PLANT NUTRITION

Table 37.1 Essential Nutrients in Plants

Figure 37.3 Magnesium deficiency in a tomato plant

Figure 37.5 Soil horizons

Figure 37.6 The availability of soil water and minerals Action of Soil Particles: charged clay particles will attract water molecules and hold them, making them unavailable to the plants. Cation Exchange: Plants will secrete H+ directly as well as give off CO2 in cellular respiration. CO2 combines with water making carbonic acid. These H+ then can be exchanged for nutrient type cations such as Ca2+ held to the soil particles, thus making the calcium ions available to the plants.

Nitrogen is a key plant nutrient Nitrogen gas can be fixed from the air by special “nitro-gen fixing bacteria” which takes N2 and converts it to NH3 using an enzyme called nitrogenase. The ammonia picks up a H+ and forms ammonium Organic material being decayed also be converted to ammonium Nitrifying bacteria convert the ammonium to nitrate ions Nitrate ions can then be absorbed by the plant Nitrate is converted back to ammonium for use in amino acids, proteins, etc.

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (Layer 3)

Figure 37.10x Nodules Symbiotic Nitrogen Fixation: This is in addition to the nitrogen fixing bacteria that are in the soil Legumes (beans, clover, soybeans, alfalfa) have nodules in their roots in which Rhizobium bacteria live. So the bacteria supplies the plant with nitrogen and the plant supplies the bacteria with CHOs. Agriculture: N-fixing crops are rotated to resupply soil with nitrogen that is removed during non-nitrogen fixing years.

Figure 37.11 Development of a soybean root nodule

Figure 37.13 Molecular biology of root nodule formation

Mycorrhizae also help with plant nutrition Def: FUNGUS and the root So a mutualistic association and symbiotic The fungus gets the sugar from the plant and the root obtains increase surface area for absorption of water and especially phosphate. Fungi also secretes growth factors to stimulate root growth and branching. Fungi also produces antibiotics to help plant avoid pathogenic bacteria and fungi in soil.

Evolutionary Adaptations Mycorrhizae may have helped plant colonize land a) early soil was poor so fungus helped to gain nutrients and gain an advantage b) nutrient poor soils, when planted, have lots of mycorrhizae associated with these plants. c) present on most plants.