Stomatal regulation of photosynthesis in apple leaves: evidence for different water-use strategies between two cultivars.
OBJECTIVE
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 (g(sw)), net CO2 assimilation rate (A(n)), respiration (R(d)) 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 (delta(13)C) was measured at the end of the growing season.


RESULTS
A single positive relationship was established between V(Cmax) (maximum carboxylation rate) and N(a) (leaf nitrogen concentration per unit area), and between J(max) (maximum light-driven electron transport rate) and N(a). A higher leaf R(d) was observed in 'Fuji'. The g(sw) responded similarly to increasing irradiance and leaf temperature in both cultivars. g(sw) responded to lower vapour pressure deficit in 'Fuji' than in 'Braeburn'. Maximal conductance (g(swmax)) was significantly smaller and A(n) was more limited by g(sw) in 'Braeburn' than 'Fuji'. Lower g(sw), E and higher intrinsic water use efficiency were shown in 'Braeburn' and confirmed by smaller leaf delta(13)C 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 A(n), higher intrinsic water use efficiency and lower delta(13)C. These physiological traits need to be considered in relation to climate adaptation, breeding of new cultivars and horticultural practice.
Massonnet
Catherine
C
UMR 1098 Développement et Amélioration des Plantes - Equipe Architecture et Fonctionnement des Espèces Fruitières, INRA - SupAgro, 2 Place Viala, 34060 Montpellier Cedex 1, France.
Costes
Evelyne
E
Rambal
Serge
S
Dreyer
Erwin
E
Regnard
Jean Luc
JL
D002247:Carbon Isotopes; D027845:Malus / Q000378:metabolism / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D013045:Species Specificity; D013696:Temperature; D014867:Water / Q000378:metabolism*
D002247:Carbon Isotopes; D014867:Water; D009584:Nitrogen