Geographic and Habitat Origin Influence Biomass Production and Storage Translocation in the Clonal Plant Aegopodium podagraria

Through physiological integration, clonal plants can support ramets in unfavourable patches, exploit heterogeneously distributed resources and distribute resources that are taken up over large areas. Physiological integration generally increases in adverse conditions, but it is not well known which factors determine the evolution of physiological integration. The aim of this study was to investigate if clonal plants from Southern and Northern populations of the clonal herb Aegopodium podagraria differed in physiological integration in terms of translocation of carbon to the rhizomes, and in biomass production using a reciprocal transplant experiment. Aegopodium podagraria from shaded conditions have been suggested to share more resources than clones from open conditions and therefore, plants from forest and open populations within the Southern and Northern regions were included. The regional growing conditions greatly affected biomass production. Plants grown in North Sweden produced more biomass and allocated more biomass to shoots, while plants grown in South Sweden allocated more biomass to rhizomes. There was a regional origin effect as plants originating from North Sweden produced more biomass in both regions. Within the Northern region, plants from shaded habitats translocated more ¹⁴C to the rhizomes, suggesting more storage there than in plants from open habitats. In addition to genetic differentiation in biomass production between Northern and Southern populations, probably as a response to a shorter growing season in the North, there appeared to be genetic differentiation in physiological integration within the Northern region. This shows that both regional and local conditions need to be taken into account in future studies of genetic differentiation of physiological integration in clonal plants.     

Flower removal increases rhizome mass in natural populations of Alstroemeria aurea (Alstroemeriaceae)

Plant architecture and phenotypic plasticity under natural conditions remain little known for many rhizomatous species. This study evaluates, in situ, the plastic responses of Alstroemeria aurea plants from three Patagonian populations to flower or flowering-shoot removal. The size and architecture of treated and untreated plants were assessed. Nutrient contents (N, P and K) were evaluated for rhizomes and roots developed in two successive years. Those plants that were deprived of their inflorescences developed, on average, a heavier rhizome than both control plants and plants from which flowering shoots had been removed. Neither of the two treatments applied altered the number of metamers or the branching pattern of the rhizomes. The contents of N, P and K were higher in rhizomes than in roots. In summer, nutrients were more concentrated in inflorescences and the new rhizome segment than in the rhizome segment developed in the previous year. The idea that fruiting failure in A. aurea promotes resource re-assignment from aerial shoots to rhizomes without altering the architecture of plants is supported. The development of the underground portion of aerial shoots in late summer-autumn allows A. aurea plants to take full advantage of short growth periods, but would impose a limit to plasticity.     

The significance of rhizome connection of semi-shrub Hedysarum laeve in an Inner Mongolian dune,China

Hedysarum laeve, a rhizomatous clonal semi-shrub, commonly dominates the inland dunes in semiarid areas of northern China. This species propagates vegetatively by extension of horizontal woody rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, the plants were experimentally manipulated by cutting rhizome connections and ¹⁴C-labelling techniques were employed to investigate the ecological significance of rhizome connections within the H. laeve clone. Severance of rhizome connections had a great effect on the performance of young ramets within a clone. Young ramets severed from their parent ramets experienced a significant reduction both in ramet growth and vegetative propagation, as compared with the intact young ramets. Within clonal fragments, consisting of three interconnected ramets including a mother ramet, a daughter ramet and a granddaughter ramet, ¹⁴C-photosynthates from the fed leaves of mother ramets were acropetally transported to all clonal component parts. The ¹⁴C-photosynthate translocation within the clonal fragment provides evidence that the young ramets were supported by their parent ramets. Our results suggest that the woody rhizome connections among the interconnected ramets are ecologically and strategically important for the species to grow in the sand dune habitat.     

Rhizome age structure of three populations ofPhragmites australis (Cav.) Trin. ex Steud.: Biomass and mineral nutrient concentrations

The rhizome age structure for populations ofPhragmites australis (Cav.) Trin. exSteud. was determined at three sites of the T?eboň Biosphere Reserve (Czech Republic). These sites were classified according to plant species composition and phosphorus availability as oligotrophic (Branná), mesotrophic (Ro?mberk East) and hypertrophic (Ro?mberk West).P.australis stands at these sites were expanding, stabilized and retreating, respectively. Rhizomes were sampled within the terrestrial parts of the reed stands (at a water depth of about 10 cm). The rhizomes were dated according to the position in the branching hierarchy and to supplementary morphological criteria. The analysis of the branching pattern revealed that at the sites studied, the rhizomes typically branch only once a year. The longest life span of rhizomes (six years) was found for the stable reed population at Ro?mberk East. The reduced rhizome life span at Ro?mberk West (four to five years), accompanied by a reduced branching frequency of horizontal rhizomes, was ascribed to a greater incidence of anaerobic conditions associated with the permanent flooding of the hypertrophic organic soil. The maximum life span of the Branná population (four years) probably corresponds to the total age of the reed population. The concentrations of nitrogen, phosphorus, and potassium in the tissue decreased with rhizome age while those of calcium and magnesium increased. The effect of rhizome age on mineral-nutrient concentrations was more pronounced than the effect of site on these concentrations. The mineral nutrient concentrations were not closely associated with reed performance.     

Partitioning of Photosynthetically Fixed 14CO2 Into Oil and Curcumin Accumulation in Curcuma Longa Grown Under Iron Deficiency

Changes in leaf growth, photosynthetic efficiency, and incorporation pattern of photosynthetically fixed ¹⁴CO₂ in leaves 1 and 2 from plant apex, in roots, and rhizome induced in Curcuma by growing in a solution culture at Fe concentration of 0 and 5.6 g m^–3 were studied. ¹⁴C was incorporated into primary metabolites (sugars, amino acids, and organic acids) and secondary metabolites (essential oil and curcumin). Fe deficiency resulted in a decrease in leaf area, its fresh and dry mass, chlorophyll (Chl) content, and CO₂ exchange rate at all leaf positions. The rate of ¹⁴CO₂ fixation declined with leaf position, maximum being in the youngest leaf. Fe deficiency resulted in higher accumulation of sugars, amino acids, and organic acids in leaves at both positions. This is due to poor translocation of metabolites. Roots and rhizomes of Fe-deficient plants had lower concentrations of total photosynthate, sugars, and amino acids whereas organic acid concentration was higher in rhizomes. ¹⁴CO₂ incorporation in essential oil was lower in the youngest leaf, as well as incorporation in curcumin content in rhizome. Fe deficiency influenced leaf area, its fresh and dry masses, CO₂ exchange rate, and oil and curcumin accumulation by affecting translocation of assimilated photosynthates.     

Carbon allocation during fruiting in Rubus chamaemorus

Background and Aims

Rubus chamaemorus (cloudberry) is a herbaceous clonal peatland plant that produces an extensive underground rhizome system with distant ramets. Most of these ramets are non-floral. The main objectives of this study were to determine: (a) if plant growth was source limited in cloudberry; (b) if the non-floral ramets translocated carbon (C) to the fruit; and (c) if there was competition between fruit, leaves and rhizomes for C during fruit development.

Methods

Floral and non-floral ramet activities were monitored during the period of flower and fruit development using three approaches: gas exchange measurements, ¹⁴CO₂ labelling and dry mass accumulation in the different organs. Source and sink activity were manipulated by eliminating leaves or flowers or by reducing rhizome length.

Key Results

Photosynthetic rates were lower in floral than in deflowered ramets. Autoradiographs and ¹⁴C labelling data clearly indicated that fruit is a very strong sink for the floral ramet, whereas non-floral ramets translocated C toward the rhizome but not toward floral ramets. Nevertheless, rhizomes received some C from the floral ramet throughout the fruiting period. Ramets with shorter rhizomes produced smaller leaves and smaller fruits, and defoliated ramets produced very small fruits.

Conclusions

Plant growth appears to be source-limited in cloudberry since a reduction in sink strength did not induce a reduction in photosynthetic activity. Non-floral ramets did not participate directly to fruit development. Developing leaves appear to compete with the developing fruit but the intensity of this competition could vary with the specific timing of the two organs. The rhizome appears to act both as a source but also potentially as a sink during fruit development. Further studies are needed to characterize better the complex role played by the rhizome in fruit C nutrition.Key words: Allocation pattern, ¹⁴C labelling, carbon translocation, carbon reserves, cloudberry, defoliation, fruit production, gas exchange, Rubus chamaemorus, source–sink relationship, flowering     

DEVELOPMENTAL STUDIES ON THE COENOCYTIC ALGA, CAULERPA SERTULARIOIDES

Thallus growth and development in the coenocyti alga Caulerpa sertularioides (Gmelin) Howe have been studied quantitatively. In unsupplemented seawater at 26 C and in a 12:12 hr light/dark cycle, new rhizomes formed near the old growing points on thalli transplanted from the ocean. Adjacent to the apices of new rhizomes, rhizoids were produced downward, regularly spaced and at a rate of about 1.5/day. Upright. shoots developed irregularly in acropetal succession behind the tips of either the parent or the new rhizomes, which arose as branches of the old. Rates of rhizome, rhizoid, and upright shoot elongation were 0.4, 0.81, and 0.54 cm/day, respectively. Thalli survived up to 2 months in unsupplemented seawater. Long-term growth was obtained by varying culture conditions. A substratum of sand, apparently rich in microorganisms, produced long-term thallus growth in seawater, and the form of development changed so that upright shoot formation was promoted and rhizome elongation halved. Similar effects were elicited by indole-3-acetic acid, 5 × 10^-5, M in seawater and by sap expressed from C. racemosa or C. sertularioides and added to seawater at 2.5–10% by volume. The regulation of development in an algal coenocyte is discussed and analogies with regulation in multicellular plants are drawn.     

Underground organs ofPhragmites communis,their growth,biomass and net production

The present paper sums up the knowledge obtained from the study of growth periodicity in the underground organs ofPhragmites communis Trin. and from the analyses of differentPhragmites stands in three regions of Czechoslovakia. A period of intense growth ofPhragmites rhizomes was recorded in summer. Spring (end of April and beginning of May) and autumn (mainly September) seem to be the periods of most active root growth. During July and August, accumulation of reserve material takes place both in new and old rhizomes. In the stands investigated, the biomass ofPhragmites rhizomes varied from 2 kg/m² to 5 kg/m², and root dry weight from 0.08 kg/m² to 3.6 kg/m². The ratio of underground to total aboveground dry weight was highly variable (1.0 to 9.9). The estimated annual net rhizome production ofPhragmites, in two different stand, was 30% (?akvický fishpond) and 60% (Nesyt fishpond) of the seasonal maximum above-ground biomass.     

Age-specific seasonal storage dynamics of<Emphasis Type="Italic">Phragmites australis</Emphasis> rhizomes: a preliminary study

Age-specific seasonal rhizome storage dynamics of a wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Japan, were investigated from April to October 2000. For each sampling date, above- and below-ground biomass and age-specific rhizome bulk density, ?_rhiz were measured. Seven rhizome age classes were recognized, from <1 year to six years old, based on their position within the branching hierarchy as main criteria and rhizome color, condition of nodal sheaths and condition of the shoots attached to vertical rhizomes as secondary criteria. P. australis stand was moderately productive, having a net aerial and below-ground production of 1980 and 1240 g m^?2, respectively, and a maximum mean shoot height of 2.33 ± 0.12 m. In spring, shoot growth started at the expense of rhizome reserves, decreasing the rhizome biomass as well as ?_rhiz. Both parameters reached the seasonal minimum in May followed by a subsequent increase, indicating a translocation of reserves to rhizomes from shoots after they become self supporting. For each sampling date, ?_rhiz increased with rhizome age. Given that the quantity of reserves remobilized by the rhizomes for spring shoot growth, as assessed by the drop in bulk density from April to May, were positively correlated (r = 0.97, P < 0.05) with rhizome age, it is proposed that for spring shoot formation older rhizomes remobilize stored reserves more actively than younger ones. Given that the accumulation of rhizome reserves (rise in bulk density) from May to August, May to September or May to November was negatively correlated (r = 0.97, 0.92 and 0.87, respectively, P < 0.05) with rhizome age, it seemed possible that younger rhizomes were ‘recharged’ at a higher rate than older ones. These resource allocation mechanisms pertaining seasonal rhizome storage dynamics are of paramount importance in formulating management and conservation strategies of wetlands and aquatic habitats. Our results indicate that a harvest of above-ground biomass from May to June would be more effective in reducing the growth than a harvest in July to August or later, when rhizome reserves have already been replenished. However, the latter may remove a larger shoot bound nutrient stock, still preserving a healthy stand for the subsequent years.     

Clonal integration and its ecological significance in Hedysarum laeve, a rhizomatous shrub in Mu Us Sandland

Hedysarum laeve, a rhizomatous clonal half-shrub, commonly dominates in inland dunes in semiarid areas of northern China. This species propagates vegetatively by the extension of horizontal rhizomes resulting in programmed reiteration of apical and/or axillary meristems. In this study, ¹⁴C labeling and experimental defoliation were employed to test the photosynthate translocation within the interconnected parent–daughter ramet pairs. A proportion of ¹⁴C-photosynthates was transported from the parent ramet into the daughter ramet, the roots of the daughter ramet, and the rhizome; these three components showed more than 70% sink activity after 24-h translocation. On the other hand, the basipetal translocation (from daughter ramet into parent ramet) was relatively small with sink activity of less than 5%, but sink activity of the rhizome exceeded 10%. Defoliation had an influence on the photosynthate translocation between parent and daughter ramets. The intact parent ramets significantly increased their ¹⁴C-photosynthate translocation into defoliated daughter ramets when compared to intact daughter ramets. The daughter ramets transported significantly more ¹⁴C-photosynthates to the defoliated parent ramets than to the intact parent ramets. A portion of ¹⁴C-photosynthates was transported into the rhizome from both parent and daughter ramets, indicating that the rhizome is supported by both ramets for photosynthates. The clonal integration between ramets of the species through rhizome connection may confer benefit both to the ramets and the genet in adverse environments. Received: April 12, 2001 / Accepted: November 26, 2001     

Phragmites australis at an extreme altitude: Rhizome architecture and its modelling

In central EuropePhragmites australis is a lowland plant, occurring rarely up to the tree line. In the Velká Kotlina cirque (Jeseníky mountains, NE Czech Republic), where it reaches its maximum altitude at about 1350 m a.s.l., its culms are 0.5–0.7 m high and the plants flower only in some years. During the last decade no germinable seeds have been observed. The architecture ofPhragmites rhizomes from this site was studied on seven randomly selected clonal fragments. They consisted of 3 to 10 partial tussocks (clumps) and 4 to 17 green shoots. The total length of the rhizomes was 9.7 to 50 m per plant. The number of nodes per plant was 96 to 431 and the longest internodes were 83 mm long. The number of side branches was 31 to 105 per plant. The branching angle depended on the type of branched rhizome. The mean angles of horizontal rhizomes, which connect individual tussocks, were relatively wide (modus 45°, arithmetic mean 37°), whereas within a tussock much sharper angles of branching prevailed (modal value 5°, arithmetic mean 15°). The mean internode-to-internode angle on continuing rhizomes was about 8°, with a wide variation. An architectural, spatially-explicit model ofPhragmites rhizome growth has been developed, showing that thePhragmites population in the studied locality can be maintained by vegetative multiplication, and seedling recruitment is not needed for its long-term persistence.     

Effects of Photoperiod and Temperature on Shoot, Root and Rhizome Growth in ThreeLotus uliginosusSchkuhr Populations

The growth of three populations of greater lotus (Lotus uliginosusSchkuhrsyn.L. pedunculatusCav.) was compared at photoperiods of 10,12 and 14 h at a maximum day/minimum night temperature of 21/16°C and at maximum day/minimum night temperatures of 27/22,21/16, 18/13 and 15/10 °C at a photoperiod of 12 h. Shortdays (10 h) favoured root and rhizome development compared tolong days (14 h). A temperature regime of 15/10 °C restrictedrhizome development compared to the 18/13 and 21/16 °C regimes.Shoot growth was restricted at the highest temperature regime(27/22 °C). The cultivar Sharnae had fewer, but heavier,rhizomes than Grasslands Maku; this may indicate adaptationto the dry summers at its site of origin (Algarve, Portugal).The response of rhizome growth to temperature and photoperiodexplains part of the performance of greater lotus in the fieldat a wide range of latitudes. Grazing management to encouragethe persistence ofL. uliginosusin pasture in temperate environmentsmay include the exclusion of grazing livestock in autumn. Inthe sub-tropics, monitoring of rhizome production in the fieldwould be required before deciding the appropriate time intervalbetween grazing.Copyright 1998 Annals of Botany Company Lotus uliginosus(Schkuhr); greater lotus; temperature; daylength; shoots; roots; rhizomes.     

In vitro propagation and field establishment of Eulophia cullenii (Wight) Bl., a critically endangered orchid of Western Ghats, India through culture of seeds and axenic seedling-derived rhizomes

An efficient protocol has been devised for the propagation and field establishment of Eulophia cullenii (Wight) Bl., a terrestrial orchid having ornamental potentialities, and is critically endangered in Western Ghats, India. Seeds extracted from 60–90-d-old capsules germinated in ½ MS, ¼ MS, Knudson C, or Mitra liquid medium developed into 1.4–2.5-mm-diameter protocorms in 60 d. Supplementation of organic additives like coconut water, peptone, yeast extract, and casein acid hydrolysate (CH) significantly enhanced protocorm growth. Upon subculture onto agar-gelled Mitra medium fortified with 0.05% CH, 56% of protocorms regenerated into shoots through the formation of linear mini-rhizomes. The regenerated shoots grew vigorously in ½ MS, producing new rhizomes. Mature rhizomes from axenic seedlings produced maximum (13?±?1.4) shoots/whole rhizome in ½ MS fortified with 44.4 μM 6-benzylaminopurine (BAP), in 120–150 d. Horizontal and longitudinal halves of the rhizome also gave multiple shoots (6–8.5) in the presence of 44.4 μM BAP. Shoots or shoot clumps sub-cultured onto ½ MS basal medium produced roots followed by rhizomes in 60–150 d. Seedlings with mature rhizomes showed 70% establishment in the nursery and added a new rhizome at the end of one growth cycle. An average of 70.6% of the rhizomes originating from seedlings during the second growth cycle sprouted to produce new shoots, when planted in the native localities. Asymbiotic germination and cloning through rhizomes thus can provide a large number of vigorous plants of E. cullenii for ornamental exploitation as well as eco-restoration, if rhizome as storage organ is ensured in the propagule.     

The Impact of Physical Disturbance and Increased Sand Burial on Clonal Growth and Spatial Colonization of Sporobolus virginicus in a Coastal Dune System

Dune plants are subjected to disturbance and environmental stresses, but little is known about the possible combined effects of such factors on growth and spatial colonization. We investigated how clones of Sporobolus virginicus , a widespread dune species, responded to the independent and interactive effects of breakage of rhizomes, breakage position and burial regime. Horizontal rhizomes were severed at three different internode positions relative to the apex to span the range of damage by disturbance naturally observed or left intact, and apical portions exposed to two burial scenarios (ambient vs. increased frequency) for three months in the field. The performance of both parts of severed rhizomes, the apical portion and the remaining basal portion connected to clone containing four consecutive ramets, was compared with that of equivalent parts in intact rhizomes. Apical portions severed proximal to the third internode did not survive and their removal did not enhance branching on their respective basal portions. Severing the sixth or twelfth internode did not affect survival and rhizome extension of apical portions, but suppressed ramet production and reduced total biomass and specific shoot length. Their removal enhanced branching and ramet production on basal portions and changed the original rhizome growth trajectory. However, the gain in number of ramets in basal portions never compensated for the reduction in ramet number in apical portions. Recurrent burial increased biomass allocation to root tissues. Burial also stimulated rhizome extension only in intact rhizomes, indicating that disturbance interacts with, and counteracts, the positive burial effect. These results suggest that disturbance and recurrent burial in combination reduces the regeneration success and spread capacity of S . virginucus . Since global change leads to increasingly severe or frequent storms, the impact of disturbance and burial on clones could be greater in future and possibly prevent colonization of mobile dunes by the species.     

Seasonal patterns of partitioning and remobilization of 14C in the invasive rhizomatous perennial Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decraene)

Resource partitioning between shoot growth, storage and reproduction is poorly understood in many clonal plant species. This study documents seasonal patterns of growth, ¹⁴C-labelled photoassimilate distribution and remobilization in the invasive rhizomatous species Fallopia japonica (Japanese knotweed). Biomass accumulation above- and below-ground in F. japonica was rapid. By September, rhizome biomass had increased 18-fold from the initial harvest in May (representing 48% of total plant biomass) and this was maintained over winter. Patterns of ¹⁴C allocation from F. japonica shoots labelled at different times of year show that as the season progressed, the rhizomes became an increasingly important sink for current assimilate (the percentage of ¹⁴C recovered from rhizomes was 35% in August and 67% in September) and the corresponding retention of assimilate by established shoots declined. The percentage of ¹⁴C exported to roots was greatest in August. Relatively little photoassimilate was exported to other shoots on the plant, or to flowers. Recycling of photoassimilate was fairly tight in this species and ¹⁴C fixed by shoots in early May 1999 or September 1999 was remobilized to the rhizome prior to shoot senescence and death. Some of this ¹⁴C was then remobilized to new shoots early the following spring. These characteristics may contribute to the success of F. japonica in colonizing a variety of contrasting habitats, often with serious management implications.     

Rhizome development ofPhragmites australis in a reed community

Variations in the height, shoot density, biomasses of above- and below-ground parts and rhizome distributions ofPhragmites australis were investigated along a line-transect in a reed community at Yufutsu Mire, Hokkaido. Relationships of performance of the reed plants to soil conditions and species compositions were also examined. Three types of rhizome development were recognized in reed plants; (1) the central part of the reed community, characterized by well developed rhizomes and dense aerial shoots, (2) the intermediate part, characterized by development of rhizomes along both the peat and surface layers and very dense aerial shoots, and (3) the marginal part, characterized by development of rhizomes only along the peat layer and sparse aerial shoots. Observation showed that rhizomes in the surface layer actively produced aerial shoots, whereas rhizomes in the peat layer contributed to the spreading of their distribution range. With the growth of rhizomes, organic debris originating from dead rhizomes and roots accumulated in the mineral soil to promote organic soil formation. In dense parts of the reed stand, species composition was poor because of the shading and litter accumulation by reed plants. The effects of microtopography and water level on the establishment of reed seedlings were also considered.     

Field growth characteristics of two aquatic carnivorous plants,Aldrovanda vesiculosa andUtricularia australis

Basic growth characteristics of two species of free-floating submerged carnivorous plants, the very rare and stenotopicAldrovanda vesiculosa and the very common and eurytopicUtricularia australis, were investigated in a 10/11-day field growth experiment within three nylon enclosures at two artificialAldrovanda sites in the T?eboň region, S Bohemia, Czech Republic, at the peak of a growing season. Growth ofAldrovanda was best at a meso-eutrophic site (biomass doubling time,T ₂, 8.4–10.7 days, mean growth of new leaf whorls 0.96 whorls days^?1, 1.6 developed branches per shoot) and slower at an oligo-mesotrophic site (T ₂ 17.2–21.5 days, growth of whorls 1.01 whorls days^?1, 0.1–0.5 branches per shoot). Growth ofUtricularia was similar at both sites (T ₂ 19.8–33.2 days or 9.1–16.8 days, growth of whorls 3.1 or 2.7 whorls days^?1, 1.5–2.1 or 0.8–1.4 developed branches per shoot at the former or latter site, respectively). Throughout the experiment, both species at the meso-eutrophic site allocated relatively more biomass to the production and growth of branches, than to that of new whorls. The results show thatAldrovanda, although usually considered as competitively weaker, can grow faster during the growing season peak thanUtricularia due to frequent branching and the subsequent rapid growth and separation of daughter shoots. Very rapid growth of rootless aquatic carnivorous plants in nutrient-poor habitats allows the consideration of ecophysiological adaptations that enable the plants to gain limiting mineral nutrients. These adaptations include carnivory, efficient nutrient reutilization from senescent shoots, and very high affinity for mineral nutrient uptake from water. Comparison of growth rates of rare and stenotopicA. vesiculosa and very common and eurytopicU. australis shows that differences in their rarity do not seem to be based on differences of growth rate.     

模拟采食干扰下克隆整合对两种箭竹分株种群更新的影响

动物对植物的采食会刺激植物进行补偿性更新生长, 克隆整合效应能够通过分株之间的物质传输增强克隆植物的这种补偿生长。现今对克隆整合效应在箭竹(Fargesia)补偿更新中的作用仍未得到全面认识。2011年10月到2012年11月, 设立了糙花箭竹(Fargesia scabrida)和缺苞箭竹(F. denudata)各40个样方, 分别进行不剪除样方内分株和剪除样方内分株数量的25%、50%、75%四种模拟采食干扰处理, 并将样方四周的根状茎切断或保持连接。从2012年6月起观测并统计了箭竹分株种群的累积出笋率、总出笋率、补充率, 以及新生分株的株高、基径和单株生物量。结果表明: (1)在不剪除分株的样方, 切断根状茎连接显著增加了糙花箭竹的出笋率和补充率, 但降低了新生分株的株高和单株生物量, 也显著降低了缺苞箭竹的出笋率和补充率; (2)保持根状茎连接时, 25%的剪除强度仅仅降低了糙花箭竹新生分株的单株生物量; 同样在保持根状茎连接的条件下, 25%、50%的剪除强度使缺苞箭竹种群的补充率有所降低, 而切断根状茎后缺苞箭竹在25%的剪除强度下的分株补充率反而升高; (3) 75%的剪除强度并未影响两种箭竹新生分株数量更新, 但造成新生分株质量显著下降; 切断根状茎连接显著降低了糙花箭竹的新生分株的株高和基径, 对缺苞箭竹影响不显著。实验证明克隆整合影响了两种箭竹新生分株的萌发、存活和生长, 但不是两种箭竹进行补偿更新的主要机制, 仅在糙花箭竹分株种群受到重度采食干扰后的更新中才起到明显的促进作用; 两种箭竹均能在50%的剪除强度下通过补偿生长恢复种群的稳定, 75%的剪除强度则会造成箭竹新生分株质量的下降。     

Moderate abiotic stresses increase rhizome growth and outgrowth of axillary buds in Alstroemeria cultured in vitro

Alstroemeria is multiplied in vitro by forced outgrowth of lateral rhizomes from rhizome explants. The multiplication rate is very low because of strong apical dominance and poor rhizome growth. We report here that moderate abiotic stresses stimulate both rhizome growth and outgrowth of lateral rhizomes, and accordingly increase multiplication. Rhizome explants were exposed to heat by a hot-water treatment (HWT) or by a hot-air treatment. Both increased rhizome growth when applied for 1 or 2?h in the range of 30?C40?°C. The maximal enhancement was 75?%. Other abiotic stresses were also examined. Cold (0?°C) and partial anaerobiosis increased rhizome growth significantly. The increases brought about by drought and salinity were not statistically significant. Because underground storage tissues like rhizomes are adaptations to survive climatic stresses, we presume that the increased sink-strength of rhizomes induced by moderate stress is related to stress adaptation. Moderate heat stress (38?°C HWT, 1?h) also resulted in protection of Alstroemeria plantlets from severe heat stress (45?°C HWT, 1?C2?h) a few hours after the moderate stress. All abiotic stresses also increased the outgrowth of lateral rhizomes.     

Translocation of Photoassimilates Between Sister Ramets in Two Rhizomatous Forest Herbs

Autoradiography and liquid scintillation techniques were usedto trace the pattern of photoassimilate translocation in twoperennial forest herbs, Aster acuminatus Michx. and Clintoniaborealis (Ait.) Raf. Vegetative shoots of C. borealis emergeearly each spring from the growing apices of a long-lived rhizomesystem. Vegetative shoots of A. acuminatus emerge in late springfrom rhizomes that decay within 2 years. In both species rametssurvive for only one growing season. Any connected plants aresisters. Mature leaves of these two species were exposed for1 h periods to ¹⁴CO₂ during spring and summer. Radioactivitycould subsequently be detected in exposed leaves (16–84per cent, depending on the season), adjacent above ground plantparts (0.7–23 per cent), roots and rhizomes (4.9–84per cent) and, when present, flowers (4–8.5 per cent).Old rhizomes of C. borealis are prominent storage sites forphotosynthate. In A. acuminatus, no significant translocationbetween sister ramets (i.e. above ground shoots connected bya common rhizome) was observed. In C. borealis, there was small,but consistent translocation between sister ramets (0.2–4per cent). Disturbance of unexposed sister ramets by defoliation,shading or herbivory increased the flow of photoassimilatesto disturbed parts in C. borealis, but not in A. acuminatus.Based on the absence of translocation flow, ramets of A. acuminatusmay be regarded as physiologically independent. Connected rametsof C. borealis show physiological integration. These resultsare correlated with ecological differences between the two species. Aster acuminatus, Clintonia borealis, translocation, ramet, vegetative reproduction, forest herb