Microbiological and biochemical properties of artificial substrates: A preliminary study of its application as Technosols or as a basis in Green Roof Systems

The development of artificial substrates or Technosols to be used in green roofs is increasing nowadays. Microbiological and biochemical aspects should be taken into consideration when designing an artificial substrate, to assure the quality of the chosen materials and the future plant development. Our purpose is to develop an appropriate substrate consisting of a mix of organic and inorganic residues. We used green compost mixed, on the one hand, with a clay-loam soil and, on the other, with crushed bricks, in two volumetric proportions (20:80 and 50:50). An incubation experiment was conducted to study the short-term evolution of physicochemical, biochemical, and microbiological substrates characteristics. Most of the enzymatic activities (β-GLA, URA, and APA) and microbiological parameters determined (microbial respiration and qCO2) showed that the compost-soil mixtures were able to maintain biochemical processes during the incubation time. In contrast, the compost-brick mixtures possessed appropriate physicochemical properties (60% of porosity, good aeration conditions, and higher oxidative enzyme activities; PPO and POD) but they presented less nutrient content (TOC, TC, and TN) and reduced microbial activity in general, which are of paramount importance in plant growth. Moreover, the PLFAs analysis (phospholipid fatty acids) showed that compost-brick may support a bacterial community throughout the experiment while in compost-soil mixtures there was further development of fungi, although its content decreased with incubation time. We conclude that both the substrate composition and the compost dose affect the development of microbial biomass at structural and functional levels. Therefore, physicochemical properties along with biochemical and microbiological aspects should be considered to design a suitable substrate for a future plant development.