Lipoxygenase-induced autoxidative degradation of terrestrial particulate organic matter in estuaries: A widespread process enhanced at high and low latitude

Abstract

There exists a substantial amount of research on abiotic (e.g. photochemical) degradation pertaining to organic matter (OM) in the marine realm. While recent research has shown its importance in the degradation of terrestrial particulate OM (TPOM), the mechanisms involved in the induction of autoxidation in estuaries remain unclear. In this study, we propose for the first time the involvement of lipoxygenase (LOX) activity in the induction of autoxidation in mixed waters. The observation of unusual profiles of palmitoleic acid oxidation products and the presence of jasmonic acid in suspended particulate matter (SPM) collected close to the Rhône River, as well as in samples from the Mackenzie and Amazon rivers, is attributed to strong LOX activity. We show the role played by salinity in the induction of this LOX activity and provide an explanation for the differences in estuarine autoxidation level. At high latitude, lower temperatures and irradiance favor photooxidative damage to higher plant debris and, consequently, hydroperoxide production. High hydroperoxide content strongly contributes to LOX activation in mixed waters. The high resulting LOX activity enhances alkoxyl radical production and thus autoxidation. On the contrary, at low latitude, photooxidative effects are limited, and riverine autoxidation is favored. The higher hydroperoxide content of TPOM may, as a consequence, thereby also contribute to a high level of LOX activity and autoxidation in estuaries. In temperate zones, land and riverine photooxidative and autoxidative damage is limited, unlike estuaries where we observed significant LOX-induced and autoxidative damage.

Electron ionization mass spectrometry fragmentation and multiple reaction monitoring quantification of autoxidation products of α‐ and β‐amyrins in natural samples

“…It was previously observed that autoxidation of terrestrial higher plants was less efficient in temperate zones than at low or high latitudes . The low autoxidation percentages of amyrins measured in the samples investigated (Table ) give good support to these previous observations.…”

“…The ketones 7 and 8 were thus proposed as tracers of abiotic degradation (autoxidation) of terrestrial higher plants in the marine realm . Although very high proportions of these tracers could be easily detected by GC/MS operating in selected ion monitoring (SIM) mode in particulate matter and sediment samples collected in the Arctic and tropical zones, their quantification in samples where terrestrial organic matter is present in lesser proportions remains more problematic.…”

Biotic and abiotic degradation of the sea ice diatom biomarker IP25 and selected algal sterols in near-surface Arctic sediments

“…However, here we show that autoxidative degradation of IP 25 may occur under more 'forced' conditions and such processes may also take place in Arctic surface sediments. Indeed, due to recent evidence of strong lipoxygenase activity (a well-known source of radicals; Fuchs and Spiteller, 2014) in bacteria associated with ice algae (Amiraux et al, 2017) and in terrestrial particulate organic matter discharged from Arctic rivers (Galeron et al, 2018), autoxidative degradation reactions can even be dominant in Arctic sediments (Rontani et al, 2012(Rontani et al, , 2017, despite the low temperatures. The autoxidation of IP 25 in sediments possessing a thick oxic layer, where the contact of ice algal detritus with oxygen may be relatively long, therefore represents a viable degradation pathway of this biomarker in near-surface sediments.…”

“…This high autoxidation efficiency likely reflects the enhanced photooxidation of senescent vascular plants in the region (thus yielding high amounts of hydroperoxides), together with high lipoxygenase activity (a potential source of radicals; Fuchs and Spiteller, 2014). Indeed, the latter mechanism has recently been observed in sinking particles dominated by ice algae (Amiraux et al, 2017) and in particles discharged from the Mackenzie River (Galeron et al, 2018).…”

Use of palmitoleic acid and its oxidation products for monitoring the degradation of ice algae in Arctic waters and bottom sediments

“…Furthermore, the oxidation products of monounsaturated fatty acids appear to be especially useful for differentiating the involvement of photo-and autoxidative degradation processes in suspended and sinking particulate matter and bottom sediment samples (for a review see Rontani, 2012). More recently, analysis of these compounds provided evidence of lipoxygenase-induced degradation in suspended (Galeron et al, 2018) and sinking (Amiraux et al, 2017) particles.…”