Chlorophyll Fluorescence (Fv/Fm)

Definition

Fv/Fm is the ratio of variable to maximum chlorophyll fluorescence from dark-adapted leaf tissue, a dimensionless number bounded 0–1 that quantifies the intrinsic (maximum) photochemical efficiency of photosystem II. Healthy, unstressed C3 foliage sits near 0.83; any sustained depression signals photoinhibition or damage to the PSII reaction centres. At GreenWorld Sector-7 it is sampled by PhytoSense Mesh pulse-amplitude-modulation (PAM) nodes clamped to tagged reference leaves and reported per cultivar cohort.

Why it matters

Fv/Fm reports photochemical injury before it is visible and before greenness (NDVI) responds — it is the facility's leading indicator of light, thermal, and toxin-load stress. Because the Phyto-Synthesis Bay drives cultivars toward high yield, PSII strain is an expected operational hazard, and CHLORA treats a falling Fv/Fm as a precursor signal for senescence. It contributes 0.30 weight to the Canopy Vitality Index (VC-MET-001).

Formula

Computed from minimal and maximal fluorescence on dark-adapted tissue:

Fv/Fm = (Fm − Fo) / Fm

where:
  Fo = minimal fluorescence, dark-adapted (measuring light only)
  Fm = maximal fluorescence under saturating pulse
  Fv = Fm − Fo  (variable fluorescence)

PAM protocol (PhytoSense Mesh node):
  dark adaptation .......... 20 min (leaf clip closed)
  measuring light .......... 0.05 µmol·m⁻²·s⁻¹ @ 650 nm
  saturating pulse ......... 8000 µmol·m⁻²·s⁻¹, 0.8 s
  reported = cohort median of valid clips

Reported to 0.01. Clips failing Fo stability (CV > 5%) discarded.

Inputs

Units & Scale

Dimensionless ratio 0–1, reported to two decimals. Aggregated per cultivar cohort as the median of valid leaf clips; facility value is the cohort-count-weighted mean. Confidence degrades if fewer than three valid clips contribute to a cohort or if clip leaf temperature falls outside 18–28 °C, where the ratio is biased low.

Sampling & Source

• Sampled every 30 minutes by PhytoSense Mesh PAM nodes on a rolling clip schedule.
• Each clip requires a completed 20-min dark adaptation; nodes stagger to maintain coverage.
• Forward-filled into the 5-min CVI recompute; flagged STALE after 60 min without a valid clip.
• Stale or low-count cohorts have their CVI weight redistributed and confidence set DEGRADED.

Thresholds

Recent Trend

Facility cohort-weighted Fv/Fm, last 14 valid roll-ups:

Interpretation Guidance

Related Metrics

Related SOPs

• SOP Library — PAM node calibration & dark-adaptation protocol.
• Photoinhibition WARN/CRIT triage — Operations SOP set in the SOP Library.
• Alarm escalation & toxin cross-referral — Monitoring Systems.