Modeling plant biomass partitioning: responses to environmental conditions and disturbance

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The aim of the present thesis is to contribute to the understanding of the plant phenotypic responses to environmental conditions and disturbances. In particular, the value of the pipe model theory as a measure of morphological plasticity of chestnut tree (Castanea sativa Mill.) in relation to the site conditions was assessed, and the main physiological mechanisms underlying biomass allocation were theoretically explored using modeling technics. The constancy of the leaf to sapwood area slope coefficient (LASA) in C. sativa was confirmed at the intra-branch level, but showed a considerable variability among branches within a tree. In particular the LASA changed according to branch type (crown branches vs. epicormic shoots) and declined with height. With a generalized linear mixed modeling approach, a new reference parameter (Ground-level LASA), corresponding to a theoretical value of LASA for a branch at ground level, was proposed and validated on an independent dataset. The variation of this measure was investigated in different environmental conditions, confirming that the sweet chestnut is able to greatly vary the allocation patterns. In particular, the Ground-level LASA was high for trees growing in sites with good water supply (concave sites) and low in water poor convex sites. The analysis of the stool uprooting phenomena in over-aged coppice stands provided an indirect evidence of the role of microtopography and water availability in the allocation patterns between above and below ground biomass. In order to further theoretically explore the key issue of biomass partitioning in plants, a fairly simple model of allocation was developed, based on the interactions between water and carbon transport processes with assimilation and growth. The model is able to reproduce consistent deviations from the allometric trajectory, showing qualitatively correct responses in a range of different environmental conditions (light and water) and during recovery from unbalanced biomass removal (e.g. recover after pruning or fire damages). In this respect this model has the potential to be a good instrument for theoretical investigation of relations between anatomical (e.g. sclerophylly) and functional (e.g. transport resistances) characters and allocation patterns.