Plant Nutrition Chapter 37

Plants require chemical elements Every organism continually exchanges energy and materials with its environment For a typical plant, water and minerals come from the soil, while carbon dioxide comes from the air

Plants derive most of their organic mass from the CO2 of air, but they also depend on soil nutrients such as water and minerals Minerals H2O O2 CO2

A chemical element is considered essential if it is required for a plant to complete its life cycle Researchers use hydroponic culture to determine which chemicals elements are essential Control: Solution containing all minerals Experimental: Solution without potassium

Nutrients Nine of the essential elements are called macronutrients because plants require them in relatively large amounts The remaining are called micronutrients because plants need them in very small amounts

Nutrients

Mineral Deficiency Symptoms of mineral deficiency depend on the nutrient’s function and mobility within the plant The most common deficiencies are those of nitrogen, potassium, and phosphorus

Mineral Deficiency Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient

Soils Topsoil is a mixture of particles of rock, living organisms, and humus (the remains of partially decayed organic material) Humus is the remains of partially decayed organic material, formed by the work of bacteria and fungi on dead organisms, feces, fallen leaves, and other organic refuse

Soils A Horizon is the topsoil, mixture of broken down rock of various textures, living organisms, and decaying matter B Horizon contains less organic matter than A Horizon and is less weathered C Horizon is mainly broken down rock, is the “parent” material for upper soil layers A B C

Soil After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles The water in these spaces mixes to form a solution with dissolved minerals and is available to plants

Soils Soil particle surrounded by film of water Soil particle Root hair Water available to plant Air space Cation exchange in soil Soil water Soil particle

Soils Soil water- a plant can’t extract all the water in the soil beaue some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root

Soils Cation exchange in soil- H+ help make nutrients available by displacing positively charged minerals that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by secreting it from root hairs and by Rs

Soil Conservation Soil can take centuries to become fertile Agriculture can deplete soil of nutrients and mismanagement can have severe impacts Dust Bowl era in 1930s- new land uses left soil exposed and after years of drought much of the topsoil was blown away

Fertilizers Agriculture takes nutrients out of the soil, they need to be replaced 1000kg of wheat takes 20kg N, 4kg P, 4.5kg K Fertilizers have been used since prehistoric times (ie: manure) Commercial fertilizer is readily available but soil doesn’t retain it long Organic fertilizers are manure, compost, etc

Irrigation Farming can take place in arid regions thanks to irrigation but it’s a huge drain on water resources

Erosion Topsoil is lost on farmland due to water and wind erosion Planting tree rows as windbreaks, terracing hillside crops, cultivating in a contour pattern can reduce erosion Goal of soil management is sustainable agriculture

Soil Reclamation Areas that are unfit for agriculture due to contamination with toxic heavy metals and organic pollutants Past reclamation focused on removal and storage of contaminated soil, this is costly and hurt the landscape Phytoremediation- uses plants to extract pollutants from the soil and concentrate them in plants which can then be removed and disposed of

Nitrogen Nutrient that contributes the most to plant growth and crop yields Part of proteins, nucleic acids, chlorophyll, etc

Nitrogen Fixation Nitrogen fixing bacteria convert N2 to NH3 (ammonia) thereby “restocking” nitrogenous minerals to the soil. This is done by the enzyme complex nitrogenase which uses 8 ATP to produce 1 NH3. The ammonia then picks up another hydrogen to form ammonium (NH4+) which the plant absorbs although most is acquired as nitrate (NO3-). Nitrifying bacteria then oxidize NH4+ to form NO3-. Plants then reduce the nitrate back into ammonium which is then incorporated into amino acids and other organic compounds.

Nitrogen Fixation

Nitrogen Symbiotic relationships with nitrogen-fixing bacteria provide some plant species with a built-in source of fixed nitrogen For agriculture, the key symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

Symbiotic Relationships Many plants have a symbiotic relationship with bacteria and fungi and their roots that enhance the nutrition of both partners. Nitrogen fixation evolved 65-150 MYA Legumes (peas, beans, soybeans, peanuts, alfalfa, clover) have swellings on their roots called nodules that contain the symbiotic bacteria. These Rhizobium “root living” bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell. Mutualistic symbiosis: bacteria get carbohydrates and plant gets nitrogen (ammonium) to make amino acids.

Symbiotic Relationships

Crop Rotation Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation A non-legume such as maize is planted one year, and the next year a legume is planted to restore the concentration of nitrogen in the soil

Mycorrhizae “fungus roots” modified roots evolved over 400 million years ago. Mutualistic symbiosis: ecto and endomycorrhize. Sugar in exchange for: increased surface area for water uptake; selective absorption of phosphate; secretion of growth factors that stimulate roots to grow and branch, and… antibiotics.

Mycorrhizae In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root In endomycorrhizae, microscopic fungal hyphae extend into the root

Epiphytes, Parasitic and Carnivorous Plants Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Parasitic Plants: extract nutrients from plants. Haustoria projections to siphon xylem and/or phloem sap or indirect association via fungal hyphae. Ex. Pickleweed, mistletoe, indian pipe, dodder. Epiphytes (growing on branches or tree trunks): nourish themselves but grows on the surface of another plant (branch, trunk) Ex. Staghorn ferns, mosses, spanish moss, bromeliad, orchids. Carniverous Plants (grow in nutrient poor soil): supplement their mineral nutrition by digesting animals Ex. pitcher plant, venus fly trap