Participation des organismes ingénieurs à l'agrégation des sols : analyse des patrons et mise en évidence des interactions

Les organismes ingénieurs sont des acteurs majeurs de la macroagrégation, un processus indispensable à la production de services écosystémiques par les sols. L'ignorance de l'origine réelle des différents types d'agrégats trouvés dans les sols, de leurs transformations au cours du temps et de leurs positions dans la matrice du sol, empêche la description et la modélisation de la dynamique de la macroagrégation du sol et des processus associés. Nous avons montré que la spectroscopie dans le proche infra-rouge (NIRS) permet d’identifier l'origine des macroagrégats construits par différents ingénieurs écosystémiques, les vers de terre et les plantes, dans différents milieux. Nous avons retrouvé dans les signatures spectrales de macroagrégats, collectés en surface et dans un bloc de sol sur le terrain, les signatures de référence de structures biogéniques obtenues dans des conditions contrôlées en microcosmes au laboratoire. Des expériences complémentaires réalisées en serre ont permis d'étudier les interactions entre racines et vers de terre dans la production de macroagrégats. Les structures biogéniques produites en présence d’une espèce de plante et d’une espèce de ver de terre ont révélé des effets additifs des deux espèces dans leurs signatures spectrales montrant une interaction plutôt que la production de structures isolées spatialement. Une dernière étude réalisée en laboratoire a montré que les effets, causés par le vieillissement de turricules sur leurs teneurs en MO, sont suffisants pour affecter les signatures spectrales des turricules et ainsi permettent de dater l’âge d’apparition d’un turricule. Mes travaux de thèse proposent une nouvelle méthodologie pour analyser les origines des macroagrégats du sol, pour quantifier l'apport relatif des ingénieurs écosystémiques à l'agrégation du sol et pour évaluer la dynamique des macroagrégats dans la structure du sol

Impact of Temporal Macropore Dynamics on Infiltration : Field Experiments and Model Simulations

Macropores greatly affect water and solute transport in soils. Most macropores are of biogenic origin; however, the resulting seasonal dynamics are often neglected. Our study aimed to examine temporal changes in biopore networks and the resulting infiltration patterns. We performed infiltration experiments with Brilliant Blue on pastureland in the Luxembourgian Attert catchment (spring, summer, and autumn 2015). We developed an image-processing scheme to identify and quantify changes in biopores and infiltration patterns. Subsequently, we used image-derived biopore metrics to parameterize the ecohydrological model echoRD (ecohydrological particle model based on representative domains), which includes explicit macropore flow and interaction with the soil matrix. We used the model simulations to check whether biopore dynamics affect infiltration. The observed infiltration patterns revealed variations in both biopore numbers and biopore–matrix interaction. The field-observed biopore numbers varied over time, mainly in the topsoil, with the largest biopore numbers in spring and the smallest in summer. The number of hydrologically effective biopores in the topsoil seems to determine the number and thereby the fraction of effective biopores in the subsoil. In summer, a strong biopore–matrix interaction was observed. In spring, the dominant process was rapid drainage, whereas in summer and autumn, most of the irrigated water was stored in the examined profiles. The model successfully simulated infiltration patterns for spring, summer, and autumn using temporally different macropore setups. Using a static macropore parameterization the model output deviated from the observed infiltration patterns, which emphasizes the need to consider macropores and their temporal dynamics in soil hydrological modeling

Vorhersage effektiver Makroporen durch Regenwurmabundanz und abiotische Umweltvariablen

Regenwürmer erzeugen Bioporen und erhöhen somit die Makroporosität von Böden. Dies kann zu präferenziellem Fließen führen und somit den vertikalen Wasser- und Stofftransport erhöhen. Das Vorkommen hydraulisch effektiver Bioporen variiert jedoch zeitlich und räumlich ebenso wie die Aktivität verschiedener Regenwurmarten. Das Ziel dieser im Rahmen der DFG Forschergruppe CAOS geförderten Studie war es, das Vorkommen effektiver Bioporen über die Abundanz relevanter Regenwurmarten und raumzeitliche Muster verschiedener abiotischer Umweltvariablen vorherzusagen. An sechs Standorten im luxemburgischen Wollefsbach-Einzugsgebiet wurden zu sechs Terminen innerhalb eines Jahres Infiltrationsversuche mit Brilliant Blue in fünffacher Wiederholung durchgeführt. In den Bodentiefen 3, 10 und 30 cm wurde die Anzahl der blau gefärbten, hydraulisch effektiven Bioporen bestimmt. Diese wurden in drei Größenklassen eingeteilt (Durchmesser: <2, 2–6, >6 mm). Zusätzlich wurden jeweils die Abundanzen aller gefundenen Regenwurmarten bestimmt. Mittels generalisierter linearer Modelle haben wir den Einfluss von Regenwurmabundanzen und verschiedenen abiotischen Umweltvariablen auf die Anzahl effektiver Bioporen untersucht. Die wichtigsten Variablen waren die Abundanzen von Lumbricus terrestris und Aporrectodea longa, Zeitreihen der Bodenfeuchte, der Luftfeuchte und des Niederschlags sowie die räumlichen Verteilungen der Landnutzung, der Hangneigung und des topographischen Feuchteindex. Die Eignung einzelner Variablen zur Vorhersage sowie die Güte der Modelle (erklärte Devianz: 5-50 %; Spearman Korrelation: 0,24-0,67) variierten erheblich zwischen den Bodentiefen und Größenklassen der vorhergesagten Bioporen. Die resultierenden Zeitreihen der Anzahl effektiver Bioporen und ihre räumlichen Verteilungen im Einzugsgebiet stellen eine wertvolle Basis für die Parametrisierung bodenhydrologischer Modelle dar. Darüber hinaus zeigen unsere Ergebnisse, wie wichtig die Berücksichtigung der zeitlichen Dynamik hydraulischer Konnektivität von Bioporen ist

Soil fauna and their potential responses to warmer soils

Soil fauna are important contributors to ecosystem functioning as well as being tremendously diverse. Effects of warming on soil fauna are understudied and complex, with multiple covariates and a mixture of direct and indirect effects. This, combined with diverse communities, results in a suite of potential responses across temporal, spatial, and biological scales. We present a conceptual diagram to relate these interacting effects and a framework for organizing and understanding past and future research in this field. Themes common in the literature include species-specificity, site-specificity, and the challenge of disentangling the connection between temperature and moisture in soils. Much extant soil biodiversity remains undiscovered and our understanding of the current roles of soil fauna in ecosystem processes is incomplete; future research needs include a focus on these issues as well as using multivariate techniques to separate multiple interacting effects from potentially covarying factors

A“Dirty” Footprint: Macroinvertebrate diversity in Amazonian Anthropic Soils

International audienceAmazonian rainforests, once thought to be pristine wilderness, are increasingly known to have been widely inhabited, modified, and managed prior to European arrival, by human populations with diverse cultural backgrounds. Amazonian Dark Earths (ADEs) are fertile soils found throughout the Amazon Basin, created by pre-Columbian societies with sedentary habits. Much is known about the chemistry of these soils, yet their zoology has been neglected. Hence, we characterized soil fertility, macroinvertebrate communities, and their activity at nine archeological sites in three Amazonian regions in ADEs and adjacent reference soils under native forest (young and old) and agricultural systems. We found 673 morphospecies and, despite similar richness in ADEs (385 spp.) and reference soils (399 spp.), we identified a tenacious pre-Columbian footprint, with 49% of morphospecies found exclusively in ADEs. Termite and total macroinvertebrate abundance were higher in reference soils, while soil fertility and macroinvertebrate activity were higher in the ADEs, and associated with larger earthworm quantities and biomass. We show that ADE habitats have a unique pool of species, but that modern land use of ADEs decreases their populations, diversity, and contributions to soil functioning. These findings support the idea that humans created and sustained high-fertility ecosystems that persist today, altering biodiversity patterns in Amazonia

Impact of pre-Columbian 'geoglyph' builders on Amazonian forests

Over 450 pre-Columbian (pre-AD1492) geometric ditched enclosures ('geoglyphs') occupy ca. 13,000 km2 of Acre state, Brazil, representing a key discovery of Amazonian archaeology. These huge earthworks were concealed for centuries under terra firme (upland interfluvial) rainforest, directly challenging the 'pristine' status of this ecosystem and its perceived vulnerability to human impacts. We reconstruct the environmental context of geoglyph construction and the nature, extent and legacy of associated human impacts. We show that bamboo forest dominated the region for ≥6000 y and that only small, temporary clearings were made to build the geoglyphs; however, construction occurred within anthropogenic forest that had been actively managed for millennia. In the absence of widespread deforestation, exploitation of forest products shaped a largely forested landscape that survived intact until the late 20th century

A "dirty" footprint: macroinvertebrate diversity in Amazonian Anthropic Soils.

Amazonian rainforests, once thought to be pristine wilderness, are increasingly known to have been widely inhabited, modified, and managed prior to European arrival, by human populations with diverse cultural backgrounds. Amazonian Dark Earths (ADEs) are fertile soils found throughout the Amazon Basin, created by pre-Columbian societies with sedentary habits. Much is known about the chemistry of these soils, yet their zoology has been neglected. Hence, we characterized soil fertility, macroinvertebrate communities, and their activity at nine archeological sites in three Amazonian regions in ADEs and adjacent reference soils under native forest (young and old) and agricultural systems

Do earthworms and roots cooperate to build soil macroaggregates ? A microcosm experiment

Soil ecosystem engineers are major actors of soil macroaggregation, a process that drives the production of ecosystem services by soils. However, our inability to identify the origins of different types of macroaggregates found in soils is an obstacle to describing and modeling their dynamics and associated processes (C sequestration; hydraulic properties). This laboratory study investigated mechanisms of biological soil macroaggregation by two different earthworm species (Apporectodea caliginosa (Savigny) and Allolobophora chlorotica (Savigny) and two plant species (Trifolium pratense, Plantago lanceolata L), in isolation and in all possible combinations. Near infrared (NIR) spectral analysis significantly discriminated macroaggregates according to the organisms that created them since each organism produced macroaggregates with distinct NIR signals (p<0.001). The largest departure from the control signal was observed with T. pratense whereas earthworms and P. lanceolata specific signals were less contrasted. Macroaggregates formed in the presence of more than one ecosystem engineers had mixed signals showing that several actors had participated in their construction. This means that roots and earthworms did not produce macroaggregates in isolation and rather added their effects in building structures of mixed origins. Further studies based on the present methodology will tell us more on below ground behaviors of ecosystem engineers and their interactive building of soil habitats

Near infrared spectroscopy (NIRS) to estimate earthworm cast age

International audienceAs ecosystem engineers, earthworms are major actors of soil aggregation, a process that drives the delivery of ecosystem services by soils. However, persistence of soil aggregates produced by earthworms, their degradation rates, and their role in the dynamics of soil organic matter (SOM) and nutrients remain poorly known. In this experiment, near infrared (NIR) spectral signatures were measured in subterranean casts of the endogeic earthworm Aporrectodea caliginosa, incubated in controlled laboratory conditions for different periods of time. In parallel, dynamics of total amounts of C and N were assessed in ageing casts. As casts aged, NIR spectral signatures went through three main stages in the maturation process: (1) rapid changes in the NIR signal during the first 48 h, (2) a maturation period from days 3–30 with much slower change in NIR spectral signatures and (3) a further stage of maturation (days 45–90), where cast signals converged towards those of control soil. The first two axes of the PCA corresponded closely to the C and N content, respectively, of the casts. C and N contents in casts remained higher than those in control soil during the whole incubation time. Drying of casts halted the mineralization of organic matter, resulting in lack of change in the NIR spectral signal as long as casts were kept dry