Effects of Carbon Sequestration Methods on Soil Respiration and Root Systems in Microcosm Experiments and In Vitro Studies

In the framework of an interdisciplinary research devoted at increasing soil capacity to act as carbon sink by means of innovative and sustainable strategies (the MESCOSAGR Project), we studied, in microcosm-scale model systems, changes of selected soil chemical properties, soil CO2 efflux, and root morpho-topology after addition of either mature compost or a biomimetic catalyst (CAT) (synthetic water-soluble iron–porphyrin), as single addition or in combination of the two treatments. Direct effects of CAT on seed germination, seedling establishment, and plant growth were also evaluated in model plant species. When applied to bare soil, CAT was able to reduce CO2 emission from soil. Soil amendment of compost alone stimulated CO2 emission from soil, whereas its combined addition with CAT strongly depressed the compost-induced CO2 release. In planted microcosms, the contribution of the rhizosphere-derived CO2 efflux markedly increased the total soil respiration and CAT addition further stimulated CO2 release from soil. It is thus suggested that iron–porphyrin, growth of maize root, and CO2 release are functionally interconnected. The increased total soil respiration observed in planted systems may be due to a larger contribution of the rhizosphere-derived CO2 efflux, as a consequence of secondary actions or specific mutual interactions of the catalyst-root system. The direct CAT effect on model plant species implied a complex pattern of dose-dependent, and, remarkably, species-specific responses, as observed in both root systems and aerial plant parts. The observed strong CAT promotion of the synthesis of photosynthetic pigments might indicate an in planta uptake and translocation of the CAT molecule, prompting to envisage potential applications of this molecule in a wider agro-biotechnological context.