Elroy L. Rice

Allelopathy—An update

SummaryThe latest previous comprehensive review of allelopathy (Rice, 1974) covered research done primarily prior to 1973. There have been numerous reviews published in recent years on specific phases of allelopathy (see III), but most of them covered research results published primarily through 1972 also. This review has been restricted, therefore, largely to research conducted subsequent to 1972, except for background information and significant papers overlooked in previous reviews.There has been almost an exponential increase in the rate of publication of papers concerned with allelopathy. Research has been particularly active in relation to the roles of allelopathy in agriculture, forestry, phytopathology, patterning of vegetation, algal succession, and old-field succession. Our increasing knowledge of the conditions under which certain crop residues cause allelopathic effects to subsequent crops should enable us soon to guard against such effects. We are on the threshold of breeding crop plants that will inhibit the chief weeds in a given area through allelopathic action, and thus decrease the need for synthetic weed killers. Our understanding of allelopathic interactions of various plant species has already been used advantageously in reforestation, and future developments are very encouraging. Our increasing knowledge of allelopathy is aiding greatly in our understanding of many ecological phenomena, such as succession and patterning of vegetation.Evidence is mounting that inhibition of nitrification increases as succession progresses toward the climax vegetation, at least in many vegetation types. This leads to a decrease in the loss of nitrogen. Addition of inhibitors to arable lands to prevent nitrification has proved to be valuable in preventing loss of nitrogen and in increasing crop yields.There has been a rapid advance in our knowledge of mechanisms of action of known allelopathic compounds, at increasingly more fundamental levels. We have known for several years, for example, that some of these compounds inhibit uptake of various minerals, but have not known the mechanism of the action. Recent research indicates this may be due, at least in part, to inhibition of a plasma membrane ATPase that is involved with ion absorption. A thorough knowledge of mechanisms of action of allelochemics is essential to our overall understanding and appreciation of the field of allelopathy.RésuméLa revue la plus complète et la dernière en date sur l’allélopathie (Rice, 1974) a couvert principalement la recherche faite avant 1973. Nombres de revues ont été publiées dans les dernières années sur des phases spécifiques d’allélopathie, mais la plupart ont couvert les résultats de la recherche publiés jusqu’en 1972. Par conséquent, cette revue est restreinte à la recherche dirigée après 1972 excepté en ce qui concerne certains renseignements et des publications importantes qui ont été négligés dans les revues antérieures.Il y a une ugmentation exponentielle dans le nombre de publications concernant l’allélopathie. La recherche a été particulièrement active sur les rôles de l’allélopathie en agriculture, foresterie, Phytopathologie, dans la distribution de la végétation, dans la succession d’algues et dans la succession d’anciens champs. La connaissance croissante des conditions sous lesquelles certains résidus des récoltes causent des effets allélopathiques sur les récoltes suivantes devrait bientôt nous permettre d’empêcher ces effets. On commence à pouvoir éléver des plantes qui empêcheront les mauvaises herbes de pousser dans une region donnée par l’action allélopathique, ce qui par conséquent diminuera l’utilisation d’herbicides synthétiques. On a déjà avantageusement utilisé les connaissances acquises sur les interactions allélopathiques de diverses espèces de plantes dans la reforestation et les développments futurs sont tres encourageants. Notre connaissance croissante d’allélopathie nous aide énormément à comprendre beaucoup de phénomènes écologiques, comme la succession et al distribution de la végétation.Il devient évident que l’inhibition de nitrification augmente à mesure que la succession avance vers le climax, du moins dans beaucoup de types de végétation. Cela produit une diminution de perte de nitrogène. L’addition d’inhibiteurs aux terres arables pour empêcher la nitrification s’est révélée un procédé valable pour empêcher la perte de nitrogène et augmenter le rendement des récoltes.Il y a eu une avance rapide dans le domaine des connaissances des méchanismes d’action des composés allélopathiques connus, à des niveaux plus fondamentaux. Par exemple, nous savons depuis plusieurs années que quelques-uns de ces composés inhibitent l’absorption de divers minéraux mais nous ne connaissons pas le méchanisme de l’action. La recherche récente indique que cela est peut-être dû, du moins en partie, à l’inhibition d’une membrane de plasma ATPase qui a à faire avec l’absorption d’ion. Une connaissance complète des méchanismes d’action des allélochimiques est essentielle à notre compréhension et appréciation du domaine de l’allélopathie.

Inhibition of Nitrogen‐Fixing and Nitrifying Bacteria by Seed Plants (I.)

In a previous study of 20 species of seed plants which are of some importance in succession in abandoned fields in Oklahoma, Euphorbia corollata L. was included among 16 species which were found to exert inhibitory activity against selected nitrogen-fixing and nitrifying bacteria (Rice 1964). The goals of the present project were to determine if two other common species of Ewphorbia (E. marginata Pursh and E. suptna Raf.) produce inhibitors of the same bacteria and, if so, to determine the relative inhibitory activities of the three species.

Plant inhibition by Johnson grass and its possible significance in old-field succession

Sorghum halepense L. is sometimes an important species in the early stages of old-field succession, occurring in almost pure stands for a protracted period. The present project was undertaken to obtain evidence concerning the ability of Johnson grass to inhibit certain species of plants with which is is associated in abandoned fields. Seed germination and seedling growth of most species of plants chosen for investigation were inhibited by leaf or rhizome extracts, decaying leaves or rhizomes, and exudates from roots and rhizomes, with the exception of Aristida oligantha Michx. which was inhibited in only a few instances and then mostly slightly. Chlorogenic acid, p-coumaric acid, and p-hydroxybenzaldehyde were the main plant inhibitors present in the leaf and rhizome extracts, p-Hydroxybenzaldehyde was present in the extracts at all sampling periods, chlorogenic acid was more pronounced in the leaf extracts, and p-coumaric acid was present only during the early months of the growing season. Dhurrin, a cyanogenic glucoside of p-hydroxybenzaldehyde, was found to be prominent in the rhizomes and probably serves as a source of p-hydroxybenzaldehyde.

Microbial decomposition of ferulic acid in soil

The suppression of plant growth by different phenolic acids is well known. This work was designed to determine if ferulic acid, a known phenolic inhibitor of plant growth, accumulates in the soil and if soil microorganisms could be isolated that metabolize it. Over 99% of the extractable ferulic acid was lost from decaying hackberry leaves in 300 days. During this time the amount in the top 15 cm of soil remained fairly constant at about 30 ppm, except for the March sample which was significantly higher than the rest. Addition of ferulic acid to soil caused an increase in CO2 evolution and in numbers of a select group of microorganisms.Rhodotorula rubra andCepnalosporium curtipes, which actively metabolize ferulic acid, were isolated, but the metabolic pathways employed appear to be different from the reported one. The reported pathway for ferulic acid breakdown is ferulic acid to vanillic acid to protocatechuic acid to β-keto-adipic acid.Rhodotorula Rubra was found to convert ferulic acid to vanillic acid, but no evidence was found for utilization of the rest of the pathway.Cephalosporium curtipes appears to use a different pathway or to metabolize intermediate compounds rapidly without accumulating them, because no phenolic compounds were found during the breakdown of ferulic acid. The presence in the soil of microorganisms that metabolize ferulic acid and other phenolic acids is ecologically significant because such organisms prevent long-term accumulations of these substances, which are toxic to many other microorganisms and higher plants.

Diversity in Tree Species in Oklahoma Upland Forests

Tree—species diversity was measured in 61 Oklahoma upland forest stands. Most stands were dominated by Quercus stellata and Quercus marilandica, but the stands with the greatest diversity were those dominated by other species. There was an inverse relation of dominance concentration (Simpson and McNaughton indexes) to species diversity and the Shannon—Wiener index. The Shannon—Wiener index was positively related to stand basal area and inversely related to stand density. Diversity decreased and concentration of dominance increased along the precipitation gradient from seat to west. Species diversity of Oklahoma forests is generally low to medium compared to southern Appalachian forests. See full-text article at JSTOR

Allelopathy — An Overview

Theophrastusl about 300 BC stated that chick pea (Cicer arietinum) does not reinvigorate the ground as other related plants (legumes) do but “exhausts” it instead. He pointed out also that chick pea destroys weeds.

Inhibition of Nitrogen-Fixing and Nitrifying Bacteria by Seed Plants: VI. Inhibitors from Euphorbia supina.

Euphorbia suinna occurs in the pioneer weed stage of succession in abandoned fields in several midwestern states of the United States. It was previously found to be very inhibitory to several test strains of nitrogen-fixing and nitrifying bacteria and to several associated seed plants. The present project was concerned wilh the identification of the chief inhibitors produced by that species, using appropriate column and paper chromatographic techniques, and by tests of bacterial inhibition employing the diffusion technique on solid media. Three hydrolyzable tannins were consistently isolated from extracts of the species. All three tannins and purified reagent tannic acid from at least two commercial sources yielded ellagic acid, gallic acid, and glucose on hydroljsis by acid or tannase. All yielded one or more additional phenolics which were not identified. The tannins from E. supina were all slightly different from each other and from commercial reagent tannic acid as indicated by different Rfs on paper, elution sequence from polyamide columns, and relative amounts of glucose, ellagic acid and gallic acid produced on hydrolysis.

Allelopathic effects ofPolygonum aviculare L. : III. Isolation, characterization, and biological activities of phytotoxins other than phenols.

We previously reported thatPolygonum aviculare has a strong allelopathic action againstCynodon dactylon (L.) Pers. and other test species. Moreover, we found that several phenolic compounds appeared to be important allelochemics in this activity. We have now isolated other potential inhibitors fromP. aviculare residues and soil underPolygonum stands, and none of these occurred in soil underC. dactylon stands. GC-MS analysis revealed that these additional inhibitors are long-chain fatty acids with 14–22 carbons. Nine were identified inP. aviculare residues and seven in soil underP. aviculare. Sodium salts of all the identified fatty acids inhibited seedling growth ofC. dactylon and at least some test strains of the nitrogen-fixing bacteria,Azotobacter andRhizobium.

Allelochemistry in marine macroalgae

Allelochemistry refers to the effect of an organic compound released from one organism upon an organism separated from its source. When the donor and receptor are plants (or microorganisms placed in the plant kingdom), allelopathy is described whether the effect is harmful or beneficial. In the aquatic environment, water disperses any water‐soluble allelochemical from its point of release, and rapid dilution along with lack of contact between competing organisms reduces potential encounter. This review centers on macroalgae as the source of allelochemicals. In all examples, the releasor organism is a macroalga, but receptor organisms include algae, invertebrates, fish, and microbes. Direct evidence in the sea is scanty, and there is a need for appropriate experiments in the laboratory and field. The compounds that are released by macrolagae (e.g., polyphenolics, halogenated phenols, and terpenoids) may be fortuitous byproducts of metabolism. But where they alter colonization, growth, or reproduction in a ...

Allelopathic effects ofPolygonum aviculare L. I. Vegetational patterning

Polygonum aviculare was observed to spread rapidly into heavy stands ofCynodon dactylon (L.) Pers. resulting in death of the latter. This indicated a strong interference againstCynodon dactylon. Measurements of selected soil minerals and physical factors indicated that competition was probably not the chief cause of that interference. Soil collected under deadPolygonum was very inhibitory to all test species exceptSporobolus pyramidatus (Lam.) Hitchc., suggesting the presence of inhibitory compounds. Tops and roots ofPolygonum, root exudates, and leachate of the tops inhibited seed germination and seedling growth of most test species. Therefore, allelopathy apeared to be the dominant component of the interference, with competition probably accentuating its effects.Polygonum aviculare was inhibitory toGossypium barbadense L. andSorghum bicolor (L.) Moench, indicating that allelopathy is an important component of the interference byPolygonum against crop yields.