Universal hydraulics of the flowering plants: vessel diameter scales with stem length across angiosperm lineages,habits and climates

Angiosperm hydraulic performance is crucially affected by the diameters of vessels, the water conducting conduits in the wood. Hydraulic optimality models suggest that vessels should widen predictably from stem tip to base, buffering hydrodynamic resistance accruing as stems, and therefore conductive path, increase in length. Data from 257 species (609 samples) show that vessels widen as predicted with distance from the stem apex across angiosperm orders, habits and habitats. Standardising for stem length, vessels are only slightly wider in warm/moist climates and in lianas, showing that, rather than climate or habit, plant size is by far the main driver of global variation in mean vessel diameter. Terminal twig vessels become wider as plant height increases, while vessel density decreases slightly less than expected tip to base. These patterns lead to testable predictions regarding evolutionary strategies allowing plants to minimise carbon costs per unit leaf area even as height increases.     

Proximal root diameter as predictor of total root size for fractal branching models

In a fractal branching pattern the same rules govern branching at each subsequent level. The initial size (diameter) and the essential branching rules thus contain the information required to construct the whole pattern. If root branching patterns have fractal characteristics, measurement of the proximal root diameter at the stem base and the branching rules as observed anywhere in the root system, would be enough to predict total root length, root diameter distribution and root length per unit dry weight (specific root length). A ‘pipe stem’ model is used to derive algebraic relations between total root size and proximal root diameter for two classes of branching patterns, determinate and proportionate. To predict total root length from the proximal root diameter, at least information is needed on the minimum root diameter, the average length of internal and external links (segments) and the proportionality factor between total cross sectional areas before and after branching. For the length of the longest root or the specific root length further information on the branching rules is needed, as it is highest for determinate and proportionate branching rules, respectively.     

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

The present study was designed to study the effect of drought on root, stem and leaf anatomy of Astragalus gombiformis Pomel. Several root, stem and leaf anatomical parameters (cross section diameter, cortex, root cortical cells, pith, leaf lamina and mesophyll thickness) were reduced under moderate to severe water deficit (20–30 days of withheld irrigation). The stele/cross section root ratio increased under moderate water deficit. The root’s and stems vascular systems showed reduced xylem vessel diameter and increased wall thickness under water deficit. In addition, the root xylem vessel density was increased in these drought conditions while it was unchanged in the stems. The stomata density was increased under prolonged drought conditions whereas the stomata size was untouched. The leaf vascular system showed reduced xylem and phloem tissue thickness in the main vein under moderate to severe water deficit. However, in the lamina the vascular tissue and the distance between vascular bundle were unaffected. Our findings suggest a complex network of anatomical adaptations such as a reduced vessel size with increased wall thickness, lesser cortical and mesophyll parenchyma formation and increased stomata density. These proprieties are required for the maintenance of water potential and energy storage under water stress which can improve the resistance of A. gombiformis to survive in arid areas.     

A survey of vessel dimensions in stems of tropical lianas and other growth forms

Summary Vessel dimensions (total diameter and length) were determined in tropical and subtropical plants of different growth forms with an emphasis upon lianas (woody vines). The paint infusion and compressed air methods were used on 38 species from 26 genera and 16 families in the most extensive survey of vessel length made to date. Within most stems there was a skewed frequency distribution of vessel lengths and diameter, with many short and narrow vessels and few long and wide ones. The longest vessel found (7.73 m) was in a stem of the liana (woody vine) Pithecoctenium crucigerum. Mean vessel length for 33 species of lianas was 0.38 m, average maximum length was 1.45 m. There was a statistically significant inter-species correlation between maximum vessel length and maximum vessel diameter. Among liana stems and among tree+shrub stems there were statistically significant correlations between stem xylem diameter and vessel dimensions. Lianas with different adaptations for climbing (tendril climbers, twiners, scramblers) were similar in their vessel dimensions except that scramblers tended to have shorter (but not narrower) vessels. Within one genus, Bauhinia, tendril climbing species had greater maximum vessel lengths and diameters than tree and shrub species. The few long and wide vessels of lianas are thought to hydraulically compensate for their narrow stem diameters. The many narrow and short vessels, which are present in the same liana stems, may provide a high resistance auxiliary transport system.     

THE GROWTH OF THE STEM TIP OF KALANCHOËU CV. ‘BRILLIANT STAR’

Stein , Diana B. and o . L. Stein . (Montana State U., Missoula.) The growth of the stem tip of Kalanchoë cv. ‘Brilliant Star.‘ Amer. Jour. Bot. 47 (2) : 132—140. Illus. I960.–The purposes of this investigation were (1) to define as clearly as possible the events in the shoot apex and its immediate derivatives during the ontogeny of the shoot; and (2) to determine the changes which occur during the transition from a vegetative to a reproductive meristem. Rate of leaf production in Kalanchoë is basically constant. The rate of leaf growth subsequent to the early primordial state is, however, dependent on the age of the plant and on the environment in which the plant is grown. By keeping these factors constant a correlation can be demonstrated between the size of the youngest visible leaf and the microscopic primordia. Throughout its ontogeny the general architecture of the shoot apex remains essentially the same. Two tunica layers cover the corpus in the vegetative shoot apex, and even in the flowering meristem these 2 layers can be detected. The apex is essentially flat and blends into the adjacent leaf primordia early in the plastochron. About 10 days after flower induction has been started the apex changes its form to a dome, primarily by increased cell division. At the same time the rate of elongation of the youngest internodes increases thus placing the flowering stem tip atop an elongated stem. Axillary development is ultimately responsible for the development of a dichasium.     

高寒草甸高原早熟禾个体性状对放牧与围封的响应

植物对放牧的响应是植物在响应过程中为生存和繁殖所形成的适应策略,研究植物表型反应对揭示草原生态系统的放牧响应机制具有重要意义。以青藏高原高寒草甸主要植物高原早熟禾(Poa alpigena)为研究对象,通过放牧和围封试验,研究其个体性状对放牧与围封的响应,旨在为草原生态系统放牧机制提供理论依据。结果表明:1)在长期放牧干扰下,除叶片数和根重外,其他性状株高、分枝数、叶长、叶宽、叶面积、茎粗、茎长、根长、根粗、穗长、总叶质量、单叶质量、茎重、穗重、全株重均出现显著变小的特征(P0.05);而短期围封对于高原早熟禾叶长、叶宽、总叶质量、单叶质量、茎重、穗重、根重等功能性状的恢复效果并不显著(P0.05),表明放牧退化草原植物性状具有保守性;2)通过构建高原早熟禾性状可塑性变化谱,发现穗重、茎重、全株重、分蘖数、茎长、株高等可塑性幅度较大,为放牧响应的敏感指标,叶片数、叶宽、茎粗、根粗的可塑性变化幅度较小,为惰性性状。     

Morpho-anatomical responses ofTrigonella foenum graecum Linn. to induced cadmium and lead stress

Effect of different concentrations of cadmium (0, 5,15, 30, 50 μg/g of soil) and lead (0,25, 50,100,200 μg/g of soil) on morphological and anatomical features ofTrigonella foenum graecum Linn, was studied at pre-flowering, flowering and post flowering stages. Morphological attributes, like number of leaves per plant, total leaf area of the plant and single leaf area, dry mass of stem, root and leaf, length of shoot, root and plant, size of stomata and stomatal pore, and the density of stomata on both epidermises were significantly reduced under metal stress at all the developmental stages. Trichome length on both epidermises increased while their density decreased under metal stress. Under cadmium stress, proportion of pith and vasculature decreased but cortex increased in the stem. Under lead stress, proportion of pith and vasculature increased but cortex decreased in the stem. In the root, proportion of vasculature and pith increased and cortex decreased in response to both cadmium and lead stresses. Dimensions of vessel element and xylem fibre in the wood of stem and root decreased under the cadmium and lead stresses. Decrease in density of vessel element in the stem and root with advancement of age was more pronounced in plants grown under cadmium and lead stresses.     

苗期水分亏缺对玉米根系发育及解剖结构的影响

利用盆栽试验,研究了不同水分亏缺[土壤含水量分别为田间持水量的75%～85%(对照)、65%～75%(轻度)、55%～65%(中度)、45%～55%(重度)]对玉米苗期根系发育及解剖结构的影响.结果表明:干旱抑制了植株生长,随着水分亏缺程度的加重,根系长度缩短、根直径变细、总生物量降低;而根系活力、根冠比、根尖多糖含量均增加;侧根根毛长度、根毛密度、根毛总长度在中度水分亏缺条件下达到最大.组织切片观察结果表明,根直径变细主要是由于根的中柱面积减小、导管直径缩小所致,不同水分亏缺处理间导管的数量差异不大,但水分亏缺使导管壁变得不规整.根尖多糖含量的增加主要表现在表皮细胞和根冠细胞内,在表皮细胞内多糖主要以游离形式分布,在根冠细胞内主要以淀粉粒形式分布.总之,在水分亏缺条件下,玉米通过改变导管结构、增加表皮细胞与根冠细胞内多糖的含量及扩大根毛总表面积,来调节根系对水分的吸收能力,增强玉米植株的抗旱性,但根毛并不随着亏缺程度的加重而无限制的增长,在过度干旱条件下,根毛会受到抑制或损伤.     

Phenotypic plasticity of <Emphasis Type="Italic">Chenopodium murale</Emphasis> across contrasting habitat conditions in peri-urban areas in Indian dry tropics: Is it indicative of its invasiveness?

Phenotypic plasticity is an important plant trait associated with invasiveness of alien plants that reflects its ability to occupy a wide range of environments. We investigated the phenotypic response of Chenopodium murale to resource variability and ontogeny. Its plant-level and leaf-level traits were studied at high-resource (HR) and low-resource (LR) sites in peri-urban areas in Indian dry tropics. Plants at LR had significantly higher root length, root/shoot biomass ratio, stem mass and root mass fractions. Plants at HR had higher shoot length, basal diameter, leaf mass fraction and leaf area ratio. Leaf-level traits like leaf area and chlorophyll a were also higher here. Mean plasticity indices for plant- and leaf-level traits were higher at HR. With increasing total plant biomass, there was significant increase in the biomass of leaf, stem, root, and reproductive parts, and root and shoot lengths, whereas root/shoot length ratio, their biomass ratio, and leaf and root mass fractions declined significantly. Allocation to roots and leaves significantly decreased with increasing plant size at both sites. But, at any size, allocation to roots was greater at LR, indicative of optimization of capture of soil nutrients, whereas leaf allocation was higher at HR. Consistently increasing stem allocation equaled leaf allocation at comparatively higher shoot lengths at HR. Reproductive biomass comprised 10–12% of the plant’s total biomass. In conclusion, the success of alien weed C. murale across environmentally diverse habitat conditions in Indian dry tropics can be attributed to its high phenotypic plasticity, resource utilization capability in low-resource habitats and higher reproductive potential. These characteristics suggest that it will continue to be an aggressive invader.     

PLANT SIZE AND FORM IN THE UNDERSTORY PALM GENUS GEONOMA: ARE SPECIES VARIATIONS ON A THEME?

This study addressed the hypothesis that phylogenetic changes in plant size at reproductive maturity may have facilitated adaptive radiation of Geonoma species within rain forest understory habitats. Leaf size, leaf form, plant size, and growth form were compared within and among 23 species of Geonoma from lowland and montane rain forest areas of Costa Rica and Colombia. Leaf size was significantly correlated with crown height in 18 of the 21 species examined, and with stem diameter in 17 of the species. In species characterized by a gradual ontogenetic transition from bifid to dissected leaves, shoots with bifid leaves were significantly smaller than shoots with dissected leaves with respect to rachis length, number of plications, and stem diameter. Among species, stem diameter below the crown explained 74% of the variation in leaf size (rachis length). Crown height and stem diameter were positively correlated among clustered species, but not among solitary species or all species combined. Leaf dissection was correlated with crown height among the 17 species with dissected leaves; species with bifid leaves were significantly smaller than species with dissected leaves with respect to leaf size and stem diameter. Solitary species had larger leaves and larger stem diameters than clustered species at the same crown heights. Morphological patterns among species generally followed within-species trends. These patterns suggest that Geonoma species are variants on a generic theme:within and among species, leaf size and complexity of form increase with stem diameter and crown height. Solitary and clustered growth forms appear to be morphologically convergent; within each of these architectural groups, the generic theme still applies. Evolutionary changes in leaf size, leaf form, and plant size, however, have clearly involved other factors in addition to variation in plant size.     

Allometry ofUrtica urens in polluted and unpolluted habitats

The allometry ofUrtica urens (small nettle), an important medicinal plant in many countries, growing in an area near pollution sources and an area away from pollution sources was determined. The allometric coefficients were determined for nonlinear relationships between plant height, stem width, root length, petiole length, leaf dry weight, petiole dry weight, leaf length, leaf width, leaf area and specific leaf area. The slopes of the linear equations were determined for the above parameters. The results showed that there is a difference in the allometry of different parts ofU. urens growing in these two areas. Air pollutants reduced the plant height, stem width, root length and petiole length and increased leaf parameters. The same pattern of growth was reflected by comparing the slopes of the straight lines of the parts of the plants growing in the two areas.     

不同光照条件下三七幼苗形态及生长指标的变化

用遮阳网设置不同透光率(自然全光照的1%、3%、8%、12%和22%)处理,对不同光照条件下三七〔Panax notoginseng(Burk.)F.H.Chen〕幼苗形态指标(株高、冠幅、块根长、主根长、块根直径、茎基径、单株须根数和单株须根长)、干物质积累(不同器官干质量)和分配以及叶片性状(单株叶面积、比叶面积和叶绿素相对含量SPAD值)的变化进行了研究。结果表明:在透光率不同的条件下三七幼苗的形态指标、不同器官干质量及分配以及叶片性状均有明显变化。其中,块根直径、单株须根长、单株须根数、不同器官(块根、须根、根、叶片和茎)干质量和植株总干质量均随透光率增大逐渐提高;株高在透光率22%条件下最高;冠幅和单株叶面积在透光率3%条件下最大;主根长、茎基径、根冠比、根质比及SPAD值均在透光率8%条件下最高;茎质比和叶质比在透光率3%和1%条件下较大;比叶面积随透光率增大逐渐降低。综合分析结果揭示:三七是一种典型的喜阴植物,种植过程中适当遮阳有利于其生长和干物质积累,其中透光率8%对三七幼苗生长较为适宜。     

放牧践踏对黄蒿功能性状的影响

植物功能性状是构成植物个体的基础,从性状角度揭示植物个体特征的变化机制尤为重要。该研究以半干旱沙质草地优势草本植物黄蒿为研究对象,探讨不同践踏强度在生长季早期对其功能性状的影响。结果表明：(1)在群落水平上,放牧践踏显著降低了生长季早期植物群落高度;而在个体水平上,黄蒿株高不是响应放牧践踏的敏感性状。(2)黄蒿的叶长、叶宽随践踏强度增加呈先增加后减少的趋势,在中度践踏强度下达到最高;茎直径随践踏强度的增加而增加;根系和全株性状随践踏强度增加无显著差异。(3)黄蒿的叶片长度、叶片宽度、单叶面积随叶片厚度的增加而减小,且叶片与一级根数目、根茎叶生物量之间均呈显著正相关关系;放牧践踏会影响黄蒿茎直径,但对其他表型性状没有显著影响;在生长发育过程中,黄蒿通过不同表型性状的非对称变化进行性状之间的权衡,践踏强度的增加对生长季早期黄蒿根茎叶生物量积累的影响很小。研究认为,黄蒿在生长季早期对放牧践踏具有较强的抵抗力,这对生长季早期半干旱沙地放牧压力的选择和物种保护具有重要的指导意义。     

陆生生境中喜旱莲子草的生长模式

喜旱莲子草(Alternanthera philoxeroides)原产南美洲, 后被引入到北美洲、大洋洲、东南亚和中国等地, 成为一个世界性的外来入侵种。对喜旱莲子草陆生种群的有效控制一直是一个难题。本文中通过种植实验建立了陆生生境中喜旱莲子草主枝长、生物量、叶面积和斑块面积等的生长模型。结果表明: (1)喜旱莲子草的主枝长、生物量、叶面积和斑块面积等均表现为指数式生长, 其日增长率(%)分别为4.28、11.27、11.59和8.67。(2)喜旱莲子草的地上重(x)－地下根茎重(y)的异速生长指数b约为3/4(01), 即总重和叶面积相对于主枝长呈二次幂增长, 由此可进一步推出总重和叶面积与斑块面积成正比; 生物量－叶面积的异速生长指数b约为1, 为等速生长(b＝1), 即单位生物量所支持的叶面积不随植株大小的变化而变化(冠层恒定性)。其叶面积比为88.24 cm²/g, 比叶面积为287.97 cm²/g。通过本研究期望对喜旱莲子草陆生局域斑块的生长进行预测, 同时为进一步建立其控制模型提供基础数据, 为制定经济有效的控制对策提供科学依据。     

闽楠容器苗各器官生物量的分配格局及水分特征研究

以1.5年生闽楠(Phoebe bournei)容器苗为研究对象,揭示其在不同高度阶段各器官的含水率及生物量的分配格局,为闽楠的培育及利用提供理论依据。研究表明：①随着高度的增加,闽楠容器苗的生物量及各器官生物量也随之增加,各器官生物量分配大小表现为根生物量＞叶生物量＞茎生物量＞枝生物量;其中茎生物量分配随着高度的增加而增加,叶生物量分配则是随着高度的增加呈现先增加后减少的变化曲线,根生物量分配随着高度增加而先减少后增加。苗高与基径,树高、基径与叶、干、根、茎（干+枝）生物量以及地上、地下和单株生物量都具有极显著相关关系;树高、基径与枝生物量相关关系不显著;②高度为20~25 cm的闽楠幼苗其茎、叶的含水率达到最大峰值50%,其变化曲线相对比较平稳,而幼苗高度处于35~45 cm时根部含水率的最大峰值是61%,变化曲线振幅相对较大;③植株根含水率与茎、叶、地上生物量积累呈显著正相关,而叶含水率则与植物各器官生物量呈显著负相关。     

贵州梵净山亮叶水青冈解剖特征的生态格局及主导因子分析

使用具有不同生物学意义的生态因子为环境变量,应用多元统计方法,分析了贵州梵净山的亮叶水青冈（Ｆａｇｕｓ ｌｕｃｉｄａ Ｌ．）叶片及木材形态解剖特征的生态格局和影响其变化的主导生态因子。结果表明,随着温度要素的增加,叶片的所有解剖特征、叶表面的气孔面各以及木材的导管直径、纤维长度均显示下降趋势,而叶表面的气孔器密度、木材的导管频率和单列射线高度呈上升趋势;随着寒冷指数（负积温）和水分因子（年降水和水     

岷江源区两种优势针叶树当年生小枝性状与生物量分配随海拔的分异规律

当年生小枝具有较少的次生组织,同时是植物分支系统中最具活力的部分,木本植物当年生小枝性状与生物量分配的海拔变化是理解物种对不同生境适应策略的重要内容。通过分析青藏高原东缘岷江源区两种优势亚高山针叶乔木(紫果云杉和岷江冷杉)当年生小枝性状(茎长、茎粗、比茎长)与不同部位器官(茎、叶)的生物量随天然生境的海拔(3500-3550 m、3650-3700 m和3800-3850 m)变化,尝试揭示两物种当年生小枝在不同海拔下的生物量权衡及其生长策略。结果表明:(1)不同海拔下茎生物量种间差异大于种内差异,3650-3700 m处的茎生物量变异最大(128.4%)。(2)云杉的茎生物量、总叶生物量与海拔间存在显著的负相关关系(P<0.05),比茎长与海拔呈显著正相关(P<0.05);冷杉的总叶生物量与海拔间为显著负相关关系(P<0.05)。(3)随着海拔的升高,云杉茎生物量分配比逐渐从33.0%降低到27.0%;而冷杉的茎生物量分配比则从23.0%渐增至28.0%。(4)3500-3550 m和3650-3700 m两处的云杉茎生物量与总叶生物量、茎长与茎粗呈异速生长关系;3500-3550 m、3650-3700 m和3800-3850 m三处的冷杉茎生物量与总叶生物量、茎长与茎粗一直呈现异速生长关系。两种针叶树的茎生物量分配比及相关性状随海拔的变化差异表明冷杉更适应高海拔的胁迫环境。     

亚低温与干旱胁迫对番茄植株水分传输和形态解剖结构的影响

为探讨亚低温和干旱对植株水分传输的影响机制,以番茄幼苗为试材,利用人工气候室设置常温(昼25 ℃/夜18 ℃)和亚低温(昼15 ℃/夜8 ℃)环境,采用盆栽进行正常灌水(75%～85%田间持水量)和干旱处理(55%～65%田间持水量),分析了温度和土壤水分对番茄植株水分传输、气孔和木质部导管形态解剖结构的影响。结果表明: 与常温正常灌水处理相比,干旱处理使番茄叶水势、蒸腾速率、气孔导度、水力导度、茎流速率、气孔长度和叶、茎、根导管直径显著减小,而使叶、茎、根导管细胞壁厚度和抗栓塞能力增强;亚低温处理下番茄叶水势、蒸腾速率、气孔导度、水力导度和叶、茎、根导管直径显著降低,但气孔变大,叶、根导管细胞壁厚度和叶、茎、根抗栓塞能力显著升高。亚低温条件下土壤水分状况对番茄叶水势、蒸腾速率、气孔导度、水力导度、气孔形态、叶、根导管结构均无显著影响。总之,干旱处理下番茄通过协同调控叶、茎、根结构使植株水分关系重新达到稳态;亚低温处理下番茄植株水分关系的调控主要通过改变叶和根导管结构实现,且受土壤水分状况的影响较小。     

Plant factors influencing phosphorus uptake by white clover from solution culture

Summary The phosphorus (P) uptake rate of several white clover populations was determined in two solution culture experiments. Populations and cultivars differed in P uptake per plant and per unit root length in both experiments. Correlation and multiple regression analysis showed that differences between populations for P uptake per plant were largely related (r²>80%) to differences in leaf area and absolute growth rate, when plants had been grown at high-P levels, and by differences in root size and absolute growth rate when plants had been grown at low-P levels. Differences between populations for P uptake per unit root length were related (r²≈50%) to leaf area and relative growth rate in experiment 1 and to transpiration rate and water influx in experiment 2, when plants were pretreated at high-P levels. Differences between populations for P uptake per unit root length were negatively related to root size when plants had been grown at low-P levels. On the basis of these and other results it is suggested that P uptake per plant is determined largely by shoot factors. However, P uptake per unit root length is negatively related to root size, because demand for P is largely determined by shoot factors, and so differences in root size lead to an apparent difference in uptake per unit of root size.     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.