Your plants root system can have too much DO and it will stunt growth.
http://www.sciencedirect.com/science/article/pii/S0304423807001203
An upper limit for elevated root zone dissolved oxygen concentration for tomato
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Youbin ZhengCorresponding Author Contact Information, a, E-mail The Corresponding Author, Linping Wanga and Mike Dixona
aDepartment of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1 Canada
Received 13 November 2006;
revised 21 February 2007;
accepted 16 March 2007.
Available online 26 April 2007.
Abstract
It is well understood that insufficient oxygen within plant root zones can greatly diminish plant productivity. However, little is known about the effect of elevated root zone oxygen concentrations. Tomato (Lycopersicon lycopersicum Mill., cv. Trust) seedlings were grown in nutrient solutions containing dissolved oxygen (DO) concentration ranging from 5.3 to 40 mg L−1 for 4 weeks. There were no visible symptoms observed on the leaves or stems in any of the treatments. Leaf chlorophyll content was higher in the 40 mg L−1 treatment than with 20 and 30 mg L−1 DO treatments. Two weeks from the start of the experiment, roots in the 40 mg L−1 treatment exhibited stunted growth, became thicker, and had fewer side and fine roots compared to roots in the lower levels of DO treatment. Almost all the measured growth parameters (fresh and dry weights of root, stem, and leaf, leaf area, stem diameter) were significantly reduced in plants grown in the 40 mg L−1 treatment compared to plants in the lower level of DO treatments, except that the plant height increased with the increasing DO concentration. Root respiration increased linearly with increasing DO concentration; however, there was no effect on leaf net CO2 exchange rate. It is suggested that it was safe to enrich root zone DO to as high as 30 mg L−1, although the growth benefit was minor by increasing DO from ambient air saturated level (not, vert, similar8.5 mg L−1) to 30 mg L−1. Higher than 30 mg L−1 could cause reduction in tomato plant growth.
Keywords: Chlorophyll content; Oxygen diffuser; Oxygen supersaturation; Root respiration; Photosynthesis
Article Outline
1.
Introduction
2.
Materials and methods
3.
Results and discussion
Acknowledgements
References
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Fig. 1. The root, stem, leaf and whole plant fresh and dry weights (g plant−1), leaf area (cm2), stem diameter (cm) and plant height (cm) of tomato seedlings in nutrient solutions with different levels of dissolved oxygen (DO). Data on the same line bearing the same letter are not significantly different at 5% level.
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Fig. 2. The relationships between tomato seedling root respiration rates and dissolved oxygen levels in nutrient solutions. “Fresh” denotes respiration rate was calculated based on root fresh weight (Y = 0.048X + 0.53, r2 = 0.9918, P = 0.0041); “Dry” denotes respiration rate was calculated based on root dry weight (Y = 0.648X + 16.50, r2 = 0.9879, P = 0.0061).
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