Architecture of the leaf of the greater reed mace, Typha latifolia L

ROWLATT, U. & MORSHEAD, H., 1992. Architecture of the leaf of the greater reed mace, Typha latifolia L. The construction of the leaf of T. latifolia is that of a lightweight cantilever beam of sandwich type mounted vertically. A continuous leaf-handed twist starts at the base of the leaf, proceeds gradually throughout its length and becomes most pronounced toward the tip. It is argued that this construction prevents buckling under natural conditions and injury in storms.     

Typha×glauca Godr.,香蒲属(香蒲科)中国新记录杂种及其形态特征

香蒲属(Typha L.)为多年生水生或沼生草本植物, 种间存在十分普遍的杂交现象, 其中一些杂种在湿地生态系统中有重要的作用。在查阅大量腊叶标本基础上, 结合野外居群生物学工作, 作者发现中国一新记录杂种, 即T.×glauca Godr. (T. angustifolia L.×T. latifolia L.), 并新拟“粉绿香蒲”作该杂种的中文名。对粉绿香蒲的形态特征进行了研究, 讨论了其与亲本水烛和宽叶香蒲的区别, 并给出检索表。     

The hierarchy of chirality

Twisting is a prevalent feature of long, thin vertical leaves; it has been shown that this twist contributes to the mechanical integrity of the leaf. We address the question as to how this twist comes about, and posit that it is a reflection of twist at a lower structural (geometric) level. The stiffness required for maintaining verticality in leaves is due to turgescent parenchyma cells, sometimes thickened epidermis, cuticle, and is generally most significantly contributed to by vascular bundles and fibers. These contain cellulose in the cell walls. Such cellulose chains spiral upward within the cell wall layers which are of a characteristic handedness. This results in an isolated cell behaving mechanically in a chiral manner; specifically elongation (contraction) of a single cell will result in rotation of the cell about its axis of particular handedness. We propose a mathematical model that shows that when cells are mechanically associated in groups, the chiral behavior of the cell will be expressed at larger scales, albeit to a mitigated degree. Thus cell extension during leaf development may explain the characteristic twist of such leaves.     

Fibre cables in the lacunae of Typha leaves contribute to a tensegrity structure

Background and Aims

Cables composed of long, non-lignified fibre cells enclosed in a cover of much shorter thin-walled, crystal-containing cells traverse the air chambers (lacunae) in leaves of the taller species of Typha. The non-lignified fibre cables are anchored in diaphragms composed of stellate cells of aerenchyma tissue that segment the long air chambers into smaller compartments. Although the fibre cables are easily observed and can be pulled free from the porous-to-air diaphragms, their structure and function have been ignored or misinterpreted.

Methods

Leaves of various species of Typha were dissected and fibre cables were pulled free and observed with a microscope using bright-field and polarizing optics. Maximal tensile strength of freshly removed cables was measured by hanging weights from fibre cables, and Instron analysis was used to produce curves of load versus extension until cables broke.

Key Results and Conclusions

Polarized light microscopy revealed that the cellulose microfibrils that make up the walls of the cable fibres are oriented parallel to the long axis of the fibres. This orientation ensures that the fibre cables are mechanically stiff and strong under tension. Accordingly, the measured stiffness and tensile strength of the fibre cables were in the gigapascal range. In combination with the dorsal and ventral leaf surfaces and partitions that contain lignified fibre bundles and vascular strands that are strong in compression, the very fine fibre cables that are strong under tension form a tensegrity structure. The tensegrity structure creates multiple load paths through which stresses are redistributed throughout the 1–3 m tall upright leaves of Typha angustifolia, T. latifolia, T. × glauca, T. domingensis and T. shuttleworthii. The length of the fibre cables relative to the length of the leaf blades is reduced in the last-formed leaves of flowering individuals. Fibre cables are absent in the shorter leaves of Typha minima and, if present, only extend for a few centimetres from the sheath into the leaf blade of Typha laxmannii. The advantage of the structure of the Typha leaf blade, which enables stiffness to give way to flexibility under windy conditions, is discussed for both vegetative and flowering plants.     

Leaf mass loss in wetland graminoids during senescence

Mass loss of senescing leaves is an important part of plant biomass turnover and has consequences for assessment of ecosystem productivity, ecosystem nutrient use efficiency, and plant nutrient resorption efficiency. Data, however, on mass loss are scarce, and often based on leaf area as the reference base. This leads to an underestimation of the mass loss, as leaf area itself shrinks during senescence. Furthermore, the few existing studies have almost exclusively used woody species. The purpose of the present study was twofold: i) to assess leaf mass loss during senescence in herbaceous species, with the example of five wetland graminoids and, ii) to compare two different methods of mass loss assessment (two species). Assuming that leaf length does not change during senescence, we assessed leaf mass per leaf length prior to and after senescence. We also estimated pre‐senescence leaf mass nondestructively based on leaf length, width and thickness. For Typha latifolia and Carex stricta, two species with graminoid type leaves but contrasting leaf structure, both methods delivered almost identical results. After the first assessment of leaf mass on July 7th, T. latifolia leaf mass initially increased by 13%, and then decreased to be 12% below the original mass after senescence. C. stricta leaf mass remained stable until senescence, but decreased then by 33%. In a second experiment, the mass of 100 mm pieces of leaves was measured before and after senescence. Calamagrostis canadensis, Carex rostrata and C. stricta lost 23–57% of their leaf mass during senescence, whereas Glyceria canadensis did not show any mass loss. We conclude that mass loss of senescing leaves of herbaceous plants can be considerable and should not be neglected in studies of productivity, nutrient use efficiency or nutrient resorption. For species with no shrinking leaf length during senescence, mass loss can be measured with leaf length as the base whereas for others, pre‐senescent mass can be estimated on the basis of leaf dimensions.     

Differential responses to salinity help explain the replacement of native Juncus kraussii by Typha orientalis in Western Australian salt marshes

The influence of salinity on Typha orientalis and Juncus kraussii was documented in experiments on germination of seeds and on growth of seedlings and adult, rhizome-bearing plants. Juncus was more salt-tolerant than Typha at all three life-history stages, but salt tolerance increased with plant age for both species. Although seeds of both species germinated at 0 and 5 ppt, the germination data overestimated salt tolerance for Typha. Only the newly emerged seedlings of Juncus were capable of growth after removal from the 5 ppt NaCl solution to fresh water. Typha seedlings that initiated growth at 0 ppt grew well at 5 ppt but not at 10 ppt, while Juncus seedlings were tolerant of 10 ppt. Although the 20 ppt treatment caused high mortality of Juncus seedlings, the 10 ppt treatment mainly reduced growth. Adult plants of Typha, which were collected from the field, survived the 20 ppt treatment, while adult Juncus survived the 40 ppt treatment. The presence of salt (10–40 ppt) shortened the growing season for adult, rhizome-bearing plants of both Juncus and Typha, with a lower maximum and earlier peak in total leaf length and maximum leaf number. Thus, the greater biomass in fresh water was achieved primarily through a longer growth period, rather than a greatly accelerated growth rate. Interactions between the two species were explored in mixed-species culture of both seedlings and adult rhizome-bearing plants. Interspecific interactions were present at low salinity, but results differed for seedlings and adult plants. Typha seedlings failed to outgrow Juncus seedlings (at 5 ppt) but adult plants of Typha outgrew Juncus (at 0 ppt). Relative yields (biomass in mixed/pure pots) for Juncus and Typha seedlings were 0.85 and 0.26 at 5 ppt. Relative yields of adult plants were 0.24 for Juncus and 1.20 for Typha at 0 ppt. For both seedlings and adults, the species that ultimately dominated the mixed-species pots produced just as much total biomass as in pure-species pots, even though initial planting density was half as high. Extrapolating findings to the field situation, it appears that Typha has a narrow regeneration niche. The indication is that Typha could invade Juncus stands only following salinity reduction (allowing seed germination and early seedling growth) and after disturbance disrupts the native vegetation. The combined conditions of prolonged low salinity and open habitat occur where street drains are cut through the salt marsh. The probability of Typha becoming established would be highest in such areas. vegetative expansion would follow with continued freshwater influx, as rhizome-bearing plants gain an interspecific advantage.     

铅锌矿废水中重金属在宽叶香蒲（Typha latifolia）的积累与分布

 本文通过对净化塘系统和对照点的水、土和宽叶香蒲组织的分析结果指出：宽叶香蒲具有较强的忍耐、吸收和积累Pb、Zn等重金属的能力。Pb、Zn等重金属在宽叶香蒲体内的积累数量与分布规律是根>地下茎>叶;老地下茎>嫩地下茎;Pb在叶的分布是老叶>成熟叶>嫩叶。在净化塘系统内,各种重金属在宽叶香蒲根部积累比例最大的是Pb,其次是Zn、Cu、Cd、Ni、Mn。     

Adaptive radiation with regard to nutrient sequestration strategies in the carnivorous plants of the genus Nepenthes

Carnivorous pitcher plants of the genus Nepenthes have evolved a great diversity of pitcher morphologies. Selective pressures for maximizing nutrient uptake have driven speciation and diversification of the genus in a process known as adaptive radiation. This leads to the evolution of pitchers adapted to specific and often bizarre source of nutrients, which are not strictly animal-derived. One example is Nepenthes ampullaria with unusual growth pattern and pitcher morphology what enables the plant to capture a leaf litter from the canopy above. We showed that the plant benefits from nitrogen uptake by increased rate of photosynthesis and growth what may provide competitive advantage over others co-habiting plants. A possible impact of such specialization toward hybridization, an important mechanism in speciation, is discussed.     

Species-specific SSR alleles for studies of hybrid cattails (Typha latifolia x T. angustifolia; Typhaceae) in North America

? Premise: Studies of hybridizing species are facilitated by the availability of species-specific molecular markers for identifying early- and later-generation hybrids. Cattails are a dominant feature of wetland communities, and a better understanding of the prevalence of hybrids is needed to assess the ecological and evolutionary effects of hybridization. Hybridization between Typha angustifolia and T. latifolia produce long-lived clones, known as Typha ×glauca, which are considered to be invasive. Although morphological variation in cattails makes it difficult to recognize early- and later-generation hybrids, several dominant, species-specific RAPD markers are available. Our goal was to find codominant, species-specific markers with greater polymorphism than RAPDs, to identify later-generation hybrids more efficiently. ? Methods: We screened nine SSR (simple sequence repeat) loci that were described from populations in Ukraine, and we surveyed 31 cattail populations from the upper Midwest and eastern USA. ? Key results: Seven SSR loci distinguished the parent taxa and were consistent with known species-specific RAPD markers, allowing easier detection of backcrossing. We used linear discriminant analysis to show that F(1) hybrid phenotypes were intermediate between the parent taxa, while those of backcrossed plants overlapped with the hybrids and their parents. Log(leaf length/leaf width), spike gap length, spike length, and stem diameter explained much of the variation among groups. ? Conclusions: We provide the first documentation of backcrossed plants in hybridizing cattail populations in Michigan. The diagnostic SSR loci we identified should be extremely useful for examining the evolutionary and ecology interactions of hybridizing cattails in North America.     

Microbiology of the phyllosphere: a playground for testing ecological concepts

Many concepts and theories in ecology are highly debated, because it is often difficult to design decisive tests with sufficient replicates. Examples include biodiversity theories, succession concepts, invasion theories, coexistence theories, and concepts of life history strategies. Microbiological tests of ecological concepts are rapidly accumulating, but have yet to tap into their full potential to complement traditional macroecological theories. Taking the example of microbial communities on leaf surfaces (i.e. the phyllosphere), we show that most explorations of ecological concepts in this field of microbiology focus on autecology and population ecology, while community ecology remains understudied. Notable exceptions are first tests of the island biogeography theory and of biodiversity theories. Here, the phyllosphere provides the unique opportunity to set up replicated experiments, potentially moving fields such as biogeography, macroecology, and landscape ecology beyond theoretical and observational evidence. Future approaches should take advantage of the great range of spatial scales offered by the leaf surface by iteratively linking laboratory experiments with spatial simulation models.     

Lifetime return on investment increases with leaf lifespan among 10 Australian woodland species

? Co-occurring species often differ in their leaf lifespan (LL) and it remains unclear how such variation is maintained in a competitive context. Here we test the hypothesis that leaves of long-LL species yield a greater return in carbon (C) fixed per unit C or nutrient invested by the plant than those of short-LL species. ? For 10 sympatric woodland species, we assessed three-dimensional shoot architecture, canopy openness, leaf photosynthetic light response, leaf dark respiration and leaf construction costs across leaf age sequences. We then used the YPLANT model to estimate light interception and C revenue along the measured leaf age sequences. This was done under a series of simulations that incorporated the potential covariates of LL in an additive fashion. ? Lifetime return in C fixed per unit C, N or P invested increased with LL in all simulations. ? In contrast to other recent studies, our results show that extended LL confers a fundamental economic advantage by increasing a plant's return on investment in leaves. This suggests that time-discounting effects, that is, the compounding of income that arises from quick reinvestment of C revenue, are key in allowing short-LL species to succeed in the face of this economic handicap.     

Evolution of the vertebrate twist family and synfunctionalization: a mechanism for differential gene loss through merging of expression domains

Twist genes are essential for embryonic development and are conserved from jellyfish to human. To study the vertebrate twist family and its evolution, the entire complement of twist genes was obtained for 9 representative species. Phylogenetic analysis showed that a single protochordate twist gene was duplicated at least twice before the teleost-tetrapod split to give rise to 3 ancestral genes, which were further duplicated or deleted, resulting in fluctuating number of twist paralogs in different vertebrate lineages. To find whether changes in gene copy number were associated with changes in gene function, embryonic expression patterns of twist orthologs were evaluated against the number of twist paralogs in different species. The results showed evidence for both neo- and subfunctionalization, and, in addition, for loss of an ancestral regulatory gene. For example, in Xenopus, twist2 was lost, but the twist1 paralog acquired, and therefore preserved, twist2 function. A general model is proposed to explain the data. In this process, termed synfunctionalization, one paralog acquires the expression domain(s) of another. The merging may lead to function shuffle. Alternatively, it may leave one paralog redundant and thus subject to deletion--while its function is retained by the surviving paralog(s). Synfunctionalization is a mechanism that, together with neo- and subfunctionalization, may work to establish equilibrium in the number of genes that regulate developmental processes; it may regulate the complexity of regulatory regions as well as gene copy number and therefore may play a role in evolution of gene function and the structure of genome.     

Lignified and nonlignified fiber cables in the lacunae of <Emphasis Type="Italic">Typha angustifolia</Emphasis>

The leaves of Typha are noteworthy in terms of their mechanical properties. We determined the mechanical properties of the fiber cables within the leaf. We found that in vegetative plants, the lignified fiber cables isolated from the leaf sheath and nonlignified fiber cables isolated from the leaf blade of Typha angustifolia differ in their diameter, swelling capacity, Young’s modulus, tensile strength, and break load. These differing properties are related to their contributions to stability in the two regions of the leaf.     

Leaf morphology shift linked to climate change

Climate change is driving adaptive shifts within species, but research on plants has been focused on phenology. Leaf morphology has demonstrated links with climate and varies within species along climate gradients. We predicted that, given within-species variation along a climate gradient, a morphological shift should have occurred over time due to climate change. We tested this prediction, taking advantage of latitudinal and altitudinal variations within the Adelaide Geosyncline region, South Australia, historical herbarium specimens (n = 255) and field sampling (n = 274). Leaf width in the study taxon, Dodonaea viscosa subsp. angustissima, was negatively correlated with latitude regionally, and leaf area was negatively correlated with altitude locally. Analysis of herbarium specimens revealed a 2 mm decrease in leaf width (total range 1-9 mm) over 127 years across the region. The results are consistent with a morphological response to contemporary climate change. We conclude that leaf width is linked to maximum temperature regionally (latitude gradient) and leaf area to minimum temperature locally (altitude gradient). These data indicate a morphological shift consistent with a direct response to climate change and could inform provenance selection for restoration with further investigation of the genetic basis and adaptive significance of observed variation.     

毛竹浸提液对苦槠幼苗生长的化感效应

为探讨毛竹(Phyllostachys edulis)扩张过程中潜在的化感作用,选择苦槠(Castanopsis sclerophylla(Lindl)Schott)为研究对象。采用水浸提的方法,用毛竹茎叶、枯落物和土壤3部分浸提液浇灌苦槠幼苗,以蒸馏水处理作为对照,对比分析质量浓度分别为0.1、0.05、0.02 g/mL的3个浓度梯度浸提液处理下苦槠幼苗生长指标及各项光合生理指标的差异。结果表明,毛竹浸提液对苦槠幼苗苗高、地径和叶绿素相对含量的影响大体上呈现高浓度抑制低浓度促进的双重浓度效应。不同来源毛竹浸提液的化感效应不尽相同,土壤浸提液对苦槠幼苗生长和光合生理均呈现抑制作用,而茎叶、枯落物浸提液低浓度时为促进作用。毛竹潜在的化感作用,在其扩张过程中可能会干扰森林主要树种更新,从而对森林群落产生威胁。     

Leaf hairs: Effects on physiological activity and adaptive value to a desert shrub

Summary The effects of leaf hairs on photosynthesis, transpiration, and leaf energy balance were measured on the desert shrub Encelia farinosa in order to determine the adaptive significance of the hairs. The pubescence reduces leaf absorptance resulting in a reduced heat load, and as a consequence lower leaf temperatures and lower transpiration rates. In its native habitat where air temperatures often exceed 40° C, the optimum temperature for photosynthesis in E. farinosa occurs at 25° C, and at leaf temperatures above 35° C net photosynthesis declines precipitously. An advantage of leaf pubescence is that it allows a leaf temperature much lower than air temperature. As a result, leaf temperatures are near the temperature optimum for photosynthesis and high, potentially lethal leaf temperatures are avoided. However, there is a disadvantage associated with leaf pubescence. By reflecting quanta that might otherwise be used in photosynthesis, the presence of leaf hairs reduces the rate of photosynthesis. A tradeoff model was used to assess the overall advantage of possessing leaf hairs. In terms of the carbon gaining capacity of the leaf, the model predicted that for different environmental conditions different levels of leaf pubescence were optimal. In other words, under aird conditions and/or high air temperatures, leaves of E. farinosa would have a higher rate of photosynthesis by being pubescent than by not being pubescent. The predictions from this model agreed closely with observed patterns of leaf pubescence in the field.C.I.W.-D.P.B. Publication No. 613     

Digital image analysis of Zostera marina leaf injury

Current methods for assessing leaf injury in Zostera marina (eelgrass) utilize subjective indexes for desiccation injury and wasting disease. Because of the subjective nature of these measures, they are inherently imprecise making them difficult to use in quantifying complex leaf injuries from multiple sources. We have developed a method using color digital photography of eelgrass leaves which are then manipulated using image processing programs and analyzed using geographic digital image analysis. The resulting false color images are then assigned by the user into uninjured and injured groupings which may then be reported as a percentage of leaf area affected. If images are rectified, leaf area (cm²) of injured and uninjured leaf segments may be determined. Although this method is time consuming and still requires some subjective judgments, it does allow for precise analysis of highly complex leaf injuries and has the potential to be a substantial improvement over existing leaf injury indexes.     

No evidence for niche segregation in a North American Cattail (Typha) species complex

Interspecific hybridization can lead to a breakdown of species boundaries, and is of particular concern in cases in which one of the parental species is invasive. Cattails (Typha spp.) have increased their abundance in the Great Lakes region of North America over the past 150 years. This increase in the distribution of cattails is associated with hybridization between broad-leaved (Typha latifolia) and narrow-leaved cattails (T. angustifolia). The resulting hybrids occur predominantly as F(1)s, which are known as T. × glauca, although later-generation hybrids have also been documented. It has been proposed that in sympatric populations, the parental species and hybrids are often spatially segregated according to growth in contrasting water depths, and that this should promote the maintenance of parental species. In this study, we tested the hypothesis that the two species and their hybrids segregate along a water-depth gradient at sites where they are sympatric. We identified the two parental species and their hybrids using molecular genetic markers (SSR), and measured shoot elevations (a proxy for water depth) at 18 sites in Southern Ontario, Canada. We found no evidence for niche segregation among species based on elevation. Our data indicate that all three lineages compete for similar habitat where they co-occur suggesting that there is potential for an overall loss of biodiversity in the species complex, particularly if the hybrid lineage is more vigorous compared to the parental species, as has been suggested by other authors.