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

Abstract

This study evaluated the abihty ot Zostera marma L (eelgrass) to balance the daily photosynthetic deflc~t by mobilization of carbon reserves stored In below-ground tlssues durlng a period of extreme w n t e r llght lln~itation A quantitative understand~ng of the mobllizat~on process and its hmltatlons is essential to the development of robust models predict~ng mnimuni llght levels r e q u~r e d to nialntaln healthy seagrass populatlons Plants were grown m runnlng seawater tanks under 2 llght reglrnes One treatment was provlded wlth 2 h irradiance-saturated photosynthes~s (H,,,) to produce severe llght limitation, whlle control plants were grown under 7 h H,,, simulating the typical w~n t e rtune condition In Monterey Bay, California, USA Although plants maintained under 2 h H,,, were more severely carbon h m t e d than plants grown under 3 h H,,, whole-plant carbon balance calculated from metabohc needs and growth rates was negative for both Q,, treatments The eelgrass studied here responded to negative carbon balances by suppressing the product~on of new roots, depleting sucrose reserves and effecting a gradual decrease In growth rate a n d a n Increase In the activlty of sucrose synthase (SS, E C 2 4 1 13) in s~n k tlssues in the termnal stages of carbon stress The 3 h H,,, plants survlved the 45 d course of the expenment while the plants grown under 2 h H,,, died within 30 d even though one-thlrd of the11 carbon reserves remalned lmmobdized In the rhizome Thus extreme l~g h t llmitatlon can prevent full mob~llzation of carbon reserves stored in below-ground tissues probably through the effects of anoxla on translocation Metabolic rates, particularly photosynthesls and resplration of the shoot, were unaffected by prolonged carbon hrmtation in both treatments The patterns observed here can provide useful indices for assess~ng the state and fate of seagrass ecosystems in advance of catastrophic declines KEY WORDS: Seagrass Carbon balance . Resource a l l~c d l i~~n .Photosynthesis . Light

Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism

“…The overall sucrose and starch content increased from early May to beginning of June in the control plots (Table S1 in the supplement) as expected from seasonal dynamics of carbohydrate accumulation (Alcoverro et al 1999). This significant time effect (see Table S2 in the supplement) was already recorded 8 d after the beginning of the experiment (t-test, p < 0.01; Fig.…”

“…Non-structural carbohydrate content was measured on Days 1, 8 and 23 of the experiment as well as 1 wk after the removal of shading screens following the method described by Alcoverro et al (1999), based on Yemm & Willis (1954). Samples of young rhizome (1 cm from the apex) were ground, extracted…”

Macroalgae blooms and their effects on seagrass ecosystems

“…Carbon translocation and storage capacity between leaves, rhizomes and roots can control the ecological success of seagrasses under light reduction conditions (Lee and Dunton, 1996;Alcoverro et al, 1999;Touchette and Burkholder, 2000;Brun et al, 2002;Peralta et al, 2002). Ammonium assimilation into amino acids and other nutrogen-organic compounds requires carbon skeletons and energy, which are from photosynthesis or mobilized from carbon-reserves in seagrasses (Brun et al, 2008;Villazán et al, 2013).…”

Annual and perennial life history strategies of Zostera marina populations under different light regimes

“…Underwater photon flux density (PFD) has been recognized as a major factor controlling the survival and distribution of seagrasses (Dennison & Alberte 1985, Dennison 1987, Alcoverro et al 1999, Nielsen et al 2002. Because compensation irradiance represents the minimum light requirement for plant survival, the duration of PFDs above light compensation points (H comp ) is closely related to the survival of seagrasses (Dennison 1987).…”