Rate of transpiration - over 90 % of water absorbed by the roots are lost to the atmosphere. Photosynthesis requires CO_2 from the atmosphere; stomata regulate the intake of CO_2 and the loss of water; increases in temperature and wind velocity increase water loss; pathways regulate stomatal opening/closing; abscisic acid regulates signal pathways in droughts by opening K^+, Cl^-, and Malate channels; stomata close for high CO_2 concentrations, open for blue light enhanced uptake of K^+, and close for high temperatures (30-34 degrees celcius), low water, and alternative photopathways (CAM).
Adaptations to flooding - systems adapted to depleted oxygen levels. Abnormal growth by large lenticels and adventitious roots; formation of aerenchyma (loose parenchymal tissue with large air spaces); and transport of oxygen to submerged plant parts by aerenchyma.
Pneumatophores - long and spongy air-filled roots that emerge above water and supply oxygen to submerged roots; while controlling the balance of salts. Succulent leaves contain water to maintain salt; and may secrete salt or block salt uptake. Ex. mangroove roots.
Water stress response - adaptations to prevent water loss. Dormancy, loss of leaves (deciduous), covering leaves with wooly trichomes, reducing stomata amount, and having stomata in pits on leave surfaces.