Assessment of DMSP turnover reveals a non-bioavailable pool of dissolved DMSP in coastal waters of the Gulf of Mexico

作者：Li, Chengxuan; Yang, Gui-Peng; Kieber, David J.; Motard-Cote, Jessie; Kiene, Ronald P.^*

来源：Environmental Chemistry, 2016, 13(2): 266-279.

DOI：10.1071/EN15052

• bacteria
• bioavailability
• carbon and sulfur fluxes
• climate
• dimethylsulfide
• DMSPd
• filtration
• GBT
• glycine betaine
• organic sulfur
• phytoplankton
• refractory
• uptake inhibitor

Environmental context DMSP is one of the most important substrates for marine bacteria and its cycling contributes substantially to fluxes of carbon and sulfur in the ocean. Accurate determination of the concentration of DMSP available to bacteria is essential to quantifying DMSP consumption rates, and this work improves those determinations by identifying non-bioavailable pools of DMSP that have previously gone unrecognised. Improved estimates of DMSP consumption rates will lead to better understanding of its role in ocean food web and biogeochemical dynamics.
Abstract Dissolved dimethylsulfoniopropionate (DMSPd) is an important substrate for marine microbes and a precursor of sulfur gases. We compared DMSPd turnover flux rates in coastal seawater measured with a S-35-DMSPd tracer to those obtained with the DMSP-uptake inhibitor glycine betaine (GBT). The S-35-DMSP tracer method yielded DMSPd turnover fluxes (35.7-215nM day(-1)) that were 1.7 to 152 times higher than those obtained in parallel samples with the GBT inhibitor method (0.34-21.6nM day(-1)). Tests confirmed that GBT functioned as planned by strongly inhibiting DMSPd degradation and that S-35-DMSPd gave accurate estimates of DMSPd loss rate constants. This left the initial DMSPd concentrations, determined by small volume drip filtration (SVDF) through Whatman GF/F filters (0.7-m nominal retention) ([DMSPd](SVDF)), as a potential cause of the discrepancy in rate estimates. Indeed, GF/F filtrate incubations showed that the initial [DMSPd](SVDF) overestimated the bioavailable DMSPd concentrations for at least two reasons: (1) a significant fraction (10-37%) of DMSP passing through GF/F filters was in particles >0.2m (likely bacteria) and therefore not dissolved, and (2) a significant pool (0.44-1.0nM) of operationally dissolved, non-particle DMSP ([DMSPd](<0.2m)), comprising 40-99% of [DMSPd](SVDF), was refractory to degradation on a time scale of days. The nature of this refractory DMSP is currently unknown. Accounting for DMSP-containing particles and the refractory DMSP pool in GF/F filtrates is necessary to obtain the true bioavailable DMSPd concentrations, which we estimate to be very low (0.006-1.0nM; mean of 0.41nM) in the coastal waters examined, and to avoid overestimation of DMSPd turnover fluxes when using the S-35-DMSP tracer technique.

• 出版日期2016
• 单位中国海洋大学