Abstract
A greenhouse experiment was conducted to study the effects of the O2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O2 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.
Highlights
Higher plants are obligate aerobic organisms needing molecular oxygen (O2 ) to accomplish the oxidation reactions supporting their life
FM was significantly reduced, passing from Ox to Ox- treatment, whereas it reached the highest level in the grafting combination
Under root hypoxia, we found a significant increase in electrolyte leakage, a condition which is strongly associated to a loss of the integrity of the cell membranes in tomato plants [28]
Summary
Higher plants are obligate aerobic organisms needing molecular oxygen (O2 ) to accomplish the oxidation reactions supporting their life. They can experience excess water in the growth substrate in either natural or agricultural ecosystems, because of erratic rainfall and/or incorrect irrigation scheduling associated to climate change. This can flow in flooding, which is a major abiotic stress threatening growth and yield of many economically important crops [1]. Greenhouse crops are generally selected for their high yield in optimum growth conditions, so tolerance to many abiotic stressors can be partially or totally neglected
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