Water relations, photosynthesis, growth and water use efficiency in tomato plants subjected to partial rootzone drying and regulated deficit irrigation.

摘要

Partial root zone drying (PRD) and regulated deficit irrigation (RDI) are water-saving irrigation systems that have been developed to increase water use efficiency (WUE) without significant yield reduction. To investigate whether a high-value horticultural crop, such as tomato, responds differently to RDI and PRD, we compared the physiological and growth responses of tomato (cv. Super Red) plants using a split-root system. Plants were grown in a greenhouse under controlled conditions, with their roots separated equally between two soil compartments. Three irrigation treatments were imposed: (i) control, receiving an amount of water equivalent to 100% of plant transpiration; (ii) PRD, in which one compartment was watered with 50% of the amount of water supplied to the controls, allowing one-half of the root system to be exposed to dry soil and switching irrigation between sides weekly; and (iii) RDI, in which 50% of the amount of water given to the controls was supplied, half to each side of the root system. Leaf relative water content (RWC) and midday leaf water potential ( Psi ) decreased substantially in RDI-treated plants, while the PRD plants exhibited relatively higher Psi and RWC values. Both PRD and RDI treatments reduced by approximately 30% the total plant dry mass compared with the control. However, plant transpiration was reduced by approximately 50% in both PRD and RDI, allowing a significant improvement in whole-plant WUE. Stomatal conductance (Gs) and leaf growth were also significantly reduced by PRD and RDI. These results may be related to a significant increase in xylem sap pH and leaf apoplastic pH. Generally, the photosynthetic apparatus of tomato leaves had high resistance to restricted water availability. In fact, the decreased Gs had no major negative impact on carbon assimilation. However, Vcmax, i.e. Rubisco [ribulose-bisphosphate carboxylase] efficiency, was significantly decreased in RDI plants with respect to the control ones. This may imply that, although the differences between the PRD and RDI treatments in our study were subtle, they may become more marked with a more prolonged and severe water deficit..