Thus, high surface tension is responsible for the large reservoir of available water in soils and growing media. Effects of Water on Seedling Growth. Dehydration first slows metabolic processes and eventually leads to a state of dormancy and, at extreme levels, to death. Water carries mineral nutrient ions into the roots and then through the xylem to the foliage where they are used in photosynthesis. Then, photosynthate and other organic compounds are then carried back throughout the plant by way of the phloem to fuel the cell metabolism and provide the organic building blocks of all plant tissue.
Water also serves as a substrate or ligand for many other important chemical reactions.
More specifically in nurseries, water is necessary to bring seeds out of dormancy and stimulate the hydrolysis of the stored starches to sugars to feed the developing embryo. The young germinant requires a steady supply of water to fuel the photosynthetic process which produces the energy needed for rapid growth. Therefore, the vast majority of water that we apply during irrigation is used just to keep the stomata open so that CO2 can easily enter the leaf. If seedlings are allowed to lose turgidity the stomata begin to close, photosynthesis slows, and eventually stops all together. Like all things, however, you can have too much of a good thing and an excess of water affects seedling growth in negative ways.