Uptake of nutrients by plants

The interplay of acid-base, solubility, and complex ion equilibria is often important in natural processes, such as the weathering of minerals, the uptake of nutrients by plants, and tooth decay. For example, limestone (CaCOj) will dissolve in water made acidic by dissolved carbon dioxide ... 

In Chapter 13, you learned that diffusion is the mixing of gases or liquids resulting from their random motions. Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration. Semipermeable membranes are barriers with tiny pores that allow some but not all kinds of particles to cross. The membranes surrounding all living cells are semipermeable membranes. Osmosis plays an important role in many biological systems such as kidney dialysis and the uptake of nutrients by plants. 

Influence on plant growth in solution culture. . Influence on the uptake of nutrients by plants Interactions v/ith enz Tnes, plant growth substances and chlorophyll. ... 

Plants may be affected by indirect modifications of the environment. Soil acidification, for example, can cause the leaching of nutrients, and the release of toxic aluminum. These effects may operate together to produce nutrient deficiencies or imbalances to plants. High soil concentrations of aluminum may prevent uptake and utilization of nutrients by plants.Increased availability of aluminum in soils has been implicated as a cause of forest declines in both Europe and the United States, possibly through the toxic effects on small feeder roots 14),... 

The most important factor influencing the uptake of strontium by plants is the Ca status of the soil, other factors include the pH and organic matter content. Lem-brechts et al. (1990) have investigated the relation between soil solution composition and 85Sr uptake by young lettuce plants. A close relationship was shown between the Sr concentrations in the plants and the Sr/Ca ratio in solution either in nutrient medium, or in soil solution. It was suggested that plants primarily withdraw their nutrients from the soil liquid phase. 

Of more relevance to the uptake of radionuclides by plants is the question of discrimination between radionuclides and their nutrient analogues. Indeed, the question of whether the physiological mechanisms of ion uptake within the root can discriminate between the radioion and its analogue has been central to the elucidation of the environmental behaviour of 137Cs and Sr since the late 1950s. Comar et al. (1957) devised a measure of the degree of discrimination by plants between strontium and calcium which they termed the observed ratio (OR), defined as ... 

Uptake of elements by plants is important in understanding essential nutrients for plants, potential health concerns for humans and animals that eat the plants, and use of plants as a remediation agent to remove toxic elements from soils. The uptake of heavy metals by wheat from fertilizers and sewage sludge applied to agricultural lands was investigated by using ICP-MS [263]. 

Plant nutrient supply from various sources should cover immediate plant nutrient demand. If the risks from leaching, volatilization, denitrification, or fixation are high, such as in rainy, tropical climates, it is important to operate in a supply/demand mode rather than in terms of total nutrient doses, The uptake of nutrients by cereals during their developmental phases is given in Figure 19.115]. 

At every step in the chain from soils to man, the essential mineral elements interact with other elements, and these Interactions may profoundly affect the availability of essential elements or the amount of the essential element required for normal growth or metabolic function. For example, a high level of sulfate in the soil may depress the uptake of selenium by plants, and cause the people that eat the plants to suffer from selenium deficiency. The availability of zinc may be depressed if the diet is high in calcium. These and other interactions must be considered in assessing whether a given soil will supply plants with needed nutrients, and, in turn, whether plants will supply the people that consume them with needed nutrients. 

It is well known that chemical compo.sition of rhizosphere solution can affect plant growth. Particularly, uptake of nutrients may be considerably influenced by the ionic concentration of the rhizosphere solution (40). Despite the difficulty of defining the exact concentration of ions in the rhizosphere surrounding each root (or even root portion), it has been unequivocally demonstrated that plants have evolved mechanisms to cope with the uneven distribution of ions in the root surrounding in order to provide adequate supply of each essential nutrient (41). These mechanisms include expression of transporter genes in specific root zones or cells and synthesis of enzymes involved in the uptake and assimilation of nutrients (40,43). Interestingly, it has been shown that specific isoforms of the H -ATPase are expressed in the plasma membrane of cell roots it has been proposed that the expression of specific isoforms in specific tissues is relevant to nutrient (nitrate) acquisition (44) and salt tolerance (45). 

Uptake and transformation of nutrients by microorganisms and plants Biological N, P... 

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). 

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