Plant Nutrition and Soil 

Soil

Highly weathered outer layer of the Earth’s crust

• Mixture of sand, rocks, clay, silt, humus, air,  and other forms of mineral and organic matter.

The Earth’s crust includes about 92 naturally occurring elements

• Most are found in the form of inorganic compounds called minerals.

Also full of microorganisms

Plant Nutrients

Photosynthesis is major source of plant nutrition via the fixation of CO2 into sugar using solar energy

Also need

• Macronutrients – used in relatively large amounts.

  • Nine = C, O, H, N, K, Ca, Mg, P, and S.

• Micronutrients – used in minute amounts.

  • Seven = Cl, Fe, Mn, Zn, B, Cu, and Mo.

Special Nutritional Strategies

Plants need ammonia (NH3) or nitrate (NO3−) to build amino acids

• However, they lack the biochemical pathways necessary to convert N2 in the atmosphere into NH3.

Symbiotic relationships have evolved between plants and nitrogen-fixing bacteria

• Legumes form nodules that house the bacterium Rhizobium.

Rhizobium

Rhizobium bacteria require oxygen and carbohydrates to support their energetically expensive lifestyle as nitrogen fixers

• Plant host supplies both.

Nodule housing Rhizobium are formed in legumes and a few other plants

Mycorrhizae

Symbiotic associations with mycorrhizal fungi are found in about 90% of vascular plants

• Substantially expand the surface area available for nutrient uptake.

• Enhance uptake of phosphorus and micronutrients.

Carnivorous Plants

• Often grow in acidic soils that lack nitrogen

• Trap and digest small animals, primarily insects, to obtain adequate nitrogen supplies

• Have modified leaves adapted for luring and trapping prey

• Prey is digested with enzymes secreted from specialized glands

• Note that they do not use prey as a carbon or energy source, as they are photosynthetic.

Parasitic Plants

• May be photosynthetic or non-photosynthetic

• At least 3,000 types of plants

• Tap into the nutrient resources of other plants

• Adaptations include structures that are inserted into the vascular tissue of the host plant so that nutrients can be siphoned into the parasite

• Examples include dodder and Indian pipe