A greenhouse crop may react to a humidity change immediately, acclimate over time, or retain a growth-stage-dependent limitation. These responses involve different timescales and measurements. A current RH reading does not reveal whether a response belongs to today’s evaporative demand, a mature leaf’s prior conditions, or the way a leaf developed. Species and the measured endpoint must stay attached to the interpretation.
Cucumber: an immediate summer response
The 1995 study of cucumber in a southern European greenhouse analyzed stomatal behaviour under variable summer conditions. Solar radiation was a major regulator. High atmospheric VPD increased transpiration, followed by a reduction in stomatal aperture, suggesting feedback associated with water stress. The response became more sensitive when high evaporative demand coincided with a rapid fall in solar radiation, and exposure duration also mattered. This is a crop- and study-specific response to changing conditions, not a universal recovery timetable or operating target. (PubMed abstract)
Vicia faba: reversible sensitivity in mature leaves
The 2003 Vicia faba ‘Windsor Long Pod’ paper tested stomatal sensitivity to CO₂ in mature leaves. Humidity conditions altered that sensitivity, and transfer between environments produced reversible acclimation. The tested endpoint was how stomata responded to CO₂; it was not a guarantee of hydration, yield, or continuously open stomata. Because the leaves were mature, the result also helps separate environmental acclimation from changes created while a leaf is still developing. (Journal of Experimental Botany)
Rose: development shapes closing capacity
The 2011 Wageningen thesis author abstract reports cultivar differences in rose stomatal closing capacity after leaves developed under elevated humidity. In the studied roses, changing humidity after full expansion did not alter the measured stomatal functioning, while expanding leaves could partly adapt as development continued. The rose and Vicia studies measured different responses in different species. Together, they caution against assuming that every mature leaf responds to a humidity change in the same way. (Wageningen Research Portal)
Ask which response you observed
When a crop appears to change after a climate shift, identify the species and cultivar, whether the leaf is expanding or mature, the prior conditions, the current conditions, and the actual response measured. For broader moisture and growth context, see how humidity impacts plant growth. Bring unresolved interpretation to a qualified crop advisor.
Related project questions
For related crop-response evidence, see cut-rose quality after different cultivation humidity histories and edema and water balance. For the wider project context, return to agricultural humidity control.
