In:
Biogeosciences, Copernicus GmbH, Vol. 20, No. 8 ( 2023-04-21), p. 1605-1619
Abstract:
Abstract. The Peruvian upwelling system is a highly productive ecosystem with a large
oxygen minimum zone (OMZ) close to the surface. In this work, we carried out a
mesocosm experiment off Callao, Peru, with the addition of water masses from
the regional OMZ collected at two different sites simulating two different
upwelling scenarios. Here, we focus on the pelagic remineralization of organic
matter by the extracellular enzyme activity of leucine aminopeptidase (LAP) and
alkaline phosphatase activity (APA). After the addition of the OMZ water,
dissolved inorganic nitrogen (N) was depleted, but the standing stock of
phytoplankton was relatively high, even after N depletion (mostly
〉 4 µg chlorophyll a L−1). During the initial phase of
the experiment, APA was 0.6 nmol L−1 h−1 even though the
PO43- concentration was 〉 0.5 µmol L−1.
Initially, the dissolved organic phosphorus (DOP) decreased, coinciding with
an increase in the PO43- concentration that was probably linked to the APA. The
LAP activity was very high, with most of the measurements in the range of
200–800 nmol L−1 h−1. This enzyme hydrolyzes terminal amino acids
from larger molecules (e.g., peptides or proteins), and these high values are
probably linked to the highly productive but N-limited coastal ecosystem.
Moreover, the experiment took place during a rare coastal El Niño event with
higher than normal surface temperatures, which could have affected enzyme
activity. Using a nonparametric multidimensional scaling analysis (NMDS)
with a generalized additive model (GAM), we found that biogeochemical
variables (e.g., nutrient and chlorophyll-a concentrations) and phytoplankton and
bacterial communities explained up to 64 % of the variability in APA. The
bacterial community best explained the variability (34 %) in LAP. The high
hydrolysis rates for this enzyme suggest that pelagic N remineralization,
likely driven by the bacterial community, supported the high standing stock
of primary producers in the mesocosms after N depletion.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-20-1605-2023
DOI:
10.5194/bg-20-1605-2023-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2158181-2
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