Allelopathic Potential of Polygonum orientale L. in Relation to Germination and Seedling Growth of Weeds

The Effect of Leaf Litter on Early Seedling Establishment in a Tropical Forest

Abstract: The presence of leaf litter of different depths within a tropical forest creates many different microsites for plant establishment. The amount and distribution of leaf litter within a forest can influence patterns of plant establishment. In this study, we de- termined the spatial variability in leaf litter in the forest understory, and investigated how different litter depths (bare, 1, 6, and 12 cm) affected the establishment of several tropical tree species in both growth house (sun and shade) and field (gap and understory) experiments in the semideciduous tropical forest of Barro Colorado Island, Panama. The tree species used in this study (Aspidospermum cruenta, Ceiba pentandra, Cordia alliodora, Gustavia superba, Luehea seemannii, Ochroma pyrimidale) were chosen to represent a range of seed masses and a gradient in the light requirement for establishment of the species. The spatial distribution of leaf litter was not correlated between adjacent sampling points within the forest understory, suggesting that the establishment environment for seedlings, with respect to litter, is highly variable at scales of 1-20 m. The presence of litter affected five of the six species, but the nature and the magnitude of the effect were species specific. The smaller seeded shade-intolerant species had fewer seedlings establishing under leaf litter than on bare ground. The species ranged from strongly negatively affected (Luehea) to moderately negatively affected (Cordia, Ochroma) to affected only by extreme amounts of litter (Ceiba). The presence of litter influenced Gustavia, one of the larger seeded shade-tolerant species, but did not affect Aspidospermum, the other larger seeded species. The effect of litter on Gustavia depended on the light environment. Gustavia had more seedlings establishing under litter in the sun, but the presence of litter had no effect in the shade. Differences among the smaller seeded shade-intolerant species in the amount they were negatively influenced by litter were not correlated with seed mass. Data from our field study were consistent with our growth house results for the shade- intolerant species. Additional data from the field study indicated that these species with similar habitat requirements differed in the developmental stage at which they were affected by the presence of litter. Luehea had fewer seeds germinating under litter while the other two species, Ochroma and Cordia, were affected only after germination. Interspecific comparisons done for each light level and litter depth indicated that the presence of litter caused reversals in the relative ranking of species success. For example, Gustavia preferentially established under relatively deep litter depths in the sun where Luehea could not establish. In conclusion, the presence of litter can potentially increase seedling diversity within the forest by creating heterogeneity in the establishment envi- ronment and by causing reversals in species' rankings.

Weed allelopathy, its ecological impacts and future prospects: a review

Abstract: Summary The importance, characteristics, positive and negative impacts, and future role of weeds as an integral part of the natural and agroecosystems are evaluated and discussed. Interference between plants in nature and the importance of differentiating between competition and allelopathy are interpreted. Allelopathy as one component of weed/crop interference, allelochemicals from weed species and their possible mechanism of action are listed and discussed. Weed species with inhibitory action against cultivated crops, other weed species, and plant pathogens, as well as self-inhibitory (autopathic) species are reviewed. Stimulatory or inhibitory allelopathic effects of different crop plants, trapping and catching species, and the potential of allelopathic weeds in inhibiting or stimulating certain parasitic weed species are discussed and evaluated. Allelopathy as a mechanism and future strategy for agricultural pest control and farm management and the potential use and development of some allelochemicals...

The Excretory Function of Higher Plants

Abstract: 1 Cellular Aspects of Secretory Activity in Plants.- 1.1 Significance of Secretory Processes for the Cell.- 1.2 Compartmentation of Metabolites and Mechanisms of Their Secretion.- 1.3 Secretion into the Free Space of the Cell.- 1.4 Secretion into the Vacuole.- 1.5 Idioblasts.- 2 Intratissular Secretion.- 2.1 Air-Bearing System of Plants.- 2.2 Internal Gases.- 2.2.1 Carbon Dioxide.- 2.2.2 Ethylene.- 2.2.3 Other Volatile Compounds.- 2.2.4 Transport of Internal Gases.- 2.3 Intratissular Secretory Structures.- 2.3.1 Secretion of Resins.- 2.3.2 Secretion of Latex.- 2.3.3 Secretion of Gum and Essential Oils.- 3 External Secretion.- 3.1 Guttation.- 3.2 Salt Glands and Secretion of Inorganic Salts.- 3.3 Secretion of Nectar.- 3.4 Secretion of Polysaccharides.- 3.5 Secretion of Proteins.- 3.6 Secretion of Essential Oils.- 3.7 Secretion of Resins.- 3.8 Secretion of Phenols.- 3.9 Secretion of Alkaloids.- 3.10 Secretion of Acetylcholine and Amines by Stinging Trichomes.- 4 Gas Excretion.- 4.1 The Pathways of Gas Release.- 4.2 Volatile Excretions as Complexes of Substances.- 4.3 Components of Gaseous Excreta.- 4.3.1 Short-Chain Hydrocarbons.- 4.3.2 Isoprene and Terpenoids.- 4.3.3 Aldehydes and Ketones.- 4.3.4 Low-Molecular Alcohols.- 4.3.5 Volatile Nitrogen-Containing Substances.- 4.3.6 Carbon Monoxide and Hydrogen.- 4.4 The Significance of Gas Excretion.- 5 Leaching.- 5.1 The Cell Wall as a Phase of Leaching.- 5.2 Leaching of Salts.- 5.3 Leaching of Organic Compounds.- 5.4 Dependence of Leaching on External Factors, Phase of Development, and Anatomy of Plants.- 5.5 Physiological Meaning of Leaching.- 6 The Elimination of Substances in Response to Extreme Factors.- 6.1 Injuries to Membranes Under Stresses.- 6.2 Metabolites Released Under Stress.- 6.2.1 Ethylene.- 6.2.2 Ethane and Other Simple Hydrocarbons.- 6.2.3 Terpenoids.- 6.2.4 Alcohols.- 6.2.5 Aldehydes and Ketones.- 6.2.6 Hydrogen Cyanide.- 6.2.7 Phenols.- 6.2.8 Alkaloids.- 6.2.9 Polyacetylenes, Thiophenes, and Traumatic Acids.- 6.2.10 Other Nitrogen- and Sulfur-Containing Compounds.- 6.2.11 Phytoalexins.- 7 Biological Effects of Plant Excreta.- 7.1 Growth Processes and Cell Destruction.- 7.1.1 Division and Elongation of Cells.- 7.1.2 Pollen Germination.- 7.1.3 Destructive Changes in Cells.- 7.2 Cellular Membranes as Targets for Action of Plant Excreta.- 7.3 Energetic Reactions.- 7.4 Metabolic Processes.- 7.5 Problems and Perspectives in the Use of Plant Excreta.- 7.5.1 Plant Resistance to Pathogens.- 7.5.2 Chemical Interactions: Plant-Insect and Plant-Plant..- 7.5.3 Use in Medicine.- Conclusion.- References.- Index of Latin Names.

Effect of pine allelochemicals on selected species in Korea

Abstract: The allelopathic potential of red pine (Pinus densiflora), pitch pine (Pinus rigida) and black pine (Pinus thunbergii) has attracted attention of Korean botanists for the last several years. It has been a point of interest why the understorey species are sparse (Lee and Monsi, 1963) and species growing there were similar with the other pine understoreys. It was hypothesized that the similarity of floristic composition of pine stands was caused by some regulating mechanism controlled by pine through the release of certain toxic substances (allelochemicals) in the soil. When the greenhouse soil was mixed with pine leaves, the growth of the plants was suppressed. However, the toxicity of the soil was gradually reduced, and ultimately diminished after several years. This further strengthened the idea of the possible release of allelochemicals by pine. Therefore, it deemed necessary to verify experimentally whether pine is indeed producing allelochemicals which, in turn, affect neighbouring plants. For this, several experiments were performed involving various species growing inside and outside the pine forests. The results obtained from various laboratory and field studies with respect to the allelopathic effects of pine and details of isolation of allelochemicals from pine materials are reported here.

Factors affecting the dominance of Silybum marianum L. (Asteraceae) in its specific habitats.

Abstract: Summary The annual Mediterranean thistle Silybum marianum L. is a synanthropic plant (i.e. related to human habitats) common in Israel. It dominates waste places and ants’ nests, and is disseminated by wind and ants. The purpose of this study has been to find out some of the possible factors during the plant’s life cycle, which may affect its dominance in its specific habitats. Our results show that: (1) There is no obvious allelopathic effect of S. marianum on the germination of other plants; (2) Its germinability is relatively high and not affected by removal of the elaiosome; (3) Thistle plants around the nests and in waste places are fast growing, have significantly higher biomass and more and larger heads than thistles in surrounding herbaceous habitats; (4) Where the thistles were removed, total number of companion species and their biomass have increased. The success of S. marianum may be primarily due to its aggressive vegetative growth, causing depression of adjacent species. Its seed production, achene dispersal modes, and germinability partly enhance its dominance. Ants’ nests probably had been the primary habitats from which ruderal (nitrophilous) species, such as S. marianum, have invaded special man-made habitats.

Liberation of organic substances from higher plants and their role in the soil sickness problem.

Abstract: Introduction ................................................................................................................................................................. 394 Liberation of Organic Substances from Higher Plants ............................................ 396 Root Excretions ................................................................................................................................................. 396 Excretions from Intact Roots ....................................................................................................... 396 Amino Acids ............................................................................................................................................. 396 Sugars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 396 Scopoletin and Scopoletin Glycoside . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 Trans-Cinnamic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Synthetic Growth Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 Enzymes .......................................................................................................................................................... 400 Excretions from Excised Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 Supplement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 Liberation of Organic Compounds from Seeds and Fruits ............................ 401 Amino Acids and Sugars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 Flavones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 Phenolic Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403 Gaseous Excretions (Ethylene, Ammonia, Hydrocyanic Acid)... 403 Liberation of Organic Compounds from Plant Residues ..................................... 403 Phenolic Compounds ......................................................................................................................... 404 3-Acetyl-6-methoxybenzaldehyde .......................................................................................... 404 Amino Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 Amygdalin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 Phlorizin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 Supplement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407 Excretions from Leaves ............................................................................................................................. 408 Absinthin .................................................................................................................................................... 408 Amino Acids ............................................................................................................................................ 409 Juglone (5-Hydroxy1,4-naphthoquinone) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 The Role of Excreted Organic Compounds in the Interaction of Higher Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 410 The Possibility of Direct Action of Excreted Compounds upon other Plants ....................................................................................................................................................................... 410 Microbial Deeompositlon of Compounds Excreted by Higher Plants to Phytotoxic Substances .............................................................................................................................. 412 Influence of the Microbial Balance in Soil by Excreted Compounds... 412 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413 Literature Cited .................................................................................................................................................... 414-

The role of toxic substances in the interactions of higher plants.

Abstract: That toxic substances may be given out to soil by higher plants and that these substances may affect the growth of the same or other species is a theory which while old is not yet generally accepted. DeCandolle (8) noted that certain species appeared to be specifically inhibitory to the growth of associated species, as, for example, Euphorbia versus flax and thistles versus oats. On the basis of these observations deCandolle developed a theory of crop rotation embodying the general idea that each member in a rotation should be a species not inhibited in its growth by toxic substances left from the preceding crop. Liebig (15), while he originally supported the theory of deCandolle-, later and as a result of his exhaustive analyses on the depletion of soil minerals by crops, came to the conclusion that not only the amounts but the balances between inorganic materials in the soil are of importance in the growth of plants. On this basis he ultimately discounted the notion that toxic substances may be of importance in regulating crop yields. From the time of Liebig until the present day, plant growth interactions have been almost unanimously interpreted in terms of mineral nutrition effects, or more recently in terms of water competition. The interest in toxic secretions of plants arose in part from a consideration of so-called soil sickness due to one-crop agriculture. Thus it was frequently observed in early experiments that as a piece of ground was continuously cropped to one plant the yields decreased and that these decreases could not be made up by additional fertilizer. Besides the injurious after-effects or yieldlowering effects of one-crop agriculture, several cases of harmful interaction between plants grown adjacent to each other in a field, or of one crop on a succeeding crop, were also recorded. Thus effects of grass on fruit trees, of walnut trees on other plants, of corn, rye, thistles, turnips, sesame, rutabaga and others, were ob-

Implications of allelopathy in agricultural plant science

Abstract: Substances potentially involved in allelopathy are liberated from plants by (a) leaching of foliage by rain, (b) abscission and litter fall, (c) volatilization from foliage, and (d) root exudation. Substances, including metabolites such as mineral nutrients, carbohydrates, amino and organic acids, and growth regulators, can be leached from a wide variety of plants by rain and dew, and the quantity and quality of losses are affected by a great number of both external and internal factors. Materials leached from one plant may have an influence upon the development of the same or other adjacent plants. Plant/plant chemical interactions have been well recognized in commercial agriculture and, in fact, form the basis of many common agricultural practices. They are currently being utilized in modern plant science in the development of bioassay systems for detecting growth regulators, the use of rootstocks to influence the growth and development of scions, in detection and eradication of diseases, and in fruit storage and ripening.