PLANTS REQUIRE NUTRIENTS

Plant material consists primarily of carbohydrates, which are made of the elements carbon, oxygen, and hydrogen. Plants gpt these three elements from carbon dioxide and water, but the soil in which the plants live also provides many other elements vital to their survival and good health. Table 15-1 lists these nutrients as macronutrients, those needed in large quantities, and micronutrients, tho.se needed only in trace quantities. Some micronutrients are needed in such trace quantities that a plants lifetime supply is provided by the seed from which the plant grew. 

Element Form Available to Plants Relative Number of Ions in Dry Plant Material  

Source Frank Saltsbuiy and Cleon Ross. Plant Physiology. Belmont. CA Wadsworth, 1985. 

In a natural. setting, nitrogen fixation is the original source of ammonium and nitrate ions in the soil. Most of this fixed nitrogen, however, is recycled from one 

Murray Nabors, lntroduction to Botany. San Francisco Benjamin-Cummings,2004. www.aw-bc.com 

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Plants require nutrients that also contain nitrogen. As discussed earlier in this chapter, ammonium nitrate is an important fertilizer, and it can be produced by the reaction... 

As animals require specific amounts of proteins, carbohydrates, vitamins, and minerals for proper growth, plants require nutrients in the form of ions derived from the soil. Insufficient quantities of protein, or even specific amino acids of proteins, can limit growth or specific biological processes in animals. Similarly, each nutrient plays a specific role in the structure of plant cells and the enzyme and energy transfer molecules that carry out the metabolic processes of plants. Because of the unique chemical characteristics of these nutrients, other elements cannot be used as substitutes for them. 

Increased knowledge about secondary nutrients and micronutrients, including plant requirements, nutrient sources, and methods of application, has resulted in th increased use. Improvements In soil testing and plant analyses have provided more knowledge about plant needs and the unde variations in plant responses to these nutrients. Higher crop yields and the use of h h-analysis NPK fertilizers also have resulted in increased needs for these nutrients. 

Increases in soil salinity can hinder the growth of plants by limiting their uptake of nutrients (Grattan and Grieve 1992). The major cations that affect saline soils are Na", Ca ", Mg ", as well K", while the major anions are CP, SO4, HCOj" and NOj". When the soil has a high pH, COf is also present. The nutrients which plants require most are Ca ", Mg " and K". However, the uptake of and Ca " is hindered by the presence of excess Na", and an increased concentration of Ca " in the soil can lead to a deficiency of Mg " (Grattan and Grieve 1992). 

Fatty acids, such as linoleic, hnolenic, and arachidonic acids, contain two or more cis carbon-carbon double bonds and are referred to as polyunsaturated fatty acids. Several of these fatty acids, including linoleic and linolenic acids, are required nutrients for humans and must be part of a healthy diet. They are termed essential fatty acids, of which there are eight. These fatty acids cannot be synthesized by human beings but are essential to human health. Therefore, they must be consumed in adequate amounts in a healthy diet, specifically in the form of ingested plant-derived foods. A diet devoid of the essential fatty acids eventually results in a fatal condition characterized by inflammation of the skin (dermatitis), failure of wounds to heal, and poor growth. The essential fatty acids serve as precursors for complex molecules termed eicosanoids, to which we return below. 

Explain the role of transpiration in getting required nutrients into plants. 

The relative order of efficiency of accumulation of the thpee radionuclides into edible tissues was Zn>Fe>Se. Most of the Zn transported to the above ground plant parts was accumulated by the seeds, however, much of the dose of each of the radionuclides remained in the roots and nutrient solution. The calculated percent of the applied dose taken up by soybean leaves is underestimated since some of the leaves abscised as the plants senesced and they were discarded. Zinc and iron have been classified as partially mobile in the phloem (8). Translocation of iron within plants is poor since new growth of plants require a continuous supply of iron via the xylem or from external applications ( ). Zinc deficiencies of plants can be corrected by applying ZnSO. in a dilute spray. However, iron deficiences of plants are usually difficult to correct which implies a lesser mobility within the plant. 

Alpha-linolenic acid (18 3n-3) is an 18-carbon fatty acid with three double bonds at carbons 9, 12, and 15. It is an essential n-3 fatty acid that is a required nutrient for human beings and can be obtained through diets including both plant and animal sources. Alpha-linolenic acid can be converted by elongases and desaturases to other beneficial n-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosa-hexaenoic acid (DHA), which are implicated in normal brain development, normal vision, and a decreased risk of heart disease. Novel dietary sources of n-3 fatty acids are desired for those who do not consume adequate amounts of fish or fish-based food products rich in long-chain n-3 fatty acids. This section summarized fruit, spice, and herb seed oils rich in a-linolenic acid (18 3n-3). These include black raspberry, red raspberry, boysenberry, marionberry, blueberry, cranberry, sea buckthorn, basil, and hemp seed oils. 

Potassium is essential to both plant and animal life. It is one of the three primary nutrients, or macronutrients, required by plants. Plants require relatively large amounts of potassium in order to grow and remain healthy. 

Virgin soil can be rich in nutrients but at levels that may not be optimal. The soil should therefore be tested for its nutrient content before planting seeds. Nutrients are depleted with repeated production of crops and hence it is important to monitor the concentration of nutrients in the soil and supplement them as required (Seiler 1986). In most third-world countries fertilizer application and irrigation are costly and, sometimes, impossible. 

The quantities of nutrients in microbes are large compared with the annual plant nutrient uptake, suggesting that even relatively limited dieback of the microbial populations can lead to release of an appreciable proportion of the plants annual nutrient requirement. Indeed, it is known that the annual uptake of P by wet tundra vegetation can be almost entirely accounted for by P released through nutrient flushes from the microbial biomass (Chapin et al, 1978). It is possible, therefore, that the supply rate of nutrients to the soil inorganic pool varies depending on the conditions for microbial population growth or decline and that plant nutrient availability fluctuates inversely to microbial nutrient demand. 

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