Selected Ectomycorrhizal Fungi of Black Spruce (Picea mariana) can Detoxify Phenolic Compounds of Kalmia angustifolia

Allelopathy has been implicated as a factor contributing toward failure of black spruce (Picea mariana) regeneration in Kalmia angustifolia-dominated sites in eastern Canada. Several phenolic acids of Kalmia origin inhibit primary root growth of black spruce. We tested the hypothesis that some well-adapted conifer ectomycorrhizae can degrade and detoxify water-soluble phenolic compounds produced by Kalmia and use the degraded products as a carbon source to stimulate growth. We found that hyphal growth of Paxillus involutus, a common ectomycorrhizal fungus of black spruce, was stimulated by water leachates of Kalmia leaf and litter. An equimolar mixture of three phenolic acids (ferulic, o-coumaric, and o-hydroxyphenylacetic acid), commonly found in Kalmia, had no negative effects on fungal growth at 1 mM concentration. The o-hydroxyphenylacetic (o-HPA) acid, which is known to be toxic to black spruce, was found to stimulate the growth of Laccaria laccata, L. bicolor, and P. involutus (isolates 211804 and 196554) by 38.4, 29.3, 25.0, and 18.9%, respectively, at 1 mM. Pure ferulic, o-coumaric, and o-HPA acids were degraded by 100, 98, and 79.5%, respectively, within 10 d in the presence of P. involutus 211804. However, L. laccata could not tolerate high concentrations of the Kalmia leachates. P. involutus and L. bicolor used o-HPA acid as a carbon source when cultured in noncarbon nutrient medium. The 0.5 and 0.2 mM o-HPA acid inhibited the root growth of black spruce. However, after solutions had been exposed to a culture of P. involutus, they had no significant effect on seedling growth of black spruce. We concluded that some ectomycorrhizal fungi, such as P. involutus and L. bicolor, are able to degrade Kalmia phenolics. Our findings point to a mechanism by which ectomycorrhizal species can control species interactions in higher plants by changing the rhizosphere chemistry.     

Allelopathic research of subtropical vegetation in Taiwan II. Comparative exclusion of understory byPhyllostachys edulis andCryptomeria japonica

On many hillsides of Taiwan there is a unique pattern of weed exclusion byPhyllostachys edulis (bamboo) andCryptomeria japonica (conifer) in which the density, diversity, and dominance of understory species are very different. Although the physical conditions of light, soil moisture, and soil nutrients strongly favor the growth of understory in a bamboo community, the biomass of its undergrowth is significantly low, indicating that physical competition among the understory species in the bamboo and conifer communities does not cause the observed differences. However, the biochemical inhibition revealed by these two plants appeared to be an important factor. The growth ofPellionia scabra seedlings, transplanted from the study site into greenhouse pots, was evidently suppressed by the aqueous leachate of bamboo leaves but was stimulated by that of conifer leaves. The radicle growth of lettuce, rye grass, and rice plants was also clearly inhibited by the leachate and aqueous extracts of bamboo leaves but not by those of conifer leaves. Six phytotoxins,o-hydroxyphenylacetic,p-hydroxybenzoic,p-coumaric, vanillic, ferulic, and syringic acids were found in the aqueous leachate and extracts of leaves and alcoholic soil extracts ofP. edulis, while the first three compounds were absent in the extracts ofC. japonica. The phytotoxicities of extracts were correlated with the phytotoxins present in both leaves and soils. The understory species might be variously tolerant to the allelopathic compounds produced by the two plants, resulting in a differential selection of species underneath. Therefore, comparative allelopathic effects ofPhyllostachys edulis andCryptomeria japonica may play significant roles in regulating the populations of the understories.Paper No. 253 of the Scientific Journal Series of the Institute of Botany, Academia Sinica, Taipei, Taiwan. This study was supported by the National Science Council of the Republic of China.     

Allelopathic compounds in leaves ofGliricidia sepium (Jacq.) kunth ex walp. and its effect onSorghum vulgare L.

Allelochemicals fromGliricidia sepium were extracted, identified, and quantified using HPLC. Fifteen toxic compounds, namely gallic acid, protocatechuic acid,p-hydroxybenzoic acid, gentisic acid,-resorcyclic acid, vanillic acid, syringic acid,p-coumaric acid,m-coumaric acid,o-coumaric acid, ferulic acid, sinapinic acid (trans andcis forms), coumarin, and myricetin were identified and quantified. These compounds from the plant extracts were tested on the seeds of the crop plant,Sorghum vulgare. Rate of germination of the seeds and root elongation were found to be inhibited by the various compounds of the extract. Different quantities ofGliricidia leaf mulch, viz., 400, 800, and 1200 g/m² applied to theSorghum grown fields, were found to effectively control weeds. Mulching improved the total yield ofSorghum. Leaf manuring and mulching showed better crop yield when applied up to 800 g ofGliricidia leaf/m². Crop yield was better in mulch-applied fields when compared to the manure-applied ones.     

Phytotoxic substances in twelve subtropical grasses

Aqueous extracts of 12 subtropical grasses inhibited seed germination and radicle growth ofLactuca sativa var. Great Lakes at osmotic concentrations as low as 10 milliosmol.Acroceras macrum,Chloris gayana, Digitaria decumbens, andPanicum maximum exhibited the highest inhibition, whileCortaderia selloana revealed the least. Toxic spots were found on chromatograms of the ether fraction of aqueous extracts.Cynodon dactylon, Setaria sphacelata, andTripsacum laxum showed more than six toxic spots, whileAndropogon nodosum,Bracharia mutica, andChloris gayana gave less than three toxic spots. The phytotoxins ferulic, syringic,p-coumaric, vanillic,p-hydroxybenzoic, ando-hydroxyphenylacetic acids were identified. These compounds are differentially distributed in the 12 grasses studied. Additionally, most of these compounds were also found in the associated soils; the control (nonherb-growth) soil provided the toxic compounds in significantly less amount than did the grass soils.     

Autointoxication mechanism ofOryza sativa I. Phytotoxic effects of decomposing rice residues in soil

The aqueous extracts of decomposing rice residues in soil exhibited inhibition on the radicle growth of lettuce and rice seeds and the growth of rice seedlings. The phytotoxicity was found in extracts obtained from the early stage of decomposition (first month), and gradually declined thereafter. The inhibition was also found in extracts obtained from rice fields, and was persistent for 4 months. The root initiation of hypocotyl cuttings of mungbeans was suppressed by extracts of decaying rice residues and extracts obtained from paddy soil. Five phytotoxins,p-hydroxybenzoic,p-coumaric, vanillic, ferulic, ando-hydroxyphenylacetic acids, and several unknowns were found in the decomposing rice residues under waterlogged conditions. At 25 ppm,o-hydroxyphenylacetic acid revealed significant inhibition on the radicle growth of rice and lettuce seeds and suppressed root initiation of mungbean seedlings. It was concluded that the growth of rice seedlings was retarded by decaying rice residues in soil; thus, this appeared to be an autointoxication phenomenon.Paper No. 176 of the Scientific Journal Series, Institute of Botany, Academia Sinica. This study was financially supported by the National Science Council, the Republic of China.     

Identification and phytotoxic activity of compounds produced during decomposition of corn and rye residues in soil

Residues from corn and rye plants were allowed to decompose in soil for periods up to 30 days at 22–23 °C, and the identity of some of the compounds produced as well as their relative phytotoxicity to lettuce seed and seedlings were determined. Paper, thin-layer, and gas chromatography were the principal methods used to identify the various compounds formed. The identities were confirmed by comparison with known synthetic compounds. Eighteen compounds were identified in the decomposing corn residues. Of these, salicylaldehyde, and butyric, phenylacetic, and 4-phenylbutyric acids were volatile, and benzoic,p-hydroxybenzoic, vanillic, ferulic,o-coumaric,o-hydroxyphenylacetic, salicylic, syringic,p-coumaric,trans-cinnamic, and caffeic acids were not volatile. Resorcinol,p-hydroxybenzaldehyde, and phloroglucinol were also found. In the decomposing rye residues, nine compounds were identified, including vanillic, ferulic, phenylacetic, 4-phenylbutyric,p-coumaric,p-hydroxybenzoic, salicylic, ando-coumaric acids, and salicylaldehyde. In the lettuce seed bioassay, most of the above compounds from corn and rye decomposition products exhibited some phytotoxicity. Phenylacetic, 4-phenylbutyric, salicylic, benzoic, ando-hydroxyphenylacetic acids were highly inhibitory to the growth of lettuce at concentrations between 25 and 50 ppm. The others reduced growth significantly at 100 ppm. Most of the phototoxic spots were located in theR _f 0.37–0.97 zone when developed in 2% acetic acid solvent.This study was supported in part by National Research Council of Canada Grant No. A2384 to Z.A. Patrick.     

Allelopathy in agroecosystems: Wheat phytotoxicity and its possible roles in crop rotation

The germination rates of cotton and wheat seeds were significantly affected by various extracts of wheat mulch and soils collected from the wheat field. This toxicity was even more pronounced against seedling growth. Five allelochemics: ferulic,p-coumaric,p-OH benzoic, syringic, and vanillic acids, were identified from the wheat mulch and its associated soil. Quantitatively, ferulic acid was found at higher concentrations thanp-coumaric acid in the soil. Various concentrations of ferulic andp-coumaric acids were toxic to the growth of radish in a bioassay. The functional aspects of allelochemic transfer from decaying residue to soil and the subsequent microbial degradation within agroecosystems are discussed, particularly as they relate to wheat crop rotation, with wheat and cotton, in Pakistan.     

Effect of lipid unsaturation on the antioxidative activity of some phenolic acids

Antioxidative properties ofp-hydroxybenzoic, vanillic, syringic, 3,4-dihydroxybenzoic,p-coumaric, ferulic, sinapic and caffeic acids were studied in the concentration range 0.02–0.20 wt% during autoxidation at 100°C of lard and sunflower oil methyl esters (MEL and MESO, respectively). In both lipid systems, the derivatives of benzoic acid had weaker inhibiting properties than did the corresponding analogues of cinnamic acid. The effectiveness and strength of the antioxidative action were considerably lower in the lipid system MESO, which was rich in linoleic acid and was more easily oxidized. Thep-hydroxybenzoic, vanillic, syringic andp-coumaric acids in this system exercised no inhibiting effect. We established that the molecules of the investigated phenolic acids initiated the chain radical process of autoxidation, and the formed antioxidant radicals propagated the chains as a result of the reaction with the lipid substrate. These reactions proceeded at a higher rate in MESO than in MEL.     

Phytotoxic Effects of 21 Plant Secondary Metabolites on <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> Germination and Root Growth

This study investigated potential phytotoxic effects on germination and root growth of 21 plant secondary metabolites (sinapinic, syringic, vanillic, ferulic, p-coumaric, chlorogenic, gallic, gentisic, protocatechuic, p-hydroxybenzoic, and trans-cinnamic acids, and eucalyptol, quercetin, vanillin, syringaldehyde, rutin, 2-benzoxazolinone, protocatechualdehyde, tyrosol, juglone, and l-mimosine) in the plant model Arabidopsis thaliana. Eleven of the 21 molecules showed significant inhibitory effects on germination, and 17 inhibited root growth. Inhibitory effects on root growth were more evident when nutrients were not added. We present dose–response curves for germination effects and IC₅₀ values for each compound, along with possible explanations of the observed inhibitory actions in terms of molecular structure.     

Effects of phenolic acids on germination and early growth of herbaceous woodland plants

Four herbaceous plant species from woodland (clearings),Deschampsia flexuosa, Scrophularia nodosa, Senecio sylvaticus, andChamaenerion angustifolium, were tested for their sensitivity to phenolic acids. Seven commonly occurring phenolic compounds were used in a germination experiment in concentrations ranging from 0.01 to 10 mM, i.e., salicylic,p-hydroxybenzoic, syringic, caffeic, vanillic,p-coumaric, and ferulic acids. Germination was delayed rather than inhibited. Radicle elongation was strongly affected; at lower concentrations stimulatory effects were observed, whereas at high concentrations radicle elongation was severely reduced. Salicylic acid was the most effective phenolic compound, whereas caffeic acid caused no effects. Early growth was studied in more detail in a second experiment withDeschampsia flexuosa andSenecio sylvaticus and the phenolic acids, ferulic and p-coumaric acid. Primary root length, number and length of secondary roots, and dry weight were stimulated at 0.01 mM but were inhibited at 10 mM of both compounds. The results are discussed in view of the allelopathic relations between trees and herbaceous understory vegetation.     

Possible allelopathic constituents ofCoffea arabica

The aqueous extracts of leaves, stems, and roots ofCoffea arabica significantly inhibited the seed germination and radicle growth of rye grass, lettuce, and fescue. When the extracts were diluted to 1% solution, significant suppression of lettuce growth was still found and was particularly pronounced in the extract of young seedlings. The paper chromato-gram of the ether fraction of an aqueous extract of coffee leaves was bioassayed with lettuce seeds and revealed a remarkable inhibition throughout the chromatogram except for the segment ofR _f 0.00–0.12. Paper without spotting extract was used as a standard. The phytotoxins present in coffee tissue were identified by paper and thin-layer chro-matography and mass spectrometry. The compounds include caffeine, theobromine, theophylline, paraxanthine, scopoletin, and chlorogenic, ferulic,p-coumaric,p-hydroxybenzoic, caffeic, and vanillic acids. All compounds except caffeic acid exhibited significant phytotoxicity to lettuce growth at a concentration of 100 ppm.Paper no. 222 of the Scientific Journal Series, Institute of Botany, Academia Sinica, Taiwan, and Journal Article 3582 of the Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma. The abstract was published in the Proceedings of 63rd Annual Meeting of American Societies for Experimental Biology, held on April 1–10, 1979, Dallas, Texas.     

Allelopathic effects ofChrysanthemum morifolium on germination and growth of several herbaceous plants

Aqueous extracts obtained from young green tops ofChrysanthemum morifolium inhibited the germination of six flowering plants, including chrysanthemum itself, provided for experiments. The same phenomenon was also clearly observed when powder made from young green tops and old leaves of chrysanthemum was used. Moreover, the growth of seedlings planted again in garden soil which was once used for the culture of chrysanthemum was greatly interrupted. Chrysanthemum cultured in used garden soil showed far less dry weight than that cultured in fresh garden soil. The weight of chrysanthemum cultured using its root exudates was also less than that cultured with water leachate of fresh garden soil, and therefore these results may be considered to indicate allelopathic effects. In order to find the allelochemicals related to this phenomenon, benzoic acid and phenolic acids such as salicylic,p-hydroxybenzoic, vanillic, gentisic, protocatechuic, syringic, gallic, ferulic, and caffeic acids were identified by gas chromatography.     

Allelopathic research of subtropical vegetation in Taiwan

Leucaena leucocephala plantations in Kaoshu, southern Taiwan, exhibit, after several years of growth, a unique pattern of weed exclusion beneathLeucaena canopy. The pattern has been observed in manyLeucaena plantations in Taiwan and is particularly pronounced in the area where a substantial amount ofLeucaena litter has accumulated on the ground. Field data showed that the phenomenon was primarily not due to physical competition involving light, soil moisture, pH, and nutrients. Instead, aqueous extracts ofLeucaena fresh leaves, litter, soil, and seed exudate showed significantly phytotoxic effects on many test species, including rice, lettuce,Acacia confusa, Alnus formosana, Casuarina glauca, Liquidambar formosana, andMimosa pudica. However, the extracts were not toxic to the growth ofLeucaena seedlings. The decomposing leaves ofLeucaena also suppressed the growth of the aforementioned plants grown in pots but did not inhibit that ofLeucaena plants. By means of paper and thin-layer chromatography, UV-visible spectrophotometry, and high-performance liquid chromatography, 10 phytotoxins were identified. They included mimosine, quercetin, and gallic, protocatechuic,p-hydroxybenzoic,p-hydroxyphenylacetic, vanillic, ferulic, caffeic, andp-coumaric acids. The mature leaves ofLeucaena possess about 5% dry weight of mimosine, the amount varying with varieties. The seed germination and radicle growth of lettuce, rice, and rye grass were significantly inhibited by aqueous mimosine solution at a concentration of 20 ppm, while that of the forest species mentioned was suppressed by the mimosine solution at 50 ppm or above. However, the growth ofMiscanthus floridulus andPinus taiwanensis was not suppressed by the mimosine solution at 200 ppm. The seedlings ofAgeratum conzoides died in mimosine solution at 50 ppm within seven days and wilted at 300 ppm within three days. It was concluded that the exclusion of understory plants was evidently due to the allelopathic effect of compounds produced byLeucaena. The allelopathic pattern was clearly shown in the area with a heavy accumulation ofLeucaena leaf litter, which was a result of drought and heavy wind influence.Paper No. 292 of the Scientific Journal Series of the Institute of Botany, Academia Sinica, Taipei, Taiwan. This study was supported in part by a grant to C.H. Chou. Part of this paper was a MS thesis submitted by Y.L. Kuo to the Department of Forestry, National Taiwan University, and presented at the Seminar on Allelochemicals and Pheromones, sponsored by the CCNAA and AIT on June 21–26, 1982.     

Effects of mixtures of four phenolic acids on leaf area expansion of cucumber seedlings grown in Portsmouth B1 soil materials

Cucumber seedlings growing in a 12 mixture of soil (Portsmouth B₁) and sand adjusted to pH 5.2 were treated every other day five times with 0, 0.0625, 0.125, 0.25, or 0.5 mol/g soil of ferulic, caffeic,p-coumaric,p-hydroxybenzoic, protocatechuic, sinapic, syringic, or vanillic acids. Treatments began when seedlings were 8 days old. The effects on mean absolute rates of leaf expansion were used to estimate the relative potencies of these phenolic acids to ferulic acid. Based on the results of this experiment, ferulic,p-coumaric,p-hydroxybenzoic, and vanillic acids were chosen for further study. Materials and procedures were identical in the second study, but treatments consisted of mixtures of the four phenolic acids at concentration combinations designed to achieve 40 % or 60 % inhibition of absolute rates of leaf expansion. Using joint action analysis, a model describing the action of the phenolic acid mixtures was developed. A model involving only two factor terms was sufficient to describe the observed responses of cucumber leaf area to the phenolic acid mixtures. The action ofp-hydroxybenzoic acid on absolute rates of leaf expansion was inhibited by the presence of the other three phenolic acids. No other antagonisms or synergisms existed among the four compounds.This research was partially supported by the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7643 and by the US-Spain Joint Committee for Scientific and Technological Cooperation project CCA-8309/166.     

Phytotoxicity of Vulpia Residues: II. Separation, Identification, and Quantitation of Allelochemicals from Vulpia myuros

Phytotoxicity-based extraction and fractionation were employed to separate and purify the allelochemicals from an aqueous extract of vulpia (Vulpia myuros) residues. Further analyses, identification, and quantitation of these allelochemicals were conducted by gas chromatography–mass spectrometry on the most toxic fraction. Twenty-one compounds were identified in the ether fraction from the vulpia residue aqueous extract. They were catechol, hydroquinone, 3,4-dimethoxyphenol, pyrogallol, coniferyl alcohol, and benzoic, succinic, hydrocinnamic, salicylic, protocatechuic, vanillic, gentisic, syringic, p-hydroxybenzoic, -hydroxybenzenepropanoic, p-hydroxyphenylacetic, p-hydroxybenzenepropanoic, hydroferulic, p-coumaric, hydrocaffeic, and ferulic acids. A chromatographic internal standard method with multiple-point calibration graphs was used to quantify the identified compounds. Quantities in the vulpia residues ranged from 1.36 to 81.0 g/g dry residue, in total accounting for 0.05% of the dry weight residue. The combined syringic and hydroferulic acids were present in the largest amount, 140.11 g/g residue. Vanillic, succinic, p-hydroxybenzenepropanoic, and salicylic acids were next in amount, ranging from 37.24 to 81.24 g/g residue. Catechol, hydrocinnamic acid, and hydroquinone were present in the smallest quantities, ranging from 1.36 to 1.82 g/g residue. The remainder of the compounds were intermediate in amount, ranging from 2.33 to 18.1 g/g residue.     

Identification and function of antioxidants from oat groats and hulls

Antioxidant components of methanolic extracts of groats and hulls from Ogle oats were identified and quantified by using gas chromatography-mass spectrometry (GC-MS) and gas chromatography after N,O-bis(trimethylsilyl)acetamide derivatization. Ferulic, p-coumaric, vanillic, p-hydroxybenzoic, 4-hydroxyphenylacetic acids and vanillin and catechol were quantified in groat and hull extracts. Additionally, caffeic acid in groat extracts, and o-coumaric, sinapic and slaicylic acids in hull extracts were quantified. Extracts from groats and hulls at levels of 0.05, 0.1, 0.2, and 0.3% w/w, based on total phenolic content, were added to soybean oil, and their antioxidant effectiveness was compared with that of 0.02% w/w tertiary butylhydroquinone (TBHQ) and a control (no additives) at 60°C in the dark by measuring peroxide values. Antioxidant activities of both extract sources increased with increased concentration. During 20 d of storage, the groat extract (0.3%) was not significantly different from TBHQ after day 16, and hull extracts (0.2 and 0.3%) were not significantly different from TBHQ on day 20. Oils containing pure phenolics at the same concentrations measured in the groat and hull extracts oxidized more quickly than did oils containing the extracts.     

Primary Metabolites and Polyphenols in Rapeseed (Brassica napus L.) Cultivars in China

Defatted meals of 10 rapeseed (Brassica napus L.) varieties were investigated for their total phenolic, phenolic acid (free, esterified, and insoluble-bound forms), and tannin contents. The antioxidant capacities (AC) of methanol extracts from samples were assessed using the 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH•), Folin–Ciocalteu method and ferric reducing antioxidant power (FRAP), and β-carotene–linoleic acid tests. In the fraction of free phenolic acids, sinapic, caffeic, ferulic, syringic, gallic, and p-coumaric acids were identified. In the fraction of esterified phenolic acids, sinapine, sinapoyl glucoside, and disinapoyl gentiobiose were identified. After basic hydrolysis, sinapic, ferulic, cinnamic, and 4-hydroxybenzoic acids were identified, and sinapic acid (SA) constituted 98.3% to 99.6% of the total esterified phenolic acids. Eleven components (sinapic, protocatechuic, p-coumaric, syringic, vanillic, gallic, caffeic, ferulic, salicylic, cinnamic, and 4-hydroxybenzoic acids) in the fraction of insoluble-bound phenolic acids were identified. The AC of the samples correlated with the total phenolic content. Overall, the total phenolics showed a better correlation with AC than the individual phenolic compounds. Moreover, SA, sinapoyl glucoside, and disinapoyl gentiobiose showed a highly significant and strong positive correlation with the AC of rapeseed meals, and the derivatives of cinnamic acid showed a higher correlation with AC than the derivatives of benzoic acid. The change in the canolol content in rapeseeds under microwave irradiation is discussed. The correlation of the canolol formed with SA and its derivatives is discussed.     

Phenolic acids affect photosynthesis and protein synthesis by isolated leaf cells of velvet-leaf

The effects ofp-coumaric, ferulic, chlorogenic, and vanillic acids on photosynthesis and protein synthesis by isolated leaf cells of velvetleaf (Abutilon theophrasti Medik) were investigated. Photosynthesis and protein synthesis were measured in cell suspensions by the incorporation of¹⁴CO₂ and [¹⁴C]leucine, respectively. None of the tested phenolic acids except vanillic reduced photosynthesis by more than 50% at the highest concentration and 30 min of incubation. At 100M concentrations and 60-min incubation periods,p-coumaric, ferulic, chlorogenic, and vanillic acids inhibited photosynthesis by 33, 37, 57, and 65%, respectively. Ferulic acid was the most inhibitory to protein synthesis and reduced the incorporation of [¹⁴C]leucine by 50% at about 1.0M after 60 min of incubation. At the highest concentrations tested in this study, vanillic and ferulic acids were inhibitory to photosynthesis and protein synthesis, respectively, whereas chlorogenic andp-coumaric acids did not inhibit either physiological process. The maximum inhibition of protein synthesis by chlorogenic acid was 19% and by vanillic acid was 28% at 100M concentrations. Chlorogenic, vanillic, andp-cou-maric acids at 0.1M caused increased protein synthesis over the untreated control. Overall, photosynthesis was more sensitive than protein synthesis to the four phenolic acids tested.Florida Agricultural Experiment Station Journal Series No. 9228.     

Allelopathy ofSasa cernua

Sasa (Sasa cernua Makino) is a very serious weed pest. Its allelopathy was studied using lettuce, wheat, timothy, and green amaranth as testing species. Cultured in the rhizosphere soil ofSasa cernua, the seedlings were inhibited by 42–80% compared with the controls cultured in normal soil and vermiculite. The phenolic fraction extracted with 1 M NaOH from the rhizosphere soil ofS. cernua caused significant inhibitions on the seed germination and seedling growth of lettuce, timothy, green amaranth, and barnyard grass.p-Coumaric, ferulic, vanillic, andp-hydroxybenzoic acids andp-hydroxybenzaldehyde were identified as the main allelochemicals in sasa soil by HPLC and [¹H]NMR. Their contents in the rhizosphere soil were 5640, 1060, 860, 810 and 630 μg/100 g soil. The neutral fraction inhibited the seed germination and seedling growth of lettuce in the TLC direct bioassay. Volatile compounds released from sasa leaves also inhibited the growth of lettuce, wheat, timothy, and green amaranth grown under light, and the growth of etiolated seedlings of barley and wheat. These results confirm thatS. cernua produces typical allelopathy through its rhizosphere soil and air space.     

Effects of three phenolic acids on chlorophyll content and growth of soybean and grain sorghum seedlings

Experiments were designed to test the hypothesis that interference with chlorophyll metabolism may be one mechanism of inhibition of plant growth in allelopathic interactions. Effects of ferulic,p-coumaric, and vanillic acids on soybean and grain sorghum growth and chlorophyll content were quantified and compared after seedlings were treated with these compounds in a nutrient culture. Following a 6-day treatment cycle, dry weights of soybean seedlings were reduced by both 10^–3 M and 5 × 10^–4 M treatments of ferulic,p-coumaric and vanillic acids. Soybean weight reductions in each case were paralleled by a significant reduction in the concentration (g Chl/mg dry wt) of chlorophylls a and b and total chlorophyll in the unifoliate leaves. Sorghum seedling growth was also reduced by each of the compounds at the 5 × 10^–4 M level, but leaf chlorophyll concentration was not below that of control plants.