<Emphasis Type="Italic">Humulus japonicus</Emphasis> Accelerates the Decomposition of <Emphasis Type="Italic">Miscanthus sacchariflorus</Emphasis> and <Emphasis Type="Italic">Phragmites australis</Emphasis> in a Floodplain

Humulus japonicus in communities of Miscanthus sacchariflorus and Phragmites australis can grow large enough to overtop other species in the Amsa-dong floodplain. Because of strong winds and the weight of Humulus, plants of M. sacchariflorus and P. australis fell in mid-August and were subject to decomposition under its dense shading. To assess the effects of H. japonicus on nutrient cycling in these communities, we collected fresh samples of M. sacchariflorus and P. australis in litterbags and decomposed them under H. japonicus for 9 months, beginning in August. Biomass and organic contents from M. sacchariflorus during this incubation period were 49–51% and 44–48%, whereas those of P. australis were 49–61% and 32–52%, respectively. Their annual k values were 1.61–1.74 and 1.46–3.54, respectively. Initial N concentrations in M. sacchariflorus and P. australis were 13 and 20 mg g⁻¹, while C:N ratios were 31 and 21, respectively. These results indicate that H. japonicus is responsible for the collapse of M. sacchariflorus and P. australis in August and also accelerates their nutrient cycling through rapid decomposition, thereby increasing nutrient circulation in floodplains.     

Water Use Efficiency and Biomass Partitioning of Three Different Miscanthus Genotypes with Limited and Unlimited Water Supply

Miscanthus species, which are C₄perennial grasses, have a highbiomass potential but yields at many sites in Europe can belimited by insufficient water supply and plant survival is endangeredunder extreme summer drought. A pot experiment was conductedto measure the influence of reduced water supply on the wateruse efficiency (WUE) and biomass partitioning of three Miscanthusgenotypes (M. x giganteus, M. sacchariflorus, and a M. sinensishybrid) in a controlled environment. The experiment consistedof three phases (phase 1 = 0–20 d; phase 2 = 21–39d; phase 3 = 40–54 d) punctuated by destructive harvests.In phase 1, soil moisture was non-limiting. In the second andthird phases, lowered soil moisture contents induced water deficits.Air vapour pressure deficit (VPD) was 0.49 ± 0.05 kPa.Water deficits caused leaf senescence in M. x giganteus andM. sacchariflorus, but not in the M. sinensis hybrid. Greenleaf conductances were lowest in M. sinensis under water deficit,indicating stomatal regulation. Water use efficiency for wholeplants of each genotype ranged from 11.5 to 14.2 g dry matter(DM) kg^-1H₂O but did not differ significantly between genotypesor water treatments under the conditions of this experiment.However, differences in dry matter partitioning to the shoot(the harvestable component) resulted in genotypic differencesin WUE, calculated on a harvestable dry matter basis, whichranged from 4.1 g DM kg^-1H₂O for M. sacchariflorus to 2.2 gDM kg^-1H₂O for M. x giganteus. Copyright 2000 Annals of BotanyCompany Miscanthus sinensis, Miscanthus sacchariflorus, Miscanthus x giganteus, water use efficiency, biomass, C₄plants, drought     

Mapping potential habitats of threatened plant species in a moist tall grassland using hyperspectral imagery

We examined the capability of hyperspectral imagery to map habitat types of under-storey plants in a moist tall grassland dominated by Phragmites australis and Miscanthus sacchariflorus, using hyperspectral remotely-sensed shoot densities of the two grasses. Our procedure (1) grouped the species using multivariate analysis and discriminated habitat types (species groups) based on P. australis and M. sacchariflorus shoot densities, (2) used estimated shoot densities from hyperspectral data to draw a habitat type map, and (3) analyzed the association of threatened species with habitat types. Our identification of four habitat types, using cluster analysis of the vegetation survey coverage data, was based on P. australis and M. sacchariflorus shoot density ratios and had an overall accuracy of 77.1% (kappa coefficient = 0.71). Linear regression models based on hyperspectral imagery band data had good accuracy in estimating P. australis and M. sacchariflorus shoot densities (adjusted R ² = 0.686 and 0.708, respectively). These results enabled us to map under-storey plant habitat types to an approximate prediction accuracy of 0.537. Among the eight threatened species we examined, four exhibited a significantly biased distribution among habitat types, indicating species-specific habitat use. These results suggest that this procedure can provide useful information on the status of potential habitats of threatened species.     

Anatomy of Ricciocarpus natans (L.) Corda, Studied by Scanning Electron Microscopy

The anatomy of the vegetative thallus in the life-forms of theamphibious liverwort Ricciocarpus natans was studied by scanningelectron microscopy. Particular attention was given to the structureof the epidermal stomatoid pores and the minute internal poresin the aerenchyma. The aquatic and terrestrial life-forms werefound to differ in (1) number and size of ventral scales, (2)presence of rhizoids and (3) width of the thallus margin. scanning electron microscopy, Ricciocarpus natans (L.) Corda, Bryophyta, liverwort, stomatoid pores, aerenchyma, structural adaptations     

Vertical differences in Phragmites australis culm anatomy along a water depth gradient

We reported on quantitative anatomical comparisons of reed culms grown under a wide range of water depth (from −10 to +230 cm). The study focused mainly on the above water parts of ramets, but also provided an insight into the submerged internodes. Investigated anatomical features were: radial thickness of the internode wall and that of each tissue constituting it (epidermis and subepidermal tissues, aerenchyma channels, cortical sclerenchyma and parenchyma); areas of aerenchyma channels and the summed transversal area of them; areas of the innermost vascular bundles involving the bundle sheath sclerenchyma, phloem and metaxylem vessels; the cross-sectional area of the pith cavity and that of the internode wall. After a 2–3% decrease below the uppermost internode, the thickness of internode tissues, except for cortical sclerenchyma, continuously increased downwards. Quantitative differences between the ramets grown at different water depths were observed only from the lower aerial internodes. Parenchyma taking part considerably in the mechanical stability of culms with its large extension and thick cell walls was more-layered and thicker (with the maximum thicknesses of approximately 1200 and 1000 μm) in ramets from 180–200 than from 20–30 cm water depth. Areas of the innermost vascular bundles increased downwards and decreased after a maximum value appearing in lower internodes of ramets grown in deeper than shallower water. Aerenchyma channels appeared farther up from the water surface in culms in shallower than deeper water: the top ends were found about 50 cm higher in culms from 20–30 than from 180–200 cm water depth. Along the transect at right angles to the shore, the radial thickness and area of aerenchyma channels were higher in ramets grown in medium water depth—the summed transversal area of them was greater than 4 mm² in internodes at the water surface, while plants from the two ends of the water depth gradient had smaller aerenchyma channels (with approximately 1 mm² total areas). In contrast, pith cavity area at the water surface continuously increased – up to 60 mm² – from shallower to deeper water. Therefore, oxygen transport in ramets grown at the open water fringe of stands may occur mostly in the pith cavity.     

Effects of oil on internal gas transport, radial oxygen loss, gas films and bud growth in Phragmites australis

Background and Aims

Oil pollution of wetlands is a world-wide problem but, to date, research has concentrated on its influences on salt marsh rather than freshwater plant communities. The effects of water-borne light oils (liquid paraffin and diesel) were investigated on the fresh/brackish wetland species Phragmites australis in terms of routes of oil infiltration, internal gas transport, radial O₂ loss (ROL), underwater gas films and bud growth.

Methods

Pressure flow resistances of pith cavities of nodes and aerenchyma of leaf sheaths, with or without previous exposure to oil, were recorded from flow rates under applied pressure. Convective flows were measured from living excised culms with oiled and non-oiled nodes and leaf sheaths. The effect of oil around culm basal nodes on ROL from rhizome and root apices was measured polarographically. Surface gas films on submerged shoots with and without oil treatment were recorded photographically. Growth and emergence of buds through water with and without an oil film were measured.

Key Results

Internodes are virtually impermeable, but nodes of senesced and living culms are permeable to oils which can block pith cavity diaphragms, preventing flows at applied pressures of 1 kPa, natural convective transport to the rhizome, and greatly decreasing ROL to phyllospheres and rhizospheres. Oil infiltrating or covering living leaf sheaths prevents humidity-induced convection. Oil displaces surface gas films from laminae and leaf sheaths. Buds emerge only a few centimetres through oil and die.

Conclusions

Oil infiltrates the gas space system via nodal and leaf sheath stomata, reducing O₂ diffusion and convective flows into the rhizome system and decreasing oxygenation of phyllospheres and rhizospheres; underwater gas exchange via gas films will be impeded. Plants can be weakened by oil-induced failure of emerging buds. Plants will be most at risk during the growing season.Key words: Phragmites australis, oil pollution, convective flow, pressure flow resistance, phyllosphere oxygenation, rhizosphere oxygenation, underwater gas films, bud emergence, stomata, pith cavity diaphragms, leaf sheath aerenchyma, rhizome aeration     

The Tolerance and Accumulation of Miscanthus Sacchariflorus (maxim.) Benth., an Energy Plant Species,to Cadmium

Miscanthus sacchariflorus (Maxim.) Benth. is a metallophyte suitable for the phytoremediation of mine wastes. The tolerance and accumulation of M. sacchariflorus to cadmium was studied by pot experiments. The results showed that O₂·^? generation rate, plasma membrane permeability and MDA content of M. sacchariflorus leaves increased with increasing Cd concentrations in soil, but significant effect was only observed when Cd concentrations were ≥ 50 mg·kg^?1. SOD and POD activities increased initially but decreased later on, whereas CAT activity only increased significantly at higher Cd concentrations, 50–100 mg·kg^?1. The content of photosynthetic pigment and growth of M. sacchariflorus were both not significantly affected when Cd concentration was ≤ 25 mg·kg^?1. In contrast, both parameters were significantly affected when Cd concentration was ≥ 50 mg·kg^?1. M. sacchariflorus could accumulate much Cd, but most of the Cd assimilated was retained in the belowground part, suggesting that M. sacchariflorus has poor ability to translocate Cd to the aboveground part. Our results suggested that although M. sacchariflorus was not a hyper-accumulator, it has a strong capacity to tolerate and stabilize the Cd. Therefore, M. sacchariflorus has a certain potential in the phytostabilization of Cd-contaminated soils.     

Assessment of Regeneration Potential in the Clonal Macrophyte Miscanthus sacchariflorus (Poaceae) after Burial Disturbance Based on Bud Bank Size and Sprouting Capacity

The demography of the bud bank and its sprouting capacity are important for understanding the population dynamics of clonal plants and their potential responses to disturbances. To this end, we investigated the size and composition of the bud bank of Miscanthus sacchariflorus (Maxim.) Hack. immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the wetlands of Dongting Lake. We then examined the sprouting capacity of axillary buds after sediment burial at 0, 5, 10, 15, and 20 cm. Total bud density of M. sacchariflorus ranged from 2524 buds m^-2 in November to 4293 buds m^-2 in March. Rhizome segments with inactive axillary buds, which represented the majority of the bud population (88.7% in November, 93.3% in May), did not sprout during the 140 days of the experiment (n = 250). The sprouting ratio was the highest for active axillary buds buried at 0 cm (64%) and decreased when buried at 10–20 cm (34%–40%). Due to the large number of active axillary buds in the bud bank (211–277 buds m^-2 from November to the following March), M. sacchariflorus could completely replace its aboveground shoot population, except in May (142 buds m^-2). Increasing burial depth delayed bud emergence and reduced the growth period of shoots; however, burial depth did not affect the resulting plant height and only reduced the accumulated biomass at 20 cm. Therefore, the belowground bud bank and its strong sprouting capacity are important factors in the maintenance of local populations and colonization of new habitats for M. sacchariflorus after burial disturbances. The present methodology, which combined measurements of bud bank demography and sprouting capacity, may reflect the regeneration potential of clonal plants after burial disturbances.     

The effects of breaking or bending the stems of two rhizomatous plants, Phragmites australis and Miscanthus sacchariflorus, on their communities

To understand the effects of disturbance on vegetation, bending and cutting experiments were conducted on two rhizomatous plant species, Phragmites australis and Miscanthus sacchariflorus, in a floodplain area of the Arakawa River, Japan. The plants were damaged in the late development growth stage on 3 August 2004 (August disturbance) and in the middle development growth stage on 29 June 2005 (June disturbance). The severity of the damage was evaluated based on shoot morphology and belowground biomass. The recoveries of the two plants from the flood-like artificial disturbance were compared with undisturbed stands. The morphological response of the shoot was higher after the June disturbance than after the August disturbance in both plants. In contrast, the recovery of belowground biomass in P. australis at the end of the growth season was higher after the August disturbance (87 and 72% for bending and cutting, respectively) compared with the June disturbance (84 and 60% for the same). The recoveries in M. sacchariflorus for the two disturbances showed the opposite trend (73 and 59% for bending and cutting, respectively, after the August disturbance, and 90 and 73% after the same disturbance in June). The study demonstrated that an event like flooding, whether it is breaking or bending, will cause greater damage if it occurs at the late development growth stage in M. sacchariflorus compared with the middle development growth stage. In contrast, P. australis tolerated disturbances up to a certain magnitude; after that, the effect was more severe in the middle development growth stage compared with late development growth stage.     

Electron-probe Microanalysis Studies of Silicon in the Elongating Basal Internodes of Avena sativa (L.), Hordeum sativum (Jess.) and Triticum aestivum (L.)

Silicon deposits in the elongating basal internodes of almostmature, field grown specimens of Avena sativa, Hordeum sativumand Triticum aestivum were investigated using electron-probemicroanalysis. In A. sativa and H. sativum silicon was foundto be confined to the cells in the endodermal layer, being presentwithin the inner tangential and radial walls, and occasionallyin the outer tangential wall. In T. aestivum some silicon wasalso located in walls of cells surrounding the vascular bundles. The anatomy of the internodal tissues is discussed for the threespecies from light micrographs. The endodermal layer is discontinuousin A. sativa and H. sativum, in the former species it partlyextends around individual vascular bundles. In T. aestivum itforms a complete cylinder around the stelar region and alsoshows considerably more thickening of the inner tangential wallthan in the other species. The results are discussed in relation to the anatomy of theinternodal tissues and the possible function of silicon in theendodermis. Avena sativa L., Hordeum sativum Jess, Triticum aestivum L., oat, barley, wheat, silicon deposition, electron-probe microanalysis     

菰适应湿地环境的解剖和屏障结构特征研究

菰(Zizania latifolia)是一种多年生挺水植物,为了探讨该植物根、茎和叶的解剖结构、组织化学及其质外体屏障的通透性生理。该文利用光学显微镜和荧光显微镜,对菰的根、茎、叶进行了解剖学和组织化学研究。结果表明:(1)菰不定根解剖结构由外而内分别为表皮、外皮层、单层细胞的厚壁机械组织层、皮层、内皮层和维管柱;茎结构由外而内分别为角质层、表皮、周缘厚壁机械组织层、皮层、具维管束的厚壁组织层和髓腔。叶鞘具有表皮和具维管束皮层,叶片具有表皮,叶肉和维管束。(2)不定根具有位于内侧的内皮层及其邻近栓质化细胞和外侧的外皮层组成的屏障结构;茎具内侧厚壁机械组织层,外侧的角质层和周缘厚壁机械组织层组成的屏障结构,屏障结构的细胞壁具凯氏带、木栓质和木质素沉积的组织化学特点,叶表面具有角质层。(3)菰通气组织包括根中通气组织,茎、叶皮层的通气组织和髓腔。(4)菰的屏障结构和解剖结构是其适应湿地环境的重要特征,但其茎周缘厚壁层和厚壁组织层较薄。由此推测,菰适应湿地环境,但在旱生环境中分布有一定的局限性。     

Development and Structure of the Root Cortex in Caltha palustris L. and Nymphaea odorata Ait.

Structural features of the mature root cortex and its apoplasticpermeability to dyes have been determined for two dicotyledonouswetland plants of differing habitats: Nymphaea odorata, growingrooted in water and mud, and Caltha palustris, growing in temporalwetlands among cattails. In mature roots, movement of the apoplasticdyes, berberine and safranin, into the roots was blocked atthe hypodermis, indicating the presence of an exodermis. A hypodermiswith an exodermis, i.e. Casparian bands in the outermost uniseriatelayer plus suberin lamellae, is present in both species. InN. odorata, hypodermal walls are further modified with cellulosicsecondary walls. Roots of N. odorata and C. palustris have anendodermis with Casparian bands only. A honeycomb aerenchymais produced by differential expansion in N. odorata and includesastrosclereids and diaphragms, while roots of C. palustris haveno aerenchyma, but some irregular lacunae are found in old roots.These aspects of cortex structure are related to an open meristemorganization, with unusual patterns of cell divisions in certainground meristem cells (called semi-regular hexagon cells) ofN. odorata. The correlation between aerenchyma pattern and hypodermalstructure appears to be related to habitat differences.Copyright2000 Annals of Botany Company Caltha palustris, Nymphaea odorata, root development, cortex, endodermis, aerenchyma, exodermis, hypodermis, permeability, wetland plants     

Comparative study on effects of four energy plants growth on chemical fractions of heavy metals and activity of soil enzymes in copper mine tailings

Four gramineous energy plants, Miscanthus sacchariflorus, M. floridulus, Phragmites australis, and Arundo donax were grown on copper tailings in the field for four years. Their phytoremediation potential was examined in terms of their effects on the fractions of heavy metals and soil enzyme activities. Results showed that plantation of these four gramineous plants has improved the proportion of organic material (OM)-binding fraction of heavy metals in copper tailings as a whole, and reduced the proportion of exchangeable and residual fractions. In particular, M. sacchariflorus growth improved significantly the proportion of the OM-binding fractions of Cu (1.73 times), Cd (1.71 times), Zn (1.18 times), and Pb (3.14 times) (P < 0.05) and reduced markedly the residual fractions of Cu (64.45%), Cd (82.38%), Zn (61.43%), and Pb (73.41%) (P < 0.05). Except for A. donax, the growth of other three energy plants improved the activity of phosphatase, urease and dehydrogenase in copper tailings to some extent. In particular, the activity of soil phosphatase and urease in planted tailings differed significantly from that of control (P < 0.05). The effect of M. sacchariflorus growth on soil enzyme was the highest, followed by P. australis, M. floridulus, and A. donax. The content of each heavy metal fraction in soil was correlated with soil enzyme activities, especially the content of OM-binding fraction, which correlated significantly with the activities of phosphatase, urease and dehydrogenase in soil. According to the effects of four gramineous plants growth on activity of soil enzymes and fractions of heavy metals, M. sacchariflorus had the optimal effects for phytoremediation. Therefore, M. sacchariflorus was a candidate plant with great potential for the revegetation of heavy metal tailings.     

不同生境对苦竹鞭根形态结构及其异速生长的影响北大核心CSCD

鞭根作为竹子吸收养分和水分的主要器官,其形态结构性状与鞭根对养分斑块的敏感性及养分获取能力紧密相关。该研究选取相邻连续的苦竹(Pleioblastus amarus)纯林和苦竹-杉木(Cunninghamia lanceolata)混交林2种林分类型,将其分为苦竹林中心区、苦竹林界面区、混交林界面区和混交林中心区4种生境,测定4种林区生境的苦竹鞭根形态结构性状指标及生物量,比较其间的连续性变化规律,以明确竹子异质性环境下的生态适应策略。结果表明:(1)不同生境下,纯林界面区的苦竹拥有更高的鞭根节点数、根尖数以及更小的根直径;纯林界面区和混交林界面区的苦竹鞭根比根长、比根面积均显著高于纯林中心区,但两个界面区的苦竹鞭根根直径则表现相反。(2)从苦竹纯林中心区至混交林中心区方向,苦竹鞭根生物量呈逐渐降低的趋势,但苦竹林界面区和混交林界面区间差异不显著。(3)生境对苦竹主要鞭根形态结构性状异速增长速率无明显影响,但显著提高了苦竹林界面区鞭根主要形态结构性状的差异性位移量;不同生境下苦竹鞭根形态结构存在显著差异,苦竹纯林界面区的鞭根形态结构可塑性较强,拥有更高的鞭根活性以及更活跃的生理功能。研究发现,生境对苦竹主要鞭根形态结构性状有显著影响,但对其异速增长速率无明显影响;鞭根直径是苦竹获取资源的重要影响因子,异质生境下苦竹趋向于采取增加鞭根面积和降低鞭根直径的策略以最大化地获取资源。     

Leaf Structural Peculiarities in Sarcopoterium spinosum, a Seasonally Dimorphic Subshrub

Extensive investigations on the anatomy of the two leaf typesin a seasonally dimorphic subshrub revealed interesting variationsbetween summer and winter leaves. Summer leaves of Sarcopoteriumspinosum possess a thick epidermis composed of tannin-containingcells and large amounts of mucilage secreted through the innerpericlinal walls towards the mesophyll. A thick cuticle is alsopresent on the surface of the leaf. In winter leaves the epidermalcells produce no mucilage while phenolics are accumulated ingranular form only. Besides these, some other variations betweensummer and winter leaves are also discussed in respect of theability of the plant to withstand the unfavourable Mediterraneanconditions. Seasonal dimorphism, leaf anatomy, Sarcopoterium spinosum     

Seasonal changes in the amount of carbohydrate and crude protein in the rhizome ofMiscanthus sacchariflorus

In the herbaceous perennials, seasonal changes in the amount of reserve substances play an important role in the production processes of whole plants. Mutohet al. (1968) indirectly estimated the amount of reserve substances stored in the rhizome ofMiscanthus sacchariflorus by measuring the bulk density of the rhizome, and found aarked seasonal changes. In the present study seasonal changes in the carbohydrate and crude protein content of the rhizome were determined and the results obtained were compared with the changes in the total amount of reserve substances estimated by means of changes in the bulk density. A good parallel seasonal relationship was confirmed between the amount of consumable carbohydrate determined chemically and the quantity of reserve substances estimated from the changes in bulk density. The total yields of carbohydrate and crude protein were ca. 75% of the available reserve substances estimated from the changes of bulk density for the old rhizomes and ca. 65% for the new rhizomes in the middle of December.     

东北草地异质生境芦苇种群根茎芽年龄结构及输出规律

为明确异质生境条件下芦苇种群根茎芽年龄结构及输出规律,揭示芦苇种群的营养繁殖特性,采用单位土体挖掘取样,分别计数各龄级根茎芽的调查与统计方法,对东北草甸草原草甸土和盐碱土两个生境单优群落芦苇种群根茎芽动态进行比较分析。结果表明,两个生境芦苇种群根茎芽库主要均由6个龄级组成;草甸土生境在6—10月均为增长型年龄结构;盐碱土生境6—7月份为衰退型年龄结构,8月份为稳定型年龄结构,9—10月份为增长型年龄结构。根茎芽数量1—4a普遍以草甸土生境高于盐碱土生境,5—6a普遍以盐碱土生境高于草甸土生境,各龄级根茎芽数量与月份之间均符合y=a+bx直线关系(P0.05)。随着龄级的增加,休眠芽比率呈逐渐下降趋势,而萌发芽比率则呈逐渐上升趋势,5个生育期的休眠芽比率和萌发芽比率与龄级之间均符合y=a+bx直线关系(P0.01)。各龄级根茎的休眠芽具有一个相对稳定的萌发输出过程,草甸土生境根茎休眠芽按每年11%的比率萌发输出,而盐碱土生境根茎休眠芽按每年7%的比率萌发输出。虽然芦苇种群根茎芽年龄结构及年龄谱在异质生境中存在显著差异,但却有着相同的季节变化规律,均以不断形成新根茎的芽来维持着种群的营养繁殖更新。     

ANATOMY AND FINE STRUCTURE OF THE MISTLETOE HAUSTORIUM (PHTHIRUSA PYRIFOLIA). I. DEVELOPMENT OF THE YOUNG HAUSTORIUM

The anatomy and fine structure of the young primary haustorium of Phthirusa pyrifolia (H.B.K.) Eichl. were studied before penetration into the host. The simple internal organization (epidermis, hypodermis, and core parenchyma) which characterizes the radicular disc at germination becomes extremely complex, especially at the distal end of the disc during haustorial development. The epidermis in the area of contact with the host surface develops into an intricate cell zone consisting of lobed and tubular portions. The tubular portions consist of finger-like projections that entwine and form bulbous tips at the contact surface. The tubular portions have unusual wall thickenings while the bulbous tips have exceedingly thin distal walls which possibly break, releasing their contents onto the host's surface. The collapsed layers characteristic of Santalalean haustoria seem to be a result of internal pressures caused by division and expansion of epidermal cells and core parenchyma. Various unusual ultrastructural features are described from the hypodermis, core parenchyma, and contact zone. Particularly striking, but yet unidentified, is a fibrillar material which often completely fills the cells of the core parenchyma in later stages of development.     

Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar lutea

The submerged roots and rhizomes of the aquatic vascular macrophyteNuphar lutea (L.) Sm. are aerated, at least in part, by pressurizedventilation. Depending on temperature differences of up to 5K between the inside of young, just-emerged leaves and the surroundingair, pressure differences of 79 to 100 Pa higher than atmosphericare detectable inside the lacunuous spongy parenchyma of theleaf blades. The pressurization is a consequence of structuralfeatures of leaf tissues separating the air filled spaces ofthe spongy parenchyma from the atmosphere. These tissues areacting as thermo-osmotic partitions. Whereas the dimensionsof the stomatal openings (about 5·6 x 2·4 µm)and of the intercellular spaces of the palisade parenchyma (diametersabout 15 µm) are too large, those of the monolayers ofcells separating the palisade and the spongy parenchyma (diameters:0·7–1·2 µm) are small enough to impedefree gaseous diffusion. This inner non-homogeneous partitioninggives rise to the so-called Knudsen diffusion, a physical phenomenonleading to pressurization of the warmer air inside the spongyparenchyma. The rising pressure difference is strong enoughto establish an air flow through the aerenchyma of the wholeplant and out of the most porous older leaves in which a temperatureinduced pressurization is never detectable. These thermo-osmoticallyactive leaves enhance the influx of air to the rhizome and thediffusion path for oxygen to the roots is shortened to the distancebetween rhizome and root tips. Therefore, pressurized ventilationin Nuphar is seen to be of considerable ecological importancefor plant life in anaerobic environments. Key words: Aeration, leaf anatomy, thermo-osmosis of gases, Nuphar lutea     

Variability and adaptability of Miscanthus species evaluated for energy crop domestication

A growing body of evidence indicates that second‐generation energy crops can play an important role in the development of renewable energy and the mitigation of climate change. However, dedicated energy crops have yet to be domesticated in order to fully realize their productive potential under unfavorable soil and climatic conditions. To explore the possibility of domesticating Miscanthus crops in northern China where marginal and degraded land is abundant, we conducted common garden experiments at multiple locations to evaluate variation and adaptation of three Miscanthus species that are likely to serve as the wild progenitors of the energy crops. A total of 93 populations of Miscanthus sinensis, Miscanthus sacchariflorus, and Miscanthus lutarioriparius were collected across their natural distributional ranges in China and grown in three locations that represent temperate grassland with cold winter, the semiarid Loess Plateau, and relatively warm and wet central China. Evaluated with growth traits such as plant height, tiller number, tiller diameter, and flowering time, the Miscanthus species showed high levels of genetic variation within and between species. There were significant site × population interactions for almost all traits of M. sacchariflorus and M. sinensis, but not M. lutarioriparius. The northern populations of M. sacchariflorus had the highest establishment rates at the most northern site owing to their strong cold tolerance. An endemic species in central China, M. lutarioriparius, produced not only the highest biomass of the three species but also higher biomass at the Loess Plateau than the southern site near its native habitats. These results demonstrated that the wild species harbored a high level of genetic variation underlying traits important for crop establishment and production at sites that are colder and drier than their native habitats. The natural variation and adaptive plasticity found in the Miscanthus species indicated that they could provide valuable resources for the development of second‐generation energy crops.