simultaneously and separately measured δ¹³C and δ¹⁸O did not differ between the two methods. The tree-ring δ¹³C and δ¹⁸O values were negatively correlated with standardized precipitation evapotranspiration index from May to August. In addition, the δ¹⁸O was significantly correlated with temperature (positive), precipitation (negative), and relative humidity (negative) from May to August. The tree-ring δ¹³C and δ¹⁸O values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series. The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement. These results are consistent with the previous studies at humid sites, suggesting that the simultaneous determination of δ¹³C and δ¹⁸O in tree-ring α-cellulose can be used in wide regions.     

CO2 uptake by a soil microcosm

Sequestration of CO₂ via biological sinks is a matter of great scientific importance due to the potential lowering of atmospheric CO₂. In this study, a custom built incubation chamber was used to cultivate a soil microbial community to instigate chemoautotrophy of a temperate soil. Real-time atmospheric CO₂ concentrations were monitored and estimations of total CO₂ uptake were made. After careful background flux corrections, 4.52 ± 0.05 g CO₂ kg⁻¹ dry soil was sequestered from the chamber atmosphere over 40 h. Using isotopically labelled ¹³CO₂ and GCMS–IRMS, labelled fatty acids were identified after only a short incubation, hence confirming CO₂ sequestration for soil. The results of this in vivo study provide the ground work for future studies intending to mimic the in situ environment by providing a reliable method for investigating CO₂ uptake by soil microorganisms.     

Effects of transport stress on pathological injury and main heat shock protein expression in the respiratory system of goats

The aim of the present study was to investigate the pathological injury and the expression of heat shock proteins in the caprine lung, trachea and bronchus under transport stress. 12 healthy male goats were selected and randomly divided into three groups. The control group (non-transported group), 2 hr transport-treated group and 6 hr transport-treated group. Morphological changes as well as the expression of heat shock proteins (HSPs, mainly HSP27, HSP70 and HSP90) in three parts of the respiratory tract were examined. Our results showed swollen mucosa and congestive blood vessels in mucous layer and submucosa, inflammatory cell infiltration as well as degeneration and necrosis of mucosal epithelial cells in trachea and bronchus of the transport-treated groups. The epithelial cells were degenerated, and the exfoliated cells and debris could be seen in the alveolar cavity. The results of immunohistochemistry showed that HSP27 and HSP70 were strongly expressed in tracheal and bronchial epithelium, glandular epithelium, vascular endothelium and bronchiole epithelium. And the amount of positive inflammatory cells was increased in transport-treated groups. Western blot results indicated that the expression of all three proteins had no obvious difference among the three groups in bronchi (p > .05). In trachea, there was no significant difference in the expression of heat shock proteins among the three groups except that the expression of HSP70 which was obviously higher in the two transported groups than the control group (p < .05). The expression level of HSP70 in the 2 hr transport-treated group was significantly higher than the 6 hr group (p < .05) and control groups (p < .05). However, there was no significant difference in the expression level of HSP27 and HSP90 in three groups (p > .05). In conclusion, our data showed that transport stress could damage the caprine respiratory system.     

Functional dynamics of the nitrogen balance of sorghum. II. Grain filling period

Maintenance of green leaf area during grain filling can increase grain yield of sorghum grown under terminal water limitation. This ‘stay-green’ trait has been related to the nitrogen (N) supply–demand balance during grain filling. This study quantifies the N demand of grain and N translocation rates from leaves and stem and explores effects of genotype and N stress on onset and rate of leaf senescence during the grain filling period. Three hybrids differing in potential height were grown at three levels of N supply under well-watered conditions. Vertical profiles of biomass, leaf area, and N% of leaves, stem and grain were measured at regular intervals. Weekly SPAD chlorophyll readings on main shoot leaves were correlated with observed specific leaf nitrogen (SLN) to derive seasonal patterns of leaf N content. For all hybrids, individual grain N demand was sink determined and was initially met through N translocation from the stem and rachis. Only if this was insufficient did leaf N translocation occur. Maximum N translocation rates from leaves and stem were dependent on their N status. However, the supply of N at canopy scale was also related to the amount of leaf area senescing at any one time. This supply–demand framework for N dynamics explained effects of N stress and genotype on the onset and rate of leaf senescence.     

A novel in situ water perfusion and extraction method for soil amino acid quantification

Classic methods of soil amino acid (SAA) determination involve field collection of soils and disturbance during storage, sieving, mixing and extraction in the laboratory. We describe a novel inexpensive method for extraction of SAA's in situ with minimal soil disturbance. In a comparison between methods of SAA extraction from a semiarid grassland site, glu-x and arginine were the dominant SAA nitrogen sources detected by the novel method while serine and glycine were the dominant SAA nitrogen sources detected using the classic method. The extraction method employed is likely to be useful for accurate determination of SAA availability to plants and soil microbes.     

土壤Cr6+污染对小麦种子萌发和幼苗生理生化特性的影响

通过土培试验,研究Cr6+对小麦种子萌发和幼苗生理生化特性的影响.结果表明,低浓度Cr6+对小麦种子萌发和幼苗的生长有促进作用,叶绿素含量、过氧化物酶(POD)活性、细胞膜透性呈现上升趋势;高浓度Cr6+处理则抑制小麦种子萌发和幼芽的生长,叶绿素含量、POD活性、超氧化物歧化酶(SOD)活性都下降,相反,细胞膜透性则明显增加.     

苜蓿有限和无限生长型鉴别方法研究

在灌溉和旱作栽培条件下多年多点的研究发现,苜蓿茎的生长存在有限和无限型,类似于大豆生长习性的研究范畴。通过对40个苜蓿材料有限和无限型典型生长特性研究发现,采用大豆生长习性鉴别方法（茎顶花序,LRV和PRV）不能对苜蓿生长型进行分类。只有选择成熟期封顶枝比例、根茎新枝数量及其高度、4个时期的营养器官与生殖器官干物质比例、最长一级次生侧枝长度为鉴别指标,结合不同生长型典型对照品种的归属进行重心法聚类分析和判别分析,结果40个苜蓿材料有9个归为有限型,12个归为无限型,19个归为中间型。进一步分析表明,选择的分析变量从不同方面反映了生长型的差异,但影响变量的最佳测定时期需要深入研究确定。