轻质分散相旋流器中结构参数对分离性能的影响

根据计算模型的计算结果给出了轻质分散相旋流器中结构参数对旋流器分离性能的影响以及影响方式，其中旋流器尺寸的增加将导致分离能力的降低，具体表现为分割尺寸d₅₀与旋流器尺寸的平方根成正比；锥段半锥角的增加也将降低旋流器的分离能力，表现为分割尺寸d₅₀随半锥角的增加而增加，主要的原因是在其它尺寸保持不变时，半锥角的增加减少了锥段的分离空间、减少了流体在锥段的停留时间；底流口以及溢流口的尺寸是以一个组合参数的形式对旋流器的分离性能产生影响的，这两个参数的变化不仅改变分割尺寸d₅₀，而且改变迁移率曲线的陡度，因此在分离固体颗粒时，可以通过改变底流口与溢流口的尺寸来改善水力旋流器对颗粒的分级性能。     

内镶片式齿型迷宫滴头抗堵塞试验研究

依据ISO滴头堵塞检测方法中“短周期堵塞测试程序”，测试了国内外15种内镶片式齿型迷宫滴头的抗堵塞性能。结果表明：用单一结构参数(流道宽度W、流道深度D、齿高度h和齿角度θ)表征其抗堵塞性能存在局限性；结构特征参数(断面最小尺寸min(D,W)、水力半径R和齿间距l)能较好反映滴头流道横、纵断面的结构特征，在不同程度上表征了流道的抗堵塞性能，且在试验条件下各自均存在抗堵塞临界值；滴头额定流量Q_r和迷宫滴头径粒比η与抗堵塞性能相关性较好，且存在抗堵塞临界值。当各参数小于其临界值时，滴头极易堵塞，且抗堵塞性能随结构特征参数、额定流量和迷宫滴头径粒比的增大而明显提高；反之，滴头抗堵塞性能较强，滴头抗堵塞性能对各参数的增大不敏感。该试验结果可为滴头流道优化设计提供参考。     

双流道泵水力设计的研究

在大量试验研究和设计实践的基础上,对双流道泵叶轮和蜗壳的一些主要几何参数进行了统计分析,发展和完善了双流道泵水力设计方法。给出了双流道泵叶轮轴面图前、后盖板圆弧半径R₁、R₂与比转数n_s及叶轮进、出口直径D_j、D₂的关系,提出了叶轮平面图流道中线方程。总结了双流道泵蜗壳基园直径D₃、进口宽度b₃、隔舌角φ₀和面积比系数y的计算公式。     

双锥型旋流器内液—液分离过程的流动数值模拟

为研究双锥型水力旋流器内液—液分离机理以提高其分离性能和降低旋流器的能量损耗，该文使用FLUENT软件中的多相流欧拉分析方法结合雷诺应力湍流模型实现了双锥型水力旋流器内液—液分离过程的三维数值模拟并预测其分离效率。该模拟适用于轻质分散相的体积率超过10%，湍流具有各向异性结构的一般广义情形。计算给出了旋流器内部的流动结构，展示了液—液两相由开始的均相来流如何在旋流器内逐渐分离、聚合、迁移的过程，基于计算结果预测了旋流器的分离效率并与实验结果进行了对比，表明预测和实验结果较为吻合，说明计算结果是有效可信的。     

黄河口生态恢复工程对湿地土壤不同形态无机硫动态变化的影响

选择黄河口生态恢复前后的未恢复区（R₀）、2007年恢复区（R₂₀₀₇）和2002年恢复区（R₂₀₀₂）的芦苇湿地为研究对象,探讨了生态恢复工程对生长季湿地土壤无机硫形态变化的影响。结果表明,生态恢复工程不同程度地改变了湿地土壤中各形态无机硫含量。相对于R₀,R₂₀₀₂和R₂₀₀₇土壤中的水溶性硫（H₂O—S）含量分别降低46.7%和44.7%,吸附性硫（Adsorbed—S）和盐酸可溶性硫（HCl—Soluble—S）含量分别增加0.4%,116.0%和50.1%,29.1%,而盐酸挥发性硫（HCl—Volatile—S）含量在R₂₀₀₂下降8.0%,在R₂₀₀₇增加19.7%。不同恢复阶段湿地土壤中各形态无机硫含量在生长季呈不同的变化特征,这一方面与不同湿地植物生长节律以及地上与地下之间的硫养分供给关系密切相关;另一方面则与不同生态补水方式导致的环境因子,尤其是pH、EC和氮养分的变化有关。随着恢复年限的增加,湿地土壤的总无机硫（TIS）含量以及其占全硫（TS）含量的比例均呈降低趋势。湿地土壤的TIS储量整体随恢复年限的增加而降低,而这种降低主要取决于H₂O—S、Adsorbed—S和HCl—Soluble—S的贡献,且以H₂O—S占优（78%~80%）。研究发现,随着黄河口湿地的逐渐恢复以及每年冬季芦苇收割活动的进行,恢复湿地土壤中的无机硫养分逐渐趋于缺乏状态,长期来看将不利于维持湿地的稳定与健康。     

超声强化超临界CO2萃取人参皂苷的研究

为了探讨超声波对超临界CO₂萃取(SCE)的影响，考察了在不同萃取温度、萃取压力、萃取时间和流体流量下，有、无超声时超临界CO₂萃取人参皂苷的萃取率。试验结果发现，超声强化超临界CO₂萃取(USCE)的合适萃取温度比没加超声(SCE)时的低10℃；在各自合适的萃取压力下，USCE的皂苷萃取率是SCE的1.64倍；CO₂流体的流量大更有利于USCE。在SCE中，超声的加入能明显提高产物的萃取率和生产效率，降低生产能耗和节     

呼伦贝尔草甸草原不同显热通量观测方法比较

显热通量（sensible heat flux，H）是反映地表湍流运动的重要参数，准确获取该参数对于区域内热量交换规律的认识和农业生产及水资源的有效管理具有重要意义。涡动相关仪（eddy covariance system，EC）和大孔径闪烁仪（large aperture scintillometer，LAS）是目前生态系统水热通量的主要测量手段，但两者观测范围的空间尺度存在差异。该研究以呼伦贝尔草甸草原生态系统为对象，通过对比分析两种方法观测的显热通量（H_LAS和H_EC）变化特征，对两者之间的差异（ΔH）及产生原因进行探究，并且定量研究了不同因子对ΔH的影响程度。结果表明，在不同时间尺度内，H_LAS和H_EC的变化趋势基本一致，显热通量主要受到净辐射的驱动作用，同时ΔH与净辐射存在正相关性；对应时刻H_LAS和H_EC之间线性回归方程斜率为1.13，拟合优度R²为0.81，说明大孔径闪烁仪在草甸草原区有着很好的适用性；EC能量平衡闭合程度会影响H_LAS和H_EC之间差异，剔除能量平衡闭合率（energy balance ratio，EBR）小于0.8的数据后，H_LAS和H_EC之间线性回归方程斜率减小至1.05，说明能量平衡闭合程度越高ΔH越小；净辐射（net radiation，R_n）、风速（wind speed，WS）、波文比（Bowen ratio，Bowen）和饱和水汽压差（saturated water vapor pressure difference，VPD）与ΔH之间相关性显著，是ΔH的主要气象环境因子；ΔH单个影响因子的解释能力从高到低依次为净辐射、风速、EC能量平衡闭合率、饱和水汽压差、波文比，任意两个不同影响因子之间均呈现双因子增强作用，解释能力较高的交互影响因子为净辐射/风速和风速/波文比。研究结果有利于准确理解LAS与EC显热通量观测过程中的空间尺度效应，同时可为区域尺度扩展和遥感地面验证过程中通量数据的质量控制提供科学参考依据。     

基于改进作物散射模型的陕西杨凌区麦田土壤水分反演研究

本文提出一种改进作物散射模型反演麦田土壤水分,该模型根据冬小麦等低矮植被的散射特性,在原模型的基础上保留植被层直接散射部分以及植被与地表相互耦合作用的信息,同时加入裸土地表的直接散射部分,并根据经验权重将两部分信息分离开,构建出适用于冬小麦等低矮植被的后向散射模型,并结合RADARSAT-2雷达数据以及陕西杨凌农田试验区的地面实测数据,计算得到改进模型的经验参数,进而对模型进行验证分析。研究结果表明：改进作物散射模型的模拟精度相对于未改进的作物散射模型有显著的提高,R_²在HH和VV极化下都达到80%以上。为了验证改进的作物散射模型算法及土壤水分反演的有效性,本研究将改进作物散射模型与TVDI光学指数模型、简化的MIMICS模型的土壤水分反演结果进行对比分析,改进的作物散射模型反演精度比TVDI和简化的MIMICS模型要好,R_²达到84.3%,均方根误差为0.028 cm_³/cm_³,简化的MIMICS模型反演结果比TVDI要好,但是精度不高,R_²为66.9%,均方根误差为0.043 cm_³/cm_³。改进的作物散射模型对地表植被比较敏感,可以有效的将冬小麦对雷达信号散射影响和裸土层散射贡献区分开,为植被覆盖下地表土壤水分的反演创造条件,给大面积大范围的地表土壤水分反演提供强有力的技术支撑。     

超临界CO2连续浓缩鱼油EPA和DHA的研究

为了克服鱼油有效组分超临界CO₂间歇萃取方法的缺点，设计建造了超临界CO₂在内径14 mm、填料高1.8 m的填料塔中连续萃取浓缩鱼油有效组分的流程。根据单因素试验的结果，对工艺参数进行优化。设计了4因素3水平并考虑部分交互作用的正交试验方案，以综合指标进行评价，得到了优化工艺参数为：填料塔压为12.5 MPa；CO₂流量为5L/min；鱼油进料流量为0.8 mL/min；塔的温度分布为40～85℃。经方差分析得知，温度分布的影响对综合指标高度显著，鱼油进料流量对综合指标的影响显著，试验范围内的压力、CO₂流量、压力和温度分布交互作用、温度分布和CO₂流量交互作用以及压力和CO₂流量交互作用对综合指标没有显著影响。     

蒸渗仪测定滴灌枣树不同时间尺度下腾发强度特征

为精确测定、准确模拟阿克苏地区滴灌枣树腾发过程,基于大型称重式蒸渗仪测定枣树全生育期逐时及逐日腾发强度（ET）,利用水量平衡方程、PM公式及经典统计原理,分析不同时间尺度下叶面积指数（LAI）、气象因素[温度（I）、风速（V）、净辐射（R_n）]、表层土壤含水率（W）与枣树腾发强度的相关关系并建立预测模型。结果表明：枣树日内腾发强度呈单峰型变化趋势,夜间变化幅度较小且腾发贡献率低。枣树全生育期逐日腾发强度变化呈先增大后减小的趋势,花期的腾发强度最大,为4.42 mm·d^-1;全生育期腾发总量为640.83 mm,其中花期和果实生长发育期耗水量占比较大,分别为38.61%和32.72%。在小时和日时间尺度上,影响腾发强度的主要因素不完全相同,且影响程度有所差异。综合考虑各影响因素,以萌芽期、花期、果实发育期为基础,分别建立以小时、日尺度下估算腾发强度的经验模型ET₁（h）=0.153+0.004T+0.012V+0.176R_n+0.002W+0.067LAI、ET₂（d）=-3.325+0.081T+0.163R_n+0.069W+2.089LAI,拟合度R²均在0.7以上,以果实发育期与成熟期数据对模型进行检验,纳什效率系数分别达0.63、0.80。经偏相关检验,冠层净辐射（R_n）对两种尺度的腾发强度均影响最显著,因此以枣树全生育期数据量为基础,仅建立冠层净辐射（R_n）与腾发强度的回归模型ET₁（h）=-0.063 3R_n²+0.361 2R_n—0.003 7、ET₂（d）=-0.018 3R_n²+0.684 7R_n–1.642 1,R²分别为0.704 7与0.743 6,可满足缺少数据支撑情况下的腾发过程估算。这些模型明确了阿克苏地区滴灌枣树腾发机制及影响程度,可为水分管理精准化提供计算基础。     

旋流器结构参数对同心环状缝隙螺旋流影响

旋流器与管道所形成的同心环状缝隙空间会因其结构参数的变化而产生差异，空间结构的变化会对环状缝隙螺旋流流场产生影响，进而影响旋流器的起旋效率。为明确旋流器结构对环状缝隙螺旋流的影响，进行了结构参数（直径×长度）为70 mm×100 mm、70 mm×150 mm、60 mm×150 mm³种旋流器所形成的同心环状缝隙螺旋流三维流速试验。试验结果表明：旋流器结构参数的变化并未改变环状缝隙螺旋流三维流速的整体分布规律，只是对轴向、径向和周向流速的大小和离散程度产生了影响，且旋流器结构参数的变化对径向、周向流速的影响较大。对于长度相同的两旋流器，直径由60 mm增大至70 mm后，各断面轴向、周向平均流速与流速波动增大，而径向平均流速降低，但流速波动增大；对于直径相同的两旋流器，长度由100mm增大至150 mm后，轴向平均流速增大，而流速波动降低，径向、周向平均流速与流速波动均逐渐增大。旋流器直径对水头损失、起旋效率的影响要远大于长度，当直径由60 mm增大至70 mm后，水头损失与起旋效率均增大；在本试验条件下结构参数为70 mm×100 mm的旋流器起旋效率最高，即旋流器的较优结构参数为70 mm×100 mm。该研究成果可为旋流器的选型以及结构优化提供一定的参考。     

微灌旋流网式一体化水砂分离器试验

现有研究以及关注的过滤设备多集中于低含砂水水源,对于缺水地区以高含砂水为水源进行微灌的研究较少,该文提出一种新型微灌用网式一体化水砂分离器,并与常规水砂分离器进行试验对比分析,旨在解决以高含沙水为水源进行微灌的堵塞问题。该文在试验对比的基础上,分别计算网式一体化水砂分离器和常规水砂分离器的主要性能参数,包括溢流参数(溢流流量和溢流浓度)、底流参数(底流流量、底流浓度、底流分流比)以及分级分离参数(分离效率和分级效率)。结果表明,网式一体化水砂分离器和常规水砂分离器的溢流流量和底流流量均与进口压力呈正相关关系,而底流分流比与进口压力呈负相关关系;在进口压力为0.26~0.34 MPa时,网式一体化水砂分离器的分割粒度为20.0~25.0μm,分离极限为83.5~89.0μm,分离精度为0.40~0.43;而常规水砂分离器的分割粒度为24.5~27.5μm,分离极限为86.0~95.0μm,分离精度为0.27~0.42。如果以分离效率80%为评价指标,在进口压力为0.26~0.34 MPa时,常规水砂分离器的平均分离粒径为65μm,而网式一体化水砂分离器的平均分离粒径为45μm。研究可为高含砂水微灌用新型过滤器提供了试验方法、试验参数和理论依据。     

Evaluation of Natural Zeolite as a Material for Permeable Reactive Barrier for Remediation of Zinc-Contaminated Groundwater Based on Column Study

The permeable reactive barrier (PRB) filled with natural zeolite plays the role of a reactive treatment zone for remediation of contaminated groundwater. Based on column lab experiments, the volume of remediated solution, the distribution (K_d) and retardation (R_d) coefficients were evaluated, confirming successful removal and retention of zinc from contaminated groundwater. The effect of hydrodynamic dispersion on zinc capturing by zeolite in PRB was evaluated by the hydrodynamic dispersion coefficient (D_L) and retarded hydrodynamic dispersion coefficient (D_LR) using the Brigham method. For different assumed distances of the barrier, the simulation of one-dimensional zinc concentration profile from the point source through the barrier has been modeled by a simple analytical pulse model. The results show that the flow rate has the most significant effect on the concentration profile, peaks, and broadening of curves. The residence contact time (τ) corresponding to higher K_d and R_d as well as lower D_L and D_LR values outcomes the optimal range of 6.2–9.4 min. This interval corresponds to the experimental performance at the bed length of 8 and 12 cm and flow rate in the range of 6.38–9.57 PV/h. The calculated minimum thickness and longevity confirm the successful application of zeolite as a material in PRB for remediation of zinc contaminated groundwater.     

中国西北棉花根系呼吸对土壤呼吸贡献率的研究

To measure the contribution of root respiration (Rr) to total soil respiration (Rt) in arid cotton fields, eighteen plots, nine for girdling and nine control, were built in an arid cotton field in the Aksu National Experimental Station of Oasis Farmland Ecosystem, Xinjiang of China. Given the difference of soil respiration between girdled plots and non-girdled control plots, the components of soil respiration, root respiration (Rr) and respiration originating from decomposition (Rd) were divided. The temperature sensitivities of R r and R d were analyzed, respectively. The results showed that the average contribution of R r to R t in arid cotton field was about 32% during the study period. The temperature-response curve of R r differed from that of Rd . The dynamic variation of R d was more related to the change of soil temperature as compared to Rr . Rr and Rd had different responses to the variation of environment, and thus new models capable of differentiating between Rr and Rd are needed for evaluating the different factors controlling these two components of soil respiration in arid cotton field.     

Diffuse PAR irradiance under clear skies in complex alpine terrain

The diffuse component of photosynthetically active radiation (PAR) is important for models that calculate carbon dioxide uptake in photosynthesis by vegetation. Few PAR measurements are usually available, especially in complex terrain. Thus, extrapolation based on models becomes the primary means for deriving diffuse PAR in complex terrain. Most models treat the diffuse PAR sky distribution isotropically to avoid complex calculations. However, this leads to errors in diffuse PAR estimation due to the anisotropic nature of PAR sky radiance distribution. This paper describes a model for estimating diffuse PAR at any given point within complex terrain from measurements at a reference site, by taking into account both the anisotropic nature of sky radiance distribution and topographic effects. The model has been validated using two different sites, Kederbichl, and Bartholomä in the National Park Berchtesgaden, Germany, with Schönau as the reference site. The results revealed, that by replacing the isotropic treatment with PAR sky radiance distribution modified from the sky radiance distribution function in the model MURAC, the simulation accuracy is greatly improved. The R² of measured to modelled diffuse PAR reached 0.64 and 0.65 at Kederbichl and Bartholomä sites, respectively, compared to the isotropic treatment of 0.14 and 0.33. The normalized root mean square error (NRMSE) also improved from 0.47 to 0.23 and 0.40 to 0.26 for the Kederbichl and Bartholomä sites. An analysis of the ratio of diffuse radiation on slope to that on the horizontal (R_d) with solar zenith angle and the Linke turbidity factor indicated that R_d varies over time. Moreover, the variations of R_d are quite different at the above two sites, suggesting that R_d varies spatially as well. Overall, R_d in complex terrain is jointly controlled by diffuse sky radiance distribution and topography. Different combinations of topographic and atmospheric conditions will alter time dependent patterns in R_d. This casts doubt on the commonly held view that R_d can be assumed to be constant for radiation models.     

Size Distribution of Wet Weather and Dry Weather Particulate Matter Entrained in Combined Flows from an Urbanizing Sewershed

Urban drainage transports a complex and heterogeneous mixture of aqueous-phase chemicals and also solid-phase particulate matter (PM). In this study, event-scale particle size distribution (PSD) of wet and dry weather flows are measured, modeled, and compared. The flows are generated from a complex urbanizing sewershed (Liguori catchment) in Cosenza, Italy. Results indicate PSDs are heterodisperse, ranging from colloidal to sand-size PM. On an event scale, dry weather PSDs are coarser than wet weather flows, yet within each flow class results indicate flow-limited behavior and only nominal variability during and between events. PSDs from each event and flow category are modeled with a cumulative gamma distribution. Results produced nonparametric distributions of shape (γ) and scaling (α) parameters as well as a d ₅₀ index. Wet weather flows generated statistically significantly higher distributions of γ and α and statistically significantly lower d ₅₀. Nonparametric parameter distributions illustrate greater, yet still nominal variability for wet weather flows.     

Changes in plant growth substances,contents and flower quality of rose cv. ‘Dolce Vita’ in response to nitrogen sources under soilless culture conditions

The aim of this study was to investigate the biochemical responses and vase life of rose cut flowers under different ratios of NO₃:NH₄:urea in soilless culture. In this study, urea was used as the source of nitrogen (N) in solution cultures. For this purpose, an experiment was conducted as completely randomized design with seven ratios of N forms and three replications. The rooted cuttings of rose cv Dolce Vita were supplied with seven different ratios of NO₃^?:NH₄⁺:urea (100:0:0, 70:15:15, 50:25:25, 50:0:50, 0:0:100, 50:50:0 and 0:100:0). Results showed that with the increase in urea and ammonium concentrations, the amounts of cuttings IAA, GA₃, zeatin, ABA and polyamines contents decreased significantly. Plants fertigated with nutrient solution containing NO₃^?:NH₄⁺:urea (50:25:25) had the highest concentrations of growth regulators, the highest stalk length and flower vase life. As the ammonium ratios in the nutrient solution increased, the flower vase life decreased significantly. It was concluded that using NO₃^?:NH₄⁺:urea at the ratio of 50:25:25 had the highest effects on improving the rose cut flowers quality by affecting plants growth regulators and can be recommended for cut rose production in soilless culture systems.     

Long-term (13 years) measurements of SO2 fluxes over a forest and their control by surface chemistry

Long-term fluxes of sulphur dioxide (SO₂) have been measured over a mixed suburban forest subjected to elevated SO₂ concentrations. The net exchange was shown to be highly dynamic with substantial periods of both upward and downward fluxes observed in excellent conditions for flux measurement. Upward fluxes constituted 30% of selected fluxes and appeared more frequently when the canopy was acidic. Upward fluxes were shown to be due to desorption from a drying surface or when ambient levels declined after periods of increased SO₂ exposure.The long term average SO₂ flux (F) was −59 ng SO₂ m⁻² s⁻¹ for the period 1997-2009 corresponding to an average SO₂ concentration of 12.3 μg SO₂ m⁻³ and a deposition velocity υ_d of 5 mm s⁻¹. The smallest deposition fluxes and υ_d were measured in dry conditions (−42 ng m⁻² s⁻¹ and 3.5 mm s⁻¹, resp.), which represented 57% of all cases. Wet canopies were more efficient sinks for SO₂ and a dew-wetted canopy had a smaller υ_d (6 mm s⁻¹) than a rain-wetted canopy (ca 10 mm s⁻¹). Seasonal variability reflected differences in chemical climate or canopy buffering properties. During the summer half-year when surface acidity was low due to higher NH₃/SO₂ ratios, a higher deposition efficiency (υ_d/υ_dmax) and lower non-stomatal resistance (R_w) were observed compared to winter conditions. Comparisons of R_c for different combinations of canopy wetness and surface acidity categories emphasized the importance of both factors in regulating the non-stomatal sinks of SO₂. Increased surface water acidity gradually led to a lower υ_d/υ_dmax and an increased R_c for all considered canopy wetness categories. The smallest υ_d/υ_dmax ratio and highest R_c were obtained for a dry canopy with high surface acidity. Conversely, a rain-wetted canopy was the most efficient sink for SO₂. The canopy sink strength was further enhanced by high friction velocities (u_*), optimizing the mechanical mixing into the canopy. Long-term trends were strongly coupled to changes in the NH₃/SO₂ ratio, which has clearly enhanced the deposition efficiency of SO₂ in recent years.     

Macromolecular Features of Amaranth Starch

High-performance size-exclusion chromatography (HPSEC), static light scattering (SLS) and dynamic light scattering (DLS) techniques were used for the structural characterization of amaranth starch, solubilized in water by microwave heating in a high-pressure vessel. Apparent average molar mass (M _w) gyration radius (R _G), and hydrodynamic radius (R _H) values were obtained from Berry and Zimm treatment of light-scattering data. When heating time increased from 35 to 90 sec, the M _w, R _G, and R _H decreased, demonstrating a possible polymer degradation due to temperature. Apparent M _r values from HPSEC at 35 sec (27 ± 2 × 10⁷ g/mol) and 50 sec (20 ± 2 × 10⁷ g/mol) were lower than those determined by SLS (35 sec = 69 × 10⁷ g/mol, 50 sec = 56 × 10⁷ g/mol). However, at 70 and 90 sec, the inverse pattern was obtained. The fractal dimensions (d′_f) from HPSEC study for samples dissolved for 35 (3.26), 50 (3.24), and 70 sec (3.14) are characteristic of a particle that has the internal structure of hard sphere, and for samples dissolved for 90 sec (2.19), are characteristic of a fully swollen, randomly branched macromolecule. From SLS, d′_f decreased with increasing treatment time (d′_f = 2.44, 2.18, 1.50, and 1.03 for 35, 50, 70, and 90 sec, respectively). The particle-scattering factors and Kratky plots, well-suited for studying the internal structure of a macromolecule, showed a sample degradation when treatment time increased. Results from DLS showed bimodal distributions with differences in the peak locations when treatment time increased. The ratio of R _G to R _H (ρ) for samples analyzed were between 0.88 and 1.3; these values are characteristic of a sphere or globular structure.     

Effects of aluminium ions on uptake of calcium,magnesium and nitrogen in Betula pendula seedlings growing at high and low nutrient supply rates

The effects of aluminium on plant nutrition in small birch plants (Betula pendula Roth) were investigated. By using relative addition rate (r _A, g g^?1 d^?1) of nutrients as the growth-controlling variable, it was possible to grow the plants at very low external nutrient concentrations and to simulate plant requirements at two different fertility levels. Before aluminium addition the plants were at steady-state relative growth rate, (R _G, g g^?1 d^?1). The two addition rates were free access of nutrients with R _G ≈ 0.215 d^?1, or nutrient-limited, R _Aand R _G=0.10 d^?1. Internal concentrations of calcium and magnesium decreased with increasing Al³⁺ conncentration in the nutrient solution while nitrogen concentrations in the plants remained unchanged or increased. It was demonstrated in both nutrition treatments that calcium and magnesium decrease per se does not reduce plant growth and that uptake has to be considered in relation to plant requirement at different growth rates. The interpretation of the effects of aluminium on Ca and Mg uptake and plant biomass development suggested that processes other than disturbances in Ca and Mg uptake are the cause of the decrease in growth.