BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:EESS Seminar talk on "X-ray imaging demonstrates that air-filled p orosity and its connectivity controls carbon mineralisation near saturatio n in intact soil cores" DTSTART:20261201T121500 DTEND:20261201T131500 DTSTAMP:20261017T232347Z UID:5245cbc87981d0cdfe26d5bff88706d2f544cf9f1803eae476bda9d9 CATEGORIES:Conferences - Seminars DESCRIPTION:Dr. John Koestel\, Agroscope \nAbstract:\nOne source of uncer tainty in the prediction of soil carbon (C) dynamics is the regulation of microbial activity by soil moisture. This important factor regulates both the survival and the activity of the microbial community through the avail ability of water\, air and substrates. The role of soil structure in the r esponse of C mineralisation to soil moisture is not taken into account in models. We need to better understand how the heterogeneity of the soil por e space and changes in soil structure affect C mineralisation through the regulation of soil water retention and thus the distribution of air and wa ter in the pore system. We hypothesized that soil structure has a predomin ant effect on the response curve close to saturation by affecting the amou nt and distribution of the air phase in soil\, in which the diffusion of g ases takes place: transport of air (O2) to microbes and transport of the m ineralisation product (CO2) back to the atmosphere.\n\nTo obtain soils of contrasting structure\, we sampled 8 intact cores (at a depth of 10-15 cm) from four blocks of an agricultural field experiment located in northern France a under conventional or no-till management. Each core (5 x 6.5 cm) was consecutively incubated over a period of one week after equilibration at water potentials of -2.5\, -10\, -20 and -30 cm and C mineralisation ra tes were estimated at day 1\, 3 and 7. Air distributions in the soil pore networks were quantified by X-ray tomography between each equilibration/in cubation period. Water retention curves\, soil dry bulk density and porosi ty were estimated from water contents (weights) measured at each potential .\n\nThe estimated porosity varied from 0.40 to 0.52 and the Van Genuchten parameter alpha (estimated from water retention curves) varied from 0.05 to 0.09 cm-1 and both were slightly smaller under no till compared to conv entional management. Air contents varied from zero to 0.09 m3 m-3 and were positively correlated to the C mineralisation rates\, which varied from 1 8 μg CO2 g-1C h-1 near saturation to 65 μg CO2 g-1C h-1 at water potenti als of -20 to -30 cm. X-ray analyses carried out at the four different wat er potentials further showed that C mineralisation rates were positively c orrelated to the volume fraction of the air-filled porosity connected to t he upper surface of the cores.\n\nThese results confirm that soil structur e is important in the C mineralisation response to soil moisture close to saturation by regulating the air content and its distribution in soil at w ater potentials ranging from 0 to -30 cm.\n\nBiography:\nJohn Koestel is a soil hydrologist and physicist. He has studied hydrology with focus on so ils and geology at the Albert-Ludwigs-University in Freiburg im Breisgau ( Germany). Working with electrical resistivity tomography to image salt tra cer transport in soils with 3-D resolution\, he obtained his PhD at the Rh einische Friedrich-Wilhelms-Universität Bonn (Germany). Afterwards\, he w as employed for 10 years at the Swedish University of Agricultural Science s in Uppsala (Sweden)\, first as postdoc\, then assistant and eventually a ssociate professor. During this time\, John worked with meta-analyses and 3-D X-ray imaging of soil structure and its dynamics. In 2020 he switched to Agroscope Reckenholz (Switzerland) as a senior researcher\, focusing on soil structure and soil functions as well as soil physical quality indica tors.  \n  LOCATION:ALP 1 107 https://plan.epfl.ch/?room==ALP%201%20107 https://epfl. zoom.us/j/69011077410#success STATUS:CONFIRMED END:VEVENT END:VCALENDAR