Photosynthetic limitations and carbon partitioning in cherry in response to water deficit and elevated [CO2

Abstract

There is significant uncertainty about the interaction between water availability and elevated [CO2] on tree growth and physiology. This study evaluated if elevated [CO2] and water stress interactively affect photosynthetic parameters and the dynamics of carbon partitioning in leaf and root of cherry (Prunus avium) seedlings. Seeds of cherry were germinated and grown for a growing season in ambient (∼350 μmol mol−1) or elevated (ambient + ∼350 μmol mol−1) CO2 concentrations in six open-top chambers. The seedlings were fertilised once a week following Ingestad principles in order to supply mineral nutrients at free access rates. Gradual water stress was imposed on rapidly growing cherry seedlings by withholding water for a 6-week drying cycle. Growth in elevated [CO2] did not affect carbon partitioning among soluble sugars. All the parameters describing photosynthetic capacity (Vc,max, Amax, Jmax, and Rd) and the photochemical efficiency (Fv/Fm) were not downward acclimated in response to elevated [CO2]. Thus, growth in elevated [CO2] did not result in photochemical and biochemical impairments. Moreover, elevated [CO2] did not cause fundamental change in plant response to water stress. Water stress, in contrast, affected both carbon partitioning and the parameters describing photosynthetic capacity. Sorbitol concentration was significantly increased in both leaf and root in response to water stress, and this increase played a main role in improving water relations of cherry. The leaf internal CO2 concentration (Ci) to external CO2 concentration (Ca) ratio was significantly lower in water-stressed seedlings than in well-watered seedlings in both [CO2] treatments at the end of drying cycle. This decreased Ci/Ca ratio and the unchanged photochemical efficiency of the water-stressed seedlings may indicate the reduction in photosynthetic capacity was not caused by metabolic impairment but resulted by increased diffusional limitations of the net CO2 assimilation rate in response to water stress.