Comparison of population growth and photosynthetic apparatus changes in response to different nutrient status in a diatom and a coccolithophore

Abstract

In many marine ecosystems, diatoms dominate in nutrient-rich coastal waters while coccolithiophores are found offshore in areas where nutrients may be limiting. In lab-controlled batch cultures, mixed-species competition between the diatom Phaeodactylum tricornutum and the coccolithophore Emiliana huxleyi and the response of each species were examined under nitrate (N) and phosphate (P) starvation. Based on the logistic growth model and the Lotka-Volterra competition model, E. huxleyi showed higher competitive abilities than P. tricornutum under N and P starvation. For both species, cell growth was more inhibited by P starvation, while photosynthetic functions (chl a fluorescence parameters) and cellular constituents (pigments) were impaired by N starvation. The decline of photosynthetic functions occurred later in E. huxleyi (day 12) than in P. tricornutum (day 9); this time difference was associated with greater damage of the photosynthetic apparatus in P. tricornutum compared with E. huxleyi. Xanthophyll cycle pigment accumulation and the transformation from diadinoxanthin to diatoxanthin was more active in E. huxleyi than P. tricornutum, under similar N and P starvation. We concluded that E. huxleyi and P. tricornutum have different mechanisms to allocate resources and energy under nutrient starvation. It appears that E. huxleyi has a more economic strategy to adapt to nutrient depleted environments than P. tricornutum. These findings provided additional evidence explaining how N versus P limitation differentially support diatom and coccolithophore blooms in natural environments.

Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores

“…Eppley, 1972;Falkowski et al, 1985), whilst nutrient limitation primarily impedes molecule synthesis (e.g. Zhao et al, 2015). Calcification, for example, is contingent on both the rate at which nutrients can be supplied to the cell (temperature-dependent) and processed into energy (light-dependent) and can proceed under nutrient limitation, as shown in our experiments, but may be less efficient under suboptimal temperature or light conditions.…”

“…Phosphate limitation primarily impedes production of the RNA, phospholipids and DNA that are essential for cell replication, and phosphate is a key component of cellular energy carriers (Zhao et al, 2015). Nitrate limitation particularly impacts the synthesis of proteins and pigments used in photosynthesis (Zhao et al, 2015). However, despite the suppression of cell division and photosynthetic activity by phosphate and nitrate limitation, respectively, the cell is still able to synthesise non-essential lipids and carbohydrates.…”

“…Nitrate and phosphate are the two key nutrients required by most phytoplankton (Arrigo, 2005;Moore et al, 2013), and they fulfil different purposes within the cell. Phosphate limitation primarily impedes production of the RNA, phospholipids and DNA that are essential for cell replication, and phosphate is a key component of cellular energy carriers (Zhao et al, 2015). Nitrate limitation particularly impacts the synthesis of proteins and pigments used in photosynthesis (Zhao et al, 2015).…”

Dynamics of triacylglycerol and EPA production in Phaeodactylum tricornutum under nitrogen starvation at different light intensities

“…According to Fig 1B, a strong decline in F v /F m was observed (from 0.6 to 0) for cultures exposed to light intensities above 100 μmol m -2 s -1 immediately after nitrogen starvation. A decline in F v /F m is generally acknowledged with reduced photosynthetic efficiency or photo damage [19,23,24]. Geider et al [13] presented a light curve for P .…”

Responses to referee comments on behalf of all authors

“…Spatial and temporal analysis of coccoliths reveals the evolution, biogeography and ecology of past species (e.g. Haq and Lohmann, 1976;Knappertsbusch, 2000;Ziveri et al, 2004;Gibbs et al, 2006;Baumann et al, 2016) and the response of species and communities to palaeoceanographic and palaeoclimatic variability (e.g. Bollmann et al, 2002Bollmann et al, , 2009Bown, 2005;Bown and Pearson, 2009).…”