Stomatal opening is controlled mainly by:

Correct option is B

· Stomata open when guard cell water potential decreases, causing water influx → turgor ↑ → pore opens.
· Driven by:
· K⁺ accumulation
· Osmotic potential
· ABA signaling
Why other options are wrong
· (a) Soil pH does not control stomata.
· (c) N content influences photosynthesis, not stomatal mechanics.
· (d) Root respiration indirect.