Document: FED-3-30-42

Acclimation of coniferous tree structure to the environment under hydraulic constraints.

MAGNANI, F.* ¹, J.GRACE ² and M.BORGHETTI ³

Inst. of Forest Tree Breeding, CNR, Florence, Italy ¹
University of Edinburgh, Edinburgh, United Kingdom ²
University of Basilicata, Potenza, Italy ³

Abstract:
Little is known with respect to the response of growth allocation to the environment among tree organs, despite the considerable effect that changes in resource allocation could have on the response of forest growth to climate change. We recently proposed a mathematical model of resource acclimation and growth in coniferous trees based on optimal growth and functional homeostasis in water transport. The assumptions were made that minimum water potentials are constrained, possibly at the risk of destructive xylem embolism, and that foliage production and tree growth are maximized within the limits imposed by this hydraulic constraint. In the research performed, we explored the implications these hypotheses had on resource allocation and forest growth given different environments. Model predictions were tested using data from three independent transects of Pinus sylvestris stands across Europe. Foliage-to-sapwood area ratios and the ratio between foliage and fine roots were predicted to decline asymptotically in dry air and were in good agreement with experimental data. Because of the effects of temperature on water viscosity, the amount of foliage that can be supported by a unit sapwood area or by a unit amount of fine roots was predicted to increase under warm climates. This was confirmed by data from a second transect of P. sylvestris stands. The model explained the large variation in foliage-to-sapwood area ratio and tree hydraulic resistance in P. sylvestris across a complex climatic gradient. The model could be used to predict tree and ecosystem responses to climate. The ability of plants to acclimate to climate change is generally thought to be an important evolutionary feature, enabling long-lived, sessile trees to face the vagaries of the environment.

Keywords: NPP, hydraulic constraints, age-related decline, transpiration, stomatal conductance, assimilation, VPD, leaf-specific conductance, Huber ratio

This abstract is being presented at: 10:30 AM in session:
GAS EXCHANGE