Photophysiology of nitrate limited phytoplankton communities in Kongsfjorden, Spitsbergen

Abstract

In Arctic coastal regions, the phytoplankton bloom is often initiated by meltwater induced stratification in spring, while subsequent nutrient depletion is believed to drive phytoplankton succession in summer. The associated changes in photophysiology are difficult to identify, because these can be governed by acclimation to light and nutrient availability as well as variations in phytoplankton biomass and taxonomic composition. In the present study, the consequences of nutrient limitation for photophysiology and growth were assessed in natural phytoplankton communities from Kongsfjorden, Spitsbergen. A series of nutrient addition experiments demonstrated N-limitation from mid-June onwards and possible co-limitation with P later in summer. The onset of N-limitation was associated with a pronounced change in taxonomic composition from a dictyochophytes to a haptophytes dominated community. Fast Repetition Rate fluorometry measurements of photosystem II (PSII) photophysiology showed that the dictyochophytes dominated community was characterized by high PSII efficiency and electron transport rates which were efficiently used for growth. Marked changes in PSII photophysiology were observed later in summer, with decreasing efficiencies, lower connectivity between reaction centers, and slower turnover rates. Simultaneously, alternative electron requirements downstream of PSII became more important and energy was likely allocated to the uptake of nutrients rather than carbon fixation and growth. Relief of nutrient limitation during the nutrient addition experiments did not lead to pronounced changes in PSII photophysiology. It is, therefore, concluded that PSII photophysiology of the phytoplankton community in Kongsfjorden is associated with changes in species composition rather than a direct effect of nutrient availability or nutrient limitation.

Impact of ocean acidification and high solar radiation on productivity and species composition of a late summer phytoplankton community of the coastal Western Antarctic Peninsula

“…It needs to be noted that C : N ratios were enhanced in all MSR treatments relative to the start community, but did not display any CO 2 ‐dependent changes (Table ). Considering also that nitrate limitation did not affect carbon buildup in previous studies (Lancelot and Mathot ; Davidson et al ; Deppeler et al ; Kulk et al ; van de Poll et al ), we suggest that transient nitrate drawdown did not negatively influence PP. Such changes in productivity did further not translate into changes in species composition, as the latter was similar between the start and the end of the first experimental phase (Fig.…”

Effects of Nitrogen Limitation on Phytoplankton Physiology in the Western Arctic Ocean in Summer

“…Zhu et al (2019) also reported that the F v / F m in the Chukchi Borderland was approximately 24% lower than in the CS waters, which was similar to the results of this study. Meanwhile, the F v / F m observed off the coast of the Arctic Ocean is known to remain high (≥0.50) throughout the year, except immediately after the spring bloom (Aardema et al, 2019; Kulk et al, 2018; McMinn & Hegseth, 2004; Mills et al, 2018; Mosharov et al, 2019). This study also showed high phytoplankton F v / F m values (0.56) in Arctic coastal waters in the summer, indicating the lack of nutrient stress.…”

“…These long‐term incubations revealed that F v / F m and ETR max increased by 12 ± 9% and 40 ± 17%, respectively, and the fraction of large (≥10 μm) phytoplankton increased by approximately 25% compared to the beginning of culture sample (Figure 11). In turn, larger cells fraction exhibited increased photosynthetic capacity (Kulk et al, 2018; Mills et al, 2018). Mills et al (2018) reported an increase in the large‐sized diatom biomass in response to nitrate enrichment in the Chukchi Sea.…”

“…These changes in phytoplankton physiological characteristics are directly linked to growth and primary productivity (Falkowski et al, 1992; Smith, 1982). The major environmental factors affecting phytoplankton growth are major nutrients, such as nitrate and phosphate (Kulk et al, 2018; Lewis et al, 2019; Mills et al, 2018), light (Zhu et al, 2019), and sometimes the micronutrient iron (Boyd, 2019; Martin et al, 1994; Rijkenberg et al, 2018). As such, one or more limiting factors are simultaneously associated with photosynthetic energy conversion for phytoplankton growth (Arrigo, 2005; Rhee & Gotham, 1981; Xu et al, 2014).…”

Primary Productivity Dynamics in the Summer Arctic Ocean Confirms Broad Regulation of the Electron Requirement for Carbon Fixation by Light-Phytoplankton Community Interaction

“…We similarly recently reported that variance of K C , derived from parallel measures of FRRf-derived ETRs and C-uptake rates, could be generally explained by patterns in light availability (Zhu et al, 2016), but importantly was much improved when considering differences in phytoplankton size structures (Zhu et al, 2017). In fact, changes in predominant species within phytoplankton communities appears to be a factor increasingly important in explaining patterns of K C (e.g., Kulk et al, 2018;Xie et al, 2018), likely reflecting selection of taxa by environmental factors that are not specifically measured as part of the assessment exercise of interest (see Hughes et al, 2018a). Patterns of K C variability over space and time therefore remain problematic to fully resolve.…”