Effect of oxygen deficiency on uptake of water and mineral nutrients by tomato plants in soilless culture

The consequences of oxygen deficiency on the root system of tomato plants i n soilless culture at the beginning of the flowering stage were assessed ov er a 72-hour period. The study of water uptake and oxygen depletion in the medium was conducted using a process of continuous computerized data proces sing. Fluctuations in composition of the nutrient solution were monitored e very two hours through an analysis of samples. Oxygen deficiency of the nut rient solution had immediate effects on the water and nutrient uptake of th e whole plant. The root asphyxia of a tomato plant caused a 20 to 30% decre ase of water uptake after 48 hours. After 10 hours it also leads to the end of the uptake process of the nutrients except nitrates. Potassium (K) was the nutrient most sensitive to oxygen deprivation since an efflux into the culture medium was observed after only 4 hours of deprivation. Nitrate upta ke was the least affected by oxygen deficiency. The persistent appearance o f nitrite in the culture medium 12 hours after the beginning of the asphyxi a process could be caused by the reduction of nitrates by the root system o f the tomato plant. The plant would use the oxygen from the reduction react ion to ensure the water and nitrate uptake processes which are the two most important limiting factors of plant nutrition. Thus it seems that under ro ot asphyxia conditions the plant would adapt to the new condition by relyin g on a metabolism of the "nitrate respiration" type.