模拟垂直流人工湿地不同木本植物根际细菌群落特征

为探讨植物种类对人工湿地中根际细菌群落结构特征分布的影响,以7种木本植物细叶水团花(Adina rubella)、南川柳(Salix rosthornii)、白棠子(Callicarpa dichotoma)、夹竹桃(Nerium oleander)、木芙蓉(Hibiscus mutabilis)、水蜡(Ligustrum obtusifolium)、大叶女贞(Ligustrum lucidum)为研究对象,运用16S rRNA细菌高通量测序技术,探究垂直流人工湿地木本植物根际微生物群落结构及其主要功能类群。结果表明:细叶水团花、水蜡根际菌群的多样性、丰富度与均匀度均高于其他5种植物,其根系能够更好地富集微生物。门水平上,变形菌门、厚壁菌门是木本植物平均相对丰度较高的门,其次为绿弯菌门、放线菌门和蓝藻门;属水平上,乳杆菌属、片球菌属、地杆菌属为木本植物的共有优势菌属;大叶女贞、白棠子、夹竹桃菌落组成差异显著,乳杆菌属、片球菌属、乳球菌属是引起7种木本植物样本间菌落差异的关键物种; 7种木本植物根际硝化功能菌属丰度普遍较低,相对丰度范围为0.11%—1.06%;反硝化功能菌属的相对丰度范...     

两栖榕在人工湿地的生长特性及其对污水的净化效果

研究了两栖榕在潜流型人工湿地的生长特性及其对污水的净化效果。一年多的实验表明,生长在人工湿地的两栖榕具有发达的侧根和不定根,保持正常的净光合速率,蒸腾速率,根系活力生长速率。两栖榕人工湿地对TN,TP,CODCr和BOD5的去除率分别为54．2％、40．9％、72．4％和74．3％,与无植物系统相比较,去除率分别提高了17％、12％、10％和11％,此外,两栖榕人工湿地系统中,水力停留时间对去除率果有一定影响。     

准噶尔荒漠3种短命植物气体交换特征的日变化

采用LI-6400便携式光合测定仪,在晴天条件下对准噶尔荒漠3种典型短命植物东方旱麦草(Eremopyrum orientale)、卷果涩芥(Malcolmia scorpioides)和四齿芥(Tetracme quadricormis)的气体交换特征的日变化规律进行了研究.结果表明:①东方旱麦草和卷果涩芥的净光合速率(简称Pn,后同)的日变化呈"双峰"型,14:00(采用时间均为北京时间,后同)左右存在明显的光合"午休"现象,四齿芥Pn的日变化呈"单峰"型,峰值出现在12:00与前两者的第一峰值出现时刻相同.3种植物蒸腾速率(简称E,后同)的日变化均呈"单峰"型,但不同植物的峰谷值出现时刻不同.水分利用效率(WUE)日变化,四齿芥呈"单峰"型,东方旱麦草和卷果涩芥呈"双峰"型,峰值分别出现在8:00～10:00之间,后两者第二峰值分别出现在16:00和18:00.②根据Pn、胞间CO2浓度(Ci)和气孔限制值(Ls)的变化方向,推测3种短命植物的光合"午休",东方旱麦草和卷果涩芥主要受非气孔因素限制,而四齿芥主要受气孔因素限制.③卷果涩芥和四齿芥两种十字花科草本日平均Pn、E 和WUE 均高于禾本科东方旱麦草,尤其卷果涩芥是一种高光合、高蒸腾、高水分利用率的物种.④相关分析结果表明,对Pn影响最显著的环境因子是光合有效辐射(PAR),对E影响最显著的因子3种植物各不相同.     

潜流湿地和表面流湿地的净化效果与植物生长比较

分别以砾石和土壤为填料构建成潜流人工湿地和表面流人工湿地,处以较大水力负荷的污水处理。比较了两种湿地对污水的净化效果,结果表明在较大水力负荷条件下两种湿地的净化效果都较差,但潜流湿地对各种污染物的净化能力都优于表面流湿地;土柱法测量了湿地植物的根系生物量,结果显示湿地植物地上部分长势差异不明显,但潜流湿地的根系生物量显著低于表面流湿地的根系生物量(P<0.05)。结合前期实验结果得出湿地净化效果不仅与湿地植物根系生物量有相关关系,还与其他因素有一定的相关关系。     

4种湿地植物光合作用特性的比较研究

以4种湿地植物鸢尾、菖蒲、水葱和千屈菜为材料,在水平潜流人工湿地处理单元中,采用便携式LI-6400光合作用测定仪在晴朗天气下测定了各材料成熟叶片净光合速率(Pn)以及光合有效辐射(PAR)、气孔导度(Gs)、细胞问CO2浓度(CI)、叶温(Tl)、叶周围气温(Ta)和蒸腾速率(Tr),以探讨其光合生理生态特性.结果表明:(1)4种湿地植物叶片净光合速率(Pn)日变化均呈不对称的双峰曲线,光合"午休"现象明显,它们的净光合速率日均值表现为水葱>菖蒲>鸢尾>千屈菜,但种间差异不显著.(2)Gs、PAR、CI和Tr与湿地植物Pn的日变化有着极显著或显著的相关关系,其中Gs、PAR、CI是影响鸢尾Pn的主要因子,影响大小的顺序为GI>PAR>CI >;Gs和Tr是影响菖蒲和千屈菜Pn的主要因子,影响大小的顺序为Gs>Tr;而Gs是影响水葱Pn的主要因子.(3)4种湿地植物Pn-PFD响应曲线及Pn-CO2响应曲线都具有相似的二次方程曲线变化规律;光补偿点表现为千屈菜>水葱>鸢尾>菖蒲,光饱和点表现为水葱>菖蒲>千屈菜>鸢尾;CO2补偿点表现为水葱>鸢尾>菖蒲>千屈菜,CO2饱和点表现为菖蒲>千屈菜>鸢尾>水葱.(4)4种湿地植物的表观量子效率为0.019 8～0.038 3 mol·mol-1,羧化效率为0.042 6～0.064 8 mol·m-2·s-1.研究发现,4种湿地植物在给定条件下的日平均净光合速率、光能利用效率和CO2同化能力无显著差异,且气孔限制是产生光合"午休"的主要原因;影响它们光合速率的主要生理生态因子各不相同,但气孔导度均为主要因子.     

低温状态下潜流湿地的氮磷去除效果

以汉石桥潜流湿地为研究对象, 通过对2014 年10 月-次年5 月中水出水水体氮磷元素去除率分析, 研究潜流湿地对水中氮磷元素的去除效果。结果表明: TN、NH₄ ⁺、NO₂ ^– 、NO₃ ^– 、TP、PO₄^3–平均去除率为23.09%, 47.68%, 39.66%,29.96%, 23.79%, 29.73%, 且各个指标去除率均表现为先降低后增加的趋势, 整体去除率均为正值, 说明该潜流湿地在秋冬春季具有一定的处理效果; pH 与温度为制约该潜流湿地氮元素去除的重要因素, 而磷元素去除受到温度影响较小;虽然冬季潜流湿地仍有一定的去除氮磷的效果, 但去除率过低, 应注重保温, 才能使潜流湿地更有效率的全年运行。     

柊叶和象草波式潜流人工湿地的对比研究

为探索柊叶和象草在人工湿地中的应用及其净化机理,该研究以柊叶和象草为人工湿地植物分别构建了波式潜流人工湿地系统,分析了柊叶和象草波式潜流人工湿地对生活污水中COD_(cr)、TN和TP的净化效果,观察了柊叶和象草两种植物在不同季节的生长状况。结果表明:经过15个月的连续运行,在表面水力负荷约0.3 m·d~(-1)的条件下,柊叶和象草波式潜流人工湿地平均去除率是COD_(cr)分别为66.1%和70.1%,TN分别为60.4%和63.7%,TP分别为74.1%和75.1%。两种植物生长良好,根系发达,象草的地上生物量是柊叶的2.1倍,地下生物量相当;冬季象草生长缓慢,柊叶部分叶片的四周干枯,但二者都不会枯亡。这说明两个人工湿地对COD_(cr)、TN和TP都具有较好的去除效果,但无显著性差异,柊叶和象草能明显提高潜流人工湿地的净化效果。     

奇妙的植物细胞线粒体

作者近年检查了番茄、辣椒、蚕豆、扁豆、大豆、赤豆、花生、西瓜、甜瓜、丝瓜、薄荷、一串红、洋葱、慈菇、蒜、韭、小麦、大麦、玉米、水稻、稗牛筋草、水杉、广玉兰、夹竹桃、女贞、珊瑚树(Viburnum odoratissimum)木槿、海桐、栀子、樱花等三十多种植物的组织细胞,发现这些植物的分生组织、分泌结构及贮藏组织的细胞线粒体一般量多,用针等适当刺激这些部位能加速植株的生长和发育,减少病虫害,提高产量。     

两种不同根系类型湿地植物的根系生长

实验设计了一个水培系统,利用生活污水培养,对4种“须根型”植物美人蕉、风车草、象草和香根草和4种根茎型植物菖蒲、水鬼蕉、芦苇和水烛的根系生长进行比较研究。该系统由用于盛污水的塑料桶（顶部直径36．5cm,底部直径30．Ocm,高34．5cm）和用于固定植物于水面的泡沫板构成。每桶种植1株植物,每种种5株。水培至10周时,须根型植物的平均根数达到1349条／株,而根茎型植物的平均根数只有549条／株。实验结束（水培第21周）时,须根型植物的平均根生物量为11．3g／株,根茎型植物的平均根生物量为7．4g／株。须根型植物根系中,d〈1mm的细根生物量占根系总生物量的51．9％,而根茎型植物d〈1mm的细根的生物量只占25．1％。根茎型植物的根生物量与地上生物量的比值为0．2,显著高于须根型湿地植物（0．1）。须根型湿地植物的根系表面积（6933cm^2／株）极显著地高于根茎型湿地植物（1897cm^2／株）。根茎型湿地植物根的平均寿命（46．6d）较须根型湿地植物根的平均寿命（34．8d）长。美人蕉的平均根数达1871条／株,根表面积达到22832cm^2／株,远较其他种高。     

曼陀罗光合特性研究

采用LI-6400型便携式光合测定仪对潜在能源植物曼陀罗(Datura stramonium L.)在6月份至9月份的光合特性指标(净光合速率、光合有效辐射强度和气孔导度)的日变化以及净光合速率和叶绿素含量的月平均值变化进行了研究,并采用非直角双曲线对曼陀罗叶片净光合速率的光响应曲线和C02响应曲线进行了拟合.结果表明:实验期间(6月份至9月份),光合有效辐射强度和曼陀罗叶片净光合速率的日变化均呈"单峰型",峰值出现在11:00左右;7月份的净光合速率峰值最高,为19.01μmol·m-2·s-1;气孔导度日变化呈"双峰型",最大峰值和次峰值分别出现在12:00和14:00.不同月份的净光合速率月平均值有极显著差异(P＜0.01),其中7月份的净光合速率月平均值最大,为9.41 μmol·m-2·s-1;不同月份叶绿素的月平均含量变化与净光合速率月平均值的变化相似,7月份叶绿素的月平均含量也最高,但叶绿素a、b及总叶绿素月平均含量有一定差异.曼陀罗叶片净光合速率的光响应曲线和CO2响应曲线相似,在光合有效辐射强度和CO2浓度较低的条件下呈线性升高,至饱和点后缓慢升高并趋于稳定;曼陀罗叶片的光补偿点为22.42 μmol·m-2·s-1,光饱和点为689.26 μmol·m-2·s-1;CO2补偿点为74.06μmol·mol-1,CO2饱和点为1 331.97μmol·mol-1.研究结果说明,曼陀罗为具有一定耐阴能力的阳性植物,但CO2同化能力较弱.     

Metabolism of alpha-Ketoglutarate by Roots of Woody Plants

The uptake and metabolism of α-ketoglutarate-5-¹⁴C by peach, apple, and privet root tissues were studied over various time intervals. As much as 80% of the absorbed ¹⁴C appeared as ¹⁴CO₂ in 320 minutes in peach roots. Apple and privet roots were less effective in this conversion with the bulk of the ¹⁴C found in the organic acid fraction. This indicates differences in organic acid metabolism among species of woody plants.

The ¹⁴C accumulated in malate earlier and in larger quantities than in citrate. Both glutamate and aspartate were labeled in 10 minutes and glutamate was labeled as early as 3 minutes. The labeling pattern does not clearly distinguish between the synthesis of glutamate by glutamic dehydrogenase or by transamination with oxaloacetate.

The rapid metabolism of α-ketoglutarate to glutamate by the 3 species studied indicates the presence of enzyme systems important in amino acid synthesis in the roots of woody plants.

     

Relationships between plant photosynthesis,radial oxygen loss and nutrient removal in constructed wetland microcosms

The objective of this study was to investigate the relationships between root radial oxygen loss (ROL), photosynthesis, and nutrient removal, based on the hypothesis that ROL is primarily an active process which is affected positively by photosynthesis, and is correlated positively with nutrient removal. Four common wetland plants were studied in small-scale monoculture wetlands. Higher ROL coincided with faster growth among the four monocultures. Significant correlation between ROL and photosynthetic rate existed in Cyperus flabelliformis wetland (P < 0.01). Both ROL and photosynthesis represented close correlations with nutrient removal rates in all four monocultures. Significant differences in ROL, photosynthetic rate, removal rates of NH₄⁺, and soluble reactive phosphorus (SRP) were found among the four species. ROL and photosynthetic rates showed single-peak daily and seasonal patterns, with maximum daily values around noon, and with maximum yearly values in summer or autumn for the four monocultures. The results suggest that the ROL of wetland plants is related to active physiological processes. Both ROL and photosynthetic rate are indices which can be used to identify wetland plants with a higher nutrient removal capacity.     

Effect of changes in shoot carbon-exchange rate on soybean root nodule activity

The effect of short- and long-term changes in shoot carbon-exchange rate (CER) on soybean (Glycine max [L.] Merr.) root nodule activity was assessed to determine whether increases in photosynthate production produce a direct enhancement of symbiotic N₂ fixation. Shoot CER, root + nodule respiration, and apparent N₂ fixation (acetylene reduction) were measured on intact soybean plants grown at 700 microeinsteins per meter per second, with constant root temperature and a 14/10-hour light/dark cycle. There was no diurnal variation of root + nodule respiration or apparent N₂ fixation in plants assayed weekly from 14 to 43 days after planting. However, if plants remained in darkness following their normal dark period, a significant decline in apparent N₂ fixation was measured within 4 hours, and decreasing CO₂ concentration from 320 to 90 microliters CO₂ per liter produced diurnal changes in root nodule activity. Increasing shoot CER by 87, 84, and 76% in 2-, 3-, and 4-week-old plants, respectively, by raising the CO₂ concentration around the shoot from 320 to 1,000 microliters CO₂ per liter, had no effect on root + nodule respiration or acetylene-reduction rates during the first 10 hours of the increased CER treatment. When the CO₂-enrichment treatment was extended in 3-week-old plants, the only measured parameter that differed significantly after 3 days was shoot CER. After 5 days of continuous CO₂ enrichment, root + nodule respiration and acetylene reduction increased, but such changes reflected an increase in root nodule mass rather than greater specific root nodule activity. The results show that on a 24-hour basis the process of symbiotic N₂ fixation in soybean plants grown under controlled environmental conditions functioned at maximum capacity and was not limited by shoot CER. Whether N₂-fixation capacity was limited by photosynthate movement to root nodules or by saturation of metabolic processes in root nodules is not known.     

Prolonged Growth of Young Spruce (<Emphasis Type="Italic">Picea koraiensis</Emphasis> Nakai) Plants at Double Atmospheric CO<Subscript>2</Subscript> Concentration Stimulates the Preferential Growth of Thick Roots

Two-year-old young spruce (Picea koraiensis Nakai) plants were grown in a climatic chamber during three summer months at double atmospheric CO₂ concentration, sufficient content of soil inorganic nitrogen, and diurnal variation of temperature and illuminance, which simulate natural growth conditions. The control plants were grown in another climatic chamber under the same conditions, but at atmospheric CO₂ concentration (350 ppm). CO₂ exchange was measured with a Li-Cor 6400 infra-red gas analyzer in attached leaves placed in a climatic chamber in the morning under growth conditions and saturating light 1200 μE/(m² s) in June, July, and August. In addition, dry weights of needles, leafless shoot parts of plant, fraction of thick (more than 0.5 mm in diameter) and thin (less than 0.5 mm in diameter) roots were recorded. The data were used to plot CO₂ exchange rates as a function of carbon dioxide concentration and to calculate the increment of shoot and root phytomass. The maximum gas exchange rates in the treated and control plants similarly depended on CO₂ concentration. The slope of the CO₂ dependence curve, which corresponded to the kinetic characteristic V _m /K _M of photosynthetic carboxylation, increased monotonically during the experiment. To the end of observation period, the proportion of thick roots in plant phytomass significantly increased in the plants grown at double atmospheric CO₂ concentration, as compared to the control plants. Thus, the increase in the rate of photosynthetic gas exchange in plants grown for three months at double atmospheric CO₂ concentration was only due to the increase in CO₂, the substrate of Rubisco carboxylation activity. We found no differences in the CO₂ characteristic for Rubisco between the treated and control plants. The ratio of needle to thin roots in the treated and control plants was similar and did not change during the experiment. The excess of photoassimilates in the treated, as compared to the control plants, was preferentially used for thick root growth. This result shows that photosynthesis in young spruce forests can deposit excess atmospheric CO₂ in the soil horizon in the form of thick root phytomass. __________ Translated from Fiziologiya Rastenii, Vol. 52, No. 5, 2005, pp. 741–746. Original Russian Text Copyright ? 2005 by Mao, Y.-J. Wang, Zhu, X.-W. Wang, Sun, Zhou, Voronin.     

Elemental distribution in tissue components of N2-fixing nodules of Psoralea pinnata plants growing naturally in wetland and upland conditions in the Cape Fynbos of South Africa

There is little information on in situ distribution of nutrient elements in N₂-fixing nodules. The aim of this study was to quantify elemental distribution in tissue components of N₂-fixing nodules harvested from Psoralea pinnata plants grown naturally in wetland and upland conditions in the Cape Fynbos. The data obtained from particle-induced X-ray emission revealed the occurrence of 20 elements (Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Y, Zr, Mo and Ba) in nodule components. Although, in upland plants, the concentrations of S, Fe, Si, Mn and Cu showed a steady increase from the middle cortex to the medulla region of P. pinnata nodules, in wetland plants, only S, Fe and Mn showed an increase in concentration from the middle cortex to the bacteria-infected medulla of P. pinnata nodules. By contrast, the concentrations of Cl, K, Ca, Zn and Sr decreased from middle cortex to nodule medulla. The alkaline earth, alkali and transition elements Rb, Sr, Y and Zr, never before reported in N₂-fixing nodules, were found to occur in root nodules of P. pinnata plants grown in both wetland and upland conditions.     

Evaluation of the impacts of herbivory by lace bugs on Chinese privet (Ligustrum sinense) survival and physiology

Biological control of Chinese privet, Ligustrum sinense, is the best long-term option for control of this widespread invasive plant in the southeastern USA. A pre-release efficacy assessment was conducted by testing the effects of damage caused by a lace bug, Leptoypha hospita, on potted privet plants in the laboratory. Inoculating 15 pairs of lace bug adults on plants resulted in a significantly higher defoliation rate and reduced leaf biomass by more than 59% compared to 0 and 3 lace bug pairs. Leaf biomass of plants inoculated with 3 and 9 pairs of lace bug did not differ significantly from control plants. The percentage of the total leaf area affected by lace bug feeding was positively correlated with the density of lace bugs inoculated. This was also evident by the reduced chlorophyll content of leaves exposed to 9 and 15 pairs of lace bugs and their offspring. Our tests showed that one generation of feeding by the lace bug caused significant defoliation as well as reduced photosynthetic activity of remaining leaves. Continuous long term feeding by the lace bug or other potential defoliating insects could result in suppression of Chinese privet populations and possibly reduction to desirable levels.     

Iron-Oxidizing Bacteria Are Associated with Ferric Hydroxide Precipitates (Fe-Plaque) on the Roots of Wetland Plants

The presence of Fe-oxidizing bacteria in the rhizosphere of four different species of wetland plants was investigated in a diverse wetland environment that had Fe(II) concentrations ranging from tens to hundreds of micromoles per liter and a pH range of 3.5 to 6.8. Enrichments for neutrophilic, putatively lithotrophic Fe-oxidizing bacteria were successful on roots from all four species; acidophilic Fe-oxidizing bacteria were enriched only on roots from plants whose root systems were exposed to soil solutions with a pH of <4. In Sagittaria australis there was a positive correlation (P < 0.01) between cell numbers and the total amount of Fe present; the same correlation was not found for Leersia oryzoides. These results present the first evidence for culturable Fe-oxidizing bacteria associated with Fe-plaque in the rhizosphere.     

The effect of urban ground cover on microclimate,growth and leaf gas exchange of oleander in Phoenix,Arizona

We assessed how small patches of contrasting urban ground cover [mesiscape (turf), xeriscape (gravel), concrete, and asphalt] altered the microclimate and performance of adjacent oleander (Nerium oleander L.) plants in Phoenix, Arizona during fall/winter (September–February) and spring/summer (March–September). Ground-cover and oleander canopy surface temperatures, canopy air temperatures and pot soil temperatures tended to be lowest in the mesiscape and highest in the asphalt and concrete. Canopy air vapor pressure deficits were lowest in the mesiscape and highest in the asphalt plot. Rates of net photosynthesis of all oleander plants were highest in October and May, and declined through mid-summer (June–July), when rates tended to be highest in the cooler mesiscape, particularly when water was limiting. During fall/winter, oleanders in the mesiscape produced 20% less biomass, 13% less leaf area, and had 12% lower relative growth rates (R_G) than those in the other ground covers. Lower nighttime temperatures in the mesiscape in December led to oleander frost damage. During spring/summer, oleanders in the mesiscape produced 11% more biomass, 16% more leaf area, and had 3% higher R_G than those in the other cover types. The effects of urban ground cover on oleander performance were season-specific; while oleander growth was greatest in the mesiscape during spring/summer, it was lowest during fall/winter and these plants experienced frost damage. Because all oleander plants produced >10 times as much biomass during the spring/summer, on an annual basis oleanders in the mesiscape produced 5–11% more biomass than plants in the warmer ground covers.     

Effects of water level fluctuation on radial oxygen loss,root porosity,and nitrogen removal in subsurface vertical flow wetland mesocosms

Laboratory experiments were conducted to investigate the effects of water level fluctuation on plant radial oxygen loss (ROL), root porosity, plant growth performance, and nitrogen dynamics in vertical subsurface flow wetland mesocosms. Four types of mesocosms were used: control with static water level, control with fluctuating water level, static water level with plants, and fluctuating water level with plants. Typha orientalis, an emergent macrophyte, was used in this study. Changes of ROL, root porosity, and plant biomass were measured every six weeks. Shoot height and density of plants were also observed. Every two weeks, the nitrogen removal efficiency of the four systems was monitored. Maximum ROL values under static and fluctuating conditions were 7.58 and 2.73 μmol/g DW/h, respectively. The porosity values of roots under static and fluctuating conditions ranged between 33–47% and 30–37%, respectively. Average removal efficiency of both total nitrogen (TN) and ammonium nitrogen (NH₄-N) in the fluctuating condition with plants was about 65%, and nitrate nitrogen removal in the static condition with plants was about 75%. Although the water level fluctuation caused a considerable reduction in ROL and root porosity, it clearly produced a significant improvement in TN and NH₄-N removal.     

Lead,zinc and iron (Fe2+) tolerances in wetland plants and relation to root anatomy and spatial pattern of ROL

Metal (Pb, Zn and Fe²⁺) tolerances, root anatomy and profile of radial oxygen loss (ROL) along the root (i.e., spatial pattern of ROL) were studied in 10 emergent wetland plants. The species studied could be classified into three groups. Group I included Alternanthera philoxeroides, Beckmannia syzigachne, Oenanthe javanica and Polypogon fugax, with high ROL along the whole length of root (‘partial barrier’ to ROL). Group II included Cyperus flabelliformis, Cyperus malaccensis, Juncus effusus, Leersia hexandra and Panicum paludosum, ROL of which was remarkably high just behind the root apex, but decreased significantly at relatively basal regions (‘tight barrier’ to ROL). Group III consisted of only Neyraudia reynaudiana, with extremely low ROL along the length of root. The results indicated that metal tolerance in wetland plants was related to root anatomy and spatial pattern of ROL. Co-evolution of metal (Fe and Zn) tolerance and flood tolerance possibly developed in wetland plants since species showing a ‘tight barrier’ to ROL (a common trait of flood-tolerant species) in basal root zones had higher Fe and Zn tolerances than those showing a ‘partial barrier’. Root anatomy such as lignin and suberin deposition contributed to a ‘tight barrier’ in root and conferred to exclusion ability in tolerant species.