Do stomata close when there is a lack of water in soil or a lack of carbon dioxide in the atmosphere?

When water is abundant:

-Temporal regulation of stomata is used:

Open during the day

Closed at night

- At night, there is no photosynthesis, so no demand for CO2 inside the leaf.

- Sunny day = demand for CO2 in leaf is high = stomata wide open.

- As there is plenty of water, plant trades water loss for photosynthesis products.

-  If the leaf's CO2 concentration is low, the stomata will stay open to continue fueling photosynthesis.

- High temperatures will also signal stomata to close.

- When limited water is available in the soil, plants try to prevent water loss.