Chapter 37: Plant Nutrition 1. What are the nutritional requirements of plants?

Figure 37.2 The uptake of nutrients by a plant: a review CO2, the source of carbon for Photosynthesis, diffuses into leaves from the air through stomata. Through stomata, leaves expel H2O and O2. H2O O2 CO2 Roots take in O2 and expel CO2. The plant uses O2 for cellular respiration but is a net O2 producer. Roots absorb H2O and minerals from the soil. Minerals

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? Macronutrients – needed in large amounts (9) Micronutrients – needed in small amounts (8) Mg++ P S N

Table 37.1 Essential Elements in Plants

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? What makes up soil? Weathered rock Topsoil – mixture of weathered rock, living organisms, & humus Humus – remains of partially decayed organic matter Loams – most fertile soils made of equal amounts of clay, silt & sand Mg++ P S N

Figure 37.5 Soil horizons The A horizon is the topsoil, a mixture of broken-down rock of various textures, living organisms, and decaying organic matter. The B horizon contains much less organic matter than the A horizon and is less weathered. The C horizon, composed mainly of partially broken-down rock, serves as the “parent” material for the upper layers of soil. A B C

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? What makes up soil? How do minerals become available to plant roots? - Cation exchange Mg++ P S N

Figure 37.6 The availability of soil water and minerals Soil particle surrounded by film of water Root hair Water available to plant Air space H2O + CO2 H2CO3 HCO3– + Soil particle K+ Cu2+ Ca2+ Mg2+ H+ – (a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root. (b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by secreting it from root hairs and also by cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil solution.

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? What makes up soil? How do minerals become available to plant roots? How is soil conservation achieved? Fertilizers N-P-K Organic Irrigation - problems Erosion prevention Mg++ P S N

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? What makes up soil? How do minerals become available to plant roots? How is soil conservation achieved? How do plants obtain nitrogen? nitrogen-fixing bacteria Mg++ P S N

Nitrogen-fixing bacteria Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants Atmosphere N2 Soil Nitrogen-fixing bacteria Organic material (humus) NH3 (ammonia) NH4 + (ammonium) H+ (from soil) Ammonifying bacteria

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants Atmosphere N2 Soil Nitrogen-fixing bacteria Organic material (humus) NH3 (ammonia) NH4 + (ammonium) H+ (from soil) NO3 – (nitrate) Nitrifying bacteria Denitrifying bacteria Ammonifying bacteria

Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants Atmosphere N2 Soil Nitrogen-fixing bacteria Organic material (humus) NH3 (ammonia) NH4 + (ammonium) H+ (from soil) NO3 – (nitrate) Nitrifying bacteria Denitrifying bacteria Root NH4 + Nitrate and nitrogenous organic compounds exported in xylem to shoot system Ammonifying bacteria Assimilation Legumes have root nodules with symbiotic bacteria Rhizobium

Figure 37.10 Root nodules on legumes (a) Pea plant root. The bumps on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant. (b) Bacteroids in a soybean root nodule. In this TEM, a cell from a root nodule of soybean is filled with bacteroids in vesicles. The cells on the left are uninfected. 5 m Bacteroids within vesicle Nodules Roots

Chapter 37: Plant Nutrition What are the nutritional requirements of plants? Why do plants need K+? What makes up soil? How do minerals become available to plant roots? How is soil conservation achieved? How do plants obtain nitrogen? What are some nutritional adaptations that aid plants? Mg++ P S N

Figure 37.13 Unusual Nutritional Adaptations in Plants Staghorn fern, an epiphyte EPIPHYTES PARASITIC PLANTS CARNIVOROUS PLANTS Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite Host’s phloem Haustoria Indian pipe, a nonphotosynthetic parasite Venus’ flytrap Pitcher plants Sundews Dodder

37.13 Sun Dew Trap Prey