Temperature Rise Increases the Bioavailability of Marine Synechococcus-Derived Dissolved Organic Matter

Jiajie Zhang; Jihua Liu; Daixi Liu; Xiao Chen; Quan Shi; Chen He; Gang Li

doi:10.3389/fmicb.2022.838707

Temperature Rise Increases the Bioavailability of Marine Synechococcus-Derived Dissolved Organic Matter

Front Microbiol. 2022 Apr 19:13:838707. doi: 10.3389/fmicb.2022.838707. eCollection 2022.

Authors

Jiajie Zhang^{1

2}, Jihua Liu^{1

2

3}, Daixi Liu^{1

2}, Xiao Chen^{1

2}, Quan Shi⁴, Chen He⁴, Gang Li⁵

Affiliations

¹ Institute of Marine Science and Technology, Shandong University, Qingdao, China.
² Joint Lab for Ocean Research and Education at Dalhousie University, Shandong University and Xiamen University, Qingdao, China.
³ Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, China.
⁴ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, China.
⁵ Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.

Abstract

Synechococcus is one group of main primary producers and plays a key role in oceanic carbon fixation and transformation. To explore how the temperature rise affects the bioavailability of Synechococcus-derived dissolved organic matter (SOM) and whether this effect would be altered by the involvement of heterotrophic bacteria, we compared the optical and molecular properties of the SOM of axenic Synechococcus sp. PCC7002 culture (Syn) to that with associated heterotrophic bacteria (SynB) under 15, 18, and 21^°C growth temperatures at exponential and decay growth phases. Our results showed that the temperature rise increased the bioavailability of the SOM of both Syn and SynB cultures by lowering the proportion of the hydrogen-poor and double-bond structure-rich humus-like components and highly unsaturated substances, as indicated by the increase of spectral slope ratio (S _R ) and biological index (BIX) and decrease of humification index (HIX). Moreover, the involvement of heterotrophic bacteria modified the Synechococcus-derived SOM, together with its intracellular dissolved organic matter (DOM) excludes, lowering the SOM bioavailability. Our results indicated that the warming in climate change scenario may enhance the bioavailability of the Synechococcus-derived SOM although it may be tempered by the involvement of heterotrophic bacteria, providing an insight for preservation of the organic carbon pool in global oceans.

Keywords: Synechococcus sp. PCC7002; bioavailability; dissolved organic matter (DOM); exponential and decay phases; heterotrophic bacteria; temperature rise.