Soil and Plant Nutrition Ch Soil and Plant Nutrition Ch. 37 study of necessary elements for plant growth

Plants… Critical role in energy flow and chemical cycling of ecosystems Transform light energy  chemical energy Transform inorganic compounds  organic compounds Dry weight 95% organic 5% minerals

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

Table 37.1 Essential Elements in Plants

Nutritional Requirements Essential nutrient required to develop from a seed through its life cycle Sunlight Carbon dioxide Water Supplies most of H and O2 for photosynthesis; 80-85% of plant 90% lost during transpiration

Soil Texture Major factors in what kind of plants will grow Texture depends upon particle size sand 20 - 200 mm; silt 2 - 20 mm; clay < 2 mm Horizons distinct soil layers Topsoil Horizon A decomposed rock, living organisms, humus Humus decomposing organic matter prevents clay from packing together crumbly soil reservoir of mineral nutrients Loams most fertile, mixture of sand, silt, clay fine particles retain water & minerals coarse particles provide air spaces

Texture and Composition of Soil Living organisms Worms aerate the soil Bacteria alter soil mineral composition Fungi, algae, protists, insects, nematodes, plant roots

Topsoil Composition Surface charges of soil particles determine binding ability Positively charged adhere… Not likely to leach away Potassium, calcium, magnesium Mineral cations enter by absorption from soil solution Cation exchange Negatively charged ions are easily released and leached away

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.

Soil Conservation & Sustainable Agriculture Irrigation causes huge drain on water resources; main source is aquifers gradually makes soil salty (hypertonic) and infertile  salinization Solutions  Drip irrigation Develop plant varieties that require less water or can tolerate more salinity Fertilizers Way to reverse nutrient depletion N, P, K mined, chemically produced, organic soil pH important organic Manure, fishmeal, compost

Soil Conservation & Sustainable Agriculture Adjusting soil pH Influences mineral availability Most prefer slightly acidic soils Controlling Erosion Water and wind are the main causes Plant rows of trees, terrace hillside crops, contour pattern No till agriculture Special plowing technique Phytoremediation Nondestructive biotechnology Harnesses the ability of some plants to extract pollutants and concentration them in portions of the plant that can be easily removed

Macro and Micronutrients Soil, water, and air all contribute to plant growth 80-90% of fresh mass is water Essential Elements Required for a plant to complete its life cycle Determined by hydroponic culture Variety of inorganic, mineral ions in the soil macronutrients (9) micronutrients (8) Mostly cofactors Deficiencies depend on role of nutrient in the plant its mobility within the plant K, N, P Phosphate-deficient Healthy Potassium-deficient Nitrogen-deficient

Genetic Modification - Improving Plant Nutrition Resistance to Aluminum Toxicity Introduction of the citrate synthase gene from bacteria Flood Tolerance Flood resistant rice (submergence gene) Smart Plants Signal when a mineral deficiency is imminent

Soil Bacteria and Plant Nutrition Rhizobacteria Soil bacteria with especially large populations in the rhizosphere Soil layer that surrounds plant roots Produce chemicals to stimulate plant growth Produce antibiotics to prevent root diseases

Bacteria and the Nitrogen Cycle

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

Development of a soybean root nodule

Nitrogen Fixing Bacteria Root nodules Legumes Roots secrete chemicals to attract nearby bacteria Bacteria emit chemicals to cause root hairs to elongate and curl to prepare for infection within the root cortex Mutualistic relationship Bacteria supplies nitrogen and legumes supply the carbs Crop rotation Legumes planted in off years to restore nitrogen in the soil If not harvested, plowed under

Mycorrhizae 1 Ectomycorrhizae. The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant. 2 Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex. Mantle (fungal sheath) Epidermis Cortex Endodermis Fungal hyphae between cortical cells (colorized SEM) 100 m Fungal hyphae Root hair 10 m (LM, stained specimen) Cortical cells Vesicle Casparian strip Arbuscules

Nutritional Adaptations Parasitism Photosynthetic but supplement diet from the host - mistletoe If lose photosynthetic ability then get all nutrition from phloem sap – dodder Indian Pipe – nonphotosynthetic parasite of mycorrhizae

Nutritional Adaptations Epiphytes live on other plants but not parasites anchored by roots and nourish themselves from water and minerals absorption ferns, mosses, orchids

Carnivorous plants: Venus fly trap (left), pitcher plant (right)

Nutritional Adaptations Carnivorous plants supplemental diets because of living in poor soil conditions Venus fly trap, Pitcher plants, Sundew

Mangroves – Root, Stems, and Reproductive adaptations