Physicochemical and biological processes affecting the recovery of exogenously applied ferulic acid from tropical forest soils

Ferulic acid (4-hydroxy-3-methoxycinnamic acid) is found in both plants and soils, and some evidence suggests its involvement in biochemical interactions between plants (allelopathy) and other organisms living in the soil. Knowledge of the processes affecting the concentrations of such potential allelochemicals in soil is essential if we are to understand their roles in the soil environment. It was the intent of this study to address the effects that soil physicochemical and biological processes have on the recovery of exogenously applied ferulic acid from tropical forest soils. Soil extractants used in this study are thought to recover potentially bioavailable concentrations of applied ferulic acid. Water and sodium acetate extractions of soil (immediately and after one and two days) were employed in the recovery of ferulic acid (added at a rate of 5.15 mmoles kg^–1) from steam-sterilized and non-sterilized forest soil materials. Sterilization of soil was used to isolate physicochemical effects from microbial effects on ferulic acid. Results indicate some sterilization treatment effects on the immediate recovery of ferulic acid. Physicochemical and biological processes of soils decreased the recovery of ferulic acid. The immediate recovery of ferulic acid from non-sterile soils is inversely related to the % organic carbon present in the soils. Certain soils have the ability to trap ferulic acid molecules for subsequent release into the soil-solution phase. Furthermore, results suggest that microbial degradation of ferulic acid may only occur in the solution (bulk) phase; ferulic acid molecules thought to be bound to soil surfaces appear to be protected from degradation.Use of trade names in this publication does not imply endorsement by the Organization for Tropical Studies, North Carolina State University or the Savannah River Ecology Laboratory of the products named nor criticism of similar ones not mentioned.     

Stimulation ofBradyrhizobium japonicum by allelochemicals from green plants

Yeast extract-mannitol broth supplemented with 3 mg.ml⁻¹ extract from aerial parts of plants was noculated withB. japonicum 3I1b110. Filter-sterilized water extracts of foxtail (Setaria viridis), lambsquarters (Chenopodium album), Johnsongrass (Sorghum halepense) and Pennsylvania smartweed (Polygonum pensylvanicum) stimulated growth of the bacterium by 3–4 times after 48 h incubation; however, similar extracts from several other plants were marginally stimulatory. Autoclaved water extracts and methanol (75%) extracts were less stimulatory than filter-sterilized water extracts. Autoclaved water extracts of nutsedge (Cyperus esculentus) and ragweed (Ambrosia psilostachya), and methanol extracts of smartweed, peat and ragweed depressed growth of the bacterium. Filter-sterilized water extracts from shoots of foxtail and lambsquarters increased growth of the bacterium linearly up to 6 mg.ml⁻¹. At that level growth in the presence of lambsquarters shoot extract was almost 20 times that of the control. Comparable growth stimulation by this extract was also found in four other strains ofB. japonicum. The water extracts from roots and stems of lambsquarters, and roots, shoots and inflorescences of foxtail at 3 mg.ml⁻¹ stimulated growth of the bacterium by more than 40 times the control.     

杂草间的他感作用及其在杂草生防中的应用

动、植物所产生的有机化合物,除了营养自身之外,还在很多方面影响着其它植物和动物的生长、健康、行为及种群生物学特征。很多人都熟悉由微生物如放线菌、细菌、真菌所产生的抗生素,它们影响着其他微生物的生长     

Effects of soil extracts from repeated plantation woodland of Chinese-fir on microbial activities and soil nitrogen mineralization dynamics

Effects of soil extracts from repeated plantation woodlands of Chinese-fir on soil fungi growth, the activities of microbial communities, and rates of net soil nitrogen mineralization were investigated. Soil extracts from replanted woodlands significantly inhibited soil non-pathogenic fungi growth, reduced soil respiration activities, and net soil nitrogen mineralization rates. However, soil extracts from replanted woodland increased the growth of pathogenic fungi. The combination of soil extracts and pathogenic fungi did not significantly reduce the growth of Chinese-fir seedlings when compared to the soil extracts alone. The combination of soil extracts with pathogenic and non-pathogenic fungi significantly increased the growth of Chinese-fir seedlings when compared to the combination of soil extracts and pathogenic fungi. The results suggest that the allelochemicals from soil extracts, rather than pathogenic fungi, are the key factor regulating the productivity and nitrogen cycling in repeated plantation woodlands.     

Phytotoxic potential of soils and wheat straw in rice rotation cropping systems of subtropical Taiwan

Using a wheat seed bio assay, the phytotoxicity of extracts obtained from wheat and rice rhizosphere soils was determined. The wheat rhizosphere soil extract was found to show phytotoxic effects. More allelopathic materials were found from the wheat-rice rotation soils than from the rice soil. Extracts obtained under basic conditions (pH 8) were found to be more inhibitory than those obtained by acid extraction (pH 5). Wheat straw was found also to contain phytotoxic substances. A comparison of two methods in concentrating the aqueous extracts, rotary evaporation and lyophilization, indicates that the former contained more substances with phytotoxic effects.     

Biological activity and chemical isolation of root saponins of six cultivars of alfalfa (Medicago sativa L.)

Wheat, cheat and Trichoderma viride bioassays were used to establish the relationship between the content of biologically active saponins in the roots and the degree of winter dormancy and/or time of six cultivars of alfalfa over the period January to August, 1988. Wheat and cheat bioassay results indicated no significant difforences among cultivars, whereas T. viride was inhibited most by extracts of roots collected during months with high rainfall and rapid growth. Cheast seedling roots were inhibited 8–10% more than those of wheat seedling roots indicating that alfalfa root saponins were more effective as allelopathic compounds in preventing growth of cheat than that of wheat alone. An average of 14 different saponins per cultivar were separated by thin-layer chromatograms. Saponins, and the aglycones produced by acid hydrolysis of the May samples, were separated by thin-layer chromatography. The conclusion is that the amount, structure, and type of saponins present in alfalfa roots vary with time.     

Population Dynamics of Criconemoides simile on Soybean

Custer and Hood soybean cultivars were inoculated with nine levels of Criconemoides simile ranging from 300 to 20,600 nematodes per plant. Rate of reproduction decreased as inoculum level was increased beyond 900-2,000 nematodes. Final population density was influenced by both composition and level of inoculum. There was an indication that substance(s). inhibitory to larvae, accumnlated in soil in which Hood was grown for 11 months, Significant reduction of fresh weight of roots of Hood, but not Custer, occurred at population densities of 37,000 and 44,700 nematodes per plant.     

3种天然二萜的化感作用及机制的研究

以黑麦草（Lolium perenne L.）和莴苣（Lacutuca sativa L.）为受试植物,研究了3种对映—贝壳杉烷二萜wangzaozin A、leukamenin E和weisiensin B对受试植物种子萌发、幼苗生长、叶绿素和膜损伤的影响,旨在评估3种二萜的化感作用潜能。结果显示：不同浓度的3种二萜对黑麦草和莴苣种子的萌发稍有降低,但明显延迟种子萌发时间;较高浓度下,3种二萜对黑麦草和莴苣幼苗的根长、苗长、鲜质量和干质量均有显著的抑制作用,并显示了浓度依赖性;同时,3种二萜显著降低黑麦草和莴苣幼苗叶片叶绿素a和叶绿素b含量,显著升高丙二醛（MDA）含量和相对电导率,而相对含水量呈下降趋势。上述结果表明,3种二萜通过影响受试植物的光合作用能力,引起细胞膜氧化损伤,导致叶片保水性降低,抑制受试植物幼苗的生长。