Photorespiration and Temperature Stress
Explain Rubisco oxygenation, the photorespiratory recovery pathway, and why temperature stress cannot be reduced to a single universal leaf limit.
Educational reference · evidence, sources, and limits shown below
Explain Rubisco oxygenation, the photorespiratory recovery pathway, and why temperature stress cannot be reduced to a single universal leaf limit.
Terms to know
- Photorespiration
- Pathway initiated when Rubisco oxygenates RuBP, consuming energy while recovering carbon from phosphoglycolate.
- Rubisco specificity
- Relative tendency of Rubisco to catalyze carboxylation versus oxygenation under defined conditions.
- Thermal acclimation
- Physiological adjustment of function after sustained exposure to a temperature regime.
- Heat injury
- Damage occurring when temperature and duration exceed protective and repair capacity.
Core science
Cannabis uses C3 photosynthesis. Rubisco can add oxygen instead of CO2 to RuBP, producing one normal three-carbon product and one two-carbon product. The photorespiratory pathway spans chloroplasts, peroxisomes, and mitochondria to recover much of that carbon, while consuming ATP and reducing net carbon gain.
Oxygenation becomes relatively more important as leaf temperature rises, CO2 availability at Rubisco falls, or stomata restrict diffusion. However, photorespiration is not simply useless waste. It interacts with nitrogen metabolism, redox balance, and dissipation of excess energy; suppressing it without redesigning the system can create other problems.
Heat stress includes more than photorespiration. Membranes, proteins, photosystems, pollen, roots, respiration, vapor-pressure demand, and water transport respond on different time scales. Air temperature is not leaf temperature, and the same peak can be tolerated differently depending on duration, humidity, airflow, night recovery, water status, acclimation, and genotype.
Why this matters in cultivation
- Record leaf and root-zone temperature in addition to air temperature. Diagnose the combined water, light, CO2, and duration context before attributing reduced growth to photorespiration.
- Avoid abrupt temperature changes when comparing treatments. Acclimation history changes the response and can obscure the true cause of injury.
Measure and record
Thermal exposure
Air, leaf, and root-zone temperature; maximum, duration, timing, and recovery period.
Gas context
CO2, RH/VPD, airflow, stomatal conductance, and intercellular CO2 if measured.
Light context
PPFD, DLI, spectrum, canopy position, and simultaneous heat load.
Response
Assimilation, fluorescence, wilt, membrane leakage, bleaching, necrosis, and recovery.
Genotype/stage
Cultivar or clone, age, reproductive stage, acclimation history, and replicate.
Common misconceptions
Correction: It is a normal feature of C3 photosynthesis whose relative rate changes with conditions.
Correction: Leaf temperature, duration, stage, water status, and genotype alter risk.
Correction: It may alter carbon fixation but does not prevent membrane, reproductive, root, or hydraulic injury.
Evidence limits
Cannabis-specific temperature-response datasets remain narrower than the genetic diversity and production environments in use. Do not turn one cultivar study into a universal threshold.
Related encyclopedia topics
- THC-ENC-064–068, THC-ENC-081–100, THC-ENC-111, and reproductive-stress lessons.
Source notes
- Taiz L, Moller IM, Murphy A, and Zeiger E. Plant Physiology and Development. 7th ed. Oxford University Press, 2022. Publisher record
- Blankenship RE. Molecular Mechanisms of Photosynthesis. 3rd ed. Wiley, 2021. Open source
- Rodriguez-Morrison V, Llewellyn D, and Zheng Y. Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science. 2021;12:646020. Open source
- Pena MM et al. Genotypic Variation in Photosynthesis and Biomass Partitioning Underlies Agronomic Performance and Cannabinoid Profile in Cannabis sativa Under Drought. Plants. 2025. 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.