Abstract
In order to prevent salt damage because seaweed enzymes can only operate under hypohaline conditions (salinity ≈ 6‰ - 12‰) but also obtain for photosynthesis an in the aquatic environment—due to a 10,000 fold strongly limited carbon source—seaweeds developed several mechanisms to meet these vital demands for survival in the harsh euhaline oceanic environment (salinity range: 32‰ - 35‰), we tested this range of adaptation mechanisms in the euhaline oceanic collected water in combination with the seaweed moisture. We obtained under laboratory conditions at 10 bar mechanical pressure for four seaweed species: Ulva lactuca, Caulerpa sertularioides, Caulerpa cf. brachypus (all three green) and Undaria pinnatifidia (brown). Oceanic water and seaweed moisture were measured for salinity, pH and by Inductively Coupled Plasma Spectroscopy (ICP)-techniques concentrations for macro-elements: (Ca, Fe, K, Mg, Mn, Na, P, & S), micro-elements ≈ [HM]: (Al, As, Cd, Co, Cr, Cu, Mo, Ni, Pb & Zn) and nutrients (N-total & P-total). The [seawater compound X]/[oceanic compound X] ration is a reflection of an inward (uptake) or excretion mechanism over the seaweed cellular membrane which is operative. Our observations gave a clear dispersion to salinity stress with on one hand the green seaweed U. lactuca and on the other the brown seaweed U. pinnatifidia. Both Caulerpa spp. took in an intermediate position. Observed in compensatory responses to salinity stress was ranging Ulva sp. both Caulerpa spp.-Undaria sp.: 1) amount pressed seaweed moisture: [ml/g Fresh Weight]; 2) salinity: (in ‰); 3) Na+ storage vacuole volume; 4) Na+:K+ ratio (reflection of K+ as osmolyticum); 5) ∑[HM] (as osmolyticum); 6) pH (seaweed moisture); 7) Nutrients (N & P); 8) availability of essential metal elements for plants (Cu, Fe, Zn, Mn, Mo, Ni); 9) transport direction of micro- and macro-elements. Finally, the role of brown vs. green seaweeds in the evolutionary eukaryotic tree of life in relation to the ability of the brown seaweeds to produce their own osmolyticum will be discussed.
Highlights
At present, terrestrial agriculture is at its limits mainly for available land area and fertilizers
In order to prevent salt damage because seaweed enzymes can only operate under hypohaline conditions and obtain for photosynthesis an in the aquatic environment—due to a 10,000 fold strongly limited carbon source—seaweeds developed several mechanisms to meet these vital demands for survival in the harsh euhaline oceanic environment, we tested this range of adaptation mechanisms in the euhaline oceanic collected water in combination with the seaweed moisture
We explained in great extent the “seaweed-paradox”: which implies that biomass production is severely hampered by a 10,000 fold slower diffusion rate of a Carbon source or Dissolved Inorganic Carbon (DIC) in the biophysical medium water in comparison to terrestrial C3 crops [10]
Summary
Terrestrial agriculture is at its limits mainly for available land area and fertilizers (reviewed: [1] [2]). 2) In support of Na+ accumulation in intracellular vacuoles the pump actively serves to excrete sodium to the oceanic environment in exchange for an osmolyticum acting compound in order to maintain cellular homeostasis For both mechanisms in seaweeds, H+ ATPase driven pumps mediate the translocation of H+ and K+/Na+. It is assumed the milieu interior of a seaweed with contains clearly visible the vacuole for sequestering abundant sodium ions and/or abundant metallic cations (Heavy Metals) which in some seaweed species can be taken up from the oceanic environment in order to act as “substitute-osmolyticum” to compensate Na+-extrusion. In this manuscript we will outline some of these mechanisms
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