Rhizome Carbohydrate Research Articles

Seagrass Tolerance to Simulated Herbivory Along a Latitudinal Gradient: Predicting the Potential Effects of Tropicalisation.

The polewards range expansion of tropical herbivorous fish into temperate latitudes is leading to overgrazing of marine habitats and community phase shifts in some regions. Here, we test the potential effects of increased herbivory on the temperate habitat-forming seagrass Posidonia australis. We used a series of simulated herbivory experiments to predict the potential impacts of climate-mediated increases in seagrass consumption along P. australis entire latitudinal range (~9° latitude) in eastern Australia (1700 km of coastline). We subjected treatment plots to two levels of simulated herbivory (10% or 80% of leaves clipped) and compared them to unclipped controls. We measured seagrass leaf growth rates and tissue chemical traits: carbohydrates in rhizomes, leaf phenolics, and nutrients (carbon, nitrogen, and C:N ratio) in leaves and rhizomes. At the warmest range-edge population, we also tested how responses to increased herbivory may vary between summer and winter, or with repeated clipping events. Clipped shoots maintained growth rates similar to unclipped controls despite losing up to 80% of leaf biomass. This was consistent along the full latitudinal range and after repeated simulated herbivory at the northernmost location. One-off clipping events impacted plant architecture, increasing the number of subdividing shoots. At the species range edge, leaves grew more in winter than in summer, and clipping tended to lower seagrass growth only in winter; however, higher levels of shoot subdivision were produced over summer than in winter. Plant chemical traits could not explain consistently the growth patterns observed despite some traits varying with latitude (e.g., leaf nitrogen content decreased with latitude and C:N ratio increased) and/or simulated herbivory. Synthesis: P. australis growth is not affected by increases in simulated herbivory and may be relatively resilient to future increases in seagrass consumption, suggesting that this species could be a relative 'winner' under future climate change conditions that lead to enhanced herbivory.

Restoration of a Lake Ontario‐connected fen through invasive Typha removal

Lake‐level regulation that began in 1960 eliminated large fluctuations of Lake Ontario water levels, altering coastal wetland plant communities. More than a half century later, the altered hydroperiod supports dense, monotypic stands of invasive cattail (Typha angustifolia and Typha × glauca), which have diminished overall plant community diversity. As a result, Lake Ontario coastal wetlands are less capable of providing many of their traditional ecological functions. One such wetland is Buttonwood Fen, a floating, lake‐connected peatland on Lake Ontario's southern shore near Rochester, NY. We implemented cattail‐control measures from 2016 to 2018 with the goal of decreasing live and dead cattail biomass and increasing cover of native fen taxa. Site manipulation included removal of dead cattail biomass, cutting new cattail growth when rhizome carbohydrate reserves were at their lowest, and hand‐wicking regrowth with herbicide in early fall. Results showed a decrease in live cattail stem density and cover and dead biomass cover, as well as an increase in cover of fen taxa. Although not a replicated study, our results suggest that removing dead cattail biomass and targeted treatment of live cattail stems via cutting and hand‐wicking with glyphosate can reduce cattail and improve site quality.

Rhizome and stolon development of bermudagrass cultivars in a transition-zone environment

ABSTRACTBermudagrass (Cynodon spp.) is a warm season turfgrass that spreads by stolons and rhizomes. The present study aimed to increase knowledge on development of stolons and rhizomes in fertile (‘LaPaloma’ and ‘Yukon’) and sterile (‘Patriot’ and ‘Tifway’) cultivars of bermudagrass. A plot trial was established in May 2013 in Legnaro, northeastern Italy. Fertile cultivars were seeded while sterile cultivars were established by vegetative plugs. Turf samples were collected from autumn 2013 until summer 2015 on March, July, and October. Total length of stolons and rhizomes was measured and total dry weight was determined. The concentration of starch in stolons and rhizomes in October was also determined. The stolon and rhizome density per unit area, the rhizome specific weight, and the rhizome/stolon length and weight ratios were calculated. Sterile cultivars had higher stolon and rhizome density compared to fertile cultivars for both length. In all cultivars, the production of stolons was favoured over that of rhizomes and rhizomes began to develop more in the second season after establishment. Cultivars did not differ significantly in starch content, indicating no relationship between stolon and rhizome density and carbohydrate reserve accumulations.Abbreviations: LD: length density per unit area; WD: weight density per unit area; SW: specific weight; LR: rhizome-to-stolon length ratio; WR: rhizome-to-stolon weight ratio; TS: total starch per unit area

Fertilization stimulate root production in cloudberry rhizomes transplanted in a cutover peatland

Cloudberry has good economic potential for Canada, but crop practices must be improved before commercial production can be established. Transplants usually consist of rhizome segments collected in natural populations; however, the very low root density of these transplants might partly explain their initial slow growth and high mortality. The objective of this study was to determine the effects of mineral fertilization and auxin applications on root initiation and elongation. Three N–P–K fertilization treatments were applied at the planting of bare rhizomes in peatlands, while auxin applications were tested in both greenhouse and field experiments. Roots of fertilized plants were two to four times longer and more numerous than those of control plants after one complete growing season but fertilization did not lead to early rooting. Rhizome segments produced new shoots before investing in root production, suggesting that rhizome carbohydrate reserves are not sufficient to allow both the shoot and root to be produced at the same time. Auxin applications to the rhizomes incurred high mortality and did not stimulate root production in both the field and greenhouse experiments. We conclude that fertilizers applied at planting can improve cloudberry initial survival rate, rooting, and early shoot growth, which could eventually lead to improved plant cover and fruit yield.

Reed stands during different water level periods: physico-chemical properties of the sediment and growth of Phragmites australis of Lake Balaton

Water level fluctuations play a vital role in regulating macrophytes of shallow lakes. Morphology and growth dynamics of Phragmites australis, together with physico-chemical parameters of the sediment, were studied at stable (not degrading) and die-back (degrading) sites of Lake Balaton over an 8-year period that included low and average water levels. Lower water level increased plant density and green leaf number, positively affecting photosynthetically available leaf area. Nevertheless, rhizome carbohydrate content was not influenced by water level decrease. The physico-chemical parameters of the sediment did not vary greatly, although the nitrogen and phosphorus content and the midsummer redox potential of the sediment were higher at the low-water period. During the transition from average to low water levels, the sediment shifted from severely anoxic to poorly oxidised levels, with more favourable nutrient content, while the amount of ammonia and sulphides decreased, too. It was shown that lowering water levels could act on plants via increased redox potential of the sediment and could counteract the die-back of Phragmites, suggesting the effectiveness of water level decrease as a management practice to counter reed die-back.

Effect of nitrogen on growth, nutrient assimilation, essential oil content, yield and quality attributes in Zingiber officinale Rosc.

A simple randomized pot experiment was conducted to determine the effect of different concentrations of nitrogen (N) on growth, biochemical, quality and yield attributes of Zingiber officinale Rosc. a medicinally important spice plant. Plants were supplied with five levels of basal nitrogen viz. 0 (Control), 40, 80, 120 and 160kgNperha. The performance of the crop was adjudged in terms of various parameters viz. plant height, number of leaves, fresh and dry weights of shoot and rhizome, total chlorophyll content, leaf and rhizome NPK content, rhizome carbohydrate and protein content, and analysed at 120 and 180days after planting (DAP). The data revealed that nitrogen application significantly stimulated most of the studied attributes. Of the five N concentrations, 120kgNperha soil proved optimum for most of the parameters studied as compared to the control at both crop stages.

Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 466:69-79 (2012) - DOI: https://doi.org/10.3354/meps09928 Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism E. Gacia1,*, N. Marbà2, J. Cebrián3,4, R. Vaquer-Sunyer2, N. Garcias-Bonet2, C. M. Duarte2,5 1Biogeodynamics and Biodiversity Group, Centre d’Estudis Avançats de Blanes, Consejo Superior de Investigaciones Cientificas (CEAB-CSIC), Blanes 17300, Spain 2Department of Global Change Research, Mediterranean Institute for Advanced Studies (IMEDEA; UIB-CSIC), Miquel Marqués 21, Esporles 07190, Spain 3Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, Alabama 36528, USA 4Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA 5The UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia *Email: gacia@ceab.csic.es ABSTRACT: Meadows of the endemic seagrass Posidonia oceanica are threatened in the Mediterranean due to a general deterioration of the light environment that becomes critical when light irradiance is insufficient to meet the carbon requirements of the system. Here, we conduct a 3 wk, in situ shading experiment (8 levels plus controls) to determine the threshold of irradiance for balanced metabolism in a shallow P. oceanica meadow and further assess the recovery of the system 1 wk later. Reduced light irradiance decreased the net community production of the meadow, which may turn negative (i.e. respiration exceeded gross community primary production) under 338 µE m−2 s−1. Shading throughout the experiment did not appear to cause sustained physiological damage to the system since values of net community production after the cessation of shading were similar to pre-experimental, ambient levels. Sediment acid volatile sulfide pools ranged between 0.002 and 0.058 mol m−2 across shading treatments, and the highest pools were observed in the most shaded sediments. At high light impairment, meristematic cell divisions were low, and carbohydrate content in young rhizomes decreased throughout the experiment. Eight days after the cessation of shading, reduced rhizome carbohydrate stores and elevated sediment sulfide levels still persisted in the previously intensively shaded areas. The present study provides evidence of resistance and resilience of the seagrass Posidonia oceanica to light impairment for short (3 wk) periods of time. Although the compensation irradiance of the system varied by ~2-fold, it provides a quantitative estimate of the irradiance threshold at which seagrass meadows may shift from being coastal carbon sinks to CO2 sources. KEY WORDS: Seagrass · Ecosystem · Production · Respiration · Compensation Irradiance · Mediterranean Full text in pdf format Supplementary material PreviousNextCite this article as: Gacia E, Marbà N, Cebrián J, Vaquer-Sunyer R, Garcias-Bonet N, Duarte CM (2012) Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism. Mar Ecol Prog Ser 466:69-79. https://doi.org/10.3354/meps09928 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 466. Online publication date: October 15, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Augmentation of nutraceuticals, productivity and quality of ginger (Zingiber officinale Rosc.) through triacontanol application

Triacontanol (TRIA) is a saturated long-chain alcohol that is known to have a growth promoting activity in a number of plants when applied exogenously. However, the information is meagre and no work has been done so far regarding its effects on ginger (Zingiber officinale Rosc.), a medicinally important spice plant and one of the most heavily consumed dietary substance in the world. With this in view, a hypothesis was designed to address whether foliar application of TRIA could enhance the growth, productivity and quality attributes of ginger. The plants were sprayed with five concentrations of TRIA viz. 10−0, 10−7, 5 × 10−6, 10−6 and 5 × 10−5 M at 25-day intervals. Among the applied treatments, foliar spray of TRIA at 10−6 M proved optimum and significantly enhanced plant height, leaf density, number of tillers per plant, fresh and dry weights of shoot and rhizome, total chlorophyll content, leaf and rhizome nitrogen, phosphorus and potassium concentrations as well as rhizome carbohydrate and protein contents at 120 and 180 days after planting (DAP). This treatment also produced positively significant effects on oleoresin and essential oil contents as well as on yield attributes. However, at the highest concentration applied (5 × 10−5 M TRIA), all the parameters were significantly inhibited. Thus, theuse of foliar application of TRIA, especially at a concentration of 10−6 M might be considered suitable for promoting the production and quality of ginger crop.

Negative relationships between the nutrient and carbohydrate content of the seagrass Thalassia testudinum

This study documents relationships between plant nutrient content and rhizome carbohydrate content of a widely distributed seagrass species, Thalassia testudinum, in Florida. Five distinct seagrass beds were sampled for leaf nitrogen, leaf phosphorus, and rhizome carbohydrate content from 1997 to 1999. All variables displayed marked intra- and inter- regional variation. Elemental ratios (meanN:P±S.E.) were lowest for Charlotte Harbor (9.9±0.2) and highest for Florida Bay (53.5±0.9), indicating regional shifts in the nutrient content of plant material. Rhizome carbohydrate content (mean±S.E.) was lowest for Anclote Keys (21.8±1.6mgg−1 FM), and highest for Homosassa Bay (40.7±1.7mgg−1 FM). Within each region, significant negative correlations between plant nutrient and rhizome carbohydrate content were detected; thus, nutrient-replete plants displayed low carbohydrate content, while nutrient-deplete plants displayed high carbohydrate content. Spearman's rank correlations between nutrient and carbohydrate content varied from a minimum in Tampa Bay (ρ=−0.2) to a maximum in Charlotte Harbor (ρ=−0.73). Linear regressions on log-transformed data revealed similar trends. This consistent trend across five distinct regions suggests that nutrient supply may play an important role in the regulation of carbon storage within seagrasses. Here we present a new hypothesis for studies which aim to explain the carbohydrate dynamics of benthic plants.

The effects of defoliation on plant community, root biomass and nutrient allocation and soil chemical properties on semi-arid steppes in northern China

Semi-arid steppes in northern China have severely deteriorated over the past 50 years, mostly due to improper grazing management. A defoliation experiment was conducted on a Leymus chinensis-dominated semi-arid steppe to provide guidelines of grazing management and favor long-term restoration of degraded grasslands. There were five defoliation treatments: non-defoliation (no cutting during growing season) as control; light defoliation (cut 15 cm above ground level); medium defoliation (10 cm); hard defoliation (5 cm) and severe defoliation (2 cm). Results showed that hard and severe defoliation significantly reduced the concentrations of soluble carbohydrates in rhizomes and fibrous roots and decreased the belowground biomass and the ratio of below/aboveground biomass. Defoliation increased plant species diversity, but decreased biomass of L. chinensis significantly. The biomass of L. chinensis under light defoliation was lower than that in control, indicating L. chinensis was highly sensitive to defoliation. Defoliation intensity in general had no significant effect on soil chemical properties during the experimental period, suggesting that soil chemical properties might have a greater tolerance to short-term heavy defoliation compared to plant community. However, prolonged intensive defoliation would result in severe ecological consequences. Further studies are required to investigate the response of soil chemical properties to long-term defoliation.

Greater seasonal carbon gain across a broad temperature range contributes to the invasive potential of Phalaris arundinacea (Poaceae; reed canary grass) over the native sedge Carex stricta (Cyperaceae)

Most invasive plants grow faster and produce more biomass than the species that they displace, but physiological mechanisms leading to invasive success are poorly understood. To foster novel control approaches, our goal was to determine whether the grass Phalaris arundinacea possessed superior physiological strategies that contributed to its success over native sedges. Data for spring, summer, and autumn diel gas-exchange, leaf morphology, and nitrogen content for plants of P. arundinacea and Carex stricta in water-saturated, drained, and periodically flooded sites in northern Indiana, USA, were compared with similar data for plants in a greenhouse. Phalaris arundinacea had higher maximum CO(2) assimilation (A) across a broad range of temperatures, greater summer/autumn net carbon gain, higher water use efficiencies, larger leaf areas per shoot, and higher specific leaf areas than did C. stricta. Species differences in gas-exchange data were similar in the greenhouse. However, long-term flooding reduced A for P. arundinacea. Greater declines in leaf A and nitrogen content from July to October compared to P. arundinacea were suggestive of earlier leaf senescence for C. stricta. We propose that superior daily and seasonal carbon gain, especially during rhizome carbohydrate storage in the summer and autumn, contribute to the success of invasive P. arundinacea over C. stricta. This advantage may be enhanced by frequent summer/autumn heat waves. The poor performance of P. arundinacea during long-term flooding is consistent with C. stricta's dominance in water-saturated soil, implying that water management strategies could be crucial to controlling P. arundinacea.

Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N

The ability to cope with NH 4 +-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH 4 + and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH 4 +-N, and the biomass production was reduced by 47% at 3700 μM NH 4 +-N compared to NO 3 −-N. Similar responses were not found in Phragmites. The amounts (mg g −1 dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH 4 + (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO 3 − treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g −1 dry wt) of soluble sugars, TNC, K +, and Mg 2+ in roots under NH 4 + (5.6; 14.3; 20.6; 1.9) compared to NO 3 − nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K +, and Mg 2+, respectively), while root internal levels of NH 4 + and Ca 2+ (0.29; 4.6 mg g −1 dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca 2+, K +, and Mg 2+ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g −1 dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH 4 + supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH 4 +-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH 4 + is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH 4 + levels when P availability is high and NO 3 − is also provided.

Johnsongrass Control, Total Nonstructural Carbohydrates in Rhizomes, and Regrowth After Application of Herbicides Used in Herbicide-Resistant Corn (Zea mays)1

Greenhouse and field experiments were conducted to evaluate the efficacy of nicosulfuron, primisulfuron, glyphosate, glufosinate, imazethapyr plus imazapyr, and quizalofop on johnsongrass biomass reduction, rhizome total nonstructural carbohydrate (TNC) content, and subsequent regrowth from rhizomes. In the greenhouse, johnsongrass plants originating from rhizome segments were controlled 88 to 97% with quizalofop, glyphosate, imazethapyr plus imazapyr, nicosulfuron, and primisulfuron and 56% with glufosinate 3 wk after treatment (WAT). Johnsongrass treated with quizalofop, glyphosate, and nicosulfuron did not regrow 6 WAT, whereas plants treated with primisulfuron, imazethapyr plus imazapyr, and glufosinate regrew from the rhizome of the treated plant. Rhizome TNC levels 3 WAT were not reduced by glufosinate or nicosulfuron, but they were reduced 64% by quizalofop, 32% by primisulfuron, 61% by glyphosate, and 29% by imazethapyr plus imazapyr. When rhizome TNC was reduced by 60% or more compared with nontreated plants, johnsongrass did not regrow from the treated rhizomes. In field experiments, nicosulfuron and glyphosate controlled johnsongrass 94 and 99%, respectively, whereas imazethapyr plus imazapyr (79%) and glufosinate (85%) provided less control 6 WAT.Nomenclature: Glufosinate; glyphosate; imazapyr; imazethapyr; nicosulfuron; primisulfuron; quizalofop; johnsongrass, Sorghum halepense (L.) Pers. #3 SORHA.Additional index words: Biomass reduction, carbohydrate analysis, corn yield, fresh weight.Abbreviations: DAT, days after treatment; POST, postemergence; TNC, total nonstructural carbohydrate; WAT, weeks after treatment.

Effect of El Nĩno on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators.

We examined the response of demographic, morphological, and chemical parameters of turtle grass (Thalassia testudinum), to much-higher-than-normal rainfall associated with an El Niño event in the winter of 1997-1998. Up to 20 inches of added rain fell between December 1997 and March 1998. triggering widespread and persistent phytoplankton blooms along the west coast of Florida. Water-column chlorophyll concentrations estimated from serial Sea WiFS imagery were much higher during the El Niño event than in the previous or following years, although the timing and magnitude of phytoplankton blooms varied among sites. Seagrass samples collected in 1997, 1998, and 1999 provided an excellent opportunity to test the responsiveness of Thalassia to decline and subsequent improvement of water quality and clarity in four estuaries. Using a scoring technique based on temporal responsiveness, spatial consistency, and statistical strength of indicators, we found that several morphological parameters (Thalassia shoot density, blade width, blade number, and shoot-specific leaf area) were responsive and consistent measures of light stress. Some morphological parameters, such as rhizome apex density, responded to declines and subsequent improvement in water clarity, but lacked the statistical discriminating power necessary to be useful indicators. However, rhizome sugar, starch, and total carbohydrate concentrations also exhibited spatially and temporally consistent variation as well as statistical strength. Because changes in shoot density, as well as water clarity, affect rhizome carbohydrate levels, a composite metric based on Thalassia shoot density and rhizome carbohydrate levels together is probably more useful than either parameter alone as an indicator of seagrass health.

Effects of Fish Farm Loadings on Seagrass (Posidonia oceanica) Distribution, Growth and Photosynthesis

The spatial extent and timing of the impact of fish farms on the distribution and performance of a Posidonia oceanica meadow were examined in an embayment of the south-eastern coast of Spain (Hornillo Bay, Murcia). Changes in seagrass distribution were determined using available seagrass mapping (from 1988, i.e., before the onset of aquaculture activities and 1998) and by successive sampling in 1994 and 1998. Environmental variables (light attenuation coefficient, water-column dissolved nutrients and organic content of sediments) together with plant performance (shoot biomass, leaf growth rate, photosynthetic activity, carbohydrate reserves, the number of leaves per shoot, epiphyte loads and herbivore pressure) were measured in plants affected by organic discharges, and were compared with those found in reference healthy plants over an annual growth cycle. Since the onset of fish farm activity, 11.29 ha of P. oceanica meadow has been completely lost and 9.86 ha significantly degraded, thus resulting in a total affected area which accounts for about 53% of the former meadow, or 7-fold the fish farming area. Unequal propagation of seagrass die-off or degradation reflects the relevance of local factors such as depth and hydrodynamism on the true extent of fish farm impact. Water transparency decreases and dissolved nutrient and organic content of sediments increases in the vicinity of cages compared to distant reference stations, thus supporting the notion of environmental gradients caused by the organic release from cages, which spreads outwards. Shoot size, leaf growth rate and the number of leaves per shoot in plants close to the fish farm decreased. Moreover, low leaf growth and low rhizome carbohydrate concentration (always relative to that found in an undisturbed area) indicated carbon budget imbalances. Since light reduction in the affected area was only modest (31% of light reaching the sea surface, while at the same depth this figure was 39% at the reference site), and light availability was well above the minimum requirement estimated for this species, neither this factor nor epiphyte overgrowth (epiphyte load was lower in the affected area) seem to explain such carbon imbalances or the observed meadow regression. Alternatively, the high herbivore pressure found in the affected zone suggests that overgrazing is one of the main causes of decreasing shoot sizes and hence of carbon imbalance, reduced growth and shoot mortality. The impact of fish farms on seagrasses, therefore, seems to be highly variable and depends on complex interactions between a large number of processes.

Rhizome growth of Calamagrostis canadensis into mounds created for tree seedling establishment

Mineral soil-capped, inverted mounds (a layer of organic matter topped by a mineral soil cap on an undisturbed in situ soil horizon) are often created as planting sites for tree seedlings in areas dominated by a very competitive grass, Calamagrostis canadensis. Mounding, however, has had variable success at slowing the spread of this grass into the planting sites. A series of three field experiments investigated the pattern of rhizome growth of C. canadensis into mounds. Experiment 1 tested the interaction of mound thickness and clonal connections of C. canadensis to plants outside the mounds; experiment 2 the removal of the organic layer containing most of the rhizomes (screefing) prior to mounding, and experiment 3 the effect of mulching and fertilising on penetration and distribution of rhizomes through the mound. The thickness of the mineral soil cap was the most important factor determining the success of C. canadensis colonisation, while clonal connections were only of importance for shallow mounds. Screefing before creating the mound resulted in a reduction of C. canadensis establishment. Rhizome penetration from plants outside of the mound was not strongly affected by fertilising and mulching. A fourth experiment, conducted in a controlled environment, tested the ability of rhizomes from buried C. canadensis sods to grow through mineral soil caps of different thickness. The grass sods had different growth potentials which were achieved by a pre-treatment of two levels of light and nutrients, resulting in high and low rhizome carbohydrate concentrations. Low reserves did not reduce the ability of rhizomes to penetrate any thickness of the mineral soil cap. Strategies of C. canadensis establishment on mounds are discussed.

Effect of in situ light reduction on the maintenance, growth and partitioning of carbon resources in Thalassia testudinum banks ex König

The effects of in situ light reduction on the subtropical seagrass, Thalassia testudinum Banks ex König, in Corpus Christi Bay, Texas were examined from April 1993 to August 1994. The annual quantum flux at the seagrass canopy level was 5207 mol · m −2 · yr −1 or 46% of surface irradiance (SI) compared with two manipulated treatments that reduced underwater light to 1628 mol · m −2 · yr −1 (14% SI) and 864 mol · m −2 · yr −1 (5% SI). All plants subjected to 5% SI died after 200 days and over 99% of the plants receiving 14% SI died by the end of the experiment (490 days). Blade widths of plants in the control groups ranged from 6.4 to 7.0 mm, but decreased within months to 4.7 mm in both treatment group as a result of light reduction. Leaf production rates were significantly higher in control plants compared to plants within the 14 and 5% SI treatment groups, with all plants showing a seasonal trend of high productivity in July and low productivity in April. Blade chlorophyll (chl) concentrations increased, while the chl a- b ratio decreased with reduced light level. Soluble carbohydrate carbon content of controls was highest in rhizomes (102–152 mg C · g −1 dry wt.) and was relatively low in leaves (50–66 mg C · g −1 dry wt.) and in roots (57–74 mg C · g −1 dry wt.). In both light treatment groups, rhizome carbohydrate carbon content was 50% lower and leaf carbohydrate carbon content was about 15% lower than in controls, while the root carbon content did not differ significantly between the treatment groups and the controls. Ammonium and sulfide concentrations of pore water in the shaded cages were significantly higher than in control cages. We conclude that indices of shoot density, blade width, leaf growth, chl a: b ratio and blade chlorophyll content may be important early warning indicators of chronic underwater light stress in T. testudinum. A quantum flux of 1628 mol · m −2 · yr −1 (14% SI) was insufficient to maintain a positive carbon balance in T. testudinum in this bay system.

Management of marine construction works using ecological modelling

A system of bridges and tunnels between Denmark and Sweden is being constructed. The environmental management of the dredging and reclamation work includes planning using a mathematical model which can forecast the effect of different spill scenarios in order to minimize adverse effects on eelgrass beds. To develop the model, plots of eelgrass beds (4 m 2 ) were covered with nets excluding 30, 60 and 90% of the light. Shoot density, leaf and root/rhizome biomass, and soluble carbohydrates in roots and rhizomes were observed in order to determine the response of the plants to shading. In selected plots, all aboveground biomass was harvested to assess the re-growth potential. The minimum level of soluble carbohydrates necessary for securing re-growth was 60-90 mg g -1 . The inclusion of the subsediment parts of the eelgrass permits model runs beyond one growth season, and the prediction of re-growth after subsequent shading and winter dormancy. The model has been satisfyingly calibrated and validated. A feedback monitoring system has been developed based on field studies of eelgrass variables, a set of pre-fixed environmental criteria and forecasting of the effects of the construction works. The system facilitates planning and management of the dredging and reclamation operations, and mitigating actions during the progression of the work.

The effects of control on the biomass, carbohydrate content and bud reserves of bracken (Pteridium aquilinum (L.) Kuhn), and an evaluation of a bracken growth model

SummaryThis paper examines the initial effects of bracken control on frond numbers and biomass, and the biomass, carbohydrate reserves and bud densities of bracken stands cut once per year, twice per year, subject to a single application of asulam or left untreated. The seasonal dynamics of these parameters are displayed; carbohydrate and biomass are both removed from the rhizome system to produce frond tissue, and are replenished at the end of the growing season. Asulam application reduced densities of both active and dormant buds, and both frond biomass and density. It did not significantly reduce rhizome biomass or carbohydrate reserves in the two years after treatment. Cutting, either once or twice per year reduced both rhizome biomass and rhizome carbohydrate reserves, as well as bud densities, though the latter were reduced in proportion to biomass. Cutting twice a year reduced the production of fronds, both in numbers and biomass. The collected data were used to evaluate a model of bracken growth, and subsequently to improve estimates of some of the model parameters. The model simulations of control treatments were compared to field data. The effects of cutting once per year and spraying with asulam were predicted accurately, but the bracken stand was more resilient to cutting twice per year than would be expected from model predictions. The combination of cutting and spraying is discussed as a potential tool in land management and the deficiencies of the model are discussed in relation to the need for future research into the biology of bracken.

The effect of accelerated sand accretion on growth, carbohydrate reserves, and ethylene production in Ammophila breviligulata (Poaceae)

In a 3‐yr field study Ammophila breviligulata responded positively to sand accretion by maintaining plant height above a rising sand surface. Vertical growth for treated plants was approximately 80 cm over 3 yr. Bunch size did not differ between treated and control plants in the first or second year. But by Year 3, bunch circumference, number of stems per bunch, and plant height above the sand surface were significantly greater in plants receiving accelerated sand accretion. During the first year, treated plants flowered significantly less than controls. The greater vertical growth necessary for the treated plants may have depleted the energy reserves of a young rhizome system otherwise used for inflorescence production. The percent of the total nonstructural carbohydrates in rhizomes in the form of sugar was greater in plants in the accelerated sand accretion treatment, perhaps sustaining the necessary rapid vertical growth. To determine whether ethylene plays a role in stimulating stem elongation, endogenous ethylene accumulation was measured in plants in the field and seedlings in the greenhouse exposed to sand accretion. Treated plants responded by accumulating higher levels of ethylene in their stems, after 10 and/or 30 d, than did control plants. However, plants treated with exogenous ethylene exhibited growth and elongation inhibition.