Temperature acclimation of leaf dark respiration in Corylus avellana: the role of relative growth rate.

Relative growth rate (RGR) is a standardized measure of growth that accounts for the difference in initial organ size. RGR sets their sink strength potential that, in combination with dark respiration (Rd), determines the carbon need of organs. Total Rd is the sum of maintenance respiration (Rm) and growth respiration (Rg). The first provides energy for the maintenance of the existing cell structures, while the latter provides energy for growth. Rd is mainly driven by temperature but it varies during the season according to temperature acclimation and organ growth. Temperature acclimation is defined as the variation of Rd following the exposure to short or long periods of different temperatures. Temperature strongly affects growth and drives the Rg component of Rd. We hypothesized that RGR has a fundamental role in Rd variation during the season. The aims of the study were as follows: 1) if there was a variation of leaf Rd over the season and if such variation could be due to acclimation and/or RGR; 2) the type of acclimation (i.e., type I or II) on fully expanded leaves and newly formed leaves; and finally, 3) if acclimation or RGR should be included to model Rd variation over the season. Leaf Rd was measured in field-grown plants from bud break to summer. Different cohorts of leaves were used to test the effect of exposure to different temperature regimes during leaf formation. The only case of acclimation was found in fully expanded leaves. It was an acclimation of Type II. Under field conditions, acclimation of filbert leaves Rd to temperature was limited since most of the Rd variation during the season was explained by RGR. Our work suggests that RGR is a fundamental parameter that should be included in addition to temperature to model seasonal Rd pattern.