• Sciences du Vivant/Ecologie, Environnement
  
• Sciences de l'environnement/Biodiversité et Ecologie
  
• Sciences de l'environnement/Environnement et Société
  
• Sciences de l'environnement/Milieux et Changements globaux
  
• Sciences de l'environnement/Ingénierie de l'environnement
  

In order to fulfil the current need for stable and specific tracers to monitor vascular- plant organic matter degradation in aquatic environments, alpha-amyrin (urs-12-en-3 beta-ol) and beta-amyrin (olean-12-en-3 beta-ol) were oxidised in vitro and their abiotic degradation products quantified in environmental samples from the Rhone River in France. Although they appear inert to photooxidation, they are clearly affected by autoxidation and the tracer potential of the resulting products was confirmed. Autoxidation of alpha- and beta-amyrins produces urs or olean-12-en-3-one, 3 beta-hydroxy-urs or olean-12-en-11- one, urs or olean-12-en-3 beta, 11 alpha-diol and urs or olean-12-en-3,11-dione. 3 beta-Hydroxy-urs-12-en-11-one and 3 beta-hydroxy- olean-12-en-11-one, the main oxidation products detected, were selected as autoxidation tracers. These compounds, specific to autoxidation, were detected in dry leaves of Smilax aspera and in suspended particulate matter samples collected in the Rhone River and evidenced the importance of autoxidation in the degradation of organic matter of terrestrial origin.

In order to fill the need for specific and stable tracers for monitoring the degradative state of particulate organic matter (OM), betulin and its degradation products were selected to trace biotic and abiotic degradation processes affecting terrestrial higher plant-derived OM in riverine environments. Samples of Quercus ilex leaves and suspended particulate matter were collected from the Marseille Luminy area and the Rhône River, respectively, and analyzed in order to validate the tracer potential of betulin oxidation products identified during in vitro simulations. Three degradation products were selected as tracers: lup-20(30)-ene-3β,28,29-triol, lupan-20-one-3β,28-diol and the 20R and 20S epimers of 3β,28-dihydroxy-lupan-29-oic acid. They were deemed sufficiently stable for tracing the different degradative processes in aquatic systems affecting OM of terrestrial higher plant origin. All were found in riverine suspended particulate matter (SPM), evidencing the advanced degradation state of riverine particulate OM (POM), as well as the importance of autoxidation in the degradation. Lup-20(30)-ene-3β,28,29-triol and lupan-20-one-3β,28-diol were also found in senescent leaves of Q. ilex, attesting to the involvement of photo- and autoxidation in the degradation of plant leaves. Alongside existing tracers, these compounds provide a better insight into the degradation state of riverine OM, as well as into the degradative processes at play, a knowledge that will be a necessary basis for further studies of the degradative state of particulate marine OM and sediments.

Isomeric cucurbic acids derive from the reduction of the keto group of jasmonic acids. These growth regulators are natural constituents of various higher plants and fungi. Elucidation of electron ionization mass spectrometry (EIMS) fragmentation pathways of the trimethylsilyl (TMS) derivatives of the different stereoisomers is essential for their characterization and quantification in natural samples.

In this short paper, it is demonstrated that autoxidation (free radical induced oxidation) of the chlorophyll phytyl side chain in senescent phytoplanktonic cells and higher plants constitutes a potential source of isophytol (3,7,11,15-tetramethylhexadec-1-en-3-ol) in the environment.To explain the formation of this isoprenoid alcohol, mechanisms involving the formation of the precursor 3-peroxy-3,7,11,15-tetramethylhexadec-1-ene are proposed.