Cannabis gas exchange, photosynthesis, transpiration, stomatal conductance, PPFD, temperature, and carbon-dioxide response under measured conditions.
Abiotic disorders
Heat Stress & Canopy Overheating
Heat injury is best evaluated at the tissue and canopy level. Leaf temperature can differ from room air temperature, and the most exposed leaves may experience a different combination of radiant load, humidity, and airflow than sensors elsewhere in the room.
What to look for
- Upper-canopy curling, edge lift, loss of posture, or scorch during the hottest period
- Symptoms concentrated near high-radiant-load zones
- Leaf temperature substantially different from a remote air-sensor reading
- Partial recovery when light or temperature demand falls
Important look-alikes
- High-light stress
- Drought or root-water limitation
- High EC
- Direct airflow injury
How to confirm
- Measure leaf temperature at symptomatic and unaffected canopy positions
- Map PPFD, temperature, RH, and airflow where symptoms occur
- Check root-zone moisture and delivery during peak demand
- Compare symptom timing with fixture output and environmental cycles
Management principles
- Reduce the environmental load that exceeds current plant water-delivery capacity
- Correct localized hot spots instead of relying only on room-average conditions
- Avoid treating heat-driven curl as proof of a nutrient problem
- Evaluate new growth after the canopy environment is stabilized
Prevention
- Measure canopy conditions at plant height
- Maintain adequate but non-damaging air movement
- Commission lighting and HVAC together rather than independently
- Monitor high-risk upper-canopy zones during peak load
Visual study guide
- Leaf-temperature versus air-temperature diagram
- Canopy heat map
- Heat curl versus root wilt comparison
- Peak-demand timeline
Evidence & further reading
Sources connected to this lesson
These references support specific biological, diagnostic, environmental, or process concepts used in this lesson. They are not a substitute for crop-specific testing or local regulatory guidance.Vapor-pressure-deficit sensing and stomatal response mechanisms in vascular plants, including hydraulic and ABA-mediated regulation.