Publisher Summary This chapter discusses the chemistry of submerged soils. The chemical changes in the submerged materials influence: (a) the character of the sediment or soil that forms, (b) the suitability of wet soils for crops, (c) the distribution of plant species around lakes and streams and in estuaries, deltas, and marine flood plains, (d) the quality and quantity of aquatic life, and (e) the capacity of lakes and seas to serve as sinks for terrestrial wastes. The single electrochemical property that serves to distinguish a submerged soil from a well-drained soil is its redox potential. The redox potential of a soil or sediment provides a quick, useful, semiquantitative measure of its oxidation–reduction status. Two recent developments have stimulated interest in the chemistry of submerged soils: the breeding of lowland rice varieties, with a high yield potential, and the pollution of streams, lakes, and seas, by domestic, agricultural, and industrial wastes. The chemistry of submerged soils is valuable: (a) in understanding the soil problems, limiting the performance of high-yielding rice varieties, and (b) in assessing the role of lake, estuarine, and ocean sediments as reservoirs of nutrients for aquatic plants and as sinks for terrestrial wastes.

The Chemistry of Submerged Soils

The soil organic matter (SOM) pool encompasses plant, animal, and microbial residues in all stages of decay and a diversity of heterogeneous organic substances intimately associated with inorganic soil components. The soil microbiota and fine roots may also be considered part of the SOM pool. The turnover of the different SOM components varies continuously due to the complex interaction of biological, chemical, and physical processes in soil. The complexity of SOM and its importance to soil fertility have challenged generations of soil scientists, and numerous studies, of which some date back more than two centuries (see historical review in Kononova, 1961), have covered a vast array of aspects of SOM.

Physical Fractionation of Soil and Organic Matter in Primary Particle Size and Density Separates

The processes of humification occur mainly under aerobic conditions. Animals that live in the soil may initially reduce the size of the fresh organic residues. Further transformations are promoted by the activity of the enzymes of bacteria and fungi living in the soil. Cellulose, proteins and fats are readily available carbon sources for the microorganisms, whereas such compounds as lignin and other phenolic plant constituents are decomposed more slowly. These, as well as some of the new substances that are formed through oxidation of phenolic units, are toxic to different degrees. They can therefore serve as carbon sources only for special species of microorganisms. Besides the organic residue derived from higher animals and plants, many substances synthesized by microorganisms can serve as carbon sources.

Chemical Composition and Physical Properties of Humic Substances

Publisher Summary This chapter discusses the factors and mechanisms governing the formation and destruction of water-stable soil aggregates. The formation and degradation of water-stable aggregates comprise a complex interrelationship of physical, biological, and chemical reactions. Agronomic systems exert pronounced effects on aggregation, but the interpretation of the controlling mechanisms in any system is complicated, by the diversity of factors, through which the effects are manifested. Aggregation, within the surface horizons of many soils, is predominantly a function of the microbiological production and decomposition of soil-binding materials. In the presence of a suitable energy source, diverse fungi, streptomycetes, and bacteria bind soil particles into water-stable aggregates. Cultivation improves aggregation when the soil moisture content falls, within a certain range, and when the soil is worked with a suitable implement. In addition to influencing the biotic and cultivation aspects of aggregation, climate-dependent environmental variables, such as moisture and temperature, play a direct role in the formation and destruction of soil aggregates.

Dynamics of Soil Aggregation

The adhesion of microorganisms to surfaces is influenced by long-range, short-range, and hydrodynamic forces. In the study of particle adhesion using well-defined, nonliving systems, long-range forces are adequately described by DLVO theory (due to Derjaguin and Landau, and Verwey and Overbeek), and hydrodynamic forces can be controlled. The quantitative description of short-range forces, however, remains a problem. In biological systems the application of DL VO theory as weIl as the quantitative description of short-range forces becomes difficult. Consequently, carefully designed experiments are required. The authors suggest that in order to advance the study of microbiaI adhesion, it is necessary for physical chemists and microbiologists to collaborate in a detailed study of adhesion in a weH characterized microbiological system. INTRODUCTION Any discussion of the physical chemistry of microbial adhesion is complicated by the nature of the particles and substrata concerned. Microorganisms are far from being "ideal" particles: they have neither a simple geometry, nor a simple, uniform molecular composition. They may be deformable, and internal chemical reactions can lead to changes in molecular composition both in the interior and at the surface of the bacteriaj indeed, molecules and ions may cross the interface. A further problem in applying physicochemical ideas in this area lies 22 P.R. Rutter and B. Vincent in identifying the nature of the strongly specific effects that frequently occur. Only certain microorganisms may adsorb on a given surface and then only under specific conditions, or at a specific stage in their growth. Clearly, the short-range interactions are very complex in biosystems. An even more fundamental problem concerns the legitimacy of applying thermodynamic principles to microbial adhesion. Considerations of whether the process of adhesion of a microorganism to a surface takes place under equilibrium conditions, and whether, after adhesion, the equilibrium state is aChieved, underlie the application of "DLVO-type theories" of particle/substratum interactions and the "wetting theories" of adhesion, as enunciated, for example, by Pethica (18). In practical terms, the establishment of the relevant equilibrium conditions requires detailed knowledge of the relative time scales over which the possible processes which could occur actually take place. Por example, the magnitude of the electrostatic interaction between a particle and a surface depends on whether the charges on the two surfaces are effectively "locked-in," or whether the surface charges can adapt (to maintain constant potential) on a time scale comparable to the time scale of the adhesion process i tself • Similarly, if, in a microorganism which becomes attached to a surface, further chemical processes occur in the interior or at the surface of the cell, then that microorganism cannot be in complete physicochemical equilibrium. Moreover, equilibrium may only be achieved in a (thermodynamically) closed system (i.e., where no exchange of matter or energy with the surroundings occurs); in an open system, which is the case for many biological systems, equilibrium may never be reached (although a temporary steady state condition may be realized). In these cases, the much more complex theory of nonequilibrium thermodynamics needs to be considered. How far, then, can physical chemists go in spanning the bridge ac ross to biological systems, in particular, in the case of microbial adhesion? In our opinion, there is tremendous insight to be gained from considerations of physicochemical phenomena at the qualitative, conceptual level, but caution is required in applying full, quantitative theories. Before even semiquantitative applications are possible, physical chemists would require the microbiologists to come halfway across the bridge to meet them, by working with as well-defined and as characterized systems as possible. This may even require, in the first instance, the modelling of Physicochemical Interactions of the Substratum 23 microorganisms as has been attempted recently, for example, by Imperial Chemical Industries (unpublished data). They h~ve managed to imitate the surface of bacteria used in the "Pruteen" process for protein production by grafting the extracellular pro tein extracts to the surface of polymer latex particles. Alternatively, physical chemists and microbiologists should collaborate on a detailed examination of a well-defined microbiological system. The adhesion of Escherichia coli to epithelial cells, for example, might prove to be suitable, although the final choice should emerge from discussion. The emphasis in this review, therefore, will be in stressing the nature of the physicochemical phenomena pertinent to microbial adhesion. We start with a review of the longand short-range interactions between particles and a macroscopic surface, first in the absence and then in the presence of macromolecules (adsorbed or in solution). We then consider particle adsorption isotherms and kinetics including the effects of shear. In some cases equations are given, but this is simply because this is frequently a useful way of summarizing a concept, rat her than expressing it in words. It is not necessarily implied that the equation is directly applicable in the biological context. INTERACTIONS BETWEEN CHARGED PARTICLES AND MACROSCOPIC BODIES One may discuss the net interaction between a charged particle and a macroscopic body in terms of the mutual force (fi) or free energy (Gi) as a fimction of separation (h) (23). The form of Gi(h) was originally formulated in the now classical DLVO theory, developed in the context of colloidal dispersions, the basic premise of which is that the total interaction between two particles is comprised of two additive terms: one (GA) due to the van der Waals forces, and one (GE) due to the overlap of the electrical double layer associated with charge groups present on the particle and macroscopic surfaces. The situation is schematically illustrated in Fig. 1. One approximate form for GA is (31): A 6 ( 2a(h + a) -ln (h + 2a)J h(h + 2a) h ~ where A is the net Hamaker coefficient for the system. 24 P.R. Rutter and B. Vincent

Microbial Adhesion and Aggregation

Oxidative Changes of Polyphenols as Influenced by Allophane1

“The union of mineral and organic matter to form the organo-mineral complex is a synthesis as vital to the continuance of life as, and less understood than, photosynthesis.”(JACKS) (1).

The nature of organic matter in soil organo-mineral complexes

In 1946 BREMNER et al(1) suggested a theory that, in soils, polyvalent metals are combined with organic matter as metal-organic matter complexes, and that these complexes are insoluble in solvents that do not themselves form complexes with metals The principle of one of the most prevailing methods for humus extraction, the neutral sodium pyrophosphate extraction proposed by BREMNER and LEES (2), is a corollary of the theory

https://www.tandfonline.com/doi/pdf/10.1080/00380768.1959.10430895

On the complex formation between soil humus and polyvalent cations

In an effort to work out a method for soil fertility evaluation and grading, principal component analysis was applied to 23 items of laboratory data for 41 Malayan paddy soil samples. As many of th...

A method of fertility evaluation for paddy soils: I. First approximation: Chemical potentiality grading

/pdf/title-major-soils-of-southeast-asia-and-the-classification-5gtj0m9mmf.pdf

Keizaburo Kawaguchi

Papers

Oxidative Changes of Polyphenols as Influenced by Allophane1

The nature of organic matter in soil organo-mineral complexes

On the complex formation between soil humus and polyvalent cations

A method of fertility evaluation for paddy soils: I. First approximation: Chemical potentiality grading

Title Major Soils of Southeast Asia and the Classification of Soils under Rice Cultivation: Paddy Soils