Coupled effect of substrate and light on assimilation and oxidation of regenerated nitrogen in the euphotic ocean

Abstract

Nitrogen (N), as a critical element for microbial metabolisms, recycles rapidly in the euphotic ocean. Oxidation by nitrifiers is a competing pathway for phytoplankton assimilation of regenerated N (NH 4 + and urea). Sharing the overlapping substrates may result in competitive exclusion, thus, niche separation for the two assemblages. Both pathways are sensitive to light, but whether light intensity will intensify or alleviate such resource competition in the euphotic zone remains poorly explored in the field at the community level. By using 15 N labeling techniques, paired kinetic responses of uptake and oxidation were conducted in single bottles under manipulated light intensities for both NH 4 + and urea. We found light stimulated the maximum rate (R m ) and specific affinities (α U ) of both NH 4 + and urea uptake. In contrast, light effects were opposite for oxidation kinetics (R m and α O ). As irradiance

Substrate regulation leads to differential responses of microbial ammonia-oxidizing communities to ocean warming

“…Our results also suggest that the projected gradual increase in atmospheric deposition of anthropogenic nitrogen (including ammonium) 7 , 51 , 52 may aid in the thermal adaption of ammonia-oxidizing microorganisms in ammonium-depleted offshore environments. However, most of the NH 4 + from the atmosphere will be utilized first by phytoplankton in the surface layer above the nitracline, due to a competitive advantage of phytoplankton toward NH 4 + relative to nitrifers 17 , 53 . If this ammonium was to be supplied directly to the niche of AOA, the offshore AOR may response positively to warming before reaching the T opt-sat .…”

Iron requirements and uptake strategies of the globally abundant marine ammonia-oxidising archaeon, Nitrosopumilus maritimus SCM1

“…Due to their key role in N-biogeochemical cycling, investigation has focused on understanding the factors that determine the distribution of Thaumarchaeota and nitrification rates throughout the water column. Photoinhibition of AOA [11–14] and competition with phytoplankton for NH 4 + [15–17] have both been evoked as explanations of why peak nitrification rates typically occur at the base of the euphotic zone. However, observations of high nitrification rates in the euphotic zone indicate that this is not universally the case [18], suggesting that our understanding of the factors shaping the distribution of AOA is incomplete.…”

Dark Ammonium Transformations in the Pearl River Estuary During Summer

“…AO D and AA D were measured on board by adding 15 NH 4 Cl (98 atom % 15 N; Sigma–Aldrich, 299251–1G, Lot#TA2540V) into 1 L HDPE bottles to reach final concentrations less than 10% of the ambient concentration in the two water layers (surface and bottom) along the PRE. Details of the method and associated applications have been presented in previous studies (Lipschultz et al, 1986; Newell et al, 2011; Ward, 2011; M. N. Xu et al, 2019). All HDPE bottles used for incubation experiments were wrapped with aluminum foil and kept in thick, opaque black bags to ensure that the experiments took place in a completely dark environment.…”

“…The orthodox view is that assimilation of by phytoplankton should occur during the daytime or, to be more exact, stimulated by light (Nelson & Conway, 1979). However, assimilation under dark conditions cannot be ignored in many coastal environments although assimilation can be lower in the night time in open ocean (M. N. Xu et al, 2019), and it can even exceed the light assimilation rate in some instances (Hampel et al, 2018; Lipschultz et al, 1986), yet our understanding of the dark assimilation of is still very limited.…”