Plant Nutrition Chapter 37

Nutritional Needs Autotrophic does not mean autonomous Plants need… sun as an energy source inorganic compounds as raw materials Water CO2 minerals

Macronutrients Plants require in relatively large amounts

Micronutrients Plants require in very small amounts Primarily cofactors

Uptake of Nutrients Organism level Cellular level What are some nutrients plants need? Cellular level How do they enter the plant? What are the mechanisms that bring them into the plant?

Nutrient Deficiencies Lack of essential nutrients Exhibit specific symptoms Dependent on function of nutrient Dependent on solubility of nutrient Mineral deficiency symptoms depend not only on the role of the nutrient but also on its mobility within the plant. If a nutrient moves about freely, symptoms will show up first in older organs because young, growing tissues have more “drawing power” for nutrients in short supply. For example, magnesium is relatively mobile and is shunted preferentially to young leaves. Therefore, a plant starved for magnesium will show signs of chlorosis first in its older leaves. The mechanism for preferential routing is the source–to–sink translocation in phloem as minerals move along with the sugars to the growing tissues. In contrast, a deficiency of a mineral that is relatively immobile will affect young parts of the plant first. Older tissues may have adequate amounts, which they are able to retain during periods of short supply. For example, iron does not move freely within a plant, and an iron deficiency will cause yellowing of young leaves before any effect on older leaves is visible. Deficiencies of nitrogen, phosphorus, and potassium are most common. Shortages of micronutrients are less common and tend to occur in certain geographic regions because of differences in soil composition. The symptoms of a mineral deficiency are often distinctive enough for a plant physiologist or farmer to diagnose its cause

Magnesium Deficiency Symptoms Chlorosis = yellowing of leaves What is magnesium’s function?

Chlorophyll Why does magnesium deficiency cause chlorosis?

Water & Mineral Uptake Water uptake Cation uptake Plants cannot extract all water from soil, only free water osmosis Cation uptake is aided by H+ secretion by root cells (proton pump) Active transport

The Role of Soils Plants are dependent on soil quality Texture/structure Relative amounts of various sizes of soil particles Composition Organic and inorganic components Fertility

Importance of Organic Matter Topsoil Most important to plant growth Rich in organic matter Humus Decomposing organic material formed by action of bacteria and fungi on dead organisms, feces, fallen leaves and other organic refuse Improves soil texture Reservoir of minerals Organisms Teaspoon of topsoil has ~5 billion bacteria that cohabit with various fungi, algae, and other protists, insects, earthworms, nematodes

Soil Health as a Global Issue Not taking care of soil health has far-reaching, damaging consequences 1930’s Dust Bowl Lack of soil conservation Growing wheat Raising cattle Land exposed to wind erosion Drought

Soil Health as a Global Issue Soil conservation and sustainable agriculture Maintaining healthy environment Production of food supply Economically viable farming industry “A sustainable agriculture does not deplete soils or people.” Wendell Berry Contour plowing cover crops crop rotation

Global Issues Fertility Erosion Irrigation Forestry destruction

Fertilizers “Organic” fertilizers “Chemical” fertilizers Manure, compost, fishmeal “Chemical” fertilizers Commercially manufactured N-P-K (ex. 15-10-5) 15% nitrogen (nitrate) 10% phosphorous (phosphoric acid) 5% potassium (potash)

Nitrogen Uptake Nitrates Nitrogen cycle by bacteria Plants can only take up nitrate (NO3-) Nitrogen cycle by bacteria Trace path!

Soybean Root Nodule N fixation by Rhizobium bacteria Symbiotic relationship with legumes

Mycorrhizae & Plant Nutrition Symbiotic relationship Mycorrihizal fungus gets sugars from plant Mycorrhizal fungus provides better absorption of water and minerals for plant

Parasitic Plants Tap into host vascular system Ex: mistletoe, Indian pipe

Carnivorous Plants Are they really carnivores? Ex: sundew, Venus fly trap, pitcher plant