Abstract
Abstract To reach the goal of large-scale seaweed cultivation in Norway, new knowledge concerning commercially important species like the kelp Saccharina latissima is essential. This includes fundamental understanding of physiological mechanisms like nutrient uptake kinetics to better understand its ecological niche and nutritional requirements. The initial short-term nitrate (NO3−) uptake kinetics in cultivated S. latissima juvenile sporophytes were evaluated under nitrogen-saturated and nitrogen-limited conditions. The uptake was measured for concentrations in a gradient from 2 to 18 μM NO3− which is representative of Norwegian coastal waters in the main growth season of winter and early spring. Preconditioning treatments led to internal nitrogen pools (total tissue nitrogen and intracellular nitrate) that were significantly lower for the N-limited than for the N-saturated sporophytes prior to the experiment. Nitrate uptake rates, related to biomass (V) and intracellular nitrogen content (U), were linearly related to the substrate concentrations for both N-limited and N-saturated sporophytes, indicating that S. latissima requires high ambient nitrate concentrations to maintain rapid growth. The sporophytes with deficient internal nitrogen pools exhibited higher uptake rates of NO3− than sporophytes with higher internal pools of nitrogen. Mathematical modelling was used to investigate the temporal development of total tissue nitrogen (QN) based on the nitrogen-specific uptake rates (U) and revealed a near linear response of U to changes in QN. The model also found that a maximum estimated value for QN was only approached after more than 20 days at external NO3- concentrations of 8 μM. These results expand the physiological understanding of cultivated S. latissima and are important for a sustainable upscaling of seaweed farm production.
Highlights
Saccharina latissima (Linnaeus) Lane, Mayes, Druehl, and Saunders 2006 is a cold water kelp species that grows rapidly in late winter and early spring when dissolved inorganic nutrients like nitrate (DIN) are available in excess and other environmental factors such as temperature, light conditions and salinity are favorable (Kerrison et al, 2015)
The aim of this study was to determine the initial short-term nitrate uptake rates and the total nitrogen and internal nitrate storage capacity for cultivated, juvenile N-saturated and N-limited S. latissima exposed to nitrate concentrations that are representative of Norwegian coastal waters
S. latissima is abundant along the Norwegian coast and has its highest growth and nutrient uptake rates during periods with high ambient nitrate concentration, typically late autumn to early spring, dependent on latitude
Summary
Saccharina latissima (Linnaeus) Lane, Mayes, Druehl, and Saunders 2006 is a cold water kelp species that grows rapidly in late winter and early spring when dissolved inorganic nutrients like nitrate (DIN) are available in excess and other environmental factors such as temperature, light conditions and salinity are favorable (Kerrison et al, 2015). To upscale and industrialize seaweed production, more knowledge on how to utilize and optimize farm locations in terms of key resources such as light and nutrient availability is essential. This would enable farmers to identify suitable cultivation depths and seasons and, ideally, predict potential biomass production. Unsaturated uptake is common for NH4+ (Phillips and Hurd, 2004; Abreu et al, 2011; Martínez et al, 2012), but it has been described for NO3− (Harrison et al, 1986; Ahn et al, 1998; Sanchez-Barredo et al, 2011; Martínez et al, 2012)
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