Products of Soil Microorganisms in Relation to Plant Growth

Abstract

A survey has been made of the range and activity of the organic products of soil microorganisms which have a direct influence on plant growth. Microbial metabolites which effect plants indirectly by the modification of the soil environment are also reviewed. The sources of substrates for the production of metabolites in soil and the farming practices which give rise to them are considered. It is stressed that an interdisciplinary approach is needed in the manipulation of microbiological activity in soil.

Microbial production of ethylene in desert soils

“…Ethylene production was stimulated by the addition of cereal straw (Goodlass and Smith, 1978;Wainwriqht and Kawlenko, 1977;Yashida and Suzuki, 1975), chitin and cellulose (Wainwriqht and Kowlenko, 1977) and finely around Bermuda arass residue (Hunt et al, 1980). Barley residues were found to be more effective than those of either cabbaqe or beans (Lynch, 1976). From these results we would expect our desert soils, which are usually low in orqanic matter content, to produce relatively low concentrations of C Z H 4 • e) Effect of orqanic amendments.…”

Systemic Resistance Induced by Rhizosphere Bacteria

“…Although SAR induction is not dependent on the development of a hypersensitive reaction (96), it is maximally expressed when the inducing pathogen causes necrosis (14). In contrast, inducing rhizobacteria typically do not cause any visible symptoms on the host, and commonly enhance plant growth (40,65). Steiner & Schönbeck (88) formulated criteria for the verification of SAR, to distinguish induced resistance from other mechanisms that can reduce disease incidence or severity.…”

“…Certain strains of rhizosphere bacteria are referred to as plant growth-promoting rhizobacteria (PGPR), because their application can stimulate growth and improve plant stand under stressful conditions (40,65). Increased plant productivity results in large part from the suppression of deleterious micro-organisms and soilborne pathogens by PGPR (84).…”

Effect of Local Concentrations of Acetic Acid Around Barley Roots on Seedling Growth

“…Volatile fatty acids, particularly acetic acid, can accumulate in soil containing plant residues (Patrick, 1971;Lynch, 1976Lynch, , 1977, and there is potential for these toxins to inhibit the germination and growth of seedlings (Lynch, 1980). The concentration of the acids produced in the soil varies depending partly on the distribution of the decaying residues (Lynch, Gunn and Panting, 1980) and therefore it is likely to vary along the root systems of seedlings.…”