Biomarker signatures of former soil uses. A case study from the catchment area of Lake Aydat (Massif Central, France).

International audienceThe history of human land use vs climate impacts on natural environments is of direct relevance in the perspective of future climate change and increasing human pressure on ecosystems. Although these impacts were discrete before agriculture and breeding development, they became critical after the industrial revolution, due to the massive anthropization of terrestrial surfaces. Natural archives such as soils and sediments potentially preserve information about past land uses. As a matter of fact, soils are reputed to retain the signature of their ancient uses [1] and lacustrine sediments integrate the evolution of environmental conditions that prevailed in the catchment basin through time

Preservation of an ancient grassland biomarker signature in a forest soil from the French Massif Central

International audienceIn response to the lack of studies focussing on the residence time of molecular biomarkers in soils, the lipid content of three soil profiles from the French Massif Central with different land use history were examined. The free neutral lipid content of two reference soil profiles developed under grassland and forest vegetation, and of a former grassland soil converted to forest about 60 years ago, was analysed using gas chromatography - mass spectrometry (GC-MS). Wax esters as well as the ratio of major homologues of n-alkanes and n-alkan-2-ones could be used to characterize the overlying vegetation in the reference forest and grassland soil profiles, but failed to distinguish the respective grassland and forest contributions to the profile of the soil that had changed use. For n-alkanes and n-alkan-2-ones, the failure might be attributed either to mixing of the molecular patterns inherited for the former and current plant cover, whereas for compounds such as wax esters simple degradation is likely to be involved. Conversely, iso- and anteiso- C15:0 fatty acid methyl esters (FAMEs; of bacterial origin), steroids (tracing cattle faecal contamination), tricyclic diterpenoids and their oxygenated derivatives, as well as methoxyserratenes (inherited from Pinaceae) and triterpenyl acetates (specific to the Asteraceae), proved to be effective in distinguishing current land use for the reference soil profilesand for the converted soil. The persistence of these compounds in the changed use soil allowed us to estimate their residence time in soil

First detection of triterpenyl acetates in soils: sources and potential as new palaeoenvironmental biomarkers

International audienceUnderstanding past reactions of ecosystems under natural and anthropic constraints is of crucial importance to anticipate the consequences of the current global changes. Unraveling natural and anthropic impacts on environments requires the reconstruction of ancient land-uses. As a part of a larger project aiming at developing new molecular biomarkers in soils that could be specific of their overlying vegetation, we have analyzed the neutral lipid content of soils developed under distinct types of plants. Soils were sampled around Lake Aydat, in Central France, of which the catchment is covered with pastures/meadows, forests and moors. The ketone/ester lipid fraction from soils under pastures or meadows contains a series of 14 pentacyclic triterpenyl acetates with a large structural diversity (Fig. 1). This discovery motivated an extensive phytochemical literature survey (240 references) that showed restricted potential sources of triterpenyl acetates. -amyrin, taraxeryl, glutinyl, -amyrin, and multiflorenyl, acetates are found in very distinct taxa and are thus poorly informative. Conversely, lupeyl, bauerenyl, isobauerenyl, taraxasteryl and -taraxasteryl acetates appear more specific since they are majoritary reported in Asteraceae. Pichierenyl, isopichierenyl and gammacerenyl acetates seem to be the more specific ones since they are produced by a single known species, Picris hieracioides L. (hawkweed oxtongue, Asteraceae)

Methoxy-serratenes as discriminant biomarkers for soils developed under conifer forests

PosterInternational audienceThe evolution of landscapes through time constitutes a challenge for both archaeologists and paleoenvironmentalists. For example, human deforestation (for cultivation and building) strongly affected the shape of continental surfaces with supposed impacts on the global carbon cycle of which the timing and extent remains controversial

Reconstitutions paléoenvironnementales des usages et de la vulnérabilité des sols : approches moléculaires

To face the challenges of our changing world, it is essential to elucidate the complex interactions liking societies, environments and climates. Investigating natural archives helps to improve our understanding of the past, present and future complex socioecological systems. Besides parent rock and pedogenesis, soils inherit their qualities from their past and current uses and management. Though fundamental for societies and environments, they are becoming a threatened natural resource. In this perspective, this article proposes an overview of palaeoenvironmental approaches for evaluating, in natural archives, land uses and soil vulnerability. Emphasis is put on molecular biomarkers. Some other complementary indicators which are often associated to them (historical, sedimentological, geochemical and biotic indicators) are also described.Pour faire face aux défis posés par les changements globaux actuels, il est essentiel d’élucider les interactions complexes qui lient sociétés, environnements et climat. Explorer les archives naturelles aide à améliorer notre compréhension des systèmes socio-écologiques passés, présents et futurs. Outre la roche mère et la pédogenèse, les sols héritent leurs qualités de leur gestion et de leurs usages anciens et actuels. Bien qu’ils soient fondamentaux pour les sociétés et les écosystèmes, ils deviennent une ressource naturelle menacée. Dans ce cadre, cet article propose un aperçu d’approches paléoenvironnementales permettant d’évaluer, au sein des archives naturelles, les usages et la vulnérabilité des sols. L’accent est porté sur les biomarqueurs moléculaires. Quelques autres indicateurs complémentaires qui y sont souvent associés (indicateurs historiques, sédimentologiques, géochimiques et biotiques) sont aussi exposés.Lavrieux Marlène. Reconstitutions paléoenvironnementales des usages et de la vulnérabilité des sols : approches moléculaires. In: Collection EDYTEM. Cahiers de géographie, numéro 18, 2015. Sols et matières organiques. Mémoires et héritages. pp. 33-40

Molecular biomarkers of land use, from soil to sediment : example of the catchement and of the lake Eydat (French Massif Central)

Cette étude propose une analyse intégrée de biomarqueurs moléculaires de sols, depuis leur site de production jusqu'à leur archivage sédimentaire lacustre. Un inventaire des lipides neutres est d'abord réalisé sur des sols d'usages contrastés : prairies/pâtures et forêts. Globalement, cette approche permet de distinguer (1) des composés linéaires ubiquistes, et (2) des composés (poly-)cycliques, généralement spécifiques. Parmi ces derniers figurent les acétates de triterpényle et les méthoxyserratènes, respectivement biomarqueurs d'Astéracées et de Pinacées. La persistance de l'empreinte moléculaire d'un ancien usage des sols est aussi démontrée. Ensuite, l'analyse multi-proxy d'une carotte sédimentaire couvrant les 6700 dernières années révèle l'impact prépondérant des activités humaines sur le fonctionnement hydrologique du lac, depuis l'époque gallo-romaine. Les assemblages moléculaires précédemment définis dans les sols sont globalement retrouvés, associés à un nouveau biomarqueur spécifique du chanvre, d'intérêt paléoenvironnemental. Une tentative de reconstitution des anciennes occupations des sols apparaît conforme aux données historiques et paléoenvironnementales antérieures.This study proposes an integrated analysis of molecular biomarkers of landuse, from their genesis in soils to their archiving in the lacustrine sediment. An inventory of neutral lipids is realized on soils of two contrasted landuses: grassland/pasture and forest. This approach globally allows to distinguish (1) ubiquist linear compounds and (2) (poly-)cyclic compounds, generally specific. Among these ones, triterpenyl acetates and methoxyserratenes are detected and are respectively biomarkers of Asteraceae and Pinaceae. The persistence of a molecular imprint of an ancient landuse is also demonstrated. Then, the multi-proxy analysis of a sedimentary core, covering the last 6700 years, shows the prominent impact of human activities on the hydrologic functioning of the lake since the gallo-roman period. Molecular assemblages previously defined in soils are globally detected in sediments, associated with a new specific biomarker of hemp, of palaeoenvironmental interest. Hypotheses for the reconstitution of past landuses appear to be consistent with previous historical and palaeoenvironmental data

Biomarqueurs moléculaires d'occupation des sols, du sol au sédiment : exemple du bassin-versant et du lac d'Aydat (Puy-de-Dôme)

This study proposes an integrated analysis of molecular biomarkers of landuse, from their genesis in soils to their archiving in the lacustrine sediment. An inventory of neutral lipids is realized on soils of two contrasted landuses: grassland/ pasture and forest. This approach globally allows to distinguish (1) ubiquist linear compounds and (2) (poly-)cyclic compounds, generally speci c. Among these ones, triterpenyl acetates and methoxyserratenes are detected and are respectively biomarkers of Asteraceae and Pinaceae. The persistence of a molecular imprint of an ancient landuse is also demonstrated. Then, the multi-proxy analysis of a sedimentary core, covering the last 6700 years, shows the prominent impact of human activities on the hydrologic functioning of the lake since the gallo-roman period. Molecular assemblages previously de ned in soils are globally detected in sediments, associated with a new speci c biomarker of hemp, of palaeoenvironmental interest. Hypotheses for the reconstitution of past landuses appear to be consistent with previous historical and palaeoenvironmental data.Cette étude propose une analyse intégrée de biomarqueurs moléculaires de sols, depuis leur site de production jusqu'à leur archivage sédimentaire lacustre. Un inventaire des lipides neutres est d'abord réalisé sur des sols d'usages contrast és : prairies/pâtures et forêts. Globalement, cette approche permet de distinguer (1) des composés linéaires ubiquistes, et (2) des composés (poly-)cycliques, généralement spéci ques. Parmi ces derniers gurent les acétates de triterpényle et les méthoxyserrat ènes, respectivement biomarqueurs d'Astéracées et de Pinacées. La persistance de l'empreinte moléculaire d'un ancien usage des sols est aussi démontrée. Ensuite, l'analyse multi-proxy d'une carotte sédimentaire couvrant les 6700 dernières années révèle l'impact prépondérant des activités humaines sur le fonctionnement hydrologique du lac, depuis l'époque gallo-romaine. Les assemblages moléculaires précédemment dé- nis dans les sols sont globalement retrouvés, associés à un nouveau biomarqueur spéci que du chanvre, d'intérêt paléoenvironnemental. Une tentative de reconstitution des anciennes occupations des sols apparaît conforme aux données historiques et paléoenvironnementales antérieures