Use of compost to improve Technosol properties and spontaneous plant-soil relationships of Mediterranean species potentially suitable for urban greening

Organic-based amendments are promising, eco-friendly solutions among soil requalification strategies. In this context, the current study explored the application of compost to Technosols (2 kg m-2) to improve soil quality, making the substrate suitable for plant growth. Changes in soil quality have been assessed before compost addition (time zero, T0) and plant transplanting and at 2, 4 and 11 months (T2, T4, and T11) after plant establishment. To test the soil suitability for plant growth, we monitored (at T2, T4, and T11) structural and functional ecological traits in the herbaceous spontaneous species Malva sylvestris L. and in transplanted Mediterranean sclerophyllous Phillyrea angustifolia L., and Quercus ilex L., often used in the urban greening, also considering plant and soil relationships. Our study demonstrated that compost increased soil nutrients availability over time, favoring M. sylvestris physiological performance in long-lasting, compared to sclerophyllous, since the beginning of the application. M. sylvestris exhibited high photosynthetic efficiency and carbon investment in photosynthetic tissues (higher leaf area and lower leaf mass per area) on compost-enriched soil. On the other hand, P. angustifolia and Q. ilex, even if they did not benefit from compost addition for photosynthetic efficiency, after 11 months, maintained higher leaf water content despite limited soil water availability. These results encourage the use of compost in ameliorating the quality of Technosols for urban greening, also evidencing that the species’choice is pivotal in obtaining benefits from plants and a period longer than one year is needed for sclerophyllous to see beneficial effects.