GREENWORLD SECTOR-7 // METRICS // VC-MET-004
ALL SYSTEMS NOMINAL · —
METRICS · PLANT VITALITY & PHYSIOLOGY

Stomatal Conductance (gsw)

VC-MET-004 — the rate of water-vapour diffusion through open stomata, the most responsive gas-exchange indicator of water status and the stomatal sub-signal of the Canopy Vitality Index.

Metric ID VC-MET-004 Category Plant Vitality & Physiology Unit mol·m⁻²·s⁻¹ Type Direct Source PhytoSense Mesh Sampling 5 min Owner Metrology & Telemetry Standards Rev C · Effective 2089-06-01
Current 0.31 Nominal 0.15–0.45 5-min cadence PhytoSense Mesh

Definition

Stomatal conductance to water vapour (gsw) is the molar flux density of water vapour through the leaf's stomatal pathway per unit driving gradient, expressed in mol·m⁻²·s⁻¹. It is the inverse of stomatal resistance and directly reports how open the stomata are — the plant's primary control valve over both transpiration and CO₂ uptake. At GreenWorld Sector-7 it is measured by PhytoSense Mesh leaf-clip gas-exchange cuvettes on tagged reference leaves and reported per cultivar cohort.

Why it matters

gsw is the fastest-responding water-status channel in the facility: stomata close within minutes of rising vapour-pressure deficit or root-zone drying, so a falling gsw is the earliest warning of impending hydraulic stress, well ahead of turgor or leaf water potential. CHLORA uses it to modulate irrigation cadence and misting, and it contributes 0.15 weight to the Canopy Vitality Index (VC-MET-001).

Formula

Derived from the cuvette water-vapour mass balance:

g_sw = E / (w_leaf − w_air)

where:
  E       = transpiration flux (mol H2O·m⁻²·s⁻¹)
  w_leaf  = mole fraction of water vapour at leaf surface
            (saturation at leaf temperature)
  w_air   = mole fraction of water vapour in cuvette air

E is measured from cuvette flow rate and the inlet/outlet
water-vapour differential:
  E = u · (w_out − w_in) / A_leaf

calibration:
  zero/span on dry N2 and a dew-point reference each shift;
  leaf temperature by IR thermopile, ±0.2 °C.

Reported to 0.01 mol·m⁻²·s⁻¹. Boundary-layer corrected.

Inputs

SymbolQuantityReference BandSource
ETranspiration flux0.5 → 4.0 mmol·m⁻²·s⁻¹PhytoSense Mesh cuvette
w_airCuvette vapour mole fractionper VPDPhytoSense Mesh
T_leafLeaf surface temperature18 → 30 °CPhytoSense Mesh IR
uCuvette flow rate300 → 500 µmol·s⁻¹PhytoSense Mesh

Units & Scale

mol·m⁻²·s⁻¹, reported to two decimals. Strongly diurnal — peaks midday, near-zero at night — so thresholds apply only to the photoperiod window; night samples are recorded but not alarmed. Aggregated per cohort as the median; facility value is cohort-count-weighted. Confidence degrades when cuvette VPD drifts outside 0.8–2.0 kPa, where the conductance estimate is least reliable.

Sampling & Source

Thresholds

Nominal · 0.15–0.45

OK

Stomata responsive, healthy gas exchange. No action.

Warning · < 0.10

WARN

Partial stomatal closure; CHLORA advisory, check VPD & root zone.

Critical · < 0.05

CRIT

Near-total closure; auto-dispatch, acute water stress.

Diurnal gating. Because gsw falls to near-zero in darkness by design, thresholds are evaluated only during the photoperiod and during the first hour after lights-on ramp. Recovery from WARN requires gsw ≥ 0.13 sustained for 15 min; CRIT clears at ≥ 0.08 for 30 min. Persistent daytime closure with rising VPD escalates to irrigation control.

Recent Trend

Facility cohort-weighted gsw, last 14 photoperiod samples:

g_sw · 14-period trend (current 0.31)

Interpretation Guidance

gsw BandReadingLikely DriverAction
0.30–0.45Wide openAmple water, moderate VPDMaintain irrigation set-points.
0.15–0.29HealthyNormal midday regulationNone; normal range.
0.10–0.14Soft closureRising VPD or mild dryingCheck VPD (VC-MET-102) & turgor (VC-MET-006).
0.05–0.09WARN closureWater stress or root-zone deficitIrrigation review; verify leaf water potential.
< 0.05CRIT shutAcute drought or root failureAuto-dispatch; emergency irrigation.
VC-MET-001

Canopy Vitality Index

gsw feeds at 15% weight.

 VC-MET-005

Leaf Water Potential

Driving water-status partner.

 VC-MET-006

Stem Turgor Pressure

Hydraulic state behind closure.

 VC-MET-008

Net Photosynthetic Rate

Co-limited by stomatal aperture.

 VC-MET-007

Sap Flow Rate

Whole-plant transpiration analogue.

 VC-MET-102

VPD

Primary environmental driver of closure.

Related SOPs