%0 Articles %T Whole-tree Lagrangian optimal stomata model and its application to predicting cambial growth of tree stem %A Liu, Che %D 2024 %J Dissertationes Forestales %V 2024 %N 356 %R doi:10.14214/df.356 %U http://dissertationesforestales.fi/article/24009 %X

Stomata are a pivotal nexus between tree physiology and the environment, and thus modelling stomatal behaviour is critical for understanding tree growth and functioning. One of such models that have been widely tested is based on Lagrangian optimality analysis of gas exchange. The objectives of the present study were expanding the optimal stomata model to the whole-tree scale and coupling it with a model of cambial growth. The coupled model connects stomatal behaviour with non-stomatal limitation on photosynthesis, waterlogging effects, and the enzymatic activities and phenology of cambial growth. It requires commonplace inputs of meteorology, photosynthetic photon flux density (PPFD) and soil water conditions and can output transpiration, assimilation and cambial growth rates simultaneously at 30-minute resolution. The model was parameterized using Bayesian statistics and tested against observations on Pinus sylvestris and Picea abies from boreal forest sites in Finland of peatland and mineral soils. The model performance on simulating transpiration rate and stem radial dimension was good. Statistical analyses of model parameters showed that young/short trees almost always had higher stomatal conductance than old/tall trees under typical vapour pressure deficit (VPD) and PPFD. Also, maximum soil-to-root hydraulic conductance and minimum marginal water use efficiency (MWUE) of the trees were positively correlated with their leaf-to-sapwood area ratio. The modelled cambial growth duration was positively correlated with leaf-specific photosynthetic production (P) of the growing season at the moister peatland but not at the dryer mineral-soil site, and otherwise phenological traits of cambial growth were not significantly correlated with P at either site, suggesting P is not sufficient for determining the growth phenology of boreal trees. The model provides an easy-to-use tool for coupled tree eco-physiological and growth simulation and insights into larger-scale sink-driven vegetation modelling.