The Fellow developed scripts to run the Millennial model which are publicly available on Github under an MIT license. In order to find the best function to represent the relationship between mineral surface area and soil organic matter, the Fellow conducted a synthesis study using 400+ sorption experiments upscaled to a global estimate of sorption capacity using relationships with environmental variables (Abramoff et al. 2021). The Fellow calibrated the temperature response using the ForHot Icelandic experiment (in prep) and presented these results at the ForHot Consortium Annual Meeting in March 2021. In collaboration with the group that runs the BBSFA experiment, the Fellow used a similar model to Millennial with representation of mineral surface area and microbes coupled to an Earth System Model similar to ORCHIDEE to simulate the depth profile and temperature sensitivity of SOC stock at BBSFA. This work is in press in a book chapter describing multi-modeling tools for soil C modeling. To better understand data needs for constraining model parameters, a simulated data experiment was conducted with a coupled C and N microbial physiology model using a Bayesian statistical framework to identify which types of data best constrained the parameters in a general microbial soil decomposition model (Saifuddin et al. 2021).
The Fellow conducted a global-scale evaluation of Millennial V2 using measurements of soil C fractions at 1300+ sites (Abramoff et al. 2022). The Fellow fit Millennial V2 with and without croplands to determine the effect of agricultural management on model parameters. The Fellow developed a novel method for estimating total litter input using a data product of aboveground litterfall combined with a separate data product estimating the partitioning between above and belowground plant parts. The global evaluation compared Millennial V2 model output to many of the datasets initially identified in Task 2.2 as well as more detailed datasets gathered to evaluate partitioning of C stock into different fractions and the mean residence time. One of the global datasets of soil fraction measurements used is a new synthesis which is currently under consideration at Nature Communications.
The Fellow considered using ORCHIDEE model output as inputs to the model. However, the Fellow identified data products that are more closely related to measurements than is ORCHIDEE model output. Nevertheless, the Fellow is developing an interface system to couple Millennial V2 and ORCHIDEE that goes beyond what was promised in WP2 because rather than running the model offline, the interface will allow data to be passed between Millennial V2 and ORCHIDEE at each timestep and include coupled C and nitrogen cycling. This work will be completed by postdoctoral fellow E. Bruni who will be co-advised by the Fellow and B.Guenet under the H2020 Grant No. 101000289.
CMIP5 simulations were not yet conducted due to the project ending 4 months early, as the Fellow secured a permanent position as an Associate Scientist at ORNL, USA. However, projections of the coupled ORCHIDEE-Millennial in response to changing climate and land use is planned in collaboration with E. Bruni as mentioned above. Relevant to Tasks 2.2 and 2.3 multiple models were fitted including Millennial V2 to decadal-scale soil C stock changes measured at 17 agricultural sites to determine how much additional C is needed to meet the goal of increasing soil C concentration by 4‰ per year, in prep for Global Change Biology (Bruni et al.). Over the time period of the Fellowship, the Fellow has published 2 first author papers, and 1 corresponding author paper. This represents a total of 3 published papers, 1 book chapter in press, 1 book chapter in revision, 3 papers in review, and 4 papers in advanced prep.
