Abstract
We study here how soil bacterial communities of different ecosystems respond to disturbances caused by enrichments with monoterpenes that are common essential oil constituents. We used fenchone, 1,8-cineol and α-pinene, and soils from phrygana, a typical Mediterranean-type ecosystem where aromatic plants abound, and from another five ecosystem types, focusing on culturable bacteria. Patterns of response were common to all ecosystems, but responses themselves were not always as pronounced in phrygana as in the other ecosystems, suggesting that these enrichments are less of a disturbance there. More specifically, soil respiration and abundance of the bacterial communities increased, becoming from below two up to 16 times as high as in control soils (for both attributes) and remained at high levels as long as these compounds were present. Bacteria that can utilize these three compounds as substrates of growth became dominant members of the bacterial communities in the enriched soils. All changes were readily reversible once monoterpene addition stopped. Bacteria with the ability to utilize these monoterpenes as carbon sources were found in soils from all ecosystems, 15 strains in total, suggesting a rather universal presence; of these, six could also utilize the organic pollutants toluene or p-xylene. These results suggest also potential novel applications of monoterpenes in combating soil pollution.
Highlights
Bacterial abundance and diversity are very high in soil ecosystems [1,2], with a wide range of environmental factors, both biotic and abiotic, determining what will appear, where, and when [3,4,5]
The stimulation of soil respiration in the presence of the three essential oil constituents that we examined ranged from 1.4 times as high as in the control up to 15 times
Given the impacts of the compounds that we examined on the soil bacterial communities, we propose the following scheme for the decomposition in the Mediterranean environment, where aromatic plants abound, as a hypothesis to be explored in future studies: Bacteria that can consume the energy-rich essential oil constituents are the primary colonizers of the litter of aromatic plants
Summary
Bacterial abundance and diversity are very high in soil ecosystems [1,2], with a wide range of environmental factors, both biotic and abiotic, determining what will appear, where, and when [3,4,5]. Soil bacteria participate in fundamental processes such as degradation of organic matter and nutrient cycling, changes in the structure of their communities affect ecosystem functioning and services directly or indirectly [6,7]. Soil bacteria may alter soil structure [8], enhance soil fertility [9,10], neutralize environmental pollutants [11,12,13], promote plant growth and vigour [14,15,16], regulate greenhouse gas fluxes between the soil and the atmosphere [17,18], and participate in several other important processes [19,20]. Various plant ingredients, including volatile secondary metabolites such as the essential oil constituents of aromatic plants that abound in the Mediterranean environment arrive at the soil through various avenues [23,24], exerting their effects on the rhizosphere and other soil microbes
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