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Delayed gametophytes are able to grow vegetatively for prolonged periods of time. As such, they are potentially very valuable for kelp aquaculture given their great promise in opening up novel opportunities for kelp breeding and farming. However, large-scale application would require more in-depth understanding of how to control reproduction in delayed gametophytes. For newly formed gametophytes, many environmental factors for reproduction have been identified, with key drivers being light intensity, temperature, and the initial gametophyte density. However, the question of whether delayed gametophytes react similarly to these life cycle controls remains open for exploration. In this study, we performed a full factorial experiment on the influences of light intensity, temperature, and density on the reproduction of multiannual delayed gametophytes of Saccharina latissima, during which the number of sporophytes formed was counted. We demonstrate that delayed gametophytes of S. latissima can reliably reproduce sexually after more than a year of vegetative growth, depending on the effects between light intensity and temperature. Under higher light intensities (≥29 µmol photons · m -2 · s -1 ), optimal reproduction was observed at lower temperatures (10.2°C), while at lower light intensities (≤15 µmol photons · m -2 · s -1 ), optimal reproduction was observed at higher temperatures (≥12.6°C). Given the seasonal lag between solar radiation and sea surface temperature in natural systems, these conditions resemble those found during spring (i.e., increasing light intensity with low temperatures) and autumn (i.e., decreasing light intensity with higher temperatures). Seasonality can be used as an aquaculture tool to better control the reproduction of delayed gametophytes., (© 2021 Phycological Society of America.)

Uptake dynamics of dissolved inorganic phosphate (DIP) and dissolved inorganic nitrate (DIN) in young Palmaria palmata (n = 49), cultivated in a range of DIP concentrations (0.0-6.0 µmol · L -1 ) and nonlimiting DIN concentration (50 µmol · L -1 ) under fully controlled laboratory conditions, were quantified in a 'pulse-and-chase' approach over 5 weeks. Two different uptake rates were specified: (1) surge uptake (V S ) after starvation and (2) maintenance uptake with filled nutrient pools (V M ). V S for DIP of 1.57 ± 0.29 µmol · cm -2  · d -1 and DIN of 15.6 ± 4.3 µmol · cm -2  · d -1 , as well as V M for DIP of 0.57 ± 0.22 µmol · cm -2  · d -1 and DIN of 5.6 ± 2.1 µmol · cm -2  · d -1 were calculated. In addition, an absolute size of the internal storage capacity (ISC) for DIP of 22 µmol · cm 2 and DIN of 222 µmol · cm 2 was determined. A DIP-to-DIN uptake ratio of 1:10 under V M showed a weekly rhythmic uptake pattern, highlighted by a high correlation between DIP and DIN uptake (R = 0.943). V S for DIN did not occur under DIP depletion, but uptake rates increased with increasing DIP availability. Hence, DIP availability limited access to DIN, which was also reflected by total dissolvable protein concentrations in sporophytes, which ranged from 10.2 ± 2.5% to 24.6 ± 8.0% dry weight depending on DIP availability. Similarly, total dissolvable carbohydrate concentration ranged from 22.1 ± 3.6% to 54.3 ± 12.3% dry weight. The data presented in this study open further insight into ecological and physiological aspects of nutrient availability in P. palmata and allow for an optimization in cultivation., (© 2020 Phycological Society of America.)

Kelp life-cycle transitions are complex and susceptible to various (a)biotic controls. Understanding the microscopic part of the kelp's lifecycle is of key importance, as gametophytes form a critical phase influencing, among others, the distributional limits of the species. Many environmental controls have been identified that affect kelp gametogenesis, whose interactive effects can be subtle and counterintuitive. Here we performed a fully factorial experiment on the (interactive) influences of light intensity, light quality, and the Initial Gametophyte Density (IGD) on Saccharina latissima reproduction and vegetative growth of delayed gametophytes. A total of 144 cultures were followed over a period of 21 d. The IGD was a key determinant for reproductive success, with increased IGDs (≥0.04 mg DW · mL -1 ) practically halting reproduction. Interestingly, the effects of IGDs were not affected by nutrient availability, suggesting a resource-independent effect of density on reproduction. The Photosynthetically Usable Radiation (PUR), overarching the quantitative contribution of both light intensity and light quality, correlated with both reproduction and vegetative growth. The PUR furthermore specifies that the contribution of light quality, as a lifecycle control, is a matter of absorbed photon flux instead of color signaling. We hypothesize that (i) the number of photons absorbed, independent of their specific wavelength, and (ii) IGD interactions, independent of nutrient availability, are major determinants of reproduction in S. latissima gametophytes. These insights help understand kelp gametophyte development and dispersal under natural conditions, while also aiding the control of in vitro gametophyte cultures., (© 2020 The Authors. Journal of Phycology published by Wiley Periodicals, Inc. on behalf of Phycological Society of America.)

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds Saccharina latissima and Laminaria digitata (Phaeophyceae) using a "pulse-and-chase" assay under fully controlled laboratory conditions. In a subsequent second "pulse-and-chase" assay, internal storage capacity (ISC) was calculated based on V M and the parameter for photosynthetic efficiency F v /F m . Sporophytes of S. latissima showed a V S of 0.80 ± 0.03 μmol · cm -2  · d -1 and a V M of 0.30 ± 0.09 μmol · cm -2  · d -1 for dissolved inorganic phosphate (DIP), whereas V S for DIN was 11.26 ± 0.56 μmol · cm -2  · d -1 and V M was 3.94 ± 0.67 μmol · cm -2  · d -1 . In L. digitata, uptake kinetics for DIP and DIN were substantially lower: V S for DIP did not exceed 0.38 ± 0.03 μmol · cm -2  · d -1 while V M for DIP was 0.22 ± 0.01 μmol · cm -2  · d -1 . V S for DIN was 3.92 ± 0.08 μmol · cm -2  · d -1 and the V M for DIN was 1.81 ± 0.38 μmol · cm -2  · d -1 . Accordingly, S. latissima exhibited a larger ISC for DIP (27 μmol · cm -2 ) than L. digitata (10 μmol · cm -2 ), and was able to maintain high growth rates for a longer period under limiting DIP conditions. Our standardized data add to the physiological understanding of S. latissima and L. digitata, thus helping to identify potential locations for their cultivation. This could further contribute to the development and modification of applications in a bio-based economy, for example, in evaluating the potential for bioremediation in integrated multitrophic aquacultures that produce biomass simultaneously for use in the food, feed, and energy industries., (© 2019 The Authors. Journal of Phycology published by Wiley Periodicals, Inc. on behalf of Phycological Society of America.)

Dissolved inorganic phosphorus (DIP) is an essential macronutrient for maintaining metabolism and growth in autotrophs. Little is known about DIP uptake kinetics and internal P-storage capacity in seaweeds, such as Ulva lactuca (Chlorophyta). Ulva lactuca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U. lactuca to a wide range of DIP concentrations (1-50 μmol · L -1 ) and a nonlimiting concentration of dissolved inorganic nitrogen (DIN; 5,000 μmol · L -1 ) under fully controlled laboratory conditions in a "pulse-and-chase" assay over 10 d. Uptake kinetics were standardized per surface area of U. lactuca fronds. Two phases of responses to DIP-pulses were measured: (i) a surge uptake (V S ) of 0.67 ± 0.10 μmol · cm -2  · d -1 and (ii) a steady state uptake (V M ) of 0.07 ± 0.03 μmol · cm -2  · d -1 . Mean internal storage capacity (ISC P ) of 0.73 ± 0.13 μmol · cm -2 was calculated for DIP. DIP uptake did not affect DIN uptake. Parameters of DIN uptake were also calculated: V S  = 12.54 ± 1.90 μmol · cm -2  · d -1 , V M  = 2.26 ± 0.86 μmol · cm -2  · d -1 , and ISC N  = 22.90 ± 6.99 μmol · cm -2 . Combining ISC and V M values of P and N, nutrient storage capacity of U. lactuca was estimated to be sufficient for ~10 d. Both P and N storage capacities were filled within 2 d when exposed to saturating nutrient concentrations, and uptake rates declined thereafter at 90% for DIP and at 80% for DIN. Our results contribute to understanding the ecological aspects of nutrient uptake kinetics in U. lactuca and quantitatively evaluating its potential for bioremediation and/or biomass production for food, feed, and energy., (© 2017 Phycological Society of America.)