The absorption of both water and minerals is important for the health, growth and fruit production of plants. Water and minerals are absorbed by the plant's roots, a process which is often aided by specialised fungi that form symbiotic relationships with the roots that are known as mycorrhizae.
The outermost cell layer of a root is known as the epidermis. It is these cells that absorb water from the environment as well as minerals that are dissolved in the water. Just past the growing tip of the root, some of the epidermal cells are elongated. These cells function to increase the surface area of the root and thereby improve its capacity to absorb water and minerals. Root hairs are easily torn off or desiccated by the sun when plants are transplanted, thereby temporarily reducing the capacity of the plant to absorb water and minerals.
Where mycorrhizal relationships exist, the fungus puts out thin, thready hyphae into the surrounding soil. These absorptive hyphae increase the area of the root system and therefore its access to water and nutrients. The water and nutriets absorbed by the hyphae are exchanged for sugars produced by the plant. Mycorrhizal plants usually perform and survive better than those without this symbiotic relationship. Mycorrhizae have a vital function in the absorption of phosphorous and the prevention of iron and manganese deficiencies in alkaline soils.
Mineral Nutrition of Plants
There are 14 essential mineral nutrients of plants, which are classified according to the amount required. Those for which plants have large requirements, or macronutrients, are nitrogen (N), potassium (K), phosphorus (P), calcium (Ca), sulphur (S) and magnesium (Mg). It is more common to see deficiencies of nitrogen, potassium and phosphorous than the other three minerals. Those minerals for which plants have smaller needs, or micronutrients are boron (B), chlorine (Cl), iron (Fe), copper (Cu), manganese (Mn), nickel (Ni), molybdenum (Mo) and zinc (Zn). The amount of minerals taken up by the plant depends both on the root's ability to absorb them and the concentration of nutrients around the root surface.
Soil pH and Mineral Absorption
Soil pH is a measure of the relative amounts of acid and alkaline ions in the soil. Equal amounts of each type of ion give a neutral soil with pH 7. The lower the pH, the more acid the soil, and the higher, the more alkaline. Phosphorous and various micronutrients are much more difficult for plants to absorb with a high-alkaline pH, and woody plants such as pin oak may show obvious symptoms of iron and manganese deficiency such as thin and pale leaves. Plants can generally tolerate a pH range of 5.5 to 8.3 if in a well-drained soil, but levels of 6.0.to 6.5 are optimal for most.
- Oregon State University Extension: Roots
- Ohio State University Extension; Mycorrhizae in Urban Landscapes; Nathan M. Kleczewski et al; 2008
- Soil and the Envronment; The Role of Mycorrhiza in the Mineral Nutrition of Plants; Victor B. Asio; 2010
- Iowa Urban and Community Forestry Council; Requirements for Plant Growth; Jeff Iles; 2001
- Montana State University Extension; Plant Nutrition and Soil Fertility; Clain Jones and Jeff Jacobsen; 2005
- Plant Physiology Online; Symptoms of Deficiency In Essential Minerals; Wade Berry