Abstract
Enhancing root-zone (RZ) dissolved inorganic carbon (DIC) levels of plants grown aeroponically can increase biomass accumulation but may also alter phytohormone profiles in planta. These experiments investigated how CO2 gas (1500 ppm) added to an aeroponic system affected phytohormone concentrations of lettuce (Lactuca sativa) and sweet pepper (Capsicum annuum) plants. Phytohormonal profiling of root and leaf tissues revealed a solitary treatment difference in lettuce plants, an increased shoot jasmonic acid (JA) concentration under elevated RZ CO2. Since JA is considered a growth inhibitor, growth promotion of lettuce under elevated RZ CO2 does not seem related to its phytohormone profile. On the other hand, pepper plants showed changes in foliar phytohormone (aminocyclopropane-1-carboxylic acid, ACC, trans-zeatin, tZ and salicylic acid, SA) concentrations, which were correlated with decreased leaf growth in some experiments. Foliar accumulation of ACC alongside decreased leaf tZ concentrations may mask a positive effect of elevated RZ CO2 on pepper growth. Diverse phytohormone responses to elevated RZ CO2 between different species may be involved in their different growth responses.
Highlights
The effects of elevated root-zone CO2 on plant growth depend on plant species, substrate pH, air temperature, irradiance, mineral nutrition, abiotic stresses such as high irradiance or salinity, the duration of root-zone CO2 enrichment and the CO2 concentration applied
Lettuce were grown in a controlled environment room (CE room), where air temperature ranged between 16 and 22 ◦ C and relative humidity ranged between 60% and 85%
9.94 ± 0.40 a 1129 ± 39 abc 1161 ± 85 ab Phytohormonal profiling revealed a solitary difference between aeroponically grown lettuce plants grown under ambient and elevated RZ CO2 : increased leaf jasmonic acid (JA) concentrations under elevated
Summary
The effects of elevated root-zone CO2 on plant growth depend on plant species, substrate pH, air temperature, irradiance, mineral nutrition, abiotic stresses such as high irradiance or salinity, the duration of root-zone CO2 enrichment and the CO2 concentration applied. Two weeks of treatment of elevated RZ CO2 (50,000 ppm) in aeroponically grown crisphead lettuce increased growth (~1.6 fold) at 36/30 ◦ C, an irradiance of 650 μmol m−2 s−1 and pH 6.5 compared to plants aerated with ambient (360 ppm) CO2. Increasing RZ CO2 in aeroponically grown lettuce alleviated midday depression of photosynthesis and increased leaf area, shoot and root production [4]. These more recent studies suggest that root-zone CO2 enrichment might be more effective in promoting growth under stressful conditions, perhaps by improving leaf water and/or nutrient status.
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