{"title":"Organic carbon decay mediated by a mesopelagic microbial community: The relevance of carbon pools and broad biochemical composition","authors":"Noah J. Craft, Alexander B. Bochdansky","doi":"10.1002/lno.12796","DOIUrl":null,"url":null,"abstract":"<p>The mesopelagic zone is a site of strong microbially driven particle attenuation with depth and thus plays a crucial role in controlling the transfer efficiency of the ocean's biological pump. However, little quantitative information exists on the dependency of decay processes on the source material. Here we followed the decay of <sup>14</sup>C-labeled dead particulate organic carbon (POC) and dissolved organic carbon (DOC) from three different phytoplankton species, and two incubations of live diatoms, in mesopelagic water over 3 months. Commonly used first-order kinetics failed to adequately describe the decay of organic material as rate constants varied from day to day. Over extended periods, decay rates for organic material exhibited two distinct phases, with rates in the second phase being inversely related to rates in the first phase. Microbial biomass (measured via adenosine triphosphate and cell counts) increased substantially during phase 1 and ebbed during phase 2. Decay rates were significantly different among the three algal sources; however, differences were even more pronounced among carbon pools and followed a distinct pattern (combined average per-day decay rates at 12°C): fresh DOC (0.6) > fresh POC (0.1) > live cells (0.06) > aged DOC/POC (0.01). Separation of POC into four broad biochemical fractions showed that components in the operationally defined lipid fraction contained the most degradable compounds for fresh material. Our research highlights the need to include the dynamics of the most easily digestible fractions of freshly released organic material, and live plankton resilient to digestion, in calculations of vertical carbon flux budgets.</p>","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":"70 3","pages":"634-649"},"PeriodicalIF":3.8000,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/lno.12796","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Limnology and Oceanography","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/lno.12796","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"LIMNOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
The mesopelagic zone is a site of strong microbially driven particle attenuation with depth and thus plays a crucial role in controlling the transfer efficiency of the ocean's biological pump. However, little quantitative information exists on the dependency of decay processes on the source material. Here we followed the decay of 14C-labeled dead particulate organic carbon (POC) and dissolved organic carbon (DOC) from three different phytoplankton species, and two incubations of live diatoms, in mesopelagic water over 3 months. Commonly used first-order kinetics failed to adequately describe the decay of organic material as rate constants varied from day to day. Over extended periods, decay rates for organic material exhibited two distinct phases, with rates in the second phase being inversely related to rates in the first phase. Microbial biomass (measured via adenosine triphosphate and cell counts) increased substantially during phase 1 and ebbed during phase 2. Decay rates were significantly different among the three algal sources; however, differences were even more pronounced among carbon pools and followed a distinct pattern (combined average per-day decay rates at 12°C): fresh DOC (0.6) > fresh POC (0.1) > live cells (0.06) > aged DOC/POC (0.01). Separation of POC into four broad biochemical fractions showed that components in the operationally defined lipid fraction contained the most degradable compounds for fresh material. Our research highlights the need to include the dynamics of the most easily digestible fractions of freshly released organic material, and live plankton resilient to digestion, in calculations of vertical carbon flux budgets.
期刊介绍:
Limnology and Oceanography (L&O; print ISSN 0024-3590, online ISSN 1939-5590) publishes original articles, including scholarly reviews, about all aspects of limnology and oceanography. The journal''s unifying theme is the understanding of aquatic systems. Submissions are judged on the originality of their data, interpretations, and ideas, and on the degree to which they can be generalized beyond the particular aquatic system examined. Laboratory and modeling studies must demonstrate relevance to field environments; typically this means that they are bolstered by substantial "real-world" data. Few purely theoretical or purely empirical papers are accepted for review.