Abstract
Abstract. Non-structural carbohydrates (NSC) play a central role in the construction and maintenance of a tree's vascular system, but feedbacks between the NSC status of trees and wood formation are not fully understood. We aimed to evaluate multiple dependencies among wood anatomy, winter NSC, and phenology for coexisting temperate (Quercus robur) and sub-Mediterranean (Q. pyrenaica) oaks along a water-availability gradient in the NW Iberian Peninsula. Sapwood NSC concentrations were quantified at three sites in December 2012 (N = 240). Leaf phenology and wood anatomy were surveyed in 2013. Structural equation modelling was used to analyse the interplay among hydraulic diameter (Dh), winter NSC, budburst date, and earlywood vessel production (EVP), while the effect of Dh and EVP on latewood width was assessed by using a mixed-effects model. NSC and wood production increased under drier conditions for both species. Q. robur showed a narrower Dh and lower soluble sugar (SS) concentration (3.88–5.08 % dry matter) than Q. pyrenaica (4.06–5.57 % dry matter), but Q. robur exhibited larger EVP and wider latewood (1403 µm) than Q. pyrenaica (667 µm). Stem diameter and Dh had a positive effect on SS concentrations, which were related to an earlier leaf flushing in both species. Sapwood sugar content appeared to limit EVP exclusively in Q. pyrenaica. In turn, Dh and EVP were found to be key predictors of latewood growth. Our results confirm that sapwood SS concentrations are involved in modulating growth resumption and xylem production in spring. Q. pyrenaica exhibited a tighter control of carbohydrate allocation to wood formation than Q. robur, which would play a role in protecting against environmental stress in the sub-Mediterranean area.
Highlights
Non-structural carbohydrates (NSC) have multiple key functions in trees, such as maintenance respiration, osmoregulation, cryoprotection, or growth control (Morin et al, 2007; Sala et al, 2012; Wang and Ruan, 2013; Deslauriers et al, 2014)
Non-structural carbohydrates in sapwood, wood anatomy, and leaf phenology were comprehensively addressed for two ring-porous species during a 1 year period, along a broad geographical range in the NW Iberian Peninsula
Our results reveal that feedbacks between earlywood vessels and soluble sugars involve changes in wood production
Summary
Non-structural carbohydrates (NSC) have multiple key functions in trees, such as maintenance respiration, osmoregulation, cryoprotection, or growth control (Morin et al, 2007; Sala et al, 2012; Wang and Ruan, 2013; Deslauriers et al, 2014). A large part of the NSC budget of the tree is invested in construction and maintenance of the vascular system, as well as in turnover of fine roots and crown development (Wang and Ruan, 2013; DeSoto et al, 2016). The hydraulic network in ring-porous oaks is highly vulnerable to dysfunction due to cavitation of their large vessels, which operate at a narrow safety margin (Delzon and Cochard, 2014; Urli et al, 2015). In ring-porous species, earlywood vessels are generally functional during only 1 year (Urli et al, 2015), and cambial resumption precedes leaf formation (Pérez-de-Lis et al, 2016).
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