Effect of Root-zone Heating on Root Growth and Activity, Nutrient Uptake, and Fruit Yield of Tomato at Low Air Temperatures

Abstract

Low-cost heating is needed to reduce chilling injuries, heating costs, and CO 2 emission during greenhouse tomato production. To acquire information about the physiological and morphological effects of root-zone heating, an economical option at low air temperatures, we grew tomato plants on a nutrient film technique hydroponic system in a heated nutrient solution. We investigated the effects of short-term root-zone heating after transplanting and long-term heating until harvest. We measured short-term plant growth, nutrient uptake, root activity (xylem exudation and root respiration rates), root indole-3-acetic acid (IAA) concentration, internal root structure, and long-term fruit weight and dry matter distribution. The minimum root-zone temperature was maintained at 16.6°C, while the minimum air temperature (5.9°C) and the minimum root-zone temperature in the control (5.8°C) were lower than optimal. After 7 days of root-zone heating, root dry weight and relative growth rate increased compared with those of the control, accompanied by increased mineral nutrient uptake and xylem exudation. These changes may explain the increased shoot growth after 21 days of heating. In roots, development of the epidermis and stele, including the xylem, was promoted by heating, in contrast to previous research on root-zone cooling at high air temperature, which promoted xylem-specific development. Although the proportion of dry matter distributed to the fruit was not changed by root-zone heating, individual fruit size and total yield were higher than in the control due to a higher total dry weight in the heating treatment. Our results suggest that root-zone heating is an effective lowcost heating technology at low air temperature because of its effects on root activity, growth, and fruit yield, but that the mechanisms may differ from those in root-zone cooling at high air temperature.

Local Temperature Control in Greenhouse Vegetable Production

“…Some similar studies have been reported (Kawasaki et al, 2013;Klock et al, 1997;Sasaki and Itagi, 1989). Around 20°C of root-zone heating increased leaf area, plant height, and relative growth rate (RGR) at low air temperature (16.2°C of daily mean temperature) (Kawasaki et al, 2014). In cucumber and tomato plants, the photosynthesis rate, stomatal conductance and shoot RGR increased with root-zone heating from 13°C to 19°C at an air temperature of 20/12°C (Wang et al, 2016).…”

“…In tomato plants, root-zone cooling from 33°C to 17°C at an air temperature of 35/22°C (day/night) increased water and nitrogen absorption, as well as enhancing xylem exudation (Nakano, 2007). Similar effects were also reported by root-zone heating and indicated that mineral nutrient transport to shoots was accelerated by xylem vessels (Kawasaki et al, 2014). These effects resulted in an increased mineral nutrient content in shoots (Gent and Ma, 2000;Klock et al, 1997;Nkansah and Ito, 1995b;Papadopoulos and Tiessen, 1987).…”

“…In tomato plants, root growth was promoted earlier than shoot growth when the root-zone was cooled from 33.7°C to 24.6°C under high air temperature conditions in summer (30.8°C; average daily mean temperature) (Kawasaki et al, 2013). A similar effect was observed when the root-zone was heated from 5.8°C to 16.6°C under low air temperature conditions in winter (5.9°C; average daily minimum night temperature) (Kawasaki et al, 2014). In cucumber plants (Cucumis sativus L.), root weight was increased when soil temperature 15 cm below the ground surface was cooled from 26.9°C to 20.6°C under an average maximum air temperature of 39.2°C (Moon et al, 2007b).…”

LCA & LCCA of a PCM application to control root zone temperatures of hydroponic crops in comparison with conventional root zone heating systems

“…The selected functional unit is 1 kg of tomato. For the analysis we suggested an increase of 20% of productivity for the new scenarios (A,B,C and D) according to the benefits of root zone temperature control found in the literature [3,4]. Climate Change and CED indicators obtained from these scenarios were also compared with the referent scenario from the EUPHOROS project [21] which does not use any heating or cooling system.…”

“…Root zone heating can decrease fuel consumption [1] while obtaining the same productivity achieved with traditional heating systems [1,2]. The use of root zone climate systems stimulates productivity [3,4] if other key parameters as humidity, solar radiation, nutrients or environmental temperature are controlled properly.…”