The Differential Responses of Coastal Diatoms to Ocean Acidification and Warming: A Comparison Between Thalassiosira sp. and Nitzschia closterium f.minutissima

Ting Cai; Yuanyuan Feng; Yanan Wang; Tongtong Li; Jiancai Wang; Wei Li; Weihua Zhou

doi:10.3389/fmicb.2022.851149

The Differential Responses of Coastal Diatoms to Ocean Acidification and Warming: A Comparison Between Thalassiosira sp. and Nitzschia closterium f.minutissima

Front Microbiol. 2022 Jun 21:13:851149. doi: 10.3389/fmicb.2022.851149. eCollection 2022.

Authors

Ting Cai^{1

2}, Yuanyuan Feng^{1

3}, Yanan Wang⁴, Tongtong Li⁴, Jiancai Wang⁴, Wei Li⁴, Weihua Zhou^{5

6

7}

Affiliations

¹ School of Oceanography, Shanghai Jiao Tong University, Shanghai, China.
² Key Laboratory of Marine Ecosystem Dynamics, Ministry of Natural Resources, Hangzhou, China.
³ Shanghai Frontiers Science Center of Polar Science, Shanghai, China.
⁴ College of Marine and Environmental Sciences, Tianjin University of Science and Technology, Tianjin, China.
⁵ CAS Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
⁶ Key Laboratory of Tropical Marine Biotechnology of Hainan Province, Sanya Institute of Oceanology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Sanya, China.
⁷ Sanya National Marine Ecosystem Research Station and Tropical Marine Biological Research Station in Hainan, Chinese Academy of Sciences, Sanya, China.

Abstract

Marine diatoms are one of the marine phytoplankton functional groups, with high species diversity, playing important roles in the marine food web and carbon sequestration. In order to evaluate the species-specific responses of coastal diatoms to the combined effects of future ocean acidification (OA) and warming on the coastal diatoms, we conducted a semi-continuous incubation on the large centric diatom Thalassiosira sp. (~30 μm) and small pennate diatom Nitzschia closterium f.minutissima (~15 μm). A full factorial combination of two temperature levels (15 and 20°C) and pCO₂ (400 and 1,000 ppm) was examined. The results suggest that changes in temperature played a more important role in regulating the physiology of Thalassiosira sp. and N. closterium f.minutissima than CO₂. For Thalassiosira sp., elevated temperature significantly reduced the cellular particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphate (POP), biogenic silica (BSi), chlorophyll a (Chl a), and protein contents, and the C:N ratio. CO₂ only had significant effects on the growth rate and the protein content. However, for the smaller pennate diatom N. closterium f.minutissima, the growth rate, POC production rate, and the C:P ratio significantly increased with an elevated temperature, whereas the cellular POP and BSi contents significantly decreased. CO₂ had significant effects on the POC production rate, cellular BSi, POC, and PON contents, the C:P, Si:C, N:P, and Si:P ratios, and sinking rate. The interaction between OA and warming showed mostly antagonistic effects on the physiology of both species. Overall, by comparison between the two species, CO₂ played a more significant role in regulating the growth rate and sinking rate of the large centric diatom Thalassiosira sp., whereas had more significant effects on the elemental compositions of the smaller pennate diatom N. closterium f.minutissima. These results suggest differential sensitivities of different diatom species with different sizes and morphology to the changes in CO₂/temperature regimes and their interactions.

Keywords: biogeochemistry; diatoms; ocean acidification; sinking rate; warming.