Uptake by Plants from Soil

Many herbicides are applied to soil, and their effectiveness is dependent upon the germinating weed seedlings acquiring a lethal dose. Successful control of weeds often depends on killing the weeds at this early stage, for older weeds are usually more difficult to kill. Generally, selectivity between crop and weed is achieved either because the crop is much more deeply 

In soil, the stronger uptake by roots of lipophilic compounds from the soil water is offset by the reduced availability due to the sorption of lipophilic chemicals onto soil organic matter as discussed above. 

Weak acids. Uptake of acidic compounds by roots is very different from that of nonionized compounds in that it is strongly dependent on the pH of the bathing medium. For example, uptake of 2,4-D into barley roots over 24 h from nutrient solution was 36 times greater at pH 4.0 than at pH 7.0. This dependency can be explained by the ion-trap effect discussed in Section 9.2.3.3, whereby weak acids are accumulated in compartments of higher pH by virtue of the greater permeation rates across membranes of the undissociated form compared to the anion. 

Within a series of substituted phenoxyacetic acids, Briggs et aC noted that uptake by barley roots was optimal for the acids whose undissociated form had log values of 1 to 3 and was less for more polar and more lipophilic compounds. This uptake was due almost entirely to raised concentrations in the cell sap, for only with the most lipophilic compound tested (log Xqw4.51) could any partitioning be measured onto macerated roots from a bathing solution of pH 5.0. The pKa values of the acids were essentially similar across the series, and so these differences in accumulation were attributed to changes in the permeability ratio Fah/ a - This ratio was optimal for 4-chlorophenoxyacetic acid (log 2.25, Pah/Fa- 4x 10 ) and declined substantially for more polar and more lipophilic analogues. 

Sorption in soil of weak-acid herbicides increases as the pH decreases (see, e.g.. Ref. 35), but this effect is much less than the effect of pH on uptake by roots. Accordingly, uptake of weak acids by plant roots is substantially greater from soils of low pH than of high pH, and this may explain why such herbicides are often found to be more effective in more acidic soils. 

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EPA. 1979. Plutonium-239 and americium-241 uptake by plants from soil. Las Vegas, NV Environmental Monitoring and Support Laboratory, U.S. Environmental Protection Agency. EPA600/3-79-026. PB298-241. 

Paterson S, Mackay D (1994) A model of organic chemical uptake by plants from soil and the atmosphere. Environ Sci Technol 28 2259-2266... 

Kumar K, Gupta SC, Baidoo SK, Chander Y, Rosen CJ (2005) Antibiotic uptake by plants from soil fertilized with animal manure. J Environ Qual 34 2082-2085... 

Schachtman DP, Reid RJ, Ayling SM (1998) Phosphorus uptake by plants from soil to cell. Plant Physiol 116 447-453. doi http //www.plantphysiol.org Schindler DW (1974) Eutrophication and recovery in experimental lakes implications for lake management. Science 184 897-899. doi http //www.sciencemag.org/cgi/content/abstract/184/4139/897 Schindler DW, Hecky RE, Findlay DL, Stainton MP, Parker BR, Paterson MJ, Beaty KG, Lyng M, Kasian SEM (2008) Eutrophication of lakes cannot be controlled by reducing nitrogen input results of a 37-year whole-ecosystem experiment. Proc Natl Acad Sci USA 105 11254-11258. doi http //www.pnas.org/content/105/32/l 1254.abstract Scott JT, Condron LM (2003) Dynamics and availability of phosphorus in the rhizosphere of a temperate silvopastoral system. Biol Fert Soils 39 65-73 Shane MW, Lambers H (2005) Cluster roots a curiosity in context. Plant Soil 274 101-125. doi http //dx.doi.org/10.1007/s 11104-004-2725-7... 

Paterson, S., D. Mackay, and A. Gladman. 1991b. A Fugacity Model of Chemical Uptake by Plants from Soil and Air. Chemosphere 23, 539-565. 

Schachtman, D. R, Reid, R, J., and Ayling, S. M, (1998). Phosphorus uptake by plants from soils to cell. Plant Physiol. 116, 447-453. 

Increases in soil cadmium content result in an increase in the uptake of cadmium by plants. The uptake by plants from soil is greater at low soil pH. Processes that acidify soil (e.g. acid rain) may therefore increase the average cadmium concentrations in foodstuffs (WHO, 1992b). 

Kabata-Pendias A (1979) Effect of lime and peat on heavy metal uptake by plants from soils contaminated by an emission of copper smelter. Rocz Glebozn, 30/3 323-328 Kabata-Pendias A, Bolibrzuch E, Tarlowski P (1981a) Impact of a copper smelter on agricultural environment. Part 1 Contamination of soils. Rocz Glebozn 32/3 207-214 (in Polish)... 

Kleier, using similar concepts, has produced a computer model that predicts phloem transport of xenobiotics based upon their physicochemical properties. Topp et Ryan et and Boersma et have attempted to assess the uptake by plants from soil of nonionized organic chemicals based upon their physicochemical properties and persistence. From our present understanding of the transport in plants of herbicides and other pesticides, it should be possible to predict approximately the behavior of new or putative herbicidal molecules. With due account taken of the complicating factors such as availability in soil, penetration across leaf cuticles, and metabolism, this approach should be applicable to compounds used on a wide range of crop and weed species in a variety of situations. 

Paterson, S., D. Mackay, and C. McFarlane. 1994. A model of organic chemical uptake by plants from soil and the atmosphere. Environ. Set Technol. 28 (13) 2259-2266. Pauliukonis, N. and R. Schneider. 2001. Temporal patterns in evapotranspiration from lysime-ters with three common wetland plant species in the eastern United States. Aquatic Bot. 71(1) 35-46. 

Topp E, Scheunert I, Attar A, et al. 1986. Factors affecting the uptake of 14C-labeled organic chemicals by planting from soil. Ecotox Environ Safety 11 219-228. 

Phosphate has been shown to remove Cd and Zn from aqueous solutions (Chen et al., 1997b), to reduce Hg mobility (Melamed and Boas, 2000), to inunobilize Pb effectively in contaminated soils (Ma et al., 1993, 1994a,b, 1995 Ma and Rao, 1999) and scrubber residues (Geysen et al., 2004) and ash (loannidis and Zouboulis, 2003), to reduce Pb uptake by plant in soils (Laperche et al., 1997), to mitigate acid mine drainage, and to reduce the transport of heavy metals in soils (Georgopoulou et al., 1995 Evangelou, 1996). 

Molshanova, I. V. (1968). Uptake of trace quantities of yttrium-91 and cerium-144 by plants from nutrient solutions and soil, Tr, Inst. Ekol. Rast. Zhivotn. Ural. Fil. Akad. Nauk SSSR 61, 31. 

Sensitive terrestrial plants die when soil zinc levels exceed 100 mg/kg or when plant zinc content exceeds 178 mg/kg DW (Table 9.5). The phytotoxic zinc level for barley (Hordeum vulgare) is not known, but zinc content of barley leaf rarely exceeds 100 mg/kg DW (Chang et al. 1983). Uptake of zinc from soils by plants depends on soil type for example, uptake is lower in coarse loamy soils than in fine loamy soils (Chang et al. 1983). Zinc uptake by barley leaf is greater with increasing rate of sludge application, but the relation is not proportional (Table 9.5). 

The presence of significant concentrations of endrin transformation products (including endrin ketone, endrin aldehyde, and endrin alcohol) in a variety of plants grown in soil treated with endrin for periods as long as 16 years prior to planting (Beall et al. 1972 Nash and Harris 1973) indicates that there may be significant uptake of endrin and/or its transformation products by plants from endrin-treated soil. 

There have been several investigations of plutonium uptake by plants and several authors have reviewed the various articles (124-126). Based on studies with plant-soil systems direct root uptake into the plant appears to be low. Concentration factors for (pCi/g dry acceptor)/(pCi/g donor) are of the order 10-5 to 10 4 (127). However, variations in the chemical form of plutonium and the presence of chelating agents in the soil can result in the concentration of more plutonium in the plant. Over five years Romney et aL (33) observed that the plutonium concentration in ladino clover increased from 3.1 dpm/g for the first year to 22.6 dpm/g in the fifth year. It should be noted that clovers release citric acid into the soil (113). 

A mycorrhiza (literally, fungus-root) is a symbiotic association between a fungus and a plant. Mycorrhizae occur most frequently on plant roots, but may be found on any tissue involved in uptake of elements from soil. Mycorrhizae, formed by numerous fungi in the orders Phycomycetes, Basidiomycetes, and Ascomycetes, can be divided into two broad groups those that penetrate host cells (endomycorrhizae) and those that do not (ectomycorrhizae). A few fungal species defy this neat classification, penetrating the cells of one host but not those of another. 

Trace elements on the surfaces of fly ash particles that are accessible to humans through air, soil, water, can affect health in several ways. The pathways by which metals from CCP may cause harm include (1) soil deposition and resulting plant uptake of metals and subsequent movement into the food chain (2) direct ingestion of soil by animals or humans (3) leaching of metals from CCP to water systems and uptake by plants, animals, or humans and (4) inhalation of dust (from soil) or respirable ash particles (Ryan Bryndzia 1997). 

To the extent that diet contributes to internal body burdens, a comparison of the relative plant uptake of actinides from soil is of interest. Several studies have compared the uptake of various transuranium elements by plants (17,18,19). However, studies which include U and Th are not as available. Figure 2 presents recent results for field-grown vegetation of soil originally contaminated in 1944 with soluble forms of U, Th and Pu (and daughter Am) (20.21). The crops examined include soybeans, snapbeans,... 

Another important uptake route for chemicals by terrestrial plants and organisms living in soils (e.g., earthworms) is uptake from soil interstitial water and/or by ingestion of soil particles. In particular, uptake of contaminants from soils by certain plant species is of great interest, because this process, which is referred to... 

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