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Stomatal Regulation of Photosynthesis in Apple Leaves: Evidence for Different Water-use Strategies between Two Cultivars

Massonnet, Catherine, Costes, Evelyne, Rambal, Serge, Dreyer, Erwin, Regnard, Jean Luc
Annals of botany 2007 v.100 no.6 pp. 1347-1356
apples, light intensity, carbon, summer, vapor pressure, fruit trees, stomatal conductance, nitrogen content, isotopes, electron transfer, photosynthesis, leaves, climate, stomatal movement, cultivars, carboxylation, models, net assimilation rate, temperature, water use efficiency, environmental factors, growing season, leaf conductance
BACKGROUND AND AIMS: Leaf responses to environmental conditions have been frequently described in fruit trees, but differences among cultivars have received little attention. This study shows that parameters of Farquhar's photosynthesis and Jarvis' stomatal conductance models differed between two apple cultivars, and examines the consequences of these differences for leaf water use efficiency. METHODS: Leaf stomatal conductance (gsw), net CO₂ assimilation rate (An), respiration (Rd) and transpiration (E) were measured during summer in 8-year-old 'Braeburn' and 'Fuji' apple trees under well-watered field conditions. Parameters of Farquhar's and Jarvis' models were estimated, evaluated and then compared between cultivars. Leaf carbon isotope discrimination (Δ¹³C) was measured at the end of the growing season. KEY RESULTS: A single positive relationship was established between VCmax (maximum carboxylation rate) and Na (leaf nitrogen concentration per unit area), and between Jmax (maximum light-driven electron transport rate) and Na. A higher leaf Rd was observed in 'Fuji'. The gsw responded similarly to increasing irradiance and leaf temperature in both cultivars. gsw responded to lower vapour pressure deficit in 'Fuji' than in 'Braeburn'. Maximal conductance (gswmax) was significantly smaller and An was more limited by gsw in 'Braeburn' than 'Fuji'. Lower gsw, E and higher intrinsic water use efficiency were shown in 'Braeburn' and confirmed by smaller leaf Δ¹³C compared with 'Fuji' leaves. CONCLUSIONS: The use of functional model parameters allowed comparison of the two cultivars and provided evidence of different water use 'strategies': 'Braeburn' was more conservative in water use than 'Fuji', due to stomatal limitation of An, higher intrinsic water use efficiency and lower Δ¹³C. These physiological traits need to be considered in relation to climate adaptation, breeding of new cultivars and horticultural practice.