Chapter 37. Plant Nutrition 2005-2006

Nutritional needs Autotrophic does not mean autonomous plants need… sun as an energy source inorganic compounds as raw materials water (H2O) CO2 minerals 2005-2006

Macronutrients Plants require these nutrients in relatively large amounts C, O, H, N, P, K, Ca, Mg, S 2005-2006

For what & from where? C O H N P K Ca Mg S synthesis CO2 H2O protein & nucleic acid synthesis soil & fertilizer P nucleic acids, ATP, phospholipids K stomate control, water balance Ca cell wall & membrane structure, regulation soil Mg chlorophyll S proteins, enzymes 2005-2006

Micronutrients Plants require in very small amounts primarily cofactors 2005-2006

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 2005-2006

Take 2 fertilizer pellets & call me in the morning Magnesium deficiency Symptoms chlorosis = yellowing of leaves what is magnesium’s function? 2005-2006

Chlorophyll Why does magnesium deficiency cause chlorosis? The chlorosis shows up in older leaves first, because plant moves Mg to newer leaves. Why? 2005-2006

Water & mineral uptake Water uptake Cation uptake plants cannot extract all water from soil, only free water osmosis Cation uptake cation uptake is aided by H+ secretion by root cells (proton pump) active transport 2005-2006

The role of soils Plants are dependent on soil quality texture / structure relative amounts of various sizes of soil particles composition organic & inorganic chemical components fertility 2005-2006

Importance of organic matter So don’t rake your lawn or bag your leaves Importance of organic matter Topsoil most important to plant growth rich in organic matter humus decomposing organic material breakdown of dead organisms, feces, fallen leaves & other organic refuse by bacteria & fungi improves soil texture reservoir of minerals organisms 1 tsp. of topsoil has ~5 billion bacteria living with fungi, algae, protists, insects, earthworms, nematodes 2005-2006

Soil health as a global issue Not taking care of soil health has far-reaching, damaging consequences 1920’s Dust Bowl lack of soil conservation growing wheat raising cattle land exposed to wind erosion drought 2005-2006

Soil health as a global issue Soil conservation & 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 2005-2006

Global issues fertility erosion irrigation forestry destruction 2005-2006

2005-2006

Fertilizers “Organic” fertilizers “Chemical” fertilizers manure, compost, fishmeal “Chemical” fertilizers commercially manufactured N-P-K (ex. 15-10-5) 15% nitrogen 10% phosphorus 5% potassium 2005-2006

What will the plant use N for? Nitrogen uptake Nitrates plants can only take up nitrate (NO3-) Nitrogen cycle by bacteria trace path of nitrogen fixation! root 2005-2006 What will the plant use N for?

Soybean root nodules N fixation by Rhizobium bacteria symbiotic relationship with bean family (legumes) 2005-2006

Increasing soil fertility Plow it under? Why would you that? Increasing soil fertility Cover crops growing a field of plants just to plow them under usually a legume crop taking care of soil’s health puts nitrogen back in soil 2005-2006 erosion control, too

Some plant oddities… 2005-2006

Parasitic plants tap into host plant vascular system Indian pipe Mistletoe 2005-2006

Plants of peat bogs High acid environment most minerals & nutrients bound up & are not available to plants must find alternative sources of nutrients 2005-2006

Carnivorous plants Are they really carnivores? Sundew Venus fly trap Pitcher plant Are they really carnivores? 2005-2006

Pitcher plant 2005-2006