Modeling the Litter Monoterpene Emission and its Ecosystem-Scale Contribution in a Swedish Forest

Modeling the Litter Monoterpene Emission and its Ecosystem-Scale Contribution in a Swedish Forest Zhanzhuo Chen1, Zhiyang Zhang2, Ross Charles Petersen3, Cheng Wu4, Riikka Rinnan2 Jing Tang2 1Graduate School of Global Food Resources, Hokkaido University, Sapporo, Hokkaido, 060-0809, Japan 2Center for Volatile Interactions (VOLT), Department of Biology, University of Copenhagen, DK-2100, Copenhagen, Denmark 3Department of Physical Geography and Ecosystem Science, Lund University, S-223 62, Lund, Sweden 4Department of Chemistry and Molecular Biology, University of Gothenburg, 41296, Gothenburg, Sweden Correspondence to: Jing Tang (jing.tang@bio.ku.dk) Abstract. Litter-released monoterpenes are an important source of biogenic volatile organic compounds (BVOC) from the soil layer, influencing atmospheric chemistry and ecosystem-climate interactions. However, the mechanisms and drivers of litter BVOC emissions remain poorly quantified in terrestrial ecosystem models. This study integrates laboratory-measured, in-situ observational data, for the boreal forest (Scots pine and Norway spruce) at Norunda site in Sweden and the process-based Lund–Potsdam–Jena General Ecosystem Simulator (LPJ-GUESS) model to calibrate and evaluate the litter monoterpene emissions module. We parameterized the model using observed monoterpene emission rates from decomposition experiments and storage-based emission processes, incorporating environmental controls such as temperature and moisture. The model results are well reproduced and aligned with monthly monoterpene with the forest floor monoterpene emission observation during June to October in 2015, with a weighted root mean square error of 0.74 µg m-2 h-2, a weighted mean absolute error of 0.6 µg m-2 h-2, and a relative root mean square error of 11.04%. In addition, modelling results show litter contributes 0.58% to 3.04% of the ecosystem-level monoterpene emission. Despite the achievement of modelling, uncertainties persist regarding the role of litter quality and soil organic matter dynamics in shaping emissions. This study offers a valuable foundation for advancing process-based litter BVOC emission from the soil layer, emphasizing its potential to enhance our understanding of soil-atmosphere interactions and improve terrestrial ecosystem models.