Rhizome dynamics and resource storage in Phragmites australis

Seasonal changes in rhizome concentrations of total nonstructural carbohydrates (TNC), water soluble carbohydrates (WSC), and mineral nutrients (N, P and K) were monitored in two Phragmites australis stands in southern Sweden. Rhizome biomass, rhizome length per unit ground area, and specific weight (weight/ length ratio) of the rhizomes were monitored in one of the stands.Rhizome biomass decreased during spring, increased during summer and decreased during winter. However, changes in spring and summer were small (< 500 g DW m-2) compared to the mean rhizome biomass (approximately 3000 g DW m^–2). Winter losses were larger, approximately 1000 g DW m-2, and to a substantial extent involved structural biomass, indicating rhizome mortality. Seasonal changes in rhizome length per unit ground area revealed a rhizome mortality of about 30% during the winter period, and also indicated that an intensive period of formation of new rhizomes occurred in June.Rhizome concentrations of TNC and WSC decreased during the spring, when carbohydrates were translocated to support shoot growth. However, rhizome standing stock of TNC remained large (> 1000 g m^–2). Concentrations and standing stocks of mineral nutrients decreased during spring/ early summer and increased during summer/ fall. Only N, however, showed a pattern consistent with a spring depletion caused by translocation to shoots. This pattern indicates sufficient root uptake of P and K to support spring growth, and supports other evidence that N is generally the limiting mineral nutrient for Phragmites.The biomass data, as well as increased rhizome specific weight and TNC concentrations, clearly suggests that reloading of rhizomes with energy reserves starts in June, not towards the end of the growing season as has been suggested previously. This resource allocation strategy of Phragmites has consequences for vegetation management.Our data indicate that carbohydrate reserves are much larger than needed to support spring growth. We propose that large stores are needed to ensure establishment of spring shoots when deep water or stochastic environmental events, such as high rhizome mortality in winter or loss of spring shoots due to late season frost, increase the demand for reserves.     

Factors affecting iron plaque on the roots ofPhragmites australis (Cav.) Trin. ex Steudel

Phragmites australis (the common reed) was collected at six sites in southern Québec and Ontario, Canada, in order to study the accumulation of iron plaque on the roots. The deposition of iron oxides on roots ofP. australis did not correlate directly with soil measurements; however, the amounts of iron-bound-to-carbonates fraction of the soil/sediment, responsible for the iron plaque accumulation, correlated with the % of water, % of organic matter, % of clay and pH of the substrate. Plants located very near flowing water accumulated more iron plaque on the roots than plants in other habitats through the summer; it is hypothesized that carbonates associated with iron come from the flowing water. In wetlands or sites near flowing water, most root iron was found on the surface, as iron plaque, while there was more iron inside the root in dry environments. Radial oxygen loss from the roots is probably the most important source of oxygen for the oxidation of iron.     

Effects of rhizome age on the decomposition rate of Phragmites australis rhizomes

The change in dried rhizome samples that were left to decompose was investigated to elucidate the effects of rhizome age on the decomposition rate of Phragmites australis. Rhizomes were classified into five age categories and placed 30 cm below the soil surface of a reed stand. After 369 days of decay, new (i.e., aged less than one year) rhizomes had lost 84% of their original dry mass, compared with a loss of 41–62% for that of older rhizomes. The exponential decay rates of older rhizomes were nearly identical to that of aboveground biomass. The nitrogen (N) concentration increased to two times its original values, but the phosphorus (P) concentration remained constant after an initial loss by leaching. The carbon to nitrogen (C:N) and carbon to phosphorus ratios (C:P) leveled out at 22:1 to 38:1 and 828:1 to 1431:1, respectively, regardless of rhizome age. The results are important to understand the nutrient cycles of reed-dominant marsh ecosystems.     

Effects of seasonal temperature on shoot growth dynamics and shoot morphology of common reed (Phragmites australis)

The shoot growth during the vegetation period andshoot morphology at the end of the season wereinvestigated in four monoclonal aquatic reed stands(Phragmites australis) with differentproductivity in Berlin and Brandenburg. Investigationswere conducted over a period of six years (1991–96) toascertain the effects of differences in temperatures.All clones showed significant year-to-year variationin shoot morphology. The mean final shoot length ofthe two clones with highest variation ranged from252 cm (1991) to 388 cm (1993; Templiner See), andfrom 170 cm (1993) to 229 cm (1994; Parsteiner See).In spite of this considerable variation, morphologicalparameters measured at the end of the growing seasonshowed only a slight relation to the average airtemperature either during the main growth phase (Aprilto June) or during the period of bud formation (Augustto October of the previous year). Contrary to meanshoot length at the end of the growing season, shootelongation during the main growth phase (from April toJune) was clearly related to the sum of daily averagetemperatures. Thus, taking into account temperaturemay enhance the accuracy of studies on reed growthwhenever these studies are carried out at localitiesdiffering in temperature or in different years.     

Effects of salinity and cutting on the development of Phragmites australis

The effects of increased salinity and cutting the above ground biomass on the growth of Phragmites australis were evaluated by investigating four experimental reed stands grown in outdoor tanks. Two stands were treated with 30 salinity and the other two stands with freshwater; one stand of each treatment was cut to 20 cm during the second growing season. Growth conditions were observed until all the plants were dead at the end of the second year. The number of shoots emerged from the freshwater-treated stand was about 70% higher than that of the saltwater-treated stand. The number of shoots emerged from cut plant stands were markedly lower than uncut stands. The average shoot height was negatively affected by salinity and shoots that emerged after cutting further decreased in height. The average number of leaves on a shoot was not significantly affected by salinity, but reduced by cutting in both treatments. Leaf length, width and the distance between leaves were decreased by both salinity and cutting. In the freshwater-treated uncut stand more than 50% of the shoots formed panicles, but this proportion was reduced to 6% by salinity, to 15% by cutting, and to 0% by the combination of salinity and cutting. This study showed again that salinity reduces the growth of aboveground components. The growth, however, was most severely retarded by cutting combined with salinity, which has many implications for better management of P. australis stands.     

Ramet size equalisation in a clonal plant,Phragmites australis

The influence of shading from older generations of dead culms (standing litter) on density, growth rate and development of size structure at the ramet level was investigated in a pure stand of Phragmites australis by experimental neutral shading of plots after removal of standing litter. Initial differences in height distribution between autumn and spring cohorts disappeared in the course of shoot growth. The Gini coefficients of shoot heights and estimated shoot weights indicated that the size structure of the shoots became more equal with increasing mean size in both shaded and unshaded plots. Relative growth rate for height (RHGR) and weight of individual shoots was negatively related to shoot size during the early and presumably storage-dependent growth period, suggesting a strong support for growth of smaller shoots. No etiolation was indicated by mean or maximum height in shaded and unshaded plots, or by the relationship between shoot height and weight. Mean shoot density was significantly lower in shaded than in unshaded plots in one of two shade treatment years. A regression model indicated a small but significant effect of shoot density on the approximately linear relationship between RHGR and the logarithm of height. The growth rate of small shoots was slightly larger at low than at high shoot density. Therefore, it is suggested that the shade from standing litter in P. australis stands can decrease shoot natality in the spring cohort, and thereby increase the support to fewer small shoots.     

Increasing the efficiency of reed plantations on stressed lake and river shores by using special clones of Phragmites australis

In an investigation aimed at comparing the variationin growth and expansion of different reed clones, 10reed clones were planted in spring of 1995 on sixexperimental fields on the River Dahme and the RiverHavel in Berlin. Their sites of origin differed innutrient supply, substrate quality and shoreexposition. The main aim of this large-scaleexperiment was to search for reed clones that would beable to colonize lake shores rapidly and to expandinto deeper water. Two years after planting thedeveloping reed stands differed significantly inmorphology and stand structure, both among clones andamong sites. This indicates that the development ofreed stands depended on the environment as well as onthe genotype. The differences in development impliedthat some of the clones would be more suited thanothers for restoration purposes, so that successfulrestoration of a degraded river or lake shores mightdepend on the selection of the best suited clones.The nitrogen contents in the aboveground biomass oftwo clones differing in nitrogen dynamics at theiroriginal sites (described as `assimilation' and`translocation' types in the literature) did notdiffer in this experiment, even though the two clonesdid differ in some morphological traits. These resultsmight be influenced by the fact that stands were stilldeveloping and that possibly clones had reached adifferent degree of maturity. Nevertheless, theysuggest that nitrogen content depends more on siteconditions, with only little genetically determineddifference, and that morphological variation isdetermined by factors other than variation in nitrogenuptake.     

Zinc distribution and zinc-binding forms in Phragmites australis under zinc pollution

The influence of zinc (Zn) on physiological and biochemical parameters was studied to elucidate the mechanism of Zn resistance in Phragmites australis. Zn concentrations in roots, stems and leaves increased with exogenous Zn concentration, while Zn content in roots was much higher than in shoots. X-ray microanalysis was used to reveal compartments in which Zn accumulated in root cortex. Zinc concentrations followed a gradient with the sequence: intercellular space>cell wall >vacuole >cytoplasm, indicating that most Zn was immobilized in the apoplast or sequestered into the vacuolar lumen. Sequential extraction of various Zn chelates revealed that the ratio of Zn extracted with different extraction media was markedly different. Ethanol, HAc (acetic acid) and NaCl-extractable Zn were dominant in both roots and leaves of P. australis. Zn-binding protein fractions were found in the roots and leaves after gel filtration chromatography, among which a polypeptide with an apparent molecular mass of 14kDa bound Zn most effectively. Two newly synthesized polypeptides of 58 and 45kDa appeared under Zn pollution, whereas a prominent fraction of 72kDa disappeared. The involvement of Zn distribution in plant tissues, subcellular compartments and chelates and Zn-inducing proteins in the acclimation mechanism of P. australis to Zn pollution is discussed.     

To the importance of genetic diversity of Phragmites australisin the development of reed stands

Reed stands in Germany and Europe were investigatedwith respect to their genetic diversity by means ofRandom Amplified Polymorphic DNA (RAPD) via thePolymerase Chain Reaction (PCR-fingerprinting).Different types of clonal distribution could bedistinguished: monoclonal reed stands and polyclonalreed stands, and among the latter, stands with low orhigh numbers of different clones as well as standswith mosaic-like coexisting or intermingling clones.Furthermore, clonal distribution and the expansion ofdifferent clones was observed within a newlydeveloping reed population. The findings appear tosupport a model of colonization postulating thatpopulations initiated by seeds are initiallygenetically diverse, but over time become dominated byone or a few clones adapted to the prevailing siteconditions. Thus, low genetic diversity seems to bethe result of a natural selection process. Clonaldiversity within a reed population and the type ofclonal distribution are discussed with regard to theirimportance for the reed stand's ability to adapt tochanging site conditions and eventually for itssurvival or die-back.     

Tolerance and bioaccumulation of copper in Phragmites australis and Zea mays

The effects of copper on the growth, tolerance indices, mineral composition (N, P, K, Fe, Zn and Mn) and metal uptake of reed (Phragmites australis [Cav. Trin. ex Steudel]) and maize (Zea mays L.) were investigated in hydroponic experiments at copper concentrations ranging from 0.5 to 157 M Cu. A reduction in root length was shown to be a good indicator of copper toxicity, concentrations of 15.7 and 78.7 M Cu inhibiting root growth in maize and reed, respectively. The reed was significantly more tolerant of copper than maize and at 7.85 M Cu (external concentration), reed can be described as a Cu tolerant plant, and maize as a Cu non-tolerant species. As a result of Cu toxicity, the concentrations of macronutrients N, P and K decreased in both shoot and root of maize, while the concentrations were hardly affected in reed tissues. Fe concentration increased in shoots and roots of maize and in roots of reed with increasing Cu treatments, leading to highly significant (p<0.01) linear relationships between tissue Fe and Cu concentrations. The bioconcentration factor (BCF) of Cu was higher in roots than in shoots of both plant species, ranging from 612 to 1592 in reed for the Cu treatments tested. In the roots of maize, BCF of Cu increased from 349 to 1931 when increasing Cu in nutrient solution from 7.85 M to 78.5 M. Therefore, reed could be useful in wastewater treatments for the removal of Cu. However, the use of reed in phytoextraction of Cu from contaminated soils is limited by the low accumulation rate in shoots and although reed can be more efficient than maize for Cu phytoextraction, harvesting the full biomass, including roots, may be required.     

Tissue culture and long-term regeneration of Phragmites australis (Cav.) Trin. ex Steud.

Phragmites australis tissue cultures were initiated from mature seeds on MS medium supplemented with 1 mgl^-1 each of 2,4-D and IAA. Cultures displayed typical embryogenic callus that was compact and bright yellow. Selection for embryogenic callus established long-term regenerable cultures. Removal of auxin from the basal medium allowed numerous complete plants to be recovered from the cultures. Histological study indicated both the presence of embryogenic-type cells and the bipolar development of regenerated plants.     

Human Facilitation of Phragmites australis Invasions in Tidal Marshes: A Review and Synthesis

Efforts to manage or prevent Phragmites australis invasion in salt and brackish marshes are complicated by the lack of a general causal role for specific human activities. The pattern of invasion within a marsh differs among sites, and each may have different causal histories. A review of the literature finds three establishment/invasion patterns: (1) from stands established on ditch- or creek-bank levees toward interior portions of high marshes, (2) from stands along upland borders toward high marsh interiors, and (3) centroid spread from high marsh stands established in ostensibly random locations. Each invasion pattern seems to have different anthropogenic precursors, therefore preventing generalizations about the role of any one human activity in all sites. However, historical and experimental evidence suggests that regardless of invasion pattern, establishment is much more likely at sites where rhizomes are buried in well-drained, low salinity marsh areas. Any human activity that buries large rhizomes, increases drainage, or lowers salinity increases chances of establishing invasive clones. To integrate these patterns and improve our understanding of the rapid spread of Phragmites, recent evidence has been synthesized into a dichotomous flow chart which poses questions about current site conditions and the potential for proposed activities to change site conditions that may facilitate invasion. This simple framework could help managers assess susceptibility and take preventative measures in coastal marshes before invasion occurs or before removal becomes very expensive.     

Plant regeneration from embryogenic cultures of Phragmites australis (Cav.) Trin. Ex Steud.

Embryogenic cultures of the common reed [Phragmites australis (Cav.) Trin. Ex. Steud.] were induced on Murashige and Skoog (1962)-based medium with 2% (w/v) sucrose, B5 vitamins and 4.5 μM 2,4-dichlorphenoxyacetic acid. Four independent culture lines, two initiated from stem nodes and two from roots, were established. These cultures underwent somatic embryogenesis. In one line of stem node origin, the somatic embryos germinated and developed into plants, following transfer of embryogenic cultures to Murashige and Skoog (1962)-based medium lacking growth regulators, with 108 ± 17 plants being recovered per 100 mg fresh weight of culture. In other lines, the somatic embryos developed roots, but not shoots. Shoot regeneration via somatic embryogenesis offers potential as anin vitro system for physiological studies, including assessments of the response of common reed to environmental pollutants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mineral composition of Phragmites australis in Scottish lochs as related to eutrophication. I. Seasonal changes in organs

Monthly levels of nitrogen, phosphorus, potassium, sodium, calcium, magnesium and iron in the organs (root, rhizome, stem, leaf and panicle) of Phragmites australis were determined from March to November, 1975 in Forfar Loch (polytrophic), Balgavies Loch (eutrophic) and Loch of the Lowes (mesotrophic), Scotland. Generally no consistent seasonal changes in the mineral levels were detected for the root, rhizome and panicle. For the stem and leaf, the levels of nitrogen, phosphorus, potassium, calcium and magnesium rose to a peak before declining for the rest of the season. Consistently higher levels of tissue nitrogen, phosphorus, potassium and calcium were found in the Forfar plants over those of Balgavies and Lowes, reflecting the very eutrophic condition in Forfar Loch. The mineral compositions in the reeds in the present study were compared with similar studies in other areas.     

Blocking Phragmites australis reinvasion of restored marshes using plants selected from wild populations and tissue culture

This study tested a vegetation strategy for controlling Phragmites australis invasion into brackish marshes as an alternative to the current technique of repeated herbicide sprays followed by burning. This strategy involves blocking P. australis by planting desired plants selected from wild populations and/or tissue culture regenerants at key points on the major routes of P. australis invasion. The planting of native species was conducted at three sites in a herbicide-treated P. australis marsh near Salem, NJ. Wild population selections of three upland marsh shrubs, Myrica cerifera, Baccharis halimifolia, and Iva frutescens, as well as two grass species, Spartina alterniflora and Spartina patens, and two rushes, Juncus gerardi and Juncus roemerianus, were planted according to their normal zonation positions. Tissue culture regenerated plants of the two grasses and two rushes, and the sedge species Scirpus robustus, were also planted. Plant growth at each site was monitored each year after planting for up to 3 years. Most plants of B. halimifolia, I. frutescens, J. roemerianus, and S. patens demonstrated a consistent vigorous growth at all three sites, whether or not the plants were collected from wild populations or were tissue culture regenerants. These multi-layered walls of plants demonstrated effectiveness in controlling the P. australis by restricting or inhibiting its spread. Upon screening 48 regenerated plants of S. patens at one of the three sites, we found that some regenerants showed enhanced characteristics for blocking P. australis, such as greater expansion and a high stem density. The availability of the tissue culture-regenerated plants of the native marsh species makes it possible to select lines from local genotypes that have desirable characteristics for wetland restoration projects, such as blocking P. australis reinvasion.     

Predicting the Effectiveness of <Emphasis Type="Italic">Phragmites</Emphasis> Control Measures using a Rhizome Growth Potential Bioassay

In the last century, Phragmites australis (common reed) has expanded from a minor component of the mid-Atlantic tidal wetlands to a dominant species in many locations. Expansion of Phragmites results in decreased plant diversity and alterations to the tidal characteristics of the marsh, resulting in decreased wetland value. Management efforts have used a variety of strategies in an attempt to control its expansion. We tested a greenhouse bioassay that provided insight into the rhizome vitality of six herbicide-treated sites in the Alloway Creek Watershed, NJ well in advance of the growing season. At three sites, rhizomes were exhumed and classified by depth (0–25 cm and 25–75 cm) and appearance (color and firmness). Concurrently, the same protocol was followed, but conducted on an areal basis at three additional sites. Material was grown in sand under greenhouse conditions void of nutrient supplements for 70 days, after which shoots were removed and the rhizomes replanted for 30 days. Effectiveness of control strategies was quantified by examining rhizome color, vitality, and shoot densities in the field. Color was indicative of quality of rhizome reserves. Less than 0.2% of the firm, brown rhizomes produced shoots upon initial planting and none produced shoots upon replanting, whereas 50.9% of white rhizomes produced shoots on initial planting. Rhizome vitality was quantified by examining shoot emergence and the morphology of the shoots. Coupling rhizome vitality with observed field densities resulted in a predictive capability, and shoot density and biomass predictions were compared to field measurements in July 2001. We tested and accurately predicted the relative shoot densities and shoot biomass of the three sites for which we collected rhizome material on an areal basis. The result is a rapid, valuable, and cost-effective monitoring tool that can quickly quantify the effects of past control methods and predict future growth potential.     

Effect of broken dead culms of Phragmites australis on radial oxygen loss in relation to radiation and temperature

The amount of oxygen released from the roots of Phragmites australis was quantified to examine the effects of airflow through dead culms, radiation, and temperature on radial oxygen loss (ROL). To investigate the effect of dead culms on ROL quantitatively, the ROL of individual plants with open dead culms was compared to that of plants with sealed dead culms as a function of light intensity and temperature. The relationship between ROL and plant morphology (aboveground biomass, shoot diameter, shoot height) was investigated. When exposed to 300, 600, and 900 μmol m⁻² s⁻¹ light, the ROL was 15.6, 22.5, and 30.9 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with open dead culms and 11.0, 16.4, and 23.3 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with sealed dead culms. The ROL from plants with open dead culms was obviously higher than that from plants with sealed dead culms in every condition. The ROL from plants with open culms was 37% and 30% higher than that from plants with sealed culms at 20°C and 30°C, respectively. The effects of plant-specific parameters such as leaf area and shoot diameter on radial oxygen loss were evident. From the point of view of rhizosphere oxidation during the growing season, the existence of open dead culms should be taken into consideration for optimal plant management in constructed wetlands. This study provides a theoretical understanding of the effects of open dead culms, light conditions, and temperature on radial oxygen loss. Handling editor: S. M. Thomaz     

扎龙湿地不同生境芦苇种群根茎构件的年龄结构

芦苇是典型的长根茎型克隆植物,天然种群主要依靠根茎的营养繁殖进行更新。采用单位土体挖掘取样,按实际生活年限划分根茎龄级的方法,对扎龙湿地芦苇种群不同龄级根茎进行调查。结果表明,6月份,4个生境芦苇种群根茎构件均由2—6a的5个龄级组成,7—10月份均由1—6a的6个龄级组成。6—10月份,1a根茎长度比率逐渐增加;除盐碱生境略有增加外,其他3个生境2a、3a比率均小幅减少;4—6a比率逐渐减小,根茎长度比率均以3a最大,依次是2a,4a,1a,5a,最高的6a最小。1—3a根茎生物量比率逐渐增加;4—6a比率逐渐减小,均以3a根茎生物量比率最大,依次是4a,2a,5a,6a,以最低1a最小。不同龄级根茎长度和生物量比率与返青后实际生长时间之间均较好地符合直线函数关系(R²>0.91,P<0.01;R²>0.81,P<0.05),6—9月份,根茎长度呈衰退型年龄结构,10月份又转为稳定型结构,整个生长季根茎生物量均为衰退型结构。不同龄级根茎构件在芦苇种群中的地位和作用不同,根茎构件的年龄结构蕴含着种群调节的重要信息。     

Host specificity testing ofRhodometra sacraria [Lep.: Geometridae], a possible biological control candidate forEmex australis in Australia

The foliage feeding geometridRhodometra sacraria L. was collected onEmex australis Steinheil in South Africa, cultured, then tested as a possible biological control agent forE. australis, in Australia. Tests on its host specificity were carried out in South Africa and Australia.R. sacraria was specific to plants of the familyPolygonaceae rather than toE. australis. Request for the reintroduction and release ofR. sacraria into Australia has not been made.      

Effects of an organic sediment on performance of young Phragmites australis clones at different water depth treatments

Performance of young Phragmites australis plants was examined after 7 weeks on an artificial nutrient-enriched inorganic substrate and on the same substrate to which an organic sediment from a eutrophic lake was added, at three different water depth treatments. Growth decreased, and proportional allocation of biomass to roots increased, with the addition of sediment. These differences were significant in shallow and deep water, but not at a medium depth. Concentrations of phosphorus and nitrogen in plant biomass decreased, and concentration of iron increased, with addition of sediment.The effects of sediment addition may have resulted from a decreased availability of nutrients in the substrate or from an impaired root functioning. Nutrient exhaustion in the substrate, due to a fast plant growth, can explain the relatively strong effects in shallow water. Deep water, on the other hand, probably restricted oxygen transport to the roots, resulting in an impaired root functioning in the low-redox sediment environment. The results show that, especially in relatively deep water, growth of undisturbed plants of P. australis may be inhibited by eutrophication of sediments, probably because of an impaired root functioning in sediments containing reduced toxic compounds (e.g. ferrous iron).