Towards efficient models for hydraulic conductivity in conifer wood. Part 1: estimation of sizes and numbers of bordered pits.

Functional traits like hydraulic conductivity and vulnerability to cavitation are increasingly important due to climate change. In conifers, water is transported through lumina of tracheids connected via bordered pits, which severely limit xylem conductivity by causing large pressure drops related to their number, dimensions and structure. According to literature, numbers and dimensions of pits correlate positively with tracheid and lumen dimensions. This reflects variations from earlywood to latewood and between rings formed under different grow conditions, contributing to major conductivity variations. The wider aim of the work is to estimate such conductivity variations in trunkwood from measurement data on radial and axial variations of tracheid dimensions. This requires several integrated models, including models estimating numbers and dimensions of pits. The article presents such models developed on data from 27 Norway spruce trees representing different sites, clones and growth rates. Measured and estimated variations of tracheid, lumen and pit properties within and between rings are illustrated, indicating on average about one third smaller and fewer pits in latewood than in earlywood tracheids, and variations in numbers and areas of pits per unit volume of xylem which may be interesting also in fields like wood drying and impregnation. [ABSTRACT FROM AUTHOR]