Potential overestimation of community respiration in the western Pacific boundary ocean: what causes the putative net heterotrophy in oligotrophic systems?

Yibin Huang, Bingzhang Chen, Bangqin Huang, Hui Zhou, Yongquan Yuan

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Abstract

Microbial metabolism is of great importance in affecting the efficiency of biological pump and global carbon cycles. However, the metabolic state of the oligotrophic ocean, the largest biome on Earth, remains contentious. We examined the planktonic and bacterial metabolism using in vitro incubations along the western Pacific boundary during September and October 2016. The integrated gross primary production (GPP) of the photic zone exhibited higher values in the region of 2°–8°N along 130°E and the western Luzon Strait, which is consistent with the regional variability of nutrients in the different ocean provinces. Spatially, the community respiration (CR) was less variable than the GPP and slightly exceeded the GPP at most of the sampling stations. Overall, the in vitro incubation results suggest a prevailing heterotrophic state in this region. A comparison of the metabolic rates from the in vitro incubations with recently published biogeochemical model results in the same region shows that our observed GPP values were close to those predicted by the model, but the measured CR was approximately 30% higher than the modeled values. We also found that most of the in vitro CR estimates were higher than the upper range of the empirical CR estimated from the sum of the contributions of the main trophic groups. Conversely, the estimates of the empirical CR support the rationality of the CR predicted by the biogeochemical model. In general, the results indicate that systematic net heterotrophy is more likely a result of the overestimation of CR measured by the light–dark bottle incubation experiments, although the exact cause of the methodological problem remains unknown.

Original languageEnglish
Pages (from-to)2202-2219
Number of pages18
JournalLimnology and Oceanography
Volume64
Issue number5
Early online date6 May 2019
DOIs
Publication statusPublished - 30 Sep 2019

Keywords

  • gross primary production
  • community respiration
  • net community production
  • bacterial production
  • Western Pacific ocean
  • metabolic state

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