Infra-red spectroscopy reveals chemical interactions driving water availability for enzyme activities in litters of typical Mediterranean tree species

Anne Marie Farnet da Silva (1) , Elisée Ferré (1) , Nathalie Dupuy (1) , Auriane de La Boussinière (1) , Catherine Rebufa (1, 2)

1 IMBE - Institut méditerranéen de biodiversité et d'écologie marine et continentale
2 ISM2 - Institut des Sciences Moléculaires de Marseille

In Mediterranean ecosystems, water is one of the main drivers of the microbial activities that support organic matter turnover in soils or litters. In addition to drought stress, coastal areas are subject to os-motic stress linked to sea spray exposure. Here we explored i) how water availability, characterized by water activity a w , is impacted by adding NaCI to litter, ii) the chemical interactions between water, NaCl and the litter matrix and iii) whether microbial activities (using lipase as a model) are affected under these conditions. Litters of two vegetal species typical of the Mediterranean area (Quercus pubescens and Pinus halepensis) were subjected to FTIR-ATR (Fourier-Transformed Infra-Red e Attenuated Total Reflectance) spectroscopy for chemical characterization. Q. pubescens and P. halepensis litters were characterized by cutin and aromatics respectively. Sorption isotherms were identical for both species litters; when NaCl was added, a shift in isotherm shape was observed at a w ranging from 0.75 to 1. FTIR also discriminated samples with and without added NaCl and revealed that cellulose is probably the polymer in interactions with ions. Very interestingly, no differences were found between lipase hydro-lytic activities with and without added NaCl: salt addition had no effect on these activities.

Mots clés: Sorption isotherms; Hydric stress; Water activity; Osmotic stress; Lipases

Domaines: Biodiversité et Ecologie; Ecologie, Environnement

Anne Marie Farnet da Silva, Elisée Ferré, Nathalie Dupuy, Auriane de La Boussinière, Catherine Rebufa. Infra-red spectroscopy reveals chemical interactions driving water availability for enzyme activities in litters of typical Mediterranean tree species. Soil Biology and Biochemistry, 2017, 114, pp.72-81. ⟨10.1016/j.soilbio.2017.06.026⟩. ⟨hal-01627795⟩