Sequential nutrient uptake as a potential mechanism for phytoplankton to maintain high primary productivity and balanced nutrient stoichiometry

Abstract

Abstract. We hypothesize that phytoplankton have the sequential nutrient uptake strategy to maintain nutrient stoichiometry and high primary productivity in the water column. According to this hypothesis, phytoplankton take up the most limiting nutrient first until depletion, continue to draw down non-limiting nutrients and then take up the most limiting nutrient rapidly when it is available. These processes would result in the variation of ambient nutrient ratios in the water column around the Redfield ratio. We used highresolution continuous vertical profiles of nutrients, nutrient ratios and on-board ship incubation experiments to test this hypothesis in the Strait of Georgia. At the surface in summer, ambient NO . This sequential uptake strategy allows phytoplankton to acquire additional cellular phosphorus and silicon when they are available and wait for nitrogen to become available through frequent mixing of NO − 3 (or pulsed regenerated NH 4 ). Thus, phytoplankton are able to maintain high productivity and balance nutrient stoichiometry by taking advantage of vigorous mixing regimes with the capacity of the stoichiometric plasticity. To our knowledge, this is the first study to show the in situ dynamics of continuous vertical profiles of N : P and N : Si ratios, which can provide insight into the in situ dynamics of nutrient stoichiometry in the water column and the inference of the transient status of phytoplankton nutrient stoichiometry in the coastal ocean.

Characteristics of phytoplankton community and water net primary productivity response to the nutrient status of the Poyang Lake and Gan River, China

“…However, Figure e,f shows that Euglenophyta distribution largely favoured Si/P ( P < .05) and Si/DIN ( P < .05) in both the Gan River and Poyang Lake, confirming that influencing phytoplankton community nutrient ratios (Si/P, N/P, and Si/N) are diverse. Liu et al () and Yin et al () also indicated that Si/N was the limiting factor for phytoplankton growth.…”

“…Primary production, which represents phytoplankton biomass and growth rates (Wang et al, ), is sensitive to environmental change (Wu, He, et al, ). It is mainly regulated by various factors that include incident irradiance (Lewis, ; Wang et al, ), ice cover (Lewis, ), nonalgal light attenuation (Deng et al, ; Wu, Lai, Zhang, Cai, & Chen, ), mixing depth (Wu et al, ), temperature (Liang et al, ), and the nutrient supply (Browning et al, ; Dou, Tang, Yang, & Wang, ; Hagstrom & Levin, ; Ke, Tan, Ma, Huang, & Wang, ; Li, Ge, Wang, Zhou, & Hu, ; Liu et al, ; Wang et al, ; Wilkerson, Dugdale, Parker, Blaser, & Pimenta, ; Yin, Liu, & Harrison, ), especially for nutrient inputs that have a significant effect on phytoplankton growth and development as well as the biogeochemical cycles of watersheds (Browning et al, ; Li et al, ; Moore et al, ; Wen et al, ). In addition, nutrient inputs, particularly nitrogen (N) and phosphorus (P), to freshwater ecosystems have continued to increase due to progressively increasing anthropogenic activities resulting from rising populations, broadening economic development, and the greater demand for food and energy production in recent years (Cao, Wang, Liao, Sun, & Huang, ; Wilkerson et al, ).…”

“…Numerous studies have addressed the effects of nutrients (N, P, C, iron [Fe], etc. ), as it relates to both concentration or structure, on phytoplankton growth (Browning et al, 2017;Dou et al, 2011;Hagstrom & Levin, 2017;Ke et al, 2014;Li et al, 2016;Liu et al, 2015;Wang et al, 2015;Wilkerson et al, 2015;Yin et al, 2017). Browning et al (2017) reported that the different ratios related to nutrient concentration and structure could alter species composition and phytoplankton growth.…”

“…Accordingly, an in-depth study on the impact of nutrients on the primary productivity and eutrophication of water is of particular urgency for the assessment of environmental water protection and the nutrient status of the Poyang Lake region. Previous studies focused on the effect of N and P on phytoplankton community distribution characteristics (Li et al, 2016;Liu et al, 2015;Wu et al, 2013) and primary productivity (Wilkerson et al, 2015;Wu, Lai, et al, 2014;Yin et al, 2017). Hagstrom and Levin (2017) argued that N, P, and Fe could limit global primary productivity.…”

Virus-mediated transfer of nitrogen from heterotrophic bacteria to phytoplankton

“…Although many nutrients are released during cell lysis, nitrogen typically limits phytoplankton growth in coastal BC waters (e.g. Yin et al, 2017), the location of the current study. High rates of bacterial mortality from viral lysis imply a continuous and substantial flux of DOM from cells into seawater.…”