title: Additive or non-additive effect of mixing oak in pine stands on soil properties depends on the tree species in Mediterranean forests.
abstract: This study investigated how oak abundance in pine stands (using relative Oak Basal Area %, OBA%) may modulate soil microbial functioning. Forests were composed of sclerophyllous species i.e. Quercus ilex mixed with Pinus halepensis Miller or of Q. pubescens mixed with P. sylvestris. We used a series of plots with OBA% ranging from 0 to 100% in the two types of stand (n=60) and both OLF and A-horizon compartments were analysed. Relations between OBA% and either soil chemical (C and N contents, quality of organic matter via solid-state NMR, pH, CaCO3) or microbial (enzyme activities, basal respiration, biomass and catabolic diversity via BIOLOG) characteristics were described. OBA% increase led to a decrease in the recalcitrant fraction of organic matter (OM) in OLF and promoted microbial growth. Catabolic profiles of microbial communities from A-horizon were significantly modulated in Q. ilex and P. halepensis stand by OBA% and alkyl C to carboxyl C ratio (characteristic of cutin from Q. ilex tissues) and in Q. pubescens and P. sylvestris stands, by OBA% and pH. In A-horizon under Q. ilex and P. halepensis stands, linear regressions were found between catabolic diversity, microbial biomass and OBA% suggesting an additive effect. Conversely, in A-horizon Q. pubescens and P. sylvestris stands, the relationship between OBA% and either cellulase activities, polysaccharides or ammonium contents, suggested a non-additive effect of Q. pubescens and P. sylvestris, enhancing mineralization of the OM labile fraction for plots characterized by an OBA% ranging from 40% to 60%. Mixing oak with pine thus favored microbial dynamics in both type of stands though OBA% print varied with tree species and consequently sustainable soil functioning depend strongly on the composition of mixed stands. Our study indeed revealed that, when evaluating the benefits of forest mixed stand on soil microbial functioning and OM turnover, the identity of tree species has to be considered.
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale, UMR 7263, Aix Marseille Université, Université d'Avignon, CNRS, IRD, Campus l'Etoile, Site de Saint-Jérôme, Avenue escadrille Normandie-Niemen, 13 397 Marseille Cedex 20, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Brunel
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale, UMR 7263, Aix Marseille Université, Université d'Avignon, CNRS, IRD, Campus l'Etoile, Site de Saint-Jérôme, Avenue escadrille Normandie-Niemen, 13 397 Marseille Cedex 20, France.
authors.forename: Raphael
authors.initials: R
authors.lastname: Gros
authors.affiliation: Aix Marseille Université, CNRS, Spectropole Campus St Jérôme, Fédération des Sciences Chimiques de Marseille, FR 1739, 13397, Marseille, France.
authors.forename: Fabio
authors.initials: F
authors.lastname: Ziarelli
authors.affiliation: Institut Méditerranéen de Biodiversité et d'Ecologie marine et continentale, UMR 7263, Aix Marseille Université, Université d'Avignon, CNRS, IRD, Campus l'Etoile, Site de Saint-Jérôme, Avenue escadrille Normandie-Niemen, 13 397 Marseille Cedex 20, France. Electronic address: anne-marie.farnet@imbe.fr.
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Farnet Da Silva
mesh_terms: D065928:Forests; D019083:Mediterranean Region; D028223:Pinus; D029963:Quercus; D012987:Soil / Q000737:chemistry*; D014197:Trees
chemical_list: D012987:Soil
keywords: Mediterranean forests; Mixed forests; Non-additive effects; Organic matter quality; Soil horizons