Archives - Allelopathy Journal

Using the BIOLOG ECO microplates technique, the differential microbial populations and their functional diversity between an allelopathic rice accession ‘PI312777’ and a non-allelopathic rice accession ‘Lemont’ were studied under phosphate (P) stress in hydroponic conditions. Under lower P regime, the number of bacteria and fungi significantly increased in the culture solutions of alleopathic rice PI312777. The principal component analysis (PCA) showed that the carboxylic acids, phenolic acids and fatty acids were the principal carbon sources for microbes growth. The results of correlation analysis indicated the carboxylic acids, phenolic acids and fatty acids were positively correlated with the rice allelopathic potential and the number of bacteria and fungi in the culture solutions. These results suggested that organic acids in alleopathic rice PI312777 culture solutions greatly influenced the growth of bacteria and fungi that were positively correlated with the rice allelopathic potential and formed an unfavorable condition for the growth of target weeds.

In recent years, the population of Stellera chamaejasme L. weed is increasing due to degradation of grasslands in northern and western China. It has caused major damage to plant ecosystem but the mechanisms to facilitate the spread of this weed is not clear. We isolated the umbelliferone, as main component from the root exudates of S. chamaejasme grown under laboratory conditions. It was also found in the root zone soil and rhizosphere soil by high performance liquid chromatography (HPLC). In bioassays the umbelliferone drastically inhibited the root growth of seedlings of Elymus dahuricus Turcz., Poa annua L. and Festuca arundinacea, the common forage grasses in meadows. Besides in the degradation experiment, the umbelliferone was completely biodegraded in soil after 2-days, however, the degradation was delayed in sterilized soil. The leaf residues were rich umbelliferone and the content remained higher for longer times. The concentration of umbelliferone in leaves residues was > 214 µg/g and persisted for more than 25 days. Thus the accumulation of umbelliferone as a main allelochemical in root exudates and leaf residue and its decomposition plays major role in allelopathy of S. chamaejasme and help the plant to become a successful invader in the natural plant ecosystem.

Greenhouse experiments were done investigate the effects of seven companion plants [wheat(Triticum aestivum L.), rye (Secale cereale L.), Trifolium (Trifolium repens L.), alfalfa (Medicagosativa L.), rape (Brassica rapa L.), mustard (Brassica juncea L.) and chrysanthemum(Chrysanthemum comarium L.)] on cucumber yields, soil enzyme activities and bacterialcommunities during the spring (April to June) and the autumn (July to September) seasons in 2014.Soil enzymes were examined by urease and phosphatase activity. PCR-denaturing gradient gelelectrophoresis (PCR-DGGE) and real-time PCR were used to analyze the soil microbial community.Results showed that soil urease decreased in cucumber + wheat intercropping system, neutralphosphatase increased in cucumber + rape and cucumber + alfalfa systems compared to cucumber monoculture. The other crops had no effects on these enzyme activities. PCR-DGGE analysisshowed that rape and mustard as component crops increased the richness, evenness and diversity ofsoil bacterial communities than cucumber monoculture. Real-time PCR analysis revealed that thesoil bacterial community abundance increased significantly in cucumber + chrysanthemum andcucumber + alfalfa intercropping system compared to cucumber monoculture in spring and autumn,respectively (P <0.05).

The green and mature senescent needles of Pinus halepensis from the Tunisian pine forests of Bizerte, Tabarka, Seliana and Oueslatia were evaluated based on their phytochemicals contents for allelopathic potential on seed germination and seedling growth of radish (Raphanus sativus L.) and wheat (Triticum aestivum L.). Aqueous extracts of green needles of Seliana and Oueslatia regions, significantly delayed the germination and adversely affected the seedlings growth. In Pot culture studies, mature and green needles powder or soil treatment with needles aqueous extracts were also very inhibitory to seedling growth. The phenolic acids compositions of green and mature needles were determined using HPLC. Analysis of the needles for their phytochemical content showed that the aqueous extracts of green needles contained higher amount of phenolic acids than in mature needles. The phenolics contents in the needles also varied with ecological sites. Needles from Seliana and Oueslatia regions had higher amount of phenolics than those from Tabarka and Bizerte regions. The aqueous extract of green needles from Seliana region had higher levels of gallic acid and 2, 4-D Pestanal, while, the mature needles from Seliana had higher level of cinnamic acid. The green and mature needle extracts were also analyzed for chemical components by GC and GC-MS and 47-compounds were identified, representing 89% of the total compounds, with ß-caryophyllene, a-pinene and myrcene being the predominant.

Cistus ladanifer is common shrub in Mediterranean Basin. Its leaves and stems secrete an exudate called labdanum, which consists of secondary metabolites, mostly phenols and terpenes. Different studies relate the phytotoxic activity of aqueous extracts, individual compounds and soils associated with C. ladanifer to the allelopathic potential of this species. The presence and persistence of exudate constituent compounds in soils increases the allelopathic interactions in these ecosystems. C. ladanifer not only adversely affects the abundance and diversity of both herbaceous and woody species, but also govern the successional dynamics of community in which present. The variability in the allelopathic response of C. ladanifer is determined by temperature, photoperiod, season and location of populations. Thus, in-depth research is necessary to differentiate the allelopathic effects of various factors and/or interactions in an ecosystem.

The effects of maize (Zea mays L.), wheat (Triticum aestivum L.) and Jerusalem artichoke (Helianthustu berosus L.) plant residues on the growth of cucumber seedlings, soil enzyme activities and microbial communities were examined. Except Jerusalem artichoke, the others increased cucumber seedlings growth. Maize and Jerusalem artichoke residues increased the soil urease activity, while, wheat and Jerusalem artichoke residues increased the soil neutral phosphatase and dehydrogenase activities. All residues decreased the viable soil fungal number and there was no difference among the residues. In contrast, all residues increased the viable bacterial numbers and it was higher in soil with Jerusalem artichoke than in soil with maize. All residues also changed the soil fungal and bacterial community compositions. Overall, maize and wheat residues were more suitable for cucumber culture than Jerusalem artichoke residue.

Benzoic acid has been identified as one of the autotoxins of ginseng (Panax ginseng). We studied the micro- and ultra-structures of ginseng root tip cells under benzoic acid stress. The radical elongation was significantly inhibited by benzoic acid at 2.5, 25 and 250 mg·L-1, and the meristematic zone was enlarged or brown stained. The hypocotyl elongation was significantly inhibited at 25 and 250 mg·L-1, and the meristematic cells of ginseng roots were damaged; the nuclear membrane and nucleolus disappeared, the numbers of organelles were decreased and even disappeared. The cell wall became thickened, and vacuoles were observed in starch grains. Gene expression responses of ginseng were revealed by qRT-PCR and results showed that genes of XTH (c37513_g1 and c59133_g3), MYBB (c42409_g1), ZAT10 (c50712_g1) and sHSP (c63168_g1) were up-regulated, while the THI gene (c49571_g1) was down-regulated by benzoic acid. Pot experiment showed that the emergence rate, plant height and root length of ginseng seedlings were inhibited by benzoic acid at 2.5, 25 and 250 mg·kg-1, leaf width and was significantly decreased at 250 mg·kg-1. Thus the gene expression and the normal growth of ginseng was changed under benzoic acid stress.

The Chenopodium ambrosioides L., (Aromatic herb) plants stimulated the growth of surrounding plants, perhaps through volatile allelochemicals. The effects of different volatile allelochemicals (volatile oil, cymene and a-terpinene) from C. ambrosioides were examined to see their effect on the root length, reactive oxygen species (ROS) levels/localization, malondialdehyde (MDA) content and antioxidant enzyme activities in maize radicles. All these allelochemicals inhibited the growth of maize radicles, increased the MDA and ROS contents in tip cells of the root cap and meristem. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were reduced. The volatile oil of C. ambrosioides and its two main components inhibited the growth of maize radical by inducing oxidative stress through the enhanced generation of ROS, accompanied by increased lipid peroxidation and inactivation of antioxidant enzyme system.

Ipomoea cairica (L.) Sweet (Convolvulaceae), one of the world’s most invasive weeds, has caused serious damage in southern China. To better understand the effects of elevated nitrogen deposition on biomass allocation, photosynthetic characteristics and allelopathic potential of I. cairica, a simulated nitrogen deposition experiment was conducted. I. cairica seedlings were exposed to three nitrogen treatments using NH4NO3 solutions (low N, 50 kg N ha-1 yr-1; medium N, 100 kg N ha-1 yr-1; and high N, 150 kg N ha-1 yr-1) for 50 days. Photosynthetic characteristics (net Photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E) and Water Use Efficiency (WUE)), chlorophyll fluorescence parameters (Fo, Fm, Fv/Fm, and Fv/Fo) in leaves of I. cairica were measured. Compared to the control, high N significantly increased the total biomass, the percentage of biomass allocated to stem, leaves area and stem length by 14.8, 20.0%, 68.7%, and 29.0%, respectively. Simulated nitrogen deposition had promoting effect on the photosynthesis rate of I. cairica, especially I. cairica treatment with medium N and high N. Phytotoxicity of leaf litter leachates from I. cairica showed the stronger phototoxic effects under the medium N or high N treatment. Our results indicate that increased atmospheric nitrogen input might benefit the invasiveness of this species.

Based on previous results, which showed that the secondary metabolite “rutin” causes oxidative damage through disturbances in plant water status; this study had focused on demonstrating its effects on the photosynthesis attributes of Arabidopsis thaliana adult plants through imaging Pulse Amplitude Modulation chlorophyll fluorescence system approach. Results showed that rutin reduced the concentration of chlorophyll pigments in Arabidopsis. Photosynthetic efficiency (Fv/Fm) was inhibited following a 7- day treatment with rutin. Non-photochemical fluorescence quenching (NPQ) decreased in Arabidopsis after treatment with rutin, and the inhibition became more severe at 500 and 750 µM rutin. There was a marked decrease in excitation energy fluxes [(qN: nonphotochemical quenching coefficient, Y(II), Y(NPQ)] in Arabidopsis. The leaf protein content in A. thaliana was reduced after the rutin treatment and the greatest reduction occurred at 1000 µM concentration.

In laboratory bioassay, we investigated the generation of reactive oxygen species (ROS) in cyanobacteria Microcystis aeruginosa induced by allelopathic effects of submerged macrophyte Ceratophyllum demersum in co-culture system and the changes in cell membrane integrity and DNA damage. We found that the growth inhibition of M. aeruginosa significantly increased with the increase in C. demersum biomass (0.5, 1.0, 3.0 and 6.0 g FW/L). The concentrations of total phenolic compounds (TPCs) secreted by C. demersum in co-culture water increased with the increase in C. demersum biomass and co-culture time. Compared with control, the level of ROS increased in a dose-dependent manner with the biomass of C. demersum and the concentration of TPCs in co-culture water from the second day. According to the propidium iodide (PI) staining results, numbers of cells losing the membrane integrity increased with ROS generation in M. aeruginosa co-cultured with 1.0, 3.0 and 6.0 g FW/L C. demersum on the fourth day. The significant DNA fragmentation was observed in M. aeruginosa cells at 6 g FW/L C. demersum group. These results suggested that the overproduction of ROS induced by the submerged macrophyte C. demersum was the major factor, resulting in the loss of cell membrane integrity and DNA fragmentation and finally leading to the death of M. aeruginosa cells.

Traditional Chinese medicinal plants of the Panax genus Araliaceae family [Ginseng, (Panax ginseng C. A. Mey.), American ginseng (Panax quinquefolium L) and Notoginseng (Panax notoginseng (Burk.) F.H. Chen)] are rare herbs. These have wide range of biological activities including cardiovascular protection, immunomodulatory ability, as antioxidants, antitumor, cholesterol lowering and anti-inflammatory activities. Hence, their constituents offer several health benefits and are thus used world over in food, health-food, daily necessities and, cosmetics etc. Cultivation of these plants continuously in the same field causes problems due to their allelopathic inhibitory effects, hence, cannot be replanted on the same soil consecutively. Allelopathic inhibition leads to low yields and poor quality products. Hence, allelopathy in continuous cropping of Panax, has became major topic of research. This review provides the available information about allelopathy in continuous cropping problem (CCP) in Panax cultivation.