Root Zone Temperature: Current Research Results
Here are some relevant studies on this topic:
Levine et al. (2023)
"Controlling root zone temperature improves plant growth …"
Experimental System
Hydroponic Lettuce (Lactuca sativa "Red Fire")
Temperature Range
15, 25, 35 °C
Findings
25 °C resulted in maximum dry mass. 35 °C reduced growth but increased pigment content.
Significance
Shows that a moderate root temperature range is ideal and that targeted management is possible.
To the study (PubMed)Hayashi et al. (2024)
"Raising root zone temperature improves plant productivity …"
Experimental System
Hydroponic lettuce under varying air temperatures
Temperature Strategy
RZT +3°C above air temperature
Findings
Increasing RZT by 3 °C above air temperature promoted growth, increased soluble proteins, mineral uptake, and metabolic activities.
Significance
Interesting approach: relative increase compared to air temperature — could suggest differential strategies.
To the study (Frontiers)Moccio et al. (2024)
"Effects of Root Zone Temperature of Hydroponic Lettuce …"
Experimental System
Lettuce, cooled vs. ambient RZT
Comparison
Cooled vs. uncooled systems
Findings
The study specifically examines the effects of cooled root zones compared to uncooled systems, including on nutrient uptake and vitamin A content.
Significance
Good approach for quantifying stress vs. optimization.
To the study (ASHS)Kang et al. (2025)
"Root-Zone Cooling Effects …"
Experimental System
Various cooling strategies in deep water culture
Cooling Methods
Gradual vs. abrupt (down to 5°C)
Findings
An abrupt cooling over 5 days inhibited mineral uptake more strongly compared to gradual cooling.
Significance
Shows that not only the value but also the rate of change is relevant.
To the study (SpringerLink)Al-Rawahy et al.
"Effect of Cooling Root-Zone Temperature …"
Experimental System
Cucumber (Cucumis sativus) in hydroponics under summer conditions
Temperature Range
22, 25, 28 °C vs. 33 °C control
Findings
Cooled RZT increased growth, leaf area, and yield compared to the non-cooled control (33 °C).
Significance
Demonstrates advantages of active temperature control at high outdoor temperatures.
To the study (CCSE)Sakamoto et al.
"Effect of Root-Zone Temperature on the Growth and Fruit Quality of Hydroponically Grown Strawberry Plants"
Experimental System
Strawberries in deep flow technique
Temperature Ranges
10 °C vs. 30 °C
Findings
At excessively high root temperature (30 °C), root cell viability decreased and death occurred; low temperature (10 °C) increased root mass but affected fruit development.
Significance
Shows that extreme values are critical for fruit plants and that the response is also crop-specific.
To the study (ResearchGate)Li et al.
"Elevated root-zone temperature promotes the growth …"
Experimental System
Cucumber under elevated CO₂
Special Feature
Combination with CO₂ enrichment
Findings
Elevated root zone temperature promoted growth and mitigated adaptation processes under high CO₂ concentration.
Significance
Interesting for closed systems with controlled climate.
To the study (ScienceDirect)Li et al. (Carrots)
"Elevated Root Zone Temperature …"
Experimental System
Carrot in hydroponics
Effect
Qualitative changes
Findings
High RZT reduced growth but increased phenolic compounds and sugar content.
Significance
Example that higher RZT can also cause qualitative changes (positive or negative).
To the study (SCIRP)
Literature & Research Overview on Measurement Technology & Monitoring of Root Zone Temperature
1. Fundamentals & Methodology
- Hydroponics Handbooks
Resh, H.M. (2022): Hydroponic Food Production – Standard work, describes various temperature management systems, also mentions measurement technology.
Savvas & Gruda (2018): Hydroponic Production of Vegetables and Ornamentals – contains chapters on temperature management in nutrient solutions. - Measurement Methods General
- PT100/PT1000 sensors and digital sensor technology are standard (often in combination with data loggers).
- Research indicates that multi-point measurements are necessary because temperature gradients occur (Kang et al. 2025).
2. Peer-reviewed Studies Focusing on Monitoring
- Moccio et al. (2024): "Effects of Root Zone Temperature of Hydroponic Lettuce on Nitrate, Pigments, and Vitamin A" (HortScience 59:255).
→ Uses continuous measurements and shows that small temperature changes are significant. - Kang et al. (2025): "Root-Zone Cooling Effects on Plant Mineral Nutrition under Different Cooling Regimes" (J. Plant Growth Regulation).
→ Emphasis on temperature profile dynamics: gradual vs. abrupt cooling. - Hayashi et al. (2024): "Raising root zone temperature improves plant productivity …" (Frontiers in Plant Science).
→ Uses precise control systems with close-meshed data acquisition to test relative temperature increases (air vs. root). - Levine et al. (2023): "Controlling root zone temperature improves plant growth and pigments in hydroponic lettuce" (Annals of Botany).
→ Three RZT levels (15, 25, 35 °C) under controlled conditions – monitoring was a prerequisite for the evaluation.
3. Further Important Notes from Literature
- Oxygen Solubility: Several works (e.g., Li et al. 2015 on tomatoes, Sakamoto et al. on strawberries) emphasize that temperature data must always be viewed in combination with O₂ concentration.
- Practical Systems: Greenhouse research recommends installing RZT sensors in return lines and reservoirs, not only in plant channels.
- Energy Aspect: There are studies on the energy efficiency of RZT controls (e.g., Japanese research on tomatoes) that show targeted monitoring can reduce energy consumption when regulating the nutrient solution instead of using large-scale air heating.
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