Phragmites australis is one of the most widespread and invasive plants on earth. Allelopathic interference has been considered as a possible way associated with its invasiveness in wetlands. A series of ecologically realistic experiments was conducted to explore allelochemical phytotoxicity of Phragmites. Germination bioassays using aqueous extracts of different organs (leaf, stem, root and rhizome) of Phragmites were tested with model seeds (Lactuca sativa and Raphanus sativus) and associated plant species (Juncus pallidus and Rumex conglomeratus). These studies showed that leaf and rhizome extracts exhibited strong inhibition on germination, biometric and physiological parameters (all P ≤ 0.001). Dose–response studies confirmed LC50 (4.68% and 11.25%) of Lactuca for leaf and rhizome extracts respectively. Root growth of Juncus and Rumex was inhibited by 75% and 30%, respectively, in leaf leachate-incorporated soil. Chlorophyll content and maximum quantum yield (Fv/Fm) were significantly reduced with leaf and rhizome leachates. The stability and quantity of water-soluble phenolics in anaerobic versus aerobic condition may influence phytotoxic effects to other species. Phragmites organs can be ranked in order of allelopathic potentiality as follows: leaf > rhizome > root > stem. The present study highlighted the potential impacts of allelochemicals on plant recruitment in wetlands invaded by Phragmites.
We explored the allelopathic potential of kudzu as a function of its phenolics. Aqueous and methanol extracts of different kudzu organs (leaf, stem, root, and seed) were assayed for allelopathy with the use of lettuce and radish seeds. Both leaf and root extracts significantly inhibited all of the measured germination indices (total germination, speed of germination, and coefficient of the rate of germination) (all P < 0.01). When treated with leaf extract, the total germination of both species was ∼ 20% less than the control. Furthermore, the leaf extract significantly reduced the speed of germination to 38 and 53% that of the lettuce and radish controls, respectively. Lettuce and radish seeds soaked in leaf and root extracts for 24 h imbibed less water (∼ 30% for both species) than those soaked in distilled water (control), suggesting that a reduction of water imbibition might be one of the mechanisms of germination retardation. Stem and seed extracts affected neither the water uptake nor the germination indices of radish and lettuce seeds. Kudzu leaves and roots contain higher amounts of total phenolics (P = 0.001) and soluble phenolics (P = 0.005) than stems and seeds, consistent with the results of the germination bioassays. In agar plate bioassays, both litter and rhizosphere soil had phytotoxic effects on the radicle growth of radish (P = 0.003) and perennial ryegrass (P = 0.001) seedlings. Perennial ryegrass and cobbler's pegs seedlings grown on leaf and root leachate-amended soil gave ∼ 40% shorter roots and shoots and ∼ 50% less dry weight than those grown in leachate-free soil. Kudzu litter was incorporated and incubated in soil for 6 wk, at which point the soluble phenolics in the soil solution were at a level (> 150 ppm) considered to be allelopathic.
Saline water intrusion is a major problem and conflicting issue in south-west coastal region of Bangladesh. The increased salinity has negative impact on agricultural diversity in this region. The present study provides an assessment of perception of local farmers about changes of agricultural diversity mainly diversity of vegetable species (both summer and winter) and standing plants with the changes of salinity level in the nearby river. This study was carried out in January to August 2005 through semi-structured questionnaire in selected villages of different salinity prone areas such as high saline zone and moderate saline zone, namely Paikgacha and Rampal, respectively. The study has revealed that in Paikgacha, the salinity varies approximately within the range from 20,000 to 45,000 micro-mhos and in Rampal it is from 10,000 to 30,000 micro-mhos. Due to increased salinity, the summer vegetable species in Paikgacha and Rampal have been reduced from 16 to 2 and 15 to 9 respectively during the period 1975-2005. For winter vegetable species, this figure wasreduced from 13 to 9 in Paikgacha but in Rampal this number remained unchanged. Standing plant species in Paikgacha and Rampal have been reduced from 31 to 14 and 35 to21 respectively during that period. Agricultural diversity is reducing in substantial rate both spatially and temporally.Nepal Agric. Res. J. Vol. 8, 2007, pp. 29-37 DOI: http://dx.doi.org/10.3126/narj.v8i0.11576
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