Intra-annual leaf phenology, radial growth and structure of xylem and phloem in different tree parts of Quercus pubescens

Abstract

Basic knowledge of the intra-annual timings of leaf development and radial growth (including the phloem part) in different tree parts is generally missing although such rudimentary data are crucial to link the structure and function of vascular tissues at the whole tree level. To understand better the time course of leaf development and radial growth patterns in different tree parts, we studied leaf phenology and intra-annual xylem and phloem formation and structure in the stem and at two locations in branches of sub-Mediterranean Quercus pubescens in 2015. Onset and end dates of cambial cell production were synchronized at the two locations in branches, but were different at the stem base. The period of cell production was thus a month longer in the stem, resulting in 82.8 and 45.1% wider xylem and phloem increments, respectively. In addition, the xylem ring was wider than the phloem ring in all three parts. Thus, phloem ring widths in stem represented 24.8% and in branches 79.4% of the xylem ring width. Earlywood occupied 52.9% (stem) and 74.9% (branches) of the xylem ring, and early phloem 53.7% (stem) and 43.3% (branches) of the phloem ring. Most of the annual radial increment (i.e. xylem and phloem increments) in stem and branches was formed prior to full leaf development. Latewood and late phloem were formed in the period of full leaf unfolding. Our study confirmed that the temporal sequence of leaf development and radial growth are not contemporary in Q. pubescens. Different intra-annual patterns of radial growth in different tree parts result in different structures of xylem and phloem, which is in line with different roles of stem and branches in terms of tree functioning.