Effects of Open-Top Chambers on physiological and yield attributes of field grown grapevines

Touriga Franca grapevines were grown in Open-Top Chamber (OTC) and in outside plot (Exterior) for 3 years (2004-2006) to investigate the impact of these structures on climatic conditions and, consequently, on physiological and yield attributes. In general, CO2 assimilation, stomatal conductance, carbohydrate concentration, maximum bulk modulus of elasticity, palisade parenchyma thickness, leaf mass per unit area and values of red/far-red ratio transmitted by leaves were lower, whereas intrinsic water use efficiency, SPAD-readings and osmotic potential at full turgor were higher in OTC leaves. However, OTC did not affect leaf water potential, maximum PSII photochemical efficiency, stomatal density and soluble proteins concentration. Also, there were no significant differences in C, P, Ca and Fe between treatments. Meanwhile, N and Mg were higher, whereas K concentration was lower in OTC leaves. The environmental conditions inside OTC provided a significant reduction in yield and Ravaz index of 2004, mainly due to a decrease in clusters weight. Regarding the vegetative growth parameters, OTC did not influence the pruning weight, but in 2006 the weight/shoot was significantly lower in OTC vines. In conclusion, the use OTC facility to study the impact of CO2 enrichment was very expedite, but the extrapolation of results to the open-field environment must be prudent due to the OTC effect.