Morphological responses to water-level fluctuations of two submerged macrophytes,Myriophyllum spicatum and Hydrilla verticillata

Aims Myriophyllum spicatum and Hydrilla verticillata are common submerged macrophytes in the Yangtze River basin. To investigate their tolerances and adaptations to water-level fluctuations, an experiment was conducted in a pond.Methods We designed five different amplitudes of water-level fluctuations as static, ±15, ±30, ±60 and ±90 cm during the 74 days of the experiment. In each amplitude treatment, two cultivation methods were examined as monoculture and mixed culture.Important findings The results showed that M. spicatum had greater morphological responses to water-level fluctuations than H. verticillata. Fluctuating amplitude had significant effects on branch number, shoot length and root dry weight (DW) of M. spicatum, whereas it only had significant effect on branch number of H. verticillata. Both fluctuating amplitude and cultivation method had significant effects on total DW of M. spicatum, which was higher in monoculture than mixed culture. The total DW of H. verticillata was affected by fluctuating amplitude only, and the largest biomass was in the amplitude of ±30 cm. Fruit DW of M. spicatum was largest in the amplitude of ±30 cm, high amplitude of water-level fluctuations would inhibit flowering and seed production. Root DW proportion was significantly affected by fluctuating amplitude and cultivation method in both species, and the root DW proportion of M. spicatum was significantly higher in the amplitude-of ±90 cm. We conclude that moderate amplitude of water-level fluctuations can promote the distribution and growth of both species, and in order to accelerate the restoration of both species in natural habitats, the optimum amplitude should be keep at ±15 to ±30 cm.     

外源NH_4~+对穗花狐尾藻根系形态和养分吸收的影响

在温室内进行静态实验,以原沉积物(CK)和分别添加0.24%和0.48%氯化铵(SN1和SN2)的沉积物作为底质培养沉水植物,探讨了高NH4+环境中穗花狐尾藻的根系形态特征及营养物质积累与干物质分配策略。结果表明,穗花狐尾藻主根直径(0.432-0.518mm)与主根/侧根比率(1.50-4.39)均随着沉积物NH4+含量升高呈现增大趋势,但单株主根总长(31.64-171.67cm)则在高NH4+环境中显著变短;其中,SN2处理中穗花狐尾藻主根数量(8.17条/株)显著低于SN1(14.67条/株)和CK(14.33条/株)处理,而SN1与CK处理之间差异不显著。SN1和SN2处理中穗花狐尾藻植株全氮含量(55.98和55.19mg/g)均显著高于CK(42.89mg/g)处理,而SN1和SN2处理中穗花狐尾藻植株全磷含量(1.63和1.53mg/g)则比CK处理中(3.71mg/g)显著降低。穗花狐尾藻植株干物质积累量(168.17-405.81mg/株)和全磷积累量(0.25-1.51mg/株)均随沉积物NH4+含量升高而显著下降,但植株全氮积累量(9.12-21.08mg/株)则表现为:SN1CKSN2。全氮和全磷在叶片中的分配率都随着沉积物NH+含量升高而显著降低,而在根系和茎秆中分配率则显著增加。     

Measurement of the photorespiratory activity of the submerged aquatic plant Myriophyllum spicatum L.

Abstract The CO₂ compensation concentrations (points) of leaves of the submerged vascular aquatic plant Myriophyllum spicatum L. were determined in a closed aqueous system at pH 7.0 by a gas chromatographic technique and over the range 10–30deg;C were found to range from 36 to 46 cm³m^?3 in medium equilibrated with 21% O₂ (0.03 kgm^?3), and 25 to 35 cm³m^?3 in medium equilibrated with 2% O₂ (0.03 kgm^?3). The rates of true (TPS) and apparent (APS) photosynthesis of leaves were measured in medium equilibrated with 21% O₂ and buffered at pH 7.0, at subsaturating concentrations (12.8–18.8 mmol m^?3) of dissolved inorganic carbor. (DIC) containing H¹⁴CO₃, by determining the initial rates of uptake by the leaves of DIC and ¹⁴C-activity from the medium. The rate of photorespiration, the difference between TPS and APS, was 7.0–13.3% of TPS over the range of 10–25°C and rose to 29% of TPS at 35°C. The magnitude of the compensation point of this plant is therefore similar to, but is much less O₂-sensitive than, those of C₃ plants, and the photorespiratory rate, at DIC concentrations near the CO₂ compensation point, is very low compared to that of C₃ plants.     

根茎型植物扁秆荆三棱对光照强度和养分水平的生长响应及资源分配策略

自然界中光照和养分因子常存在时空变化,对植物造成选择压力。克隆植物可通过克隆生长和生物量分配的可塑性来适应环境变化。尽管一些研究关注了克隆植物对光照和养分因子的生长响应,但尚未深入全面了解克隆植物对光照和养分资源投资的分配策略。以根茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)为研究对象,在温室实验中,将其独立分株种植于由2种光照强度(光照和遮阴)和4种养分水平(对照、低养分、中养分和高养分)交叉组成的8种处理组合中,研究了光照和养分对其生长繁殖及资源贮存策略的影响。结果表明,扁秆荆三棱的生长、无性繁殖及资源贮存性状均受到光照强度的显著影响,在遮阴条件下各生长繁殖性状指标被抑制。且构件的数目、长度等特征对养分差异的可塑性响应先于其生物量积累特征。在光照条件下,高养分处理的总生物量、叶片数、总根茎分株数、长根茎分株数、总根茎长、芽长度、芽数量等指标大于其他养分处理,而在遮阴条件下,其在不同养分处理间无显著差异,表明光照条件可影响养分对扁秆荆三棱可塑性的作用,且高营养水平不能补偿由于光照不足而导致的生长能力下降。光照强度显著影响了总根茎、总球茎及大、中、小球茎的生物量分配,遮阴条件下,总生物量减少了对地下部分根茎和球茎的分配,并将有限的生物量优先分配给小球茎。总根茎的生物量分配未对养分发生可塑性反应,而随着养分增加,总球茎分配下降,说明在养分受限的环境中球茎的贮存功能可缓冲资源缺乏对植物生长的影响。在相同条件下,根茎生物量对长根茎的分配显著大于短根茎,以保持较高的繁殖能力;而总球茎对有分株球茎的生物量分配小于无分株球茎,表明扁秆荆三棱总球茎对贮存功能的分配优先于繁殖功能。研究为进一步理解根茎型克隆植物对光强及基质养分环境变化的生态适应提供了依据。     

Resource allocation in the submerged plant Vallisneria natans related to sediment type, rather than water-column nutrients

1. Phenotypic plasticity in resource allocation by Vallisneria natans was investigated in a greenhouse experiment, using three types of sediment [sandy loam, clay, and a 50 : 50 (by volume) mixture of the two sediments] and two levels of water‐column nutrient. The clay was collected from a highly eutrophic lake in Jiangsu Province, China, and the N and P concentrations applied in nutrient media were at the upper limits observed in most lakes of China. 2. Growth and biomass allocation were significantly affected by sediment type, rather than water‐column nutrients. Plant growth in clay and the mixture were similar, and 2.4–3.4 times higher than that in sandy loam. Compared with the plants grown in clay or the mixed sediments, the plants grown in sandy loam allocated relatively more biomass to root (11–17% versus 7–8% of total biomass), and relatively less to leaf (76–82% versus 86–87% of total biomass). Plastic variations in root area were induced by sediment type alone (P < 0.05), whereas the impacts of sediment type and water‐column nutrients on leaf area were insignificant (P > 0.05). 3. Plant N and P concentrations were significantly affected by both sediment type and water‐column nutrients. Increased nutrient availability in the water column enhanced plant N concentration by 3.5–20.2%, and plant P concentration by 19.1–25.8%. 4. Biomass accumulation and plant nutrient concentration in plants grown in different sediment types and water‐column nutrients indicate that sediment type had more significant impacts on growth and N and P concentrations of V. natans than did water‐column nutrients. Changes in phenotype are a functional response to nutrient availability in sediment, rather than to water‐column nutrients.     

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.     

Signalling mechanisms underlying the morphological responses of the root system to nitrogen in Arabidopsis thaliana

Plants display considerable developmental plasticity in response to changing environmental conditions. The adaptations of the root system to variations in N supply are an excellent example of such developmental plasticity. In Arabidopsis, four morphological adaptations to the N supply have been characterized: (i) a localized stimulatory effect of external nitrate on lateral root elongation; (ii) a systemic inhibitory effect of high tissue nitrate concentrations on the activation of lateral root meristems; (iii) a suppression of lateral root initiation by high C:N ratios, and (iv) an inhibition of primary root growth and stimulation of root branching by external L-glutamate. These responses have provided valuable experimental systems for the study of N signalling in plants. This article will highlight some recent progress made in this direction from studies using the Arabidopsis root system. One recent development of note has been the emerging evidence of a regulatory role of nitrate transporters in some of the responses. It has been reported that the AtNRT1.1 (CHL1) dual-affinity nitrate transporter acts upstream of the ANR1 MADS box gene in mediating the stimulatory effect of a localized nitrate supply on lateral root proliferation. The AtNRT2.1 high-affinity nitrate transporter seems to be involved in the repression of lateral root initiation by high C:N ratios. The systemic inhibitory effect of high nitrate supply on lateral root development, which is mediated by abscisic acid (ABA), may be linked to the recently identified ABA receptor, FCA. The newly discovered root architectural response to external L-glutamate potentially offers a valuable experimental tool for studying the biological function of plant glutamate receptors and amino acid signalling.     

杉木种子萌发及幼苗生长对光强的响应

设置不同光强梯度(透光率分别为100%、40%、20%、10%和5%,光照强度PPFD分别为201.3、77.0、37.5、19.2、9.8 μmol·m^-2·s^-1),研究光对杉木种子萌发和幼苗早期生长的影响,分析杉木种子萌发、幼苗存活、生长、形态响应、生物量积累及其分配格局对不同光环境的响应策略.结果表明: 杉木种子的萌发率、存活率、建植率和萌发指数在不同光强梯度下均有显著差异,且40%的透光率是种子最适萌发条件,萌发率最高,而全光照下存活率和建植率最高;随光照强度的减弱,杉木幼苗茎长增大,根长、子叶长、子叶厚、真叶数呈降低趋势,而基径在各光照强度间无显著差异;总生物量、根生物量、茎生物量、叶生物量均表现为全光照下最大.随着光照强度的减弱,光合组织与非光合组织生物量比、叶生物量比呈降低趋势,茎生物量比呈增加趋势,根冠比和根生物量比无显著差异.弱光环境促进杉木种子萌发,不利于杉木幼苗存活和生长.在弱光环境下,杉木幼苗通过增大茎生物量来提高对弱光环境的耐受力.     

Morphological plasticity of wheat and barley roots in response to spatial variation in soil strength

Root systems of individual crop plants may encounter large variations in mechanical impedance to root penetration. Split-root experiments were conducted to compare the effects of spatial variation in soil strength on the morphological plasticity of wheat and barley roots, and its relationship to shoot growth. Plants of spring barley (Hordeum vulgare cv Prisma) and spring wheat (Triticum aestivum cv Alexandria) were grown for 12 days with their seminal roots divided between two halves of a cylinder packed with sandy loam soil. Three treatment combinations were imposed: loose soil where both halves of the cylinder were packed to 1.1 g cm^–3 (penetrometer resistance 0.3 MPa), dense soil where both halves were packed to 1.4 g cm^–3 (penetrometer resistance 1 MPa), and a split-root treatment where one half was packed to 1.1 and the other to 1.4 g cm^–3. In barley, uniform high soil strength restricted the extension of main seminal root axes more than laterals. In the split-root treatment, the length of laterals and the dry weight of main axes and laterals were increased in the loose soil half and reduced in the dense soil half compared with their respective loose and dense-soil controls. No such compensatory adjustments between main axis and laterals and between individual seminal roots were found in wheat. Variation in soil strength had no effect on the density of lateral roots (number per unit main axis length) in either barley or wheat. The nature and extent of wheat root plasticity in response to variation in soil strength was very different from that in response to changes in N-supply in previous experiments. In spite of the compensatory adjustments in growth between individual seminal roots of barley, the growth of barley shoots, as in wheat, was reduced when part of the root system was in compacted soil.     

Plastic,inquisitive roots and intelligent plants in the light of some new vistas in plant biology

Abstract

Metaphors, such as those used in the title of this article, are often useful for the comprehension of specialised topics in plant biology. A brief attempt is made to elucidate one of these metaphors, plant “intelligence”, as it relates to the plastic responses of roots and root systems to their environment. Tropisms and nastic movements of root apices are two expressions of an inherent plasticity of form exhibited by roots. In soil, roots are exposed to multiple stimuli, many of which can potentially elicit such movements. Hence, a key question is how roots respond to and process the different stimuli which simultaneously reach their surfaces. Assuming that roots always use the same site along their length to express their movement responses, and that they also use an auxin‐based information‐transduction pathway, the most evident choices for the processing of stimuli are that roots either prioritise the various incoming stimuli and respond only to the strongest or they amalgamate stimuli and mount an averaged compromise response to all of them. The proposal that plants may be “intelligent”, especially in respect to their plastic growth responses, is one that draws upon knowledge of this faculty from animal biology. Also implied is that plants and animals are sufficiently similar to share usage of this term “intelligence”. But an alternative view is that plants and animals are sufficiently different and so intelligence is an unfitting term. Following the line of enquiry into creative evolution initiated by Henri Bergson, plants can be viewed differently to animals. The tendency of plants is towards instinctive behaviour rather than intelligent behaviour.     

An automatic system to study the responses of respiration and photosynthesis by submerged macrophytes to environmental variables

An apparatus to measure the rates of respiration and photosynthesis of aquatic plants in water at velocities of up to 200 mm s^–1 in a closed water-flow system with partial recirculation, is described. The temperature, the light regime and the concentration of dissolved oxygen are controlled automatically. Typical results are given for Ranunculus penicillatus var. calcareus which were repeatable between the same season in different years and compared with published data.     

Morphological and rheological properties of the three different species of basidiomycetes Phellinus in submerged cultures

AIMS: The objective of this work was to investigate the morphological and rheological properties in submerged culture of the three different basidiomycetes Phellinus (P. baumii, P. gilvus and P. linteus) that produce pharmacologically important exopolysaccharides (EPS). METHODS AND RESULTS: In flask cultures, pH proved to be a critical factor affecting mycelial growth, morphological change and EPS production. The macroscopic morphologies observed under different pHs in flask cultures were also comparable: i.e. starfish-like pellets with a lesser extent of free mycelium appeared in P. baumii, whereas smooth pellets with higher amounts of free mycelium were observed in P. gilvus and P. linteus. The pelleted fermentations were further characterized in a 5-l stirred-tank fermenter by image analysis with respect to mean diameter, core area and pellet circularity. Phellinus baumii showed the largest pellet size (5.2 mm in diameter), whereas P. linteus had extremely small and spherical pellets. The culture broth of P. baumii and P. gilvus yielded extremely high apparent viscosities, ranging from 5 to 7 Pa s. CONCLUSIONS: Three important species of Phellinus showed significantly different morphological and rheological properties. The morphological variation of the three Phellinus species was closely linked to EPS productivity and the apparent viscosity of the whole broth. SIGNIFICANCE AND IMPACT OF THE STUDY: The morphological change in the three species of Phellinus was a good indicator for identifying cell activity for EPS production. Our finding may be beneficial for further optimization of other fungal fermentation processes for large-scale production of EPS.     

三种高寒植物幼苗生物量分配及性状特征对光照和养分的响应

为了解高寒植物幼苗对生境资源异质性的适应策略,以高寒草甸中常见的3种草本植物大耳叶风毛菊(Saussurea macrota)、甘西鼠尾草(Salvia przewalskii)和千里光(Senecio scandens)为材料,比较研究了这3种植物幼苗对不同光照和养分资源的响应。结果表明:光照和养分异质性显著影响了3种植物幼苗的性状特征和生物量分配,并存在一定的交互影响。随着光照的降低,3个物种的幼苗的生物量和根分配呈现降低趋势,但是其株高、比叶面积、叶分配、茎分配却逐渐升高。在低养分条件下,3个物种幼苗的总生物量、株高、比叶面积和叶分配均降低,而根分配均却显著增加。对于光照和养分资源异质性而言,光照异质性对高寒植物生物量分配和性状特征的改变具有更大的影响。喜阴物种大耳叶风毛菊和喜光物种甘西鼠尾草比中性生境物种千里光表现出了较大的性状特征和生物量分配的可塑性指数。     

Interactive effects of nitrate concentrations and carbon dioxide on the stoichiometry,biomass allocation and growth rate of submerged aquatic plants

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Genes controlling legume nodule numbers affect phenotypic plasticity responses to nitrogen in the presence and absence of rhizobia

We investigated the role of three autoregulation of nodulation (AON) genes in regulating of root and shoot phenotypes when responding to changing nitrogen availability in the model legume, Medicago truncatula. These genes, RDN1‐1 (ROOT DETERMINED NODULATION1‐1), SUNN (SUPER NUMERIC NODULES), and LSS (LIKE SUNN SUPERNODULAOR), act in a systemic signalling pathway that limits nodule numbers. This pathway is also influenced by nitrogen availability, but it is not well known if AON genes control root and shoot phenotypes other than nodule numbers in response to nitrogen. We conducted a controlled glasshouse experiment to compare root and shoot phenotypes of mutants and wild type plants treated with four nitrate concentrations. All AON mutants showed altered rhizobia‐independent phenotypes, including biomass allocation, lateral root length, lateral root density, and root length ratio. In response to nitrogen, uninoculated AON mutants were less plastic than the wild type in controlling root mass ratio, root length ratio, and lateral root length. This suggests that AON genes control nodulation‐independent root architecture phenotypes in response to nitrogen. The phenotypic differences between wild type and AON mutants were exacerbated by the presence of nodules, pointing to resource competition as an additional mechanism affecting root and shoot responses to nitrogen.     

Effects of elevated carbon dioxide concentration and soil temperature on the growth and biomass responses of mountain maple (Acer spicatum) seedlings to light availability

Aims Some shade-tolerant understory tree species such as mountain maple (Acer spicatum L.) exhibit light-foraging growth habits. Changes in environmental conditions, such as the rise of carbon dioxide concentration ([CO₂]) in the atmosphere and soil warming, may affect the performance of these species under different light environments. We investigated how elevated [CO₂] and soil warming influence the growth and biomass responses of mountain maple seedlings to light availability.Methods The treatments were two levels of light (100% and 30% of the ambient light in the greenhouse), two [CO₂] (392 μmol mol^-1 (ambient) and 784 μmol mol^-1 (elevated)) and two soil temperatures (T soil) (17 and 22°C). After one growing season, we measured seedling height, root collar diameter, leaf biomass, stem biomass and root biomass.Important findings We found that under the ambient [CO₂], the high-light level increased seedlings height by 70% and 56% at the low T soil and high T soil, respectively. Under the elevated [CO₂], however, the high-light level increased seedling height by 52% and 13% at the low T soil and high T soil, respectively. The responses of biomasses to light generally followed the response patterns of height growth under both [CO₂] and T soil and the magnitude of biomass response to light was the lowest under the elevated [CO₂] and warmer T soil. The results suggest that the elevated [CO₂] and warmer T soil under the projected future climate may have negative impact on the colonization of open sites and forest canopy gaps by mountain maple.     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

川滇高山栎灌丛萌生过程中的营养元素供应动态

萌生更新是森林更新的重要方式, 是硬叶栎林受到干扰后植被恢复的主要机制。以位于青藏高原东南缘的川西折多山东坡川滇高山栎(Quercus aquifoliodes)灌丛为研究对象, 调查分析了砍伐后灌丛萌生过程中基株根系和萌株生物量动态、营养元素含量, 以及基株根系和土壤对萌株生长过程中的营养元素供应动态。结果表明, 川滇高山栎灌丛平均地上和地下生物量分别为(11.25 ± 0.92) t·hm^-2和(34.85 ± 2.02) t·hm^-2, 具有较大的根冠比(3.10:1); 萌生过程中, 萌株生物量呈线性增加趋势, 以灌丛活细根生物量变化为最大, 其次是活中根和活粗根, 树桩和根蔸生物量变化最小; 萌生过程中, 灌丛细根和中根N、P含量表现为先增加、后降低的变化趋势, 萌生初期树桩、粗根和根蔸中N和K的含量明显下降, 根蔸中Ca含量略有下降, 而P没有明显下降, 根系Mg含量变化幅度较大, 灌丛地下根系储存了较多的营养元素; 土壤、树桩、粗根和根蔸是川滇高山栎灌丛砍伐后0-120天萌生生长的主要营养来源, 砍伐后60天, 萌株生长所需的营养除K元素主要来源于根系外, 其余营养元素主要来源于土壤; 在砍伐后60-120天, 基株根系对萌株生长所需的N、K和Ca贡献较大, 而对P和Mg的贡献较小; 在砍伐后120-180天, 根系除K元素对萌生生长还保持较大的贡献外, 对其余营养元素的贡献均较小。高山栎林管理要注重加强地下根系的保护。