Cellular Respiration and Night Metabolism
Trace carbohydrate oxidation through glycolysis, the tricarboxylic-acid cycle, and mitochondrial electron transport and relate night conditions to carbon cost and crop function.
Educational reference · evidence, sources, and limits shown below
Trace carbohydrate oxidation through glycolysis, the tricarboxylic-acid cycle, and mitochondrial electron transport and relate night conditions to carbon cost and crop function.
Terms to know
- Glycolysis
- Cytosolic pathway converting sugars to pyruvate while producing ATP and reducing equivalents.
- Tricarboxylic-acid cycle
- Mitochondrial pathway oxidizing carbon intermediates and supplying reducing equivalents and biosynthetic precursors.
- Oxidative phosphorylation
- ATP production driven by mitochondrial electron transport and a proton gradient.
- Maintenance respiration
- Respiratory energy supporting ion gradients, repair, turnover, and existing living tissue.
Core science
Plant mitochondria respire day and night. Glycolysis converts sugars to pyruvate; mitochondrial metabolism oxidizes carbon and transfers electrons to the respiratory chain; oxygen acts as the terminal electron acceptor; and ATP synthase produces ATP. Respiration also supplies intermediates for amino acids, lipids, cell walls, pigments, and defense compounds.
Respiratory cost has growth and maintenance components. Constructing new tissue requires energy and carbon skeletons; maintaining more living biomass raises continuing costs. Temperature strongly influences reaction rates, but acclimation, substrate availability, tissue age, and oxygen change the response. Roots, meristems, developing flowers, and wounded tissues can have high demand even when they are not photosynthetic.
Night metabolism includes starch mobilization, sucrose transport, growth, nutrient assimilation, repair, and clock-regulated processes. A dark period is not an inactive pause. Night temperature changes respiratory carbon use, transport, and growth, but no single warmer-or-colder rule applies. Condensation risk is a separate surface-temperature and dew-point control problem rather than evidence of a respiration optimum.
Why this matters in cultivation
- Evaluate night temperature by crop response and carbon balance, not by a simplistic claim that colder always saves energy. Root temperature and dew-point risk can move independently from air temperature.
- Hypoxic root zones restrict oxidative phosphorylation regardless of shoot carbohydrate supply. Correct oxygen delivery before assuming roots need more sugar or fertilizer.
Measure and record
Day/night regime
Air, leaf, and root-zone temperature; timing, transitions, and dark-period duration.
Carbon context
DLI, leaf area, pruning, starch or soluble sugars if measured, and recent stress.
Oxygen risk
Root-zone moisture, porosity, solution temperature, dissolved oxygen, and pump events.
Growth
Night/day elongation, biomass interval, flower development, root growth, and recovery.
Energy balance
Lighting and HVAC schedule, canopy temperature distribution, and condensation observations.
Common misconceptions
Correction: Mitochondrial respiration continues in illuminated tissues.
Correction: It consumes transported or stored carbon and requires ATP.
Correction: Carbon saving must be balanced against transport, growth, root function, condensation, and genotype.
Evidence limits
Room CO2 concentration is not a direct crop-respiration measurement. Quantifying crop respiration requires a room-specific CO2 mass balance or controlled flux method that accounts for ventilation or leakage, enrichment, substrate and microbial exchange, occupants, and sensor placement.
Related encyclopedia topics
- THC-ENC-043, THC-ENC-065–071, THC-ENC-083, THC-ENC-096–097, and carbon-assimilation lessons.
Source notes
- Taiz L, Moller IM, Murphy A, and Zeiger E. Plant Physiology and Development. 7th ed. Oxford University Press, 2022. Publisher record
- THC – Teaching Healthy Cultivation. Cannabis Plant Science Source Packet v1. May 2026. Project source packet.
- Collado CE et al. Supplemental Greenhouse Lighting Increased the Water Use Efficiency, Crop Growth, and Cutting Production in Cannabis sativa. Frontiers in Plant Science. 2024;15:1371702. Open source
- Tusi A and Shimazu T. The Essential Factor of Ventilation Rate in Prediction of Photosynthetic Rate Using the CO2 Balance Method. Reviews in Agricultural Science. 2020;8:279–299. Open source
This lesson summarizes the source material and its evidence limits for education. Use direct measurement, controlled comparison, and the cited sources when conditions differ or a decision carries meaningful risk.