Root-Zone Warming Differently Benefits Mature and Newly Unfolded Leaves of Cucumis sativus L. Seedlings under Sub-Optimal Temperature Stress

Abstract

Sub-optimal temperature extensively suppresses crop growth during cool-season greenhouse production. Root-zone (RZ) warming is considered an economical option to alleviate crop growth reduction. In this study we cultivated cucumber seedlings in nutrient solution under different air-RZ temperature treatments to investigate the effects of RZ warming on seedling growth- and photosynthesis-related parameters in leaves. The air-RZ temperature treatments included sub-optimal RZ temperature 13°C and sub-optimal air temperature 20/12°C (day/night) (S13), RZ warming at 19°C and sub-optimal air temperature (S19), and RZ warming at 19°C and optimal air temperature 26/18°C (day/night) (O19). In addition, for each air-RZ temperature treatment, half of the seedlings were also treated with 2% (m/m) polyethylene glycol (PEG) dissolved in nutrient solution to distinguish the effect of root-sourced water supply from RZ temperature. At the whole-plant level, S19 significantly increased the relative growth rate (RGR) by approximately 18% compared with S13, although the increase was less than in O19 (50%) due to delayed leaf emergence. S19 alleviated both diffusive and metabolic limitation of photosynthesis in mature leaves compared with S13, resulting in a photosynthetic rate similar to that in O19 leaves. In newly unfolded leaves, S19 significantly promoted leaf area expansion and alleviated stomatal limitation of photosynthesis compared with S13. PEG addition had a limited influence on RGR and leaf photosynthesis, but significantly suppressed new leaf expansion. Thus, our results indicate that under sub-optimal temperature conditions, RZ warming promotes cucumber seedling growth by differently benefiting mature and newly unfolded leaves. In addition, RZ warming enhanced root-sourced water supply, mainly promoting new leaf expansion, rather than photosynthesis.

Irrigation has more influence than fertilization on leaching water quality and the potential environmental risk in excessively fertilized vegetable soils

“…With respect to micronutrients in plant tissues, there was no significant influence by irrigation and fertilization. The microelement plays a very important role in plant growth at both the physiological and molecular levels, however, plants could maintain a relatively stable microelement content unless under severe growth conditions [ 49 ].…”

Melatonin Has the Potential to Alleviate Cinnamic Acid Stress in Cucumber Seedlings

“…Seedlings (with a fully developed true leaf and a newly unfolded young leaf) were transferred onto hydroponic devices (Wang X. Z. et al, 2016; three seedlings/device) filled with 5 L of a nutrient solution (Yamazaki, 1982; full-strength) supplemented with MT at the same concentrations applied at seed stage. Seedlings growing on nutrient solution with no MT provided the control treatment.…”

Local Temperature Control in Greenhouse Vegetable Production

“…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 cucumber plants, heating the root-zone to 19°C from 13°C increased xylem exudation at 20/12°C (day/night) air temperature (Wang et al, 2016).…”

“…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 the sweet pepper (Capsicum annuum L.), an increase in stomatal conductance and a decrease in leaf water potential were also observed, while the leaf area and dry weight of the whole plant increased, when the root-zone control under suboptimal air temperature conditions in tomato plants (Kawasaki et al, 2013(Kawasaki et al, , 2014.…”