Roots and Soil

It is not only those parts of a plant exposed to the air that can emit VOCs. The roots of plants and trees are also known to exchange VOCs with the surrounding soil. However, only a limited number of PTR-MS studies on this topic have so far been reported in the research literature. Two such studies, which were reported by Pegoraro et al, have been briefly described previously in the section dealing with isoprene emissions (see Section 5.7.1) [216,217]. 

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One of the most important functions of the pedosphere is the cycling of elements that occurs within soils and the transfers that occur between the atmosphere, lithosphere, biosphere, and hydrosphere through soils. Soil is an interface between the atmosphere and lithosphere, between the biosphere and lithosphere, and between roots and soil organisms and the atmosphere. In many ways, soil acts as a membrane" covering the continents and regulating the flow of elements between these other systems of the Earth. 

It is sometimes claimed that mucilage and similar gels may help to maintain hydraulic conductivity between root and. soil (52). However, the hydraulic conductivity of soils is often substantially decreased when soils are irrigated with waste water. Apart from the inducement of sodicity, which is real in many cases, the decreases in hydraulic conductivity are attributed largely to the production of microbial biomass, particularly extracellular polysaccharides (e.g.. Ref. 53). These extracellular polysaccharides form gels that may store large quantities of water and allow water and ions to diffu.se through them at rates not much less than those of free water, but they could be expected to restrict mass flow of water and thus nutrients, to roots (54). 

A. D. Rovira, Interactions between plant roots and soil microorganisms. Annual Review of Microbiology /9 24l (1965). 

J. A. Palta and P. J. Gregory. Drought affects the fluxes of carbon to roots and soil in C pulse-labelled plants of wheat. Soil Biol. Biochem. 29 1395 (1997). 

Vanillin occurs in the roots of many species and in the soil surrounding the growing plants, but at low pH it remains tightly bound in both roots and soils (15, 17). The analogous acid, vanillic, appears to be much more biologically active ( 18, 2 ), and no further studies of vanillin are planned at this time. 

Goss MJ, Kay BD (2005) Soil aggregation. In Zobel RW, Wright SF (eds) Roots and soil management interactions between roots and the soil. ASA, CSSA, and SSSA, Madison WI, USA, pp 163-180... 

Hanson PJ, Edwards NT, Garten CT, Andrews JA (2000) Separating root and soil microbial contributions to soil respiration a review of methods and observations. Biogeochem 48 115-146... 

It is reasonable to assume the effect of plant roots and tops on the soil would be the same. However, this is not the case. Plant roots profoundly affect the chemical characteristics of soil. Because they are in intimate contact with the soil, roots are constantly extracting nutrients and water from the soil and exuding materials into it. The intimate relationship, which includes physical, microbiological, biochemical, bioorganic, and chemical interactions between roots and soil, is illustrated in Figure 4.3. 

Figure 4.3. Plant roots with adhering soil illustrating the interaction between plant roots and soil.

Further transformations of N take place at the oxic interfaces between the soil and floodwater and root and soil where NH4+ diffusing in from the neighbouring anoxic soil may be nitrified to NOs. Subsequently, NOs diffusing out into the anoxic soil may be denitrified to N2. This process results in significant losses of N from wet soils but its importance in submerged soils is unclear (Section 5.3). 

Residual action moderate mobility and ready availability to roots and soil-borne organisms lo - lo 0.5 - 20... 

The major amount of radioactive material (70%) was fpund in leaves, 7.8% in roots and soil and 6% as COo. Bligh-Dyer extraction of the leaves gave 49.6%... 

Mathesius, U., Conservation and divergence of signalling pathways between roots and soil microbes — the Rhizobium-legame symbiosis compared to the development of lateral roots, mycor-rhizal interactions and nematode-induced galls. Plant Soil, 255, 105, 2003. 

Pease, D. S., and Anderson, J. U. (1969). Opal phytoliths in Bouteloua eriopoda Torr. roots and soils. Soil Sci. Soc. Am. Proc. 33,321-322. 

Soil solute movement is an extremely important phenomenon because it ensures the transfer of nutrients within the soil, thus making them available to plant roots and soil organisms. Unfortunately, solute movement may be undesirable at times because it may involve contaminants. 

Bhupinderpal-Singh, Nordgren, A., Ottoson-Lofvenius, M. et al. (2003). Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest extending observations beyond the first year. Plant, Cell and Environment, 26, 1287-96. 

Measurements of soil CO2 concentrations versus depth commonly reveal an increase in CO2 content with depth. The profiles and the maximum CO2 levels found at a given depth are climatically controlled (Amundson and Davidson, 1990) due to rates of C inputs from plants, decomposition rates, etc. Given that most plant roots and soil C are concentrated near the surface, the production rates of CO2 would be expected to decline with depth. Cerling developed a pro-duction/diffusion model to describe steady-state soil CO2 concentrations ... 

Decomposition is essentially a microbial process whose rate is regulated by a suite of physical and biological controls. At the microscopic level, many of the biochemical details of microbial degradation of specific carbon and nitrogen compounds have been well documented. However, beyond this scale, most of our understanding of decomposition becomes empirical in nature. As we have highlighted in this review, there exists a wealth of data on the decomposition of plant litter while root and soil OM have received significantly... 

Pierret, A., Moran, C. J., and Pankhurst, C. E. (1999). Differentiation of soil properties related to the spatial association of wheat roots and soil macropores. Plant Soil 211, 51-58. 

Soil chemistry centers around the soil solution, the aqueous solution that reacts with, and is between, the solid phase and roots and soil microbes. A solution is defined as a mixture and usually means an aqueous solution—a mixture of solutes and water. Soil and rock minerals can be considered solid solutions, because they contain foreign ions that are mixed into the mineral s structure. Soil chemistry involves both aqueous and solid solutions. This chapter presents the chemistry of ions reacting with H+, OH-, 02 , and H2O in the soil solution and soil minerals. 

In actual "damage to forest" ("acid rain"- probiems) investigations, the main matrices which must be anaiyzed are needles, leaves, pieces of wood, roots and soil. The elements Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, Sr, Ti, V, and Zn can be determined routinely in such samples by ICP/DCP-spectrometry (Table 9). The concentrations of the heavy metals Cd, Pb, Hg, As and others are in most cases too low (exception soil, for these analytical techniques). A similar picture can be obtained for the field of bioindicators for environmental influences (plants, animals, organs of man) (Schramel et al., 1984 Wolf et al., 1984) (Table 10). In case of soils and sludges, in most the samples one can obtain all relevant elements, such as the legally regulated heavy metals Cd, Pb, Zn, Cu, Ni, and Cr (Table 11,12) (Schramel et al., 1982). 

In the sampled species, the translocation of antimony from the roots to the epigeal parts appears not to be affected by the Sb levels in the roots and soils. The correlations... 

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