Severe Light Limitation Research Articles

Resource allocation and sucrose mobilization in light-limited eelgrass Zostera marina

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 187:121-131 (1999) - doi:10.3354/meps187121 Resource allocation and sucrose mobilization in light-limited eelgrass Zostera marina Teresa Alcoverro1,*, Richard C. Zimmerman2, Donald G. Kohrs2, Randall S. Alberte3 1Centre d'Estudis Avançats de Blanes (CSIC), Carretera Sta. Bàrbara s/n, 17300 Blanes, Girona, Spain 2Moss Landing Marine Laboratories, San Jose State University Foundation, PO Box 450, Moss Landing, California 95039, USA 3Areté Associates Inc. 1725 Jefferson Davis Hwy, Arlington, Virginia 22202, USA *E-mail: teresa@ceab.csic.es ABSTRACT: This study evaluated the ability of Zostera marina L. (eelgrass) to balance the daily photosynthetic deficit by mobilization of carbon reserves stored in below-ground tissues during a period of extreme winter light limitation. A quantitative understanding of the mobilization process and its limitations is essential to the development of robust models predicting minimum light levels required to maintain healthy seagrass populations. Plants were grown in running seawater tanks under 2 light regimes. One treatment was provided with 2 h irradiance-saturated photosynthesis (Hsat) to produce severe light limitation, while control plants were grown under 7 h Hsat, simulating the typical wintertime condition in Monterey Bay, California, USA. Although plants maintained under 2 h Hsat were more severely carbon limited than plants grown under 7 h Hsat, whole-plant carbon balance calculated from metabolic needs and growth rates was negative for both Hsat treatments. The eelgrass studied here responded to negative carbon balances by suppressing the production of new roots, depleting sucrose reserves, and effecting a gradual decrease in growth rate and an increase in the activity of sucrose synthase (SS, E.C. 2.4.1.13) in sink tissues in the terminal stages of carbon stress. The 7 h Hsat plants survived the 45 d course of the experiment while the plants grown under 2 h Hsat died within 30 d, even though one-third of their carbon reserves remained immobilized in the rhizome. Thus, extreme light limitation can prevent full mobilization of carbon reserves stored in below-ground tissues, probably through the effects of anoxia on translocation. Metabolic rates, particularly photosynthesis and respiration of the shoot, were unaffected by prolonged carbon limitation in both treatments. The patterns observed here can provide useful indices for assessing the state and fate of seagrass ecosystems in advance of catastrophic declines. KEY WORDS: Seagrass · Carbon balance · Resource allocation · Photosynthesis · Light Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 187. Publication date: October 14, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Hydrodynamic and chemical conditions during onset of a red-tide assemblage in an estuarine upwelling ecosystem

The hydrodynamics and nitrogen/silicon biogeochemistry accompanying the development of a red-tide assemblage were examined in the Ría de Vigo (northwest Spain), a coastal embayment affected by upwelling, during an in situ diel experiment in September 1991. Despite a low N:Si molar ratio (0.5) of nutrients entering the surface layer, which was favourable for diatom growth, the diatom population began to decline. Limited N-nutrient input, arising from moderate coastal upwelling in a stratified water column, restricted net community production (NCP = 630 mg C m−2 d−1). In addition, light-limitation of gross primary production (GPP = 1525 mg C m−2 d−1) was observed. The relatively high f-ratio (= NCP:GPP) recorded (0.41, characteristic of intense upwelling conditions) would have been as low as 0.15 had not GPP been limited by light intensity. Temporal separation of carbohydrate synthesis during the photoperiod from protein synthesis in the dark could be inferred from the time-course of the C:N ratio of particulate organic matter. Severe light-limitation would lead to diatom collapse were the diatoms not able to meet all their energy requirements during the hours of darkness. Under the hydrodynamic, nutrient and light conditions of the experiment, an assemblage of red-tide-forming species began to develop, aided by their ability to migrate vertically and to synthesize carbohydrates during the light in surface waters and protein during the dark at the 4 m-deep pycnocline. Thermal stratification, reduced turbulence, intense nutrient mineralization, and the limited nitrogen input through moderate upwelling were all favourable to the onset of a red-tide assemblage.

Nitrogen Assimilation and Partitioning in the Mediterranean Seagrass Posidonia oceanica

Abstract. The supply of nitrogen (N) often limits the productivity of marine macrophytes. In vitro and in vivo assays of glutamine synthetase (GS) activity were employed to investigate patterns of N assimilation by the Mediterranean seagrass Posidonia oceanica (L.) DELILE. Biomass‐specific GS activity wa measured in root tissue, in leaves within a shoot, in shoots collected at two sites during two season and over a depth range of 5–33 m. Root tissue was less important than shoot tissue in assimilating inorganic N in P. oceanica, due both to the small roots' biomass (ca. 3% of total plant biomass and greatly lower (10‐ to 50‐fold) GS activities. While the GS activity and N assimilatory potentia (biomass × GS activity; μmol N‐h‐‐1) were greatest in leaf 2, leaves 1 and 3–5 assimilated N a significant rates. Shoots from a site characterized by elevated N availability in the winter water column and no significant sediment N reservoir exhibited GS activities that were 9‐times higher than shoot from a more oligotrophic site. Shoot GS activities in July increased linearly from 5 to 33 m and wer correlated with light availability as defined by Hsat, (daily period during which photosynthetic reaction are light‐saturated). This may represent metabolic compensation by P. oceanica to maintain N influx. Factors contributing to the ecological success of P. oceanica include the ability to assimilate N under conditions of severe light limitation (< 35 μmol photons. m‐2. s‐1), and metabolic plasticity to ensur the de novo generation of N‐containing organic compounds.

Patterns of abundance and dominance of the phytoplankton of Rostherne Mere, England: Evidence from an 18-year data set

Rostherne Mere is a small but relatively deep, turbid and highly eutrophic lake. In recent years, the productivity and dynamics of its phytoplankton have been particularly sensitive to the interaction between light income and thermal stability. Analysis reveals that interannual differences in the size and duration of phytoplankton crops, as well as in the predominating species, are not random but that there is a reproducible coherence with weather-generated external forcing. Severe light-limitation restricts phytoplankton development outside the stratified period, though delayed stratification in spring may promote relatively large diatom crops. In summer,Microcystis will usually dominate provided its recruitment period coincides with high water clarity. OtherwiseCeratium generally dominates. Examples of extremely stable stratification leading toScenedesmus dominance and of persistent episodes of summer mixing favouringOscillatoria dominance are found to agree well with previous matrix models.

Competition between purple and brown phototrophic bacteria in stratified lakes: sulfide, acetate, and light as limiting factors

The affinities for sulfide and acetate under mixotrophic conditions have been determined for the brown Chlorobium phaeobacteroides and the purple Thiocapsa roseopersicina isolated from a bloom in Lake Kinneret (Israel) at a depth of about 18 m. C. phaeobacteroides exhibited a far higher affinity for sulfide than T. roseopersicina. For acetate, the opposite was observed. In light-limited continuous cultures, C. phaeobacteroides preferentially used sulfide, whereas in mixotrophic cultures of T. roseopersicina sulfide could be detected without detectable acetate. Competition experiments under increasingly severe light limitation resulted in co-existence of the two strains. Relatively high light intensities resulted in a dominance of T. roseopersicina over C. phaeobacteroides, whereas at lower intensities C. phaeobacteroides became dominant. However, at light intensities below 2 μEin · m−2· s−1, T. roseopersicina was completely excluded. At low light intensities, C. phaeobacteroides is able to grow at a much higher rate than T. roseopersicina. The maintenance rate constant μe of C. phaeobacteroides is −0.001 h−1, whereas that of T. roseopersicina is −0.011 h−1. However, high light intensities inhibit the growth rate of C. phaeobacteroides, but not that of T. roseopersicina. The explanation of the high numbers of C. phaeobacteroides in Lake Kinneret appears to be the combination of low light intensities and low sulfide concentrations. As a result, the incorporation of acetate is enhanced. The low numbers of T. roseopersicina can be explained by the high maintenance energy requirements of this organism, which exceed the available light at the depth of the bloom.

Competition between purple and brown phototrophic bacteria in stratified lakes: sulfide, acetate, and light as limiting factors

The affinities for sulfide and acetate under mixotrophic conditions have been determined for the brown Chlorobium phaeobacteroides and the purple Thiocapsa roseopersicina isolated from a bloom in Lake Kinneret (Israel) at a depth of about 18 m. C. phaeobacteroides exhibited a far higher affinity for sulfide than T. roseopersicina. For acetate, the opposite was observed. In light-limited continuous cultures, C. phaeobacteroides preferentially used sulfide, whereas in mixotrophic cultures of T. roseopersicina sulfide could be detected without detectable acetate. Competition experiments under increasingly severe light limitation resulted in co-existence of the two strains. Relatively high light intensities resulted in a dominance of T. roseopersicina over C. phaeobacteroides, whereas at lower intensities C. phaeobacteroides became dominant. However, at light intensities below 2 μEin · m −2 · s −1, T. roseopersicina was completely excluded. At low light intensities, C. phaeobacteroides is able to grow at a much higher rate than T. roseopersicina. The maintenance rate constant μ e of C. phaeobacteroides is −0.001 h −1, whereas that of T. roseopersicina is −0.011 h −1. However, high light intensities inhibit the growth rate of C. phaeobacteroides, but not that of T. roseopersicina. The explanation of the high numbers of C. phaeobacteroides in Lake Kinneret appears to be the combination of low light intensities and low sulfide concentrations. As a result, the incorporation of acetate is enhanced. The low numbers of T. roseopersicina can be explained by the high maintenance energy requirements of this organism, which exceed the available light at the depth of the bloom.

The chemistry of the Delaware estuary. General considerations1

Many properties were measured in the Delaware estuary from freshwater to its mouth (30‰ salinity). Distinctive mixing patterns in property‐salinity plots illustrate predictable behavior for different parameters. For example, alkalinity always shows an expected positive linear relationship and dissolved organic carbon a negative linear relationship (indicative of conservative mixing). In contrast, phosphate shows a nonlinear plot suggestive of an estuarine source, nitrate a nonlinear plot suggestive of biochemical reactivity, and dissolved iron a nonlinear plot indicative of geochemical reactivity.The upper estuary has very high levels of nutrients, especially nitrate (near 200 µM), and a measurable depletion of surface water dissolved oxygen (equivalent to an apparent oxygen utilization of 100–250 µg‐atoms O·liter−1 in winter and summer). However, oxygen levels appear to be consistently above 35% saturation in the upper estuary and are near saturation throughout most of the estuary. The high nutrients do not cause algal blooms in the upper estuary; instead primary productivity appears maximal in the lower estuary. It is postulated that high suspended sediment in the upper estuary causes severe light limitation and as a result moderate utilization of nutrients sustains moderate productivity throughout the estuary and throughout the year.