The effects of elevated [CO2] and water availability on growth and physiology of peach (Prunus persica) plants

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Abstract
Peach (Prunus persica L.) seedlings were germinated and grown for two growing seasons either in open top chambers (OTC) with ambient (350 μmol mol-1) or elevated (700 μmol mol-1) [CO2], or in an outside control plot, all located inside a glasshouse. The seedlings were grown in 10 dm3 pots and were fertilised once a week following Ingestad principles in order to supply mineral nutrients at free access rates. In the second growing season, rapid onset of water stress was imposed on rapidly growing peach seedlings by withholding water for a four-week drying cycle. In elevated [CO2], seedlings had a total dry mass which was 33% higher than that in ambient [CO2]. This increase was largely a consequence of increased height growth. [CO2] and irrigation treatments had only small effects on allocation, and there was no increase in root allocation with low water availability possibly as consequence of the high-nutrient regime. Specific leaf area was significantly reduced in elevated [CO2], and probably resulted from increases in starch concentrations. Stomatal conductance (g s) was not affected by elevated [CO2] both in well-watered and water-stressed seedlings. The combination of increased assimilation rate (A) and unchanged g s led to large increases in intrinsic water use efficiency in response to elevated [CO2]. The A/C i curves were used to derive the parameters describing photosynthetic capacity, Amax, Jmax and Vcmax . These parameters were similar among [CO2] treatments; thus, there was no downward acclimation of photosynthesis in elevated [CO2]. Moreover, Amax, Jmax and Vcmax scaled linearly with leaf N content per unit leaf area. This indicates that the whole-plant source-sink balance of peach seedlings was not disrupted by growth in elevated [CO2], because root volume and nutrient supply were non-restricting. These values may be used in scaling up models to improve their ability to predict the magnitude of tree responses to climate change in the Mediterranean area.