The importance of allochthonous organic matter quality when investigating pulse disturbance events in freshwater lakes: a mesocosm experiment

Extreme precipitation is occurring with greater frequency and intensity as a result of climate change. Such events boost the transport of allochthonous organic matter (allo-OM) to freshwater ecosystems, yet little is known about the impacts on dissolved organic matter (DOM) quality and seston elemental stoichiometry, especially for lakes in warm climates. A mesocosm experiment located in a Turkish freshwater lake was designed to simulate a pulse event leading to increased inputs of allo-OM by examining the individual effects of increasing water colour (HuminFeed®, HF), the direct effects of the extra energetic inputs (alder tree leaf leachate, L), and the interactions of the single treatment effects (combination of both sources, HFL), along with a comparison with unmanipulated controls. Changes in the DOM quality and nutrient stoichiometry of the allo-OM treatment additions was examined over the course of the experiments. Results indicated that there was an increase of high recalcitrant DOM components in the HF treatment, in contrast to an increase in less aromatic microbially derived molecules for the L treatment. Unexpectedly, seston C:P ratios remained below a severe P-limiting threshold for plankton growth and showed the same temporal pattern in all mesocosms. In contrast, seston N:P ratios differed significantly between treatments, with the L treatment reducing P-limiting conditions, whilst the HF treatment increased them. The effects of the combined HFL treatment indicated an additive type of interaction and chlorophyll-a was highest in the HFL treatment. Our results demonstrate that accounting for the optical and stoichiometric properties of experimental allo-OM treatments is crucial to improve the capacity to explain extrapolated conclusions regarding the effects of climate driven flooding on freshwater ecosystems in response to global climate change. Graphical abstract

Phytotoxic Substances Involved in Teak Allelopathy and Agroforestry

Teak (Tectona grandis L.f.) is one of the most valuable timber species, and is cultivated in agroforestry systems in many countries across the tropical and subtropical regions of the world. The species is also one of the most essential trees in home gardens in South Asia due to its wood quality and medicinal value in folk remedies. It is a deciduous tree species, and the amount of litter that falls from teak trees is huge. The decomposition rate of the litter is relatively fast in tropical humid conditions. The interactions between teak and weeds, or crops, under the teak trees have been evaluated in terms of allelopathy. Evidence of allelopathy is documented in the literature over the decades. The leachate and extracts of teak leaves suppress the germination and growth of several other plant species. Phytotoxic substances, such as phenolics, benzofurans, quinones, terpens, apocarotenoids and phenylpropanoids, in the teak leaves, were isolated and identified. Some phytotoxic substances may be released into the soil under teak trees from leaf leachate and the decomposition of the litters, which accumulate by annual leaf fall and can affect the germination and growth of undergrowth plant species as allelopathic substances. The allelopathy of teak is potentially useful for weed management options in agroforestry and other agriculture systems to reduce commercial herbicide dependency. It was also reported that agroforestry systems with teak enhance income through the production of crops and woods, and provide energy efficiency for crop cultivation.

Evaluation of Different Control Methods Against Citrus Rind Borer

The Citrus rind borer also known as citrus pock caterpillar is still the most critical pest-infesting pummelo (Citrus maxima Merr.) in the Philippines particularly in Davao region. Management of the pest is indispensable for successful pummelo production. The study was conducted to determine the best cost-effective treatment to manage the pest-infesting pummelo. The experiment was laid out in Completely Randomized Design (CRD) with five treatments replicated three times. The treatments were: curry tree leaf leachate, neem tree leaf leachate, bagging with an ordinary net, treated check (Chlorpyrifos + Beta-cyfluthrin), and untreated check. Data were analyzed using Analysis of Variance while the differences among treatment means were computed using the Tukey's Honest Significant Difference. Results revealed that the cost-effective treatment against the destructive citrus rind borer is the bagging treatment. Bagging of fruits is more economical and environmentally sound over the use of chemical pesticides (Chlorpyrifos + Beta-cyfluthrin).

Allelopathic effect of Anogeissus pendula Edgew. and Grewia flavescens A.Juss on Desmodium species in Alwar district of Rajasthan

The effect of leaf leachates of Anogeissus pendula Edgew. and Grewia flavescens A.Juss was evaluated on growth of the three species of Desmodium in Alwar district of Rajasthan (27°4’ to 28°4’ N and 76°7’ to 77°13’ E). Anogeissus pendula reduced the seed germination of Desmodium repandum from 85% in control to 43% at 2% concentration, Desmodium gangeticum from 80% in control to 50% at 6% concentration and Desmodium triflorum from 78% in control to 28% at 0.1% concentration of leaf leachates. Similarly, the leaf leachates of Grewia flavescens reduced the seed germination of Desmodium repandum from 85% in control to 40% at 2% concentration, Desmodium gangeticum from 80% in control to 50% even at 0.1% concentration and Desmodium triflorum from 78% in control to 21% at 0.5% concentration. The leaf leachates of both the species also reduced the elongation of radicle and plumule of three Desmodium species; however, the adverse effect of leaf leachate of Grewia flavescens was more severe than that of the other species. Among the three Desmodium species, the allelopathic effect of Grewia flavescens and Anogeissus pendula was more severe on Desmodium triflorum as compared to the other two species. It may be suggested that the population of three species of Desmodium is partly regualated by the allelopathic effect of Anogeissus pendula and Grewia flavescens in this tropical dry deciduous forest.

Allelopathic effect of Dendrocalamus stocksii (Munro.) on growth and yield of ground nut (Arachis hypogaea)

The present study was conducted to assess allelopathic effect of Dendrocalamus stocksii (Munro.) on the growth and yield of ground nut (Arachis hypogaea). Bamboo leaf leachate was prepared by soaking the dry leaves in tap water for 24 hours in a ratio of 1:10 w/v. Using prepared leachate as stock solution the leachate of various concentrations viz., control (0%), 25, 50 and 75 and 100 per cent were prepared by adding tap water accordingly. The results revealed the concentration-dependent significant (p=0.05) inhibitory effect of bamboo leaf leachates on the germination, radicle and plumule length of groundnut in laboratory condition. The leaf leachate of 100% concentration reduced down the germination percentage (56%), radicle length (3.00 cm) and plumule length (5.36 cm) as compared to control treatment where the germination percentage (86.66%), radicle length (5.02 cm) and plumule length (12.08 cm) were maximum. Similarly, the allelopathic effect of leaf leachate on transplanted seedlings of groundnut in prepared beds inside the poly house were significantly (p=0.05) inhibitory for the test seed weight and straw yield/ha. Minimum test seed weight (430.33 g) was recorded in the treatment of 25 % concentration as compared to control (601.33 g) and straw yield per hectare in the treatment of 100 % concentration (2421.1 kg/ha) as compared to control (4729.4 kg/ha). However, the non- significant effect of leaf leachate was observed on other yield parameters i.e., number of tillers per plant, number of pods / plant, test seed weight, seed yield per plant, number of seeds per pod and grain yield per ha. Finally, it is concluded that the harmful effect of leaf leachates of Dendrocalamus stocksii is more prominent in early stage of germination, emergence of radicle and plumule etc., rather than after transplanting; it is recommended to avoid the effect of these allelochemicals in early growth stage in field condition.

Allelopathic effect of Leucaena leucocephala on Pansy (Viola tricolor L.)

The present study on allelopahtic effect of L. leucocephala on pansy (V. tricolor L.) both laboratory and nursery conditions were undertaken. Leucaena which significantly reduced the seed germination in all treatments at 2% (43%), 3% (42%) and 4% (40%) over Control (Distilled water), except in treatment at 1% (55%) wheregermination was found to be maximum over Control (Distilled water), this result shows the stimulatory effect on germination at 1% concentration of leaf leachate under laboratory condition. Leucaena soil in combination with Field soil showed stimulatory effect on the growth parameters in Pansy. Highest germination percentage (82%), fresh shoot weight (2.82g), fresh root weight (0.22g), dry shoot weight (0.50g), dry root weight (0.05g), vigor index (99.36) were recorded in treatment amended with soil 50% Leucaena soil and 50% Field soil and inhibitory effect was seen in pansy when amended into with 100% Leucaena soil under nursery condition. From this study it appears that Leucaena produces allelopahtic substrates, increase in concentration exhibit adverse effect on germination and growth parameters. Hence it is suggested that pansy could be affected economically but this tree can very well adapt to diversified soil condition.