Seawater carbonate chemistry and photosynthetic performance of Thalassiosira (Conticribra) weissflogii (Bacillariophyta)

The purpose of this study was to investigate the effects of ocean acidification and nutrient level on the growth and photosynthetic performance of the diatom Thalassiosira (Conticribra) weissflogii. Cells were exposed to varying levels of CO2 [current CO2 (LC), 400 μatm; high CO2 (HC), 1000 μatm] and nutrients, with NO3− and PO43− concentrations enriched, respectively, at 50 μmol/l and 5 μmol/l [high nutrient (HN)], 20 μmol/l and 2 μmol/l [mid-level nutrient (MN)] and 10 μmol/l and 1 μmol/l [low nutrient (LN)]. After acclimatization for over 20 generations, no significant differences in growth rates were observed between LC and HC cultures under both HN and LN conditions; whereas, HC significantly reduced the growth rate under MN conditions. Lower nutrient loading significantly inhibited the growth rates of both LC and HC cultures; whereas, HC (but not LC) significantly decreased chlorophyll a and carotenoid contents in LN treatments. HC conditions significantly increased maximum relative electron transport rates (rETRmax) and saturating light intensity (Ik) of HN cultures, with rETRmax showing a positive relationship with growth rates stimulated by nutrient enrichments. The maximum (Fv/Fm) and effective quantum yield (Yield) were all inhibited under LN conditions, with the greatest reduction in Yield observed under LC conditions, corresponding to the highest nonphotochemical quenching, lowest light use efficiency (α) and lowest rETRmax. Based on these results, ocean acidification and nutrient availability may influence photosynthetic performance in T. weissflogii individually or interactively, with the future growth of marine diatoms mediated by these codependent environmental drivers.

本研究旨在探究海洋酸化与营养盐水平对硅藻威氏海链藻（Thalassiosira (Conticribra) weissflogii）生长及光合性能的影响。实验设置了不同CO2浓度[当前CO2水平（LC）：400 μatm；高CO2水平（HC）：1000 μatm]与营养盐梯度，其中硝酸根（NO3−）与磷酸根（PO43−）浓度分别设置为：高营养盐组（HN）：50 μmol/l与5 μmol/l、中营养盐组（MN）：20 μmol/l与2 μmol/l、低营养盐组（LN）：10 μmol/l与1 μmol/l。经20代以上的驯化培养后，在HN与LN条件下，LC与HC培养组的生长速率无显著差异；而在MN条件下，HC组的生长速率显著降低。较低的营养盐负荷显著抑制了LC与HC两组的生长速率；此外，在LN处理组中，HC组（而非LC组）的叶绿素a与类胡萝卜素含量显著下降。HC条件显著提升了HN培养组的最大相对电子传递速率（maximum relative electron transport rates, rETRmax）与饱和光强（saturating light intensity, Ik），且rETRmax与营养盐富集促发的生长速率呈正相关关系。最大光化学量子产量（Fv/Fm）与有效量子产量（effective quantum yield, Yield）在LN条件下均受到抑制，其中LC组的Yield降幅最大，对应最高的非光化学淬灭、最低的光能利用效率（light use efficiency, α）与最低的rETRmax。综上，海洋酸化与营养盐有效性可分别或交互影响威氏海链藻的光合性能，未来海洋硅藻的生长将受这两类协同作用的环境因子调控。