Phytoextraction of salts by Atriplex Nummularia Lindl. irrigated with reject brine under varying water availability

Abstract

Reverse osmosis is a widely known technology used to produce fresh water from brackish waters. However, the reject brine from desalination plants poses a serious threat to the environment due to soil and groundwater salinization. The aim of this study was to investigate the potential of Atriplex nummularia to extract salts from a soil irrigated with reverse osmosis brine, at varying moisture levels. A field experiment was conducted in a split-plot design, with randomized complete blocks replicated four times. Treatments consisted of irrigation with reject brine in the main plots, with four relative percentages of the soil moisture at field capacity (100, 85, 70, and 50%), and two levels of organic fertilization in the subplots (0 and 1.5?L plant^?1 of goat manure). The mineral composition of leaves and stems indicated that the highest salt extraction by plants occurred when soil moisture was maintained at 100% field capacity. The salt extraction capacity of A. nummularia indicates a high potential for phytoremediation of soils affected by brine disposal from reverse osmosis plants.     

The effects of forest on stream water quality in two coastal plain watersheds of the Chesapeake Bay

Forest had varying effects on stream nutrients in two coastal plain basins of the Delmarva Peninsula, USA. In the Choptank basin, forest was strongly associated with low stream total nitrogen (TN) and nitrate (NO₃⁻) concentrations (r²0.70), and forest placement along first order streams was important in maintaining low stream nitrogen (N) concentrations (r²0.35). In addition, a multiple regression model explained 40% of the stream total phosphorus (TP) variance and indicated that forest directly adjacent to streams (0–100 m) acted as a TP source and forest further away (100–300 m) from streams acted as a TP sink. In contrast, stream nutrients in the nearby Chester basin demonstrated a strong relationship with soil hydrologic properties. Forest had no significant effect on stream N and P because the finer-textured soils, higher stream slopes, and higher runoff potential of the Chester basin appeared to result in less baseflow compared to that in the Choptank basin. This reduced the opportunity for forest to intercept N via plant uptake and denitrification in the high runoff potential soils of the Chester basin. The high percentage of stormflow (40%) coupled with high stream slopes resulted in high soil erosion potential, which may explain the higher TP stream concentrations measured in the Chester compared to that in the Choptank. Differences in the hydrologic pathway appear to explain the different effects of forest on water quality in these two basins.     

Nutrient and Microbial Dynamics in Biosolids Amended Soils Following Rainfall Simulation

Municipal waste treatment plants are mandated by U.S. EPA to treat domestic wastewater prior to releasing it to receiving streams. The dewatering and high temperature drying processes at the plant are considered effective in reducing microbial contaminants in the waste. The resulting solid material (biosolid) is rich in nutrients that may serve as a value-added product for plant growth. In this study, we examined the nutrient value of biosolids, their potential biological and chemical risks that could result from surface application to two Mid-Atlantic soils: Bojac (coarse-loamy, mixed, thermic Typic Hapludult) and Cullen (clayey, mixed, thermic Typic Hapludult). Soils were placed on tilt beds and packed to their respective bulk density. Biosolids were added at a rate of 2.24 Mg/ha equivalent and mixed with the top 5 cm of the soil bed. Simulated rain was applied at a rate of 65 mm h^?1 for 45 minutes. Surface runoff and percolation water were collected and analyzed for elemental content, Escherichia coli (E. coli) and total coliform bacteria. Among the nutrient elements of concern (P, Zn, Mn, and Cu) in biosolids, none were found to be higher than the specified EPA limits. The concentration of P was highest in runoff and percolation water from beds packed with Bojac and biosolids. The combined effects of high clay (35%), Al (1.14%), and Fe (5.11%) in Cullen increased its P-adsorbing capacity. Low levels of E. coli and other coliform bacteria were present in samples from biosolids-treated beds packed with Cullen. Microbial counts in runoff and percolation samples varied with soil type; in some instances they were ten-fold higher in Bojac than in Cullen. The results obtained in this study suggest that surface runoff from land applications of biosolids might contribute to microbial contamination of receiving waters near agricultural fields.     

Addition of HPMA affects seed germination, plant growth and properties of heavy saline-alkali soil in northeastern China: comparison with other agents and determination of the mechanism

China has a large area of inland saline-alkali land, equivalent to 40% of the total cultivated land in the country. The principal features of these lands are high salt content, high pH, and poor soil structure with low water infiltration and poor drainage. These conditions effectively prevent the exploitation of such land for agriculture. In this study, we have compared 17 soil conditioning agents for their abilities to promote seed germination and growth under both laboratory and field conditions. One of these, Hydrolyzed Polymaleic Anhydride (HPMA), was identified as a highly effective agent for soil improvement. Laboratory germination experiments and laboratory and field cultivation of a variety of plants both showed that addition of HPMA could significantly increase the germination percentage and plant growth rate. Distinct from other Ca-carrier agents such as gypsum, HPMA increases the dissolution of CaCO₃, which is abundant in the calcareous saline-alkali soils. This allows Ca²⁺ in soil solution to displace the over-abundant Na⁺ in the soil colloids. This process greatly improves soil properties such as the bulk density, which decreased, and the capillary soil rise height of water and soil water infiltration rate, which increased. Direct SEM and AFM imagery showed flocculent soil precipitation (soil aggregates) after HPMA addition, and a looser structure of those aggregates. The addition of HPMA also reduced the soil pH and EC. These changes in soil chemical and physical properties are a likely explanation for the soil improvement effected by HPMA. The high content of insoluble CaCO₃ in saline-alkali land such as that in northeastern China (up to 13%) favors the further exploration of HPMA as an ameliorative agent.     

Increasing the okra salt threshold value with biochar amendments

Soil salinity is a severe worldwide environmental problem that adversely affects soil properties and the crop growth such as okra. We hypothesized that biochar soil amendments could increase the okra salt threshold, alleviate salt stress and improve soil productivity. In this study, a pot experiment was conducted to investigate whether biochar could ameliorate the effects of salinity on okra plants. Three biochar amendment (BA) soil applications (0%, 5% and 10% by mass of soil) were considered for seven irrigation water salinity levels (0.75, 1.0, 2.0, 4.0, 5.0, 6.0 and 7.0?dS?m^?1) in a randomized block design with three replications. The Maas and Hoffman salt tolerance model was used to evaluate the effects of BA on okra plant growth parameters (e.g. yield, biomass) and water use efficiency for each salinity treatment. The results showed that increasing the soil salinity levels caused significant decreases in plant yields and yield components. However, biochar application rates of 5% and 10% increased the okra threshold by 19.7% and 81.2%, respectively, compared to the control (0%). The 10% biochar application rate also resulted in the greatest okra plant growth and increased yield, indicating that the effects of salt stress were ameliorated; moreover, the soil bulk density was decreased, and the water content was increased. Hence, biochar soil amendments could be considered as an important agronomic practice that could potentially overcome the adverse effects of salt stress.     

塔里木盆地南缘旱生芦苇生态特征与水盐因子关系

选择位于塔里木盆地南缘极端干旱区的克里雅河流域于田绿洲为靶区,结合经典统计学和冗余分析技术,研究了旱生芦苇生态特征与水盐因子的分布规律及相互关系。统计学分析显示:芦苇沿河岸至荒漠方向株高、盖度和地上生物量减少、地下生物量增加,水分与土壤盐分也呈现一定的梯度变化规律。冗余分析结果表明:水分为芦苇生态特征变化的关键驱动因子,地下水埋深和土壤水分与芦苇的生态特征呈现极显著的相关关系,钠吸附比、全盐与芦苇的生态特征呈现显著的相关关系,其他指标与芦苇生态特征的相关性均不显著。水盐因子对芦苇生态特征影响的重要性排序为地下水埋深土壤水分钠吸附比全盐HCO-3pH值Cl-/SO2-4。综合水盐要素,水分对芦苇生态特征的影响大于盐分。     

放牧对祁连山高寒典型草原土壤质量的影响

土壤质量是维持陆地生态系统稳定性与功能多样性的基础。放牧作为草地资源最广泛的利用方式之一,其对草地土壤质量的影响却缺乏量化标准,且两者之间的作用机理尚不明确。以祁连山高寒草原两个季节性牧场为研究对象,结合生态系统耦合与生态系统多功能性,探究了放牧对高寒草原土壤质量的影响与潜在机制。试验结果表明：基于最小数据集,不同放牧率下土壤质量指数差异显著(P<0.05),冬季牧场和春秋季牧场放牧率分别在2.45头月^-1 hm^-2和0.80头月^-1 hm^-2时土壤质量指数最高。土壤速效磷、有机碳、氮磷比和土壤pH是决定冬季牧场土壤质量的关键因子,而春秋季牧场中则是土壤有机碳、碳氮比和土壤pH;两个季节性牧场土壤质量指数与物种丰富度指数(P<0.05)和香浓维纳多样性指数(P<0.0001)呈显著正相关。高寒草原季节性牧场放牧地植物群落物种多样性与土壤因子耦合度在0.67—0.81之间,平均耦合度为0.74,属于中度协调;随着放牧率的增加,生态系统多功能性指数逐渐减低且与土壤质量指数变化趋势相似,...     

Radionuclides in plants growing on sludge and water from uranium mine water treatment

Chemical treatment of uranium mine acid drainage generates sludge containing high radioactivity levels with, for example, ²³⁸U and ²²⁶Ra concentrations at about 18 and 9 kBq kg⁻¹ dry weight, respectively. Spontaneous vegetation, such as grass (Polygonum sp.), reeds (Phragmites australis), and bullrush (Typha latifolia) growing in sludge dewatering ponds concentrated uranium and uranium daughter radionuclides. However, bullrush growing in natural wetlands by the stream receiving treated mine water discharges contained even higher radionuclide concentrations, e.g., 21 Bq kg⁻¹ dry weight of ²³⁸U, about four times higher than bullrush growing on sludge, probably because the uranium in water is more bioavailable to Typha than uranium in the chemical sludge. It is suggested that wetlands with plant species could be used as a secondary treatment to further reduce radioactivity in chemically treated uranium mine water and to improve water quality in streams receiving treated water discharges. Furthermore, it is concluded that vegetation both from sludge drying ponds and from streams receiving treated water discharges, due to the high radionuclide concentrations in the vegetation, is not suitable as cattle feeding.     

不同秸秆填埋量对盐碱土水盐运移及垂柳反射光谱的影响

在宁夏西北盐化生态脆弱区的典型盐碱化土地,通过随机区组试验,探究在栽植穴填埋秸秆2000(T_1)、7000(T_2)、12000kg/hm~2(T_3)及17000 kg/hm~2(T_4)等作隔盐层对土壤水盐运移及垂柳(Salix babylonica)反射光谱的影响,将地下土壤水盐变化与地上植物生长及生理状况相结合,以期更准确的反映出各处理对盐碱土壤改良效果及地上植被恢复情况。研究结果表明:(1)填埋一定量的秸秆作隔盐垫层可以改变地下土壤水盐的剖面分布特征。T_2、T_3和T_4处理与对照组相比,20—80 cm土层土壤含水量都显著提高,填埋的秸秆层起到了蓄水保墒的作用;都明显降低了0—80 cm土层土壤盐分含量和盐溶质浓度;但这3种处理之间无显著差别。T_1由于填埋秸秆量过少,无显著蓄水控盐效果。(2)通过检测植物叶片反射光谱可以反映出地上植物生长及生理状况的变化。填埋一定量的秸秆作为隔盐垫层有助于改善垂柳的生理状况。T_2的垂柳叶片光合色素含量最高,光合特性及营养状况最好,其他光谱参数结果都显著提高。T_3显著提高叶绿素含量和光合特性,但效果均不如T_2,且营养状况差。T_4处理类胡萝卜素含量与叶片水分含量均处于最高水平,但叶绿素含量、营养状态以及光合特性都显著降低。T_1处理效果最差。(3)在地下填埋秸秆作隔盐层,会通过对地下土壤水盐运移及微域生态系统环境的调节,影响到地上植物生长及生理状况。综合地下水盐分布与地上植物叶片反射光谱的结果,T_2是宁夏引黄灌区盐碱地改良中最适宜的秸秆填埋量。     

不同水盐梯度下功能多样性和功能冗余对荒漠植物群落稳定性的影响

功能多样性和功能冗余是物种多样性的两个组成部分,也是影响群落稳定性的两个重要因素。基于不同水盐梯度下植物功能多样性、功能冗余、物种多样性和群落稳定性及其相关关系的计算结果,分析功能多样性和功能冗余对群落稳定性的影响,结果表明:(1)功能多样性、物种多样性和群落稳定性均表现为高水高盐和中水中盐群落显著高于低水低盐群落(P0.05);(2)高水高盐群落,功能多样性与物种多样性的相关系数小于功能冗余与物种多样性的相关系数,且功能多样性与稳定性的相关系数也小于功能冗余与稳定性的相关系数,而中水中盐和低水低盐群落的相关系数则呈现相反的规律;(3)中水中盐和低水低盐群落的功能多样性的标准化偏回归系数均大于功能冗余的标准化偏回归系数;(4)典范对应分析中,土壤含水量可以解释总特征根的22.7%,而土壤含盐量仅可以解释总特征根的1.3%;(5)高水高盐群落的稳定比最接近20/80,稳定性最高;低水低盐群落远离20/80,稳定性最低。改进后的Godron稳定性测定方法与物种种群密度变异系数方法得出的结果相同。综上可知,功能多样性和功能冗余两者中与物种多样性关系更为密切者对群落稳定性的影响也越大,且两者均可提高群落稳定性,也就证明冗余假说在温带干旱荒漠区域的隐域性植物群落中是成立的;群落稳定性、功能多样性、功能冗余及物种多样性主要是受土壤含水量的影响,土壤含盐量对其影响较小。     

Plant salt-tolerance mechanism: A review

Almost all crops that are important to humans are sensitive to high salt concentration in the soil. The presence of salt in soil is one of the most significant abiotic stresses in farming. Therefore, improving plant salt tolerance and increasing the yield and quality of crops in salty land is vital. Transgenic technology is a fast and effective method to obtain salt-tolerant varieties. At present, many scholars have studied salt damage to plant and plant salt-tolerance mechanism. These scholars have cloned a number of salt-related genes and achieved high salt tolerance for transgenic plants, thereby showing attractive prospects.In this paper, the salt-tolerance mechanism of plants is described from four aspects: plant osmotic stress, ion toxicity, oxidative stress, and salt tolerance genes. This review may help in studies to reveal the mechanism of plant salt tolerance, screen high efficiency and quality salt tolerance crops.     

The impact of agricultural land use changes on soil organic carbon dynamics in the Danjiangkou Reservoir area of China

Aims

Over recent decades, a large uncultivated area has been converted to woodland and shrubland plantations to protect and restore riparian ecosystems in the Danjiangkou Reservoir area, a water source area of China’s Middle Route of the South-to-North Water Transfer Project. Besides water quality, afforestation may alter soil organic carbon (SOC) dynamics and stock in terrestrial ecosystems, but its effects remain poorly quantified and understood.

Methods

We investigated soil organic C and nitrogen (N) content, and δ ¹³C and δ ¹⁵N values of organic soil in plant root-spheres and open areas in an afforested, shrubland and adjacent cropped soil. Soil C and N recalcitrance indexes (RIC and RIN) were calculated as the ratio of unhydrolyzable C and N to total C and N.

Results

Afforestation significantly increased SOC levels in plant root-spheres with the largest accumulation of C in the afforested soil. Afforestation also increased belowground biomass. The C:N ratios in organic soil changed from low to high in the order the cropped, the shrubland and the afforested soil. The RIC in the afforested and shrubland were higher than that in cropped soil, but the RIN increased from the afforested to shrubland to cropped soil. The δ¹⁵N values of the organic soil was enriched from the afforested to shrubland to cropped soil, indicating an increased N loss from the cropped soil compared to afforested or shrubland soil. Changes in the δ¹³C ratio further revealed that the decay rate of C in the three land use types was the highest in the cropped soil.

Conclusions

Afforestation increased the SOC stocks resulted from a combination of large C input from belowground and low C losses because of decreasing soil C decomposition. Shifts in vegetation due to land use change could alter both the quantity and quality of the soil C and thus, have potential effects on ecosystem function and recovery.     

再生(污)水灌溉生态风险与可持续利用

作为一个农业大国,水资源贫乏及地域分布不均匀造成了我国严重的农业用水危机。为缓解我国农业用水危机,污水灌溉及再生水灌溉已成为解决农业灌溉水源不足的一项重要措施。在总结污水灌溉及再生水灌溉生态风险的基础上,针对国内研究现状,分析了我国再生水灌溉利用的可行性。研究发现,再生水灌溉的污染风险远小于污水灌溉,且再生水灌溉还具有回用成本低、减少农作物生产成本等经济效益,以及减少污染物向水环境中排放、改善土壤质量等环境效益。与污水灌溉相比再生水在农业灌溉上具有较大的应用前景,应加大其推广与应用的力度。最后,根据国内外的研究现状,提出了一些再生水灌溉可持续管理措施及其安全利用的相关建议。     

活性焦对晋北盐碱地土壤性质和两种植物生长的影响

固废基改良剂是盐碱地改良的有效手段之一。活性焦作为一种多孔废弃物,应用于盐碱地预期可以起到改善土壤性质、减缓植物盐碱胁迫的作用。为了阐明活性焦对晋北盐碱地的改良效应,本研究设置不同用量活性焦(CK, 0 g·kg^-1;A₁₀, 10 g·kg^-1;A₂₀, 20 g·kg^-1;A₅₀, 50 g·kg^-1),分析其对盐碱地土壤性质和植物生长的影响。结果表明: 施用活性焦能显著提高土壤的水稳性团聚体含量,并降低土壤盐分含量、pH值和电导率。与CK相比,种植碱茅和玉米土壤的团聚体平均重量直径增加5.1%～32.2%,pH值降低0.4%～4.1%,钠吸附比(SAR)降低4.8%～18.7%,电导率降低7.4%～8.2%。施用适量活性焦能够降低植物细胞的质膜损伤,提高叶片叶绿素和Ca²⁺含量,从而有效促进植物生长,碱茅和玉米的生物量均在A₂₀处理达到最大。表明盐碱土施用20 g·kg^-1活性焦(A₂₀)可改善根际土壤环境,提高植物对Ca²⁺等的选择性吸收,从而降低盐分对植物细胞的损伤,促进盐碱生境中植物的生长。     

Influence of salt stress on seed yield and oil quality of two sunflower hybrids

Sunflower is a major oil seed crop worldwide, and it is also an important crop in Mediterranean areas where salinity is an increasing problem. In this paper, the effect of saline irrigation water on seed yield and quality of sunflower was evaluated. A pot experiment was carried out over two crop seasons on two hybrids – a standard one (Carlos) and a high oleic one (Tenor) – submitted to five salinity levels of irrigation water (0.6, 3, 6, 9 and 12 dS m^?1). Soil salinity was monitored over the entire crop cycle, and leaf ion content was determined at maturity. Tenor showed higher Na⁺ and Mg²⁺ content but lower K⁺ values. No difference between the two hybrids was observed for Cl^? content. A progressive increase in leaf Na⁺, K⁺ and Cl^? contents and Na⁺/K⁺ ratio with increasing salinity level was observed. Seed weight per head, 1000 achene weight, number of seeds per plant and oil yield significantly decreased under salt stress in both hybrids. The percent seed yield decrease was higher per unit increase in electrical conductivity of irrigation water, ECw (8%), than per unit increase in electrical conductivity of saturated‐soil extracts, ECe (5%). Concerning oil fatty acid composition, the main significant difference as result of salt stress was a progressive increase in oleic acid content, from 82.2% to 86.7% for Tenor and from 21.8% to 27.3% for Carlos, which was consistent with a decrease in linoleic acid content, from 5.9% to 3% for Tenor and from 66% to 61.3% for Carlos. These results confirm the possible inhibition of oleate desaturase under salt stress.     

Evaluating effects of weed cutting on water level and ecological status in Danish lowland streams

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Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.     

Anthropogenic disturbance and streams: land use and land‐use change affect stream ecosystems via multiple pathways

1. Ecosystems are strongly influenced by land use practices. However, identifying the mechanisms behind these influences is complicated by the many potential pathways (often indirect) between land use and ecosystems and by the long‐lasting effects of past land use. To support ecosystem restoration and conservation efforts, we need to better understand these indirect and lasting effects. 2. We constructed structural equation models (SEM) to evaluate the direct and indirect effects of contemporary (2002) land use (agriculture and development) and change in land use from 1952 to 2002 on present‐day streams (n = 190) in Maryland, U.S.A. Additional variables examined included site location, system size, altitude, per cent sand in soils, riparian condition, habitat quality, stream water NO₃‐N and benthic macroinvertebrate and fish measures of stream condition. Our first SEM (2002 Land Use) included the proportions of contemporary agriculture and development in catchments in the model. The second SEM (Land Use Change) included five measures of land use change (proportion agricultural in both times, developed in both times, agricultural in 1952 and developed in 2002, forested in 1952 and developed in 2002 and agricultural in 1952 and forested in 2002). 3. The data set fit both SEMs well. The 2002 Land Use model explained 71% of variation in NO₃‐N and 55%, 42% and 38% of variation in riffle quality, macroinvertebrate condition and fish condition, respectively. The Land Use Change model explained similar amounts of variation in NO₃‐N (R² = 0.72), riffle quality (R² = 0.57) and macroinvertebrate condition (R² = 0.44) but slightly more variation in fish condition (R² = 0.43). 4. Both models identified pathways through which landscape variables affect stream responses, including negative direct effects of latitude on macroinvertebrate and fish conditions and positive direct and indirect effects of altitude on NO₃‐N, riffle quality and macroinvertebrate and fish conditions. The 2002 Land Use model showed contemporary development and agriculture had positive total effects on NO₃‐N (both through direct pathways); contemporary development had negative effects on macroinvertebrate condition. The Land Use Change model showed that contemporary developed land that was forested in 1952 had no effects on NO₃‐N; current developed land that was developed or agricultural in 1952 showed positive effects on NO₃‐N. Forests that were agricultural in 1952 had negative effects on NO₃‐N, suggesting reduced NO₃‐N export with reforestation. The Land Use Change model also showed negative total effects of all types of contemporary developed land (developed, agricultural or forested in 1952) on benthic condition. Developed land that was forested in 1952 had negative effects on fish condition. Forest sites that were agricultural in 1952 had negative effects on fish and macroinvertebrate conditions, suggesting a long‐term imprint of abandoned agriculture in stream communities. 5. Our analyses (i) identified multiple indirect effects of contemporary land use on streams, (ii) showed that current land uses with different land use histories can exhibit different effects on streams and (iii) demonstrated an imprint of land use lasting >50 years. Knowledge of these indirect and long‐term effects of land use will help to conserve and restore streams.     

盐生植物盐爪爪的耐盐生理特性探讨

当前土壤盐渍化日益严重,是限制植物生长的一个主要环境因子,然而在盐碱自然环境中生长着许多耐盐植物,为更好地了解盐生植物的耐盐机理,该文从无机离子Na+,K+,Ca2+含量、脯氨酸水平、水势变化、丙二醛含量和盐胁迫的表型等生理参数以及半定量RT-PCR检测脯氨酸合成关键酶基因(P5CS)的表达规律等方面探讨盐胁迫下盐爪爪的耐盐特性。结果表明:(1)随着盐浓度的升高,Na+在根和肉质化的叶中显著地富集,且叶中积累的Na+比根中更多;(2)在盐胁迫条件下,随着盐浓度的增加,脯氨酸的含量和脯氨酸合成关键酶基因的表达显著地增强;(3)Na+和脯氨酸是植物有效的渗透调节剂,可使处于低水势的植物细胞仍能从细胞外高浓度的盐溶液中吸收水分;(4)在0和700 mmol·L-1Na Cl处理下,盐爪爪肉质化叶中丙二醛的含量较其它处理高,这表明植物在这两个处理下可能受到了氧化胁迫;(5)从盐胁迫3个月的生长表型来看,低盐环境中生长的盐爪爪植株的生物量更多,肉质化的叶嫩且绿。综上所述,结合对野外生境的调查和实验室长期的盐胁迫表型结果表明盐爪爪的生长是需盐的,相对低的盐浓度环境对盐爪爪的生长是顺境,而无盐或高浓度盐环境对于盐爪爪的生长来说都是逆境。该研究结果为全面深入研究盐爪爪的耐盐特性,以及更好地利用盐爪爪的生物和基因资源改良土壤和提高作物和林木的耐盐性奠定基础。     

Dissolved organic carbon and nitrogen in urban and rural watersheds of south-central Texas: land use and land management influences

Dissolved organic carbon (DOC) and nitrogen (DON) concentrations were quantified in urban and rural watersheds located in central Texas, USA between 2007 and 2008. The proportion of urban land use ranged from 6 to 100% in our 12 study watersheds which included nine watersheds without waste water treatment plants (WWTP) and three watersheds sampled downstream of a WWTP. Annual mean DOC concentrations ranged 20.4–52.5 mg L^?1. Annual mean DON concentrations ranged 0.6–1.9 mg L^?1. Only the rural watersheds without a WWTP had significantly lower DOC concentrations compared to those watersheds with a WWTP but all the streams except two had significantly reduced DON compared to those with a WWTP. Analysis of the nine watersheds without a WWTP indicated that 68% of the variability in mean annual DOC concentration was explained by urban open areas such as golf courses, sports fields and neighborhood parks under turf grass. There was no relationship between annual mean DON concentration and any land use. Urban open area also explained a significant amount of the variance in stream sodium and stream sodium adsorption ratio (SAR). Ninety-four percent of the variance in annual mean DOC concentration was explained by SAR. Irrigation of urban turf grass with domestic tap water high in sodium (>181 mg Na⁺ L^?1) may be inducing sodic soil conditions in watershed soils in this region resulting in elevated mean annual DOC concentrations in our streams.