Wood vessel diameter is related to elevation and genotype in the Hawaiian tree Metrosideros polymorpha (Myrtaceae)

We tested the hypothesis that trees growing at high elevations with occasional freezing temperatures have smaller diameter xylem vessels than trees of the same species growing at lower and warmer elevations. The young branch wood of the wide-ranging Hawaiian tree species Metrosideros polymorpha (Myrtaceae) was examined in three natural field populations (high, middle, and low elevations: 2469, 1280, and 107 m a.s.l., respectively) and contrasted with seedlings from these populations that were grown in a common garden at middle elevation (1190 m). Previous studies showed that these populations have some genetic differences and have distinctive leaf structure and ecophysiological traits. Vessel diameter was significantly smaller in the high elevation field and common garden plants than in middle elevation plants. However, high elevation vessels were wider in common garden plants compared to field plants, indicating that vessel diameter is determined both by genotype (parental populations) and environment (growing conditions different from those of parents). Reduced vessel diameter has implications for resistance to cavitation induced by freezing and/or drought in plants growing near tree line in Hawaii.     

Patterns of functional clonal traits and clonal growth modes in contrasting grasslands in the central Apennines,Italy

Abstract. Aim: Patterns of plant functional traits related to clonality (clonal growth modes; CGM) in plant communities were studied and hypotheses on the importance of the selected traits in plant communities supported by soils differing in moisture and nutrient status were tested. Material and Methods: Selected plant functional traits, such as the position of the mother‐daughter plants connections, length of spacers, frequency of multiplication, persistency of ramets connections, presence of storage organs and bud protection were studied in two contrasting plant communities (xeric and mesic abandoned pastures) typical of central Apennines, Italy. Results and Discussion: Clonality was shown to be of great importance in both mesic and xeric grasslands. The major differences between the two communities were due to the dominant CGMs: turf graminoids (having effective protection of growth meristems in dense tussocks) dominated xeric grasslands, while rhizomatous graminoids (typical of competitive resource‐rich environments) dominated mesic grasslands. Below‐ground CGOs (clonal growth organs), shorter spacers, higher multiplication potential, permanent ramet connection, large bud bank and increased importance of bud protection were found to be of importance in water stressed xeric grassland. Contrary to our expectations, the mesic (less stressed) grasslands have the higher number of clonal plants possessing storage organs.     

Anatomical Adaptations to Xeric Conditions in Maihuenia (Cactaceae), a Relictual, Leaf-Bearing Cactus

Maihuenia and Pereskia, constitute Pereskioideae, the subfamily of Cactaceae with the greatest number of relictual features, but the two genera differ strongly in habit and ecological adaptations. Plants of Maihuenia occur in extremely xeric regions of Patagonia and are small cushion plants with reduced, terete leaves and soft, slightly succulent trunks. Plants of Pereskia occur only in mesic or slightly arid regions and are leafy trees with hard, woody trunks and thin, broad leaves. Maihuenias have many more anatomical adaptations to arid conditions than do pereskias: maihuenias lack sclerenchyma in their phloem and cortex (M. poeppigii also lacks xylem sclerenchyma and can contract during drought); their wood consists of vessels, axial parenchyma, and wide-band tracheids and can store water as well as minimize embolism damage; one species channelizes water flow by producing intraxylary bark; and at least some stem-based photosynthesis occurs because maihuenias have small patches of persistent stem epidermis that bears stomata and overlies a small amount of aerenchymatous chlorenchyma. Pereskias lack all these features. Although closely related, maihuenias have fewer relictual features than do pereskias, and plants of Pereskia probably are more similar to the ancestral cacti. Received 8 March 1999/ Accepted in revised form 29 May 1999     

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.     

华北低山丘陵区常用树种木质部解剖特征及水其力学抗旱性

木本植物木质部解剖特征与水分运输和干旱适应策略密切相关,但目前对华北低山丘陵区常用树种这方面的研究仍然不足。为研究这一地区植物木质部解剖特征与抗旱性的关系,研究以抗旱树种和非抗旱树种各5种为研究对象,通过测定与木质部横截面导管、薄壁组织相关的大量解剖学性状和非结构性碳浓度,比较两类树种木质部解剖特征的差异和解剖性状间的关联,以探究这些树种水力学的干旱适应策略差异。结果显示:1)10个树种的16个木质部性状均有较大变异性;2)两类树种间的平均导管直径和导管密度无显著差异,但抗旱树种导管壁厚度、最大导管直径、旁管薄壁组织比例和轴向薄壁组织比例以及非结构性碳(NSC)浓度显著大于非抗旱树种;3)抗旱树种的导管壁厚度与平均导管直径、最大导管直径和潜在最大导水率均呈显著正相关关系,最大导管直径与潜在最大导水率呈显著正相关关系,但非抗旱树种不存在这些关系。本研究抗旱树种同时具有较大的最大导管直径和较厚的导管壁,在保证较高的水分运输效率的同时又具备一定的抗栓塞能力,较多的旁管薄壁组织和NSC也为抗旱树种提供了更大的木质部水储存和栓塞修复能力。     

Stem diameter variations and cold hardiness in walnut trees

The effect of freezing temperatures on stem diameter was measured in the field and in climatic chambers using linear variable differential transformers (LVDT sensors). In acclimated stems, there was reversible stem shrinkage associated with freeze-thaw cycles. The maximum shrinkage correlated with stem diameter (thickness of the bark). The wood was responsible for only 15% of the shrinkage associated with a freeze event, and experiments with isolated bark showed that connection with the wood was not necessary for most of the freeze-induced shrinkage to occur. Considering the amount of stem shrinkage associated with summer drought in walnut, the amount of contraction of the bark with freezing was actually much less than might be predicted by water relations theory. Reversible stem shrinkage occurred in living tissues, but not in autoclaved tissues. For the latter, swelling was observed with freezing and this swelling could be explained by the bark alone. Similar swelling was observed during September and October for non-acclimated plants. Water was lost with each freeze-thaw cycle starting with the first, and freezing injury of the bark, with discoloration of tissues, was also observed in non-acclimated plants. Given that the diameter fluctuation patterns were dramatically different for acclimated versus non-acclimated plants, and for living versus autoclaved tissues, LVDT sensors could represent a novel, non-invasive approach to testing cold hardiness.     

不同土壤水分条件下中国沙棘雌雄株叶片形态结构及生理生化特征

在不同土壤水分条件下,对中国沙棘雌雄株叶片的形态结构以及生理生化特征进行了研究.结果表明： 在土壤水分条件较差时,中国沙棘雌雄株的叶片结构旱化特征较明显,并且雌株的叶片厚度、上下表皮厚度、侧脉维管束距离均较小,而下表皮毛厚度、密度和栅栏组织与海绵组织的比值均较大,表现出较强的干旱适应性和生态可塑性;雌雄株叶片的游离脯氨酸、可溶性糖和丙二醛含量升高,其中雌株叶片的游离脯氨酸和可溶性糖含量上升幅度大于雄株,而雄株叶片的丙二醛含量上升幅度明显大于雌株.随着土壤水分条件的改变,雌雄株叶片的超氧化物歧化酶和过氧化氢酶活性变化较大.在干旱胁迫下,中国沙棘雌株的生理生化指标多元隶属度值大于雄株.雌株对干旱胁迫的适应性和生理调节能力更强.     

田菁营养器官的解剖结构特征

运用石蜡切片法与组织离析法研究田菁营养器官解剖结构特征。结果表明,田菁根部显示典型的次生结构特征,内皮层具凯氏带;根表面有大量根瘤,根瘤菌分布在根部皮层,维管组织相连形成输导组织网。茎部表皮细胞壁出现角质层,皮层含有特化的厚角组织,由大型薄壁细胞构成,维管组织具有含晶韧皮纤维。茎瘤3～4个,大小不等且不连续分布,茎瘤外层为皮层,内层为含菌组织。叶片为异面叶,角质层与表皮层较厚,栅栏组织发达,近叶厚的1/2,海绵组织细胞间隙大,气孔小且多。田菁根、茎的木质部发达,有较多大孔径的导管及丰富的木纤维,叶片栅海比、组织结构紧密度(CTR)较大。田菁的解剖特点显示出其具有的固氮特性以及耐盐、抗旱的生态适应性。     

Linking wood anatomy with growth vigour and susceptibility to alternate bearing in composite apple and pear trees

• Excess vegetative growth and irregular fruit‐bearing are often undesirable in horticultural practice. However, the biological mechanisms underlying these traits in fruit trees are not fully understood. Here, we tested if growth vigour and susceptibility of apple and pear trees to alternate fruit‐bearing are associated with vascular anatomy.
• We examined anatomical traits related to water transport and nutrient storage in young woody shoots and roots of 15 different scion/rootstock cultivars of apple and pear trees. In addition, soil and leaf water potentials were measured across a drought period.
• We found a positive correlation between the mean vessel diameter of roots and the annual shoot length. Vigorously growing trees also maintained less negative midday leaf water potential during drought. Furthermore, we observed a close negative correlation between the proportions of total parenchyma in the shoots and the alternate bearing index.
• Based on anatomical proxies, our results suggest that xylem transport efficiency of rootstocks is linked to growth vigour of both apple and pear trees, while limited carbohydrate storage capacity of scions may be associated with increased susceptibility to alternate bearing. These findings can be useful for the breeding of new cultivars of commercially important fruit trees.

     

海南龙血树的形态组织学研究

采用植物解剖学、显微切片技术等,分别对海南龙血树含有树脂的茎、不含树脂的茎、幼根和叶片等进行了系统的组织学研究。结果表明：老茎主要由栓化层、皮层、形成层和基本组织4部分组成,树脂主要分布在基本组织内维管束的导管和纤维中。叶片为等面叶,气孔主要分布在下表皮上、具有明显的孔下室,上下表皮内侧分布着大量的纤维束。幼根由根被细胞、皮层和维管柱组成。根、茎、叶的部分薄壁细胞中均含有晶束。海南龙血树营养器官的结构特征与干旱、高温和贫瘠的生态环境相适应。这些结果可为海南龙血树的开发和利用提供基本的解剖学证据。     

The nature of plant adaptations to salinity stress has trophic consequences

In different ecosystems herbivores highly prefer particular plant species. This is often explained in a stoichiometric framework of nutrient‐based plant adaptations to herbivory. We hypothesize that such super‐palatability can also arise as an evolutionary by‐product of osmoregulatory adaptations of plants to stressful environmental conditions, as salinity, drought and cold. Here, we investigate in a coastal salt marsh why some plant species are highly preferred by migratory brent geese Branta bernicla bernicla in spring while others are avoided. This salt marsh is an important spring staging site for the geese. Sufficient energy storage in a short period is critical to enable their northward migration to Siberia and subsequent reproduction. We test if geese prefer plants that balance their internal osmotic potential with the saline environment through energy‐rich soluble sugars over plant species that use (compartmentalized) salts for this. We find that plant nitrogen and acid detergent fiber content, classic predictors of herbivore preferences, poorly explain which plants the geese prefer. Instead, plant species that are highly preferred by the geese adapt to salinity by high soluble sugar concentrations while avoided species do this by high plant salt concentrations. Thus, the type of osmoregulatory adaptation to stress displayed by different plant species is a good predictor for the food preference of geese on this salt marsh. We suggest that variation in other types of osmoregulation‐based stress adaptations, as plant cold adaptations in tundras and plant drought adaptations in savannas, have similar important consequences for trophic interactions.     

Mechanical Properties of the Rhizome of Arundo donax L.

Abstract: The mechanical properties of rhizome segments of Arundo donax L. were studied in three dimensions: longitudinal (X), transverse-vertical (Y), transverse-horizontal (Z). Tensile, cyclic loading and torsional tests demonstrate that the distinct anisotropy found in the hollow stems is less pronounced in the rhizome. Morphological and anatomical examinations suggest that the mechanical anisotropy of the stem is caused by the arrangement parallel to the stem of the vascular bundles and sclerenchymatous fibres, embedded in lignified parenchyma. Anatomical inhomogeneity is less pronounced in the rhizome due to the short internode lengths, and predominance of nodal regions, where sclerenchymatous fibres form a complex three-dimensional arrangement embedded in unlignified starch-storing parenchyma. Cyclic loading experiments indicate viscoelastic behaviour of the rhizomatous tissues under tensile stress. Additionally, viscoelastic behaviour under torsional stress was studied. Mechanical behaviour of the rhizome under tension up to fracture is discussed with regard to the fracture surfaces, analysed by SEM.     

Induction of Frost Hardiness in Stem Cortical Tissues of Cornus stolonifera Michx. by Water Stress: I. Unfrozen Water in Cortical Tissues and Water Status in Plants and Soil

Water supply and day length were varied in cold hardiness studies of red osier dogwood plants (Cornus stolonifera Michx.). The frost killing temperature, the content and freezing of stem cortical tissue water along with soil moisture content and tension were evaluated. Seven days of water stress in long and short day photoperiod regimes caused a rapid decrease in soil moisture content and plant water potential. During the same period, the frost hardiness increased from −3 to −11 C. Further water stress treatment had little effect. Control plants in short days showed only a gradual decrease in plant water potential and only gradually increased in frost hardiness while control plants in long days were unchanged. Freezing studies using nuclear magnetic resonance showed that increased hardiness in water-stressed plants resulted from both an increased tolerance of freezing and an increased avoidance of freezing, the latter resulting from higher solute concentration in the tissue solutions. The short day controls also showed similar changes; however, the changes were smaller over the 21 days of the study.     

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。     

酸枣叶片结构可塑性对自然梯度干旱生境的适应特征

叶片是植物体暴露于环境中面积最大的器官,其最易感知环境变化而发生形态和结构上的改变。为探究植株叶片结构对不同生境的适应机理,研究以生长在烟台-石家庄-宁夏-新疆不同地域气候条件形成的自然梯度干旱环境中的酸枣为试验材料,应用植物显微技术研究酸枣叶片的结构的可塑性对不同自然梯度干旱环境的适应特征。结果表明:酸枣叶表皮着生有表皮毛,表皮细胞外覆有角质层与蜡质。叶肉为全栅型,栅栏组织发达,海绵组织退化,叶肉中有晶体及大量的分泌细胞。从烟台至新疆随生境梯度干旱加剧,酸枣叶片叶面积逐渐变小,叶片厚度依次增加,叶表皮角质层加厚,且上角质层厚度大于下角质层厚度;叶片上下表皮细胞长径及短径先增后降,栅栏组织总厚度和密度依次增大、层数减少,各层栅栏组织细胞的长径逐渐增加。叶脉薄壁细胞相对厚度逐渐减小,导管管径增大,晶体(草酸钙晶体)数增多。在梯度干旱环境中酸枣植株通过减小叶面积、提高栅栏组织密度、增加叶片及角质层厚度降低蒸腾作用,减少水分散失;通过增大导管管径提高水分利用率;通过增加晶体数量提高叶片机械性能,改变细胞的渗透势、提高吸水和保水能力。上述叶片结构的变化是酸枣植株长期对不同自然梯度干旱生境的适应特征。由此可知,叶片形态结构中叶面积、叶片厚度、角质层及叶肉组织(栅栏组织)随环境变化的可塑性较大。     

Drought resistance in early and late secondary successional species from a tropical dry forest: the interplay between xylem resistance to embolism,sapwood water storage and leaf shedding

The mechanisms of drought resistance that allow plants to successfully establish at different stages of secondary succession in tropical dry forests are not well understood. We characterized mechanisms of drought resistance in early and late‐successional species and tested whether risk of drought differs across sites at different successional stages, and whether early and late‐successional species differ in resistance to experimentally imposed soil drought. The microenvironment in early successional sites was warmer and drier than in mature forest. Nevertheless, successional groups did not differ in resistance to soil drought. Late‐successional species resisted drought through two independent mechanisms: high resistance of xylem to embolism, or reliance on high stem water storage capacity. High sapwood water reserves delayed the effects of soil drying by transiently decoupling plant and soil water status. Resistance to soil drought resulted from the interplay between variations in xylem vulnerability to embolism, reliance on sapwood water reserves and leaf area reduction, leading to a tradeoff of avoidance against tolerance of soil drought, along which successional groups were not differentiated. Overall, our data suggest that ranking species' performance under soil drought based solely on xylem resistance to embolism may be misleading, especially for species with high sapwood water storage capacity.     

干旱胁迫下紫穗槐叶片解剖特征的变化

研究了重度、中度、轻度干旱胁迫条件下2年生紫穗槐幼苗叶片的形态解剖学特征变化.结果表明:随着干旱胁迫程度的增加,叶片厚度、上下表皮的厚度逐渐减小,栅栏组织和海绵组织的厚度也减小,而栅栏组织与海绵组织的比值、主脉维管束相对直径、主脉突起度与中脉厚度则增大.气孔面积随干旱程度的增加呈下降趋势,但气孔分布的密度增加.在干旱逆...     

Possible Mechanisms Limiting Movement of Ralstonia solanacearum in Resistant Tomato Tissues

The distribution and appearance of Ralstonia solanacearum in the upper hypocotyl tissues of root‐inoculated tomato seedlings of resistant rootstock cultivar LS‐89 (a selection from Hawaii 7998) and susceptible cultivar Ponderosa were compared to clarify the mechanism that limits the movement of the bacterial pathogen in resistant tomato tissues. In stems of wilted Ponderosa plants, bacteria colonized both the primary and the secondary xylem tissues. Bacteria were abundant in vessels, of which the pit membranes were often degenerated. All parenchyma cells adjacent to vessels with bacteria were necrotic and some of them were colonized with bacteria. In stems of LS‐89 plants showing no discernible wilting symptoms, bacteria were observed in the primary xylem tissues but not in the secondary xylem tissues. Necrosis of parenchyma cells adjacent to vessels with bacteria was observed occasionally. The pit membranes were often thicker with high electron density. The inner electron‐dense layer of cell wall of parenchyma cells and vessels was thicker and more conspicuous in xylem tissues of infected LS‐89 than in xylem of infected Ponderosa or mock‐inoculated plants. Electron‐dense materials accumulated in or around pit cavities in parenchyma cells next to vessels with bacteria, and in vessels with bacteria. Many bacterial cells appeared normal in vessels, except for those in contact with the pit membranes. These results indicate that R. solanacearum moves from vessel to vessel in infected tissues through degenerated pit membranes and that restricted movement in xylem tissues was the characteristic feature in LS‐89. The limitation in bacterial movement may be related to the thickening of the pit membranes and/or the accumulations of electron‐dense materials in vessels and parenchyma cells.     

高寒地区不同海拔藏茴香茎解剖结构比较研究

采用石蜡切片法,分别对5种不同海拔高度藏茴香茎初生解剖结构进行比较研究,并用一维和二维(面积)的度量指标进行观测,以期探索随海拔升高,藏茴香茎结构的变化规律,从而探讨藏茴香对高寒气候的适应性,为藏茴香这一食用、药用植物资源开发利用提供基础资料。结果表明:藏茴香茎的初生结构由表皮、皮层、维管柱构成,随着海拔升高,藏茴香茎的表皮厚度、髓厚度、髓射线宽度以及通气组织的面积逐渐增加,而维管组织与基本组织的比值不断缩小,皮层的细胞层数、厚度逐渐下降;维管束的数量、厚度不断降低,但维管束的发育程度和导管的直径有逐渐增加的趋势。藏茴香茎表皮的不断增厚,可以减少植物体内热量的散失,并有效地降低强紫外线对植物造成的伤害。基本组织比例的增加,有利于贮藏更多的生理调节性物质,增加植物的抗寒能力;通气组织逐渐发达,可极大地降低空气在植物体内的扩散阻力,形成氧气由地上部运输到地下部的通道,还可增加植物体的浮力,减轻了植物体比重,对植物体起到了良好的支撑作用。藏茴香茎解剖结构随海拔的变化,体现了植物对环境的适应性。研究中发现的随着海拔升高,茎皮层的细胞层数和厚度以及茎中维管束的数量和厚度均下降,但维管束的发育程度和导管直径增加的现象,还有待于进一步研究。     

Co-ordination between xylem anatomy,plant architecture and leaf functional traits in response to abiotic and biotic drivers in a nurse cushion plant

Background and AimsPlants in dry Mediterranean mountains experience a double climatic stress: at low elevations, high temperatures coincide with water shortage during summer, while at high elevations temperature decreases and water availability increases. Cushion plants often act as nurses by improving the microclimate underneath their canopies, hosting beneficiary species that may reciprocally modify their benefactors’ microenvironment. We assess how the nurse cushion plant Arenaria tetraquetra subsp. amabilis adjusts its hydraulic system to face these complex abiotic and biotic constraints.MethodsWe evaluated intra-specific variation and co-ordination of stem xylem anatomy, leaf functional traits and plant architecture in response to elevation, aspect and the presence of beneficiary species in four A. tetraquetra subsp. amabilis populations in the Sierra Nevada mountains, southern Spain.Key ResultsXylem anatomical and plant architectural traits were the most responsive to environmental conditions, showing the highest mutual co-ordination. Cushions were more compact and had smaller, more isolated conductive vessels in the southern than in the northern aspect, which allow minimization of the negative impacts of more intense drought. Only vessel size, leaf mass per area and terminal branch length varied with elevation. Nurse cushions co-ordinated plant architecture and xylem traits, having higher canopy compactness, fewer leaves per branch and fewer, more isolated vessels than non-nurse cushions, which reflects the negative effects of beneficiary plants on nurse water status. In non-nurse cushions, plant architecture co-ordinated with leaf traits instead. The interacting effects of aspect and elevation on xylem traits showed that stress due to frost at high elevation constrained xylem anatomy in the north, whereas stress due to drought had a parallel effect in the south.ConclusionsTrait co-ordination was weaker under more demanding environmental conditions, which agrees with the hypothesis that trait independence allows plants to better optimize different functions, probably entailing higher adjustment potential against future environmental changes.