Daily Changes in Rates of Nutrient and Water Uptake, Xylem Sap Exudate, and Sapflow of Hydroponically Grown Tomatoes

To establish an adequate control algorism for nutrient solution control to produce high-quality tomato fruits without yield reduction caused by water stress, characteristics of nutrient solution uptake and calcium ion transportation through sapflow were investigated in hydroponically grown tomatoes. Daily changes in rates of nutrient and water uptake and xylem exudation of tomatoes and inorganic contents of xylem sap exudate were measured in a recirculating NFT system. Daily change in the amount of nutrient solution absorbed by tomato plants was closely correlated with solar radiation and a peak of nutrient solution uptake appeared about two hours after the peaks of solar radiation and air temperature. The xylem sap exudation began to increase after solar radiation increased and the peak of sapflow rate appeared simultaneously as when the solar radiation reached to the first peak, but decreased thereafter, then later showed the second peak approximately two hours after sunset. The absorption rates of P and Mg ions per unit amount of nutrient solution absorbed were smaller than those of NO₃ and K ion. Ca ion was more absorbed compared to other cations during nighttime. Sapflow rate in a petiole of unfolded leaf was greater than those in the cluster stems. The sapflow rates in old cluster stems attached to lower nodes were greater than those in the newly developed cluster stems attached to upper nodes. When the radiation was high during daytime, sapflow in the newly developed cluster stem attached to upper nodes was also higher during nighttime. Ca contents of tomato fruits varied by cluster numbers standing for their developmental stage and those in the first and third clusters were greater than that in the fifth cluster. Results indicate that Ca delivery to the fruits can be manipulated by controlling nutrient solution composition in a certain period of time during tomato cultivation. The protocol for management of nutrient solution can be applied for Ca-rich fruit production that reduces blossom-end rots and increases storability of tomato fruits.