Plant Nutrition

What happens to the nutrients taken in by the plant?  90% of water is lost in transpiration; functions as a solvent; keeps cells turgid; some of the H and O in sugars come from water  The CO 2 is assimilated into sugars made during photosynthesis; most of the dry weight of a plant comes from CO 2.

What happens to the nutrients taken in by the plant?  Mineral nutrients (NO 3 -, K +, PO 4 3-, etc.) used in organic molecules like proteins & nucleic acids and in plant function.  95% of plant dry weight are organic substances  5% is inorganic substances

Plant Requirements  Essential Nutrient—required for plant growth from seed to seed  Macronutrients—required in large amounts, C, O, H, N, S, P, K, Ca, Mg  Micronutrients—required in small amounts; Fe, Cl, Cu, Mn, Zn, Mo, B, Ni

Soil & Plant Nutrition  Topsoil—mixture of particles derived from rock  Humus—residue of partially decayed organic matter  Topsoil has bacteria, fungi, algae, protists, insects, earthworm, and nematodes and the roots of plants

Soil & Agriculture  In nature, mineral nutrients are recycled by the decomposition of dead organic matter in the soil  Agriculture depletes the mineral content of the soil because the plants are harvested—not left to decay

Fertilizers  Replenish nutrients to the soil  Contain nitrogen, phosphorus, and potassium  Manure, fishmeal, and compost are “organic” fertilizers

Nitrogen as a Plant Nutrient  Nitrogen most often limits the growth of plants and yields of crops  Nitrogen is required for plants to make proteins, nucleic acids, and other organic molecules  Ironically, the atmosphere is 80% nitrogen

Nitrogen as a Plant Nutrient  Plants cannot use nitrogen in the atmospheric form  It must be in the form of NH 4 + or NO 3 -  The conversion of nitrogen to these useable forms is done by bacteria and called NITROGEN FIXATION  Nitrogen fixing bacteria are abundant in soils rich with organic matter.  They produce the enzyme nitrogenase which fixes nitrogen into a useable form

Symbiosis of Plants & Soil Microbes  Nitrogen fixation (roots and bacteria)  Mycorrhizae (roots and fungi)

Nitrogen Fixation  Includes bacteria in the Rhizobium genus  These bacteria live in root nodules of legumes (beams, peanuts, alfalfa)  Mutualism—plant gets fixed nitrogen; bacteria get carbohydrates & organic compounds  Plant Rotation—Plant non-legume crop one year—plant legume the next year

Mycorrhizae  Modified roots with symbiotic associations of fungi & roots  Fungi gets steady supply of sugar  Plant gets increased surface area for water uptake and other minerals, growth factors secreted by the fungus, and antibiotics produced by the fungus