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Publications
Publications (79)
Plant species often separate strongly along steep environmental gradients. Our objective was to study how coupling between plant physiology and environmental conditions shapes vegetation characteristics along a distinct hydrological gradient. We therefore investigated species photosynthesis in air and under water within a limited area from dry-as-d...
Background:
Submerged plants composed of charophytes (green algae) and angiosperms develop dense vegetation in small, shallow lakes and in littoral zones of large lakes. Many small, oligotrophic plant species have declined due to drainage and fertilization of lakes, while some tall, eutrophic species have increased. Although plant distribution has...
We investigated temperature effects on eelgrass Zostera marina L. growing close to its southern distribution limit along the eastern coast of North America in Virginia, USA. We combined growth and survival experiments with microelectrode measurements of internal meristematic oxygen and analyses of metabolic compounds. Eelgrass shoots were grown at...
Nye danske søer-design af optimal miljøtilstand og biodiversitet Danmark er internationalt førende ved at have skabt omkring 50 nye søer større end 10 ha. Med få undtagelser kender vi imidlertid ikke deres naturkvalitet. Med optimalt fysisk design og forvaltning kan nye søer sikre overlevelse af kritisk truede eller sjaeldne arter. Derfor har fersk...
Seagrasses grow submerged in aerated seawater but often in low O 2 sediments. Elevated temperatures and low O 2 are stress factors.
Internal aeration was measured in two tropical seagrasses, Thalassia hemprichii and Enhalus acoroides , growing with extreme tides and diel temperature amplitudes. Temperature effects on net photosynthesis ( P N ) and...
Photosynthesis of most seagrass species seems to be limited by present concentrations of dissolved inorganic carbon (DIC). Therefore, the ongoing increase in atmospheric CO2 could enhance seagrass photosynthesis and internal O2 supply, and potentially change species competition through differential responses to increasing CO2 availability among spe...
Charophytes are benthic macroalgae that live in fresh and brackish waters. Given the historic deterioration of their habitats and their competitive inferiority relative to tall rooted plants under eutrophic conditions, it is hypothesized that charophytes are among the most threatened autotrophs. Also, it is expected that charophytes with generalist...
Small rosette plants in oligotrophic, softwater lakes, such as Lobelia dortmanna and Littorella uniflora , have highly permeable root surfaces that allow acquisition of CO 2 from the sediment for photosynthesis. In the absence of an oxygen supply from photosynthesis, these permeable roots increase the risk that the plants are deprived of oxygen whe...
Eelgrass (Zostera marina L.) occasionally experiences severe die-offs during warm summer periods with variable water column oxygen partial pressures (pO2). Eelgrass is known to be very intolerant to tissue anoxia with reduced growth and increasing mortality after ≤ 12 h anoxia in the dark at temperatures of ≥ 25 °C. In the present study we experime...
Distinct ‘fairy rings’ consisting of narrow fringes of eelgrass (Zostera marina l.) expand radially over a bottom of chalk plates outside the calcium carbon- ate cliffs of the island of Møn, Denmark. We conducted a survey to evaluate possible explanations for the formation of the rings and, more specifically, for the apparent die- off of eelgrass s...
1. Lake eutrophication has increased phytoplankton blooms and sediment organic matter. Among higher plants, small, oligotrophic rosette species (isoetids) have disappeared, while a few tall, eutrophic species (elodeids) may have persisted. Despite recent reduction of nutrient loading in restored lakes, the vegetation has rarely regained its former...
The tolerance of eelgrass (Zostera marina L.) to anoxia was assessed experimentally to evaluate the potential role of short-term anoxia on eelgrass performance. Eelgrass ramets (terminal leaf bundles with rhizomes and roots) were submerged in anoxic seawater for variable periods of time (0.5 to 48h) at three temperatures (20, 25 and 30°C) in darkne...
During coastal eutrophication, fast-growing, ephemeral macroalgae bloom at the expense of slow-growing, perennial macroalgae. This change in community composition has been explained by a differential ability to exploit and utilize inorganic nitrogen among macroalgae with different growth strategies. However, some coastal areas are becoming phosphor...
Extreme environmental gradients generate distinct patterns in species distributions dependent on their stress tolerance and competitive capability. This is the situation along the steep land-water gradient in a stone quarry on Öland's alvar. Availability of water and nutrients varies profoundly between bare limestone slabs with no soil, via tempora...
Constraints imposed by the spherical form and gelatinous matrix of centimeter-thick colonies of the cyanobacterium Nostoc zetterstedtii on its functional properties were tested by examining the scaling of its composition, light absorption, photosynthesis, and respiration to individual size. In three summer experiments with colonies collected from t...
Nostoc pruniforme is a freshwater cyanobacterium forming large spherical colonies of up to several centimeters in diameter. The size and shape result in low surface area to volume (SA/V) ratios that potentially put severe constraints on resource acquisition. In the present study we have specifically examined how N. pruniforme copes with the acquisi...
Submersed plants have different strategies to overcome inorganic carbon limitation. It is generally assumed that only small rosette species (isoetids) are able to utilize the high sediment CO(2) availability. The present study examined to what extent five species of submersed freshwater plants with different morphology and growth characteristics (L...
We examined how the freely floating macrophyte, Stratiotes aloides L., sampled from a CO2-supersaturated pond, changes leaf morphology, photosynthesis and inorganic carbon acquisition during its different submerged and emerged life stages in order to evaluate whether S. aloides requires consistently supersaturated CO2 conditions to grow and complet...
We analysed the development of submerged macrophytes in Lake Fure, Denmark, experiencing a 30‐fold increase of phosphorus input from year 1900 to 1970 and a subsequent decline to twice the 1900 level in 2005. Nutrient enrichment stimulated phytoplankton growth and restricted macrophyte distribution by reducing water transparency from a summer mean...
INTRODUCTION Seagrasses form important underwater marine and estuarine ecosystems on all continents except Antarctica. Seagrass ecosystems are highly productive, forming extensive habitats which support highly diverse communities. The seagrasses themselves assimilate and cycle nutrients and other chemicals. Their extensive above- and below-ground b...
Temporal and spatial variation of d34S, total sulfur (TS) concentration, and elemental sulfur concentration (S0) in leaves, roots, and rhizomes of Zostera marina was followed between June 2002 and May 2003 at four locations in Roskilde Fjord and Øresund, Denmark. These were related to temporal changes in sediment sulfide concentrations, sulfur pool...
Measurements of oxygen variability and transport in seagrasses and other submerged plants are difficult to conduct and interpret
due to the existence of several sources and sinks of oxygen driving internal transport at different rates depending on conditions
in the water column and sediment. Oxygen release and transport in seagrasses have mostly be...
Seagrasses are, like all vascular plants, obligate aerobes, which require a continuous supply of oxygen to sustain aerobic metabolism of both above- and below-ground tissues. Compared to their leaves, seagrass roots and rhizomes may experience oxygen deprivation for shorter periods, but these below-ground tissues exhibit physiological adaptations w...
The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (PO2...
and Aims Submerged plants possess well-developed aerenchyma facilitating intra-plant gas-phase diffusion of O2 to below-ground tissues, which are usually buried in anoxic sediments. However, aquatic habitats differ in terms of O2 fluctuations in the water column and in O2 consumption of the sediment, and aquatic plants differ in aerenchymal volume...
The spatial and seasonal variation in the concentration and stable isotopic composition of carbon and nitrogen was studied in Zostera marina (eelgrass) meadows in Roskilde Fjord and Øresund, Denmark. Organic carbon (C org) and nitrogen (Norg) concentrations in new tissues (leaf, rhizome, roots) ranged from 11 to 40 mmol g 21 C and 0.4 to 3.6 mmol g...
1. Lobelia dortmanna is a common representative of the small isoetid plants dominating the vegetation in nutrient‐poor lakes in Europe and North America. Because of large permeable root surfaces and continuous air lacunae Lobelia exchanges the majority of O 2 and CO 2 during photosynthesis across the roots. This leads to profound diel pulses of O 2...
1 Oxygen and sulphide dynamics were examined, using microelectrode techniques, in meristems and rhizomes of the seagrass Thalassia testudinum at three different sites in Florida Bay, and in the laboratory, to evaluate the potential role of internal oxygen variability and sulphide invasion in episodes of sudden die-off. The sites differed with respe...
Sudden events of seagrass die-off have been suggested to be induced by invasion of the phytotoxin sulphide under environmental stress generating low oxygen supply in seagrass tissues. Laboratory experiments were conducted with eelgrass (Zostera marina L.) to measure intra-plant changes in oxygen and sulphide by means of microelectrodes at different...
Quantifying the dynamics of the early stages in the life cycle of mangroves is essential to predict the distribution, species composition and structure of mangrove forests, and their maintenance and recovery from perturbations. The growth and population dynamics of two stands of the mangrove Kandelia candel in Halong Bay (Viet Nam) were examined fo...
Seasonality and depth zonation of two common intertidal northern Vietnamese seagrass species, Halophila ovalis and Zostera japonica, were investigated in a 50 m long intertidal transect from 1999 till 2001. Z. japonica occurred in the middle intertidal (1.2 m above mean chart datum to mean sea level at 2.1 m above chart datum). H. ovalis occurred d...
The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by e...
We examined the variability in oxygen content of meristematic tissues in eelgrass in order to evaluate its potential role in events of sudden mass mortality within eelgrass beds. Oxygen content within intact eelgrass plants could be described by use of microelectrode techniques at high temporal and spatial resolution in the laboratory and in the fi...
This study investigated if siltation-associated changes in the sediments are detrimental to seagrasses. We chose Cymodocea rotundata as the test species because it is considered one of the Southeast Asian seagrass species most sensitive to siltation. The approach included the (1) evaluation of the effects of silted sediments on plant growth, evalua...
We present a comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalgae measured
by SCUBA-diving along 162 transects in 27 Danish fjords and coastal waters, coupled to 1,400 data series of water chemistry
(especially nitrogen) and Secchi depth transparency collected between March and October. Danish co...
We present a comparative analysis of 1400 data series of water chemistry (particularly nitrogen and phosphorus concentrations),
phytoplankton biomass as chlorophylla (chla) concentrations, concentrations of suspended matter and Secchi depth transparency collected from the mid-1980s to the mid-1990s
from 162 stations in 27 Danish fjords and coastal...
Marine sediment properties were quantified along SE Asian siltation gradients and across different habitat types to assess the extent of terrestrial sediment influence and derive indicators of of terrestrial sediment input. Three sites in the Andaman Sea (Ranong, Phuket and Trang; Thailand), one site in the Gulf of Thailand (Pak Phanang; Thailand)...
Biomass, photosynthesis and growth of the large, perennial brown alga Laminaria saccharina (L.) Lamour. were examined along a depth gradient in a high-arctic fjord, Young Sound, NE Greenland (74°18′N; 20°14′W), in order to evaluate how well the species is adapted to the extreme climatic conditions. The area is covered by up to 1.6-m-thick ice durin...
The photosynthetic performance of sea ice microalgae, benthic microalgae, coralline red algae (Phymatolithon foecundum) and brown macroalgae (Laminaria saccharina, Fucus evanescens and Desmarestia aculeata) in an ice-covered high-Arctic fjord (Young Sound, NE Greenland) was studied with in situ instruments for oxygen microprofiling and active chlor...
Experimental additions of nutrients to the sediment of Enhalus acoroides stands were performed at four sites and three times along the year in Cape Bolinao, NW Philippines to test the hypothesis that seagrass growth in tropical environments is limited by the availability of nutrients. Both the nitrogen content (as % DW) and the nitrogen incorporati...
A literature review of the effects of the reducing conditions of the sediment on seagrass metabolism, growth and survival, and of the morphological and physiological adaptations that seagrasses show to cope with sediment anoxia is presented and major gaps in knowledge are identified. The hypothesis that sediment anoxia controls the survival of seag...
Differences in ramet size (i.e. the mass of a shoot with its share of leaves, rhizome and roots) and allocation of mass and nutrients to different ramet components were quantified based on a comparative analysis of these properties in a large set of seagrass meadows under contrasting conditions of nutrient availability in the Philippines and Thaila...
7 pages, 4 figures. The growth rate and nutritional status of Rhizophora apiculata seedlings were analyzed across mangrove stands with different sediment composition in The Philippines and Southern Thailand. Plant growth differed 10-fold and the production of new leaves, roots and branches varied between 50- and 100-fold across sites. Most (>60%) o...
The nitrogen balance of a shallow water eelgrass Zostera marina L. bed was assessed in April and August 1995 by quantifying pools of nitrogen in plants and sediment and by measuring rates of nitrogen inputs and losses in vegetated and bare sediments. The total pool of nitrogen in the vegetated sediment doubled from April to August. The exchange of...
The response of mixed Southeast Asian seagrass beds to siltation was analyzed based on field data, a transplantation experiment and experimental manipulation of light availability in seagrass populations along a silt gradient at Cape Bolinao, The Philippines. Seagrass species diversity, shoot density and depth penetration declined with increasing a...
The spatial distribution of oxygen and the dynamics of the oxic microzone around roots of Cymodocea rotundata were studied using oxygen microelectrodes under constant light conditions and during light-dark transitions. Under daylight steady state conditions, oxygen was present at concentrations up to 75 % of air saturation at the root surface, and...
The patterns of change in species richness and biomass of Southeast Asian seagrass communities along siltation gradients were compared at different sites in The Philippines and Thailand. Seagrass species richness and community leaf biomass declined sharply when the silt and clay content of the sediment exceeded 15%.Syringodium isoetifoliumandCymodo...
The ability to sustain growth at low availability of nitrogen (N) was examined in 6 species of macroalgae with different growth strategies by comparing substrate dependent growth kinetics. The N required to support optimal growth and the N uptake kinetics of 2 slow-growing algae, Fucus vesiculosus and Codium fragile, and 4 fast-growing species, Cha...
Nutrient enrichment of shallow coastal waters changes the composition of plant commu-nities so that slow-growing, benthic macrophytes are replaced by fast-growing algae such as phyto-plankton and ephemeral macroalgae. This scenario suggests that fast-growing algae suffer more from nutrient limitation than slow-growing algae at low nutrient availabi...
Changes in the size of intracellular nitrogen pools and the potential feedback by these pools on maximum N uptake (NH4+ and NO3−) rates were determined for Chaetomorpha linum (Müller) Kützing grown sequentially under nutrient-saturating and nutrient-limiting conditions. The size of individual pools in N-sufficient algae could be ranked as residual...
The role of internal and external phosphorus recycling to support high seagrass productivity was evaluated by an in situ study of Z. marina. The phosphorus requirements during rapid growth in spring and summer exceeded uptake from external sources, and the deficit was met by internal recycling of phosphorus reabsorbed from old tissues before they w...
The seasonal variation and distribution of rosmarinic acid and caffeic acid in leaves and roots-rhizomes of eelgrass (Zostera marina L.) were examinated by using an isocratic high-performance liquid chromatography (HPLC) method developed for separation and quantification of the two phenolic compounds in crude plant extracts. The variation in phenol...
The nitrogen dynamics of an eelgrass Zostera marina L. population were. assessed during an annual cycle by using measurements of seasonal changes in eelgrass biomass, production, losses and nitrogen content of different plant tissues. Estimated nitrogen uptake and reclamation (internal recycling) were compared to incorporation and theoretical requi...
Nitrogen acquisition and dynamics of eelgrass Zostera marina L. were assessed during a late summer period of high plant growth and low nitrogen availability in the water column. Nitrogen uptake through leaves and roots, translocation within the plant, and the role of nitrogen reclamation from older plant parts were estimated using N-15-techniques a...
The physico-chemical environment and the resource needs of phytoplankton, periphyton and macrophytes are markedly different. In this paper we compare the characteristics of the different phototrophs with respect to water movements and diffusive boundary layers, nutrient demands, carbon and oxygen dynamics, and light climate and light requirements....
Eelgrass (Zostera marina L.) collected in the field was analysed for nitrogen content in different tissues. Cultured eelgrass plants were pre-incubated with 15NNH4+ (90 μmol NH4+ 1−1) and subsequently incubated in enriched seawater (50 μmol NH4+ 1−1) with ambient at.% 15N in order to follow changes in nitrogen content and translocation among diffe...
In Roskilde Fjord, Denmark, epiphyte biomass increased exponentially with leaf age during the first 10-14 d of colonization. On older leaves epiphyton gradually approached a phase with only small changes in biomass. Algal doubling times were 3.6-4.6 d on young leaf segments and increased to >14 d on old leaves. When corrected for biomass losses due...
The effect of nutrient enrichment on epiphyte development was examined by following the seasonal development of epiphyte biomass on eelgrass (Zostera marina L.) at four localities along a nutrient gradient in Roskilde Fjord, Denmark between March and December 1982. In the most nutrient-poor area, epiphyte biomass followed a distinct bimodal seasona...
A study done at Hvidøre in the Øresund, Denmark, in 1979 showed that algae and bacteria occurred on eelgrass leaves throughout the year. Algal species composition, biomass and productivity varied markedly with season, depending on both environmental conditions and growth pattern of the host macrophyte. Bacteria and the diatom Cocconeis scutellum Eh...
A dense epiphyte community develops on Lobelia dortmanna L. during spring in the mesotrophic waters of Lake Almind, Denmark. This community has attenuated the incident light at 0.5 m depth by 67.4–81.7% within two years. The attenuation is spectrally selective, the proportion of red light transmitted increasing with epiphyte density. Epiphyte atten...
The seasonal changes of eelgrass biomass and net production were recorded in an eelgrass bed in the Oresund, Denmark, from August 1978 through December 1979. The eelgrass biomass varied from 170 g dry wt · m−2 in early spring to 622 g dry wt · m−2 in autumn. The ratio of maximum biomass to minimum biomass was 23 for leaves and 2.5 for roots and rhi...
This paper discusses how natural parameters and human activity regulate biomass and growth of eelgrass. Biomass and growth measurements of epiphytic algae also provide a convenient method for assessing the effect of inorganic nutrient loading in different parts of a receiving area. Eelgrass is suitable as an indicator of trace metal pollution as it...
Ophelia, nr. suppl. 1, 57-64
Ophelia, nr. suppl. 1, 49-55
