Chlorophyll Fluorescence, Photosynthesis and Growth of Tomato Plants as Affected by Long-Term Oxygen Root Zone Deprivation and Grafting

A greenhouse experiment was conducted to study the effects of the O-2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O-2 concentrations in the root zone, namely Ox (saturation level) and Ox-(2-3 mg L-1), were applied for 30 days on self-grafted cherry tomato Dreamer or grafted onto the hybrids Arnold, Beaufort, Maxifort and Top Pittam. Root hypoxia increased minimum fluorescence (by 10%) while it decreased variable fluorescence and the maximum quantum yield of PSII (up to 16 and 8%, respectively). Moreover, it reduced leaf photosynthesis, transpiration and stomatal conductance (by 12, 17 and 13%, respectively), whereas it increased leaf electrolyte leakage (by 2.1%). The graft combinations showed a different ability in buffering the effects of root hypoxia on plant growth and related components, and these differences were related to their root biomass. The minimum fluorescence was negatively correlated to plant growth, so it may be a useful indicator to select tolerant rootstocks to root hypoxia. Our results suggest the occurrence of both diffusive and metabolic constraints to tomato photosynthesis under root hypoxia, a condition that can be mitigated by selecting rootstocks with a more developed root system.