Abstract
Five different experiments were conducted to investigate the effects of secondary metabolites of aromatic plants on physiological and agronomical characteristics of tomato subjected to biological cultivation, as well as their effects in soil environment. In the first experiment, effects of incorporating into the soil compost derived from spearmint (Mentha spicata L.) or sage (Salvia fruticosa Mill.) on tomato seedlings and on soil parameters were investigated. The composts were incorporated into the soil at doses of 0, 2, 4, 8% (w:w, compost:soil) in combination with organic or conventional fertilizers. Regardless of the type of fertilization applied, net photosynthesis, stomatal conductance and quantum yield of photochemical energy conversion of tomato seedlings treated with 8% spearmint compost incorporated into the soil, were significantly increased. The combination of 8% of spearmint compost with the organic fertilizer and its incorporation into the soil, significantly reduced the ...
Five different experiments were conducted to investigate the effects of secondary metabolites of aromatic plants on physiological and agronomical characteristics of tomato subjected to biological cultivation, as well as their effects in soil environment. In the first experiment, effects of incorporating into the soil compost derived from spearmint (Mentha spicata L.) or sage (Salvia fruticosa Mill.) on tomato seedlings and on soil parameters were investigated. The composts were incorporated into the soil at doses of 0, 2, 4, 8% (w:w, compost:soil) in combination with organic or conventional fertilizers. Regardless of the type of fertilization applied, net photosynthesis, stomatal conductance and quantum yield of photochemical energy conversion of tomato seedlings treated with 8% spearmint compost incorporated into the soil, were significantly increased. The combination of 8% of spearmint compost with the organic fertilizer and its incorporation into the soil, significantly reduced the population of weeds in particular of the broadleaved ones. In addition, it caused positive effects on shoot and root dry weight of tomato seedlings. In soil environment, ammonia-oxidizing bacteria belonging to Nitrosomonas and Νitrosospira were not affected by any of the compost fertilizer combination added into the soil. On the other hand, populations of soil-borne fungi were significantly affected, increasing linearly with the increasing quantities of the applied spearmint or sage composts. In a second experiment, the effects of incorporating into the soil dry plant material of spearmint and sage (chosen among several aromatic plants and cereals) on tomato seedlings and in soil environment without previous composting were investigated. This experiment intended to compare the effects of decomposing and of already composted material of the aromatic plants on above mentioned parameters. Incorporation into the soil of the decomposing spearmint plant material, had a significant positive effect on germination, seedling height (up to 195% compared to untreated control), dry weight (up to 698% compared to untreated control) and on length and width of the most robust leaf, at all doses applied (2, 4 and 8%, w:w, plant material:soil). Effects on total soil-borne fungal populations were similar to those reported for the composts of the aromatic plants. In a third experiment, the degradation process of spearmint essential oils and terpenes when the decomposing material was incorporated into the soil at doses of 0, 2, 4 and 8% (w:w, plant material:soil), was examined. The degradation process was studied by GC-MS analysis of soil samples collected at 0, 15, 35 and 60 days following plant material incorporation into the soil. In all treatments (doses of incorporated plant material), spearmint essential oil content in the soil was reduced more than 94% compared to the content at zero time. GC-MS analysis of distilled spearmint oil, indicated decrease of monoterpene (mainly of carvone) and increase of sesquiterpene concentration (mostly of caryophyllene, bourbonene, calamelene and epibicyclosesquiphellandrene), substances well known to activate the chemical defence of plants. In a fourth experiment, the allelopathic action of spearmint essential oil and of its main component, the monoterpene carvone, against tomato (Lycopersicon esculentum L.) and against four weeds (Abutilon theophrasti L., Datura stramonium L., Oryza sativa L. and Phalaris paradoxa L.), was investigated in vitro. Results indicated strong inhibition (allelopathic phenomenon) of germination, growth, and fresh weight of P. paradoxa and D. stramonium and minor, but significant, of A. theophrasti and O. sativa. In the presence of 3.22 μl of spearmint oil, germination of tomato was reduced by 50% comparing to untreated control. With respect to germination and first growth, tomato was in general sensitive, even at the lower tested concentrations of spearmint oil and of carvone . In a fifth experiment, the effects of essential oils of spearmint (M. spicata), lavender (Lavandula stoechas), oregano (Origanum vulgare subsp. hirtum), and sage (S. fruticosa), as well of the monoterpenes carvone, fenchone, carvacrol, 1,8-cineole, α-pinene and terpinen-4-ol against soil borne-fungi (in pure and mixed cultures), in growth media (in vitro) and in the soil environment were investigated. ..............................................
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