Re: how does the amount of water affect plant growth

The study of water and plants is termed plant water relations.

Plants need water for cell metabolism, cell expansion, turgor support of their 
nonwoody cells and for transpiration. Submerged or floating aquatic plants 
also require water for external support. Too little water and plant growth 
will be stunted or plants will die. For example, if there is insufficient 
water in soil, stomata will close and a plant will be unable to 
photosynthesize because it cannot get carbon dioxide gas.

Many plants also will suffer if the soil is waterlogged. Most plant roots 
require oxygen in the soil for normal growth and development. Waterlogging of 
soil also favors growth of anaerobic organisms which reduce inorganic ions to 
toxic forms. For example, manganese often becomes toxic to roots in 
waterlogged soils.

References


Re: Why do plants die when you over water them?


Uptake and Movement of Water Through the Tree


Manganese Toxicity in Rice