Abstract: Aims The accumulation of granite spoils destroys the soil structure leading to increased carbon emissions, and the low stability of the carbon pools still exists after ecological restoration by reconstructing the soil. Root system as a key interface of plant-soil-microorganism interactions, and its configuration characteristics significantly affect the transformation process of soil organic carbon. However, the effect of root conformation on the transformation of organic carbon in reconstituted soils is not clear yet. Methods This paper presents a comparative analysis of the physico-chemical properties, organic carbon fractions, enzyme activities and microbial community characteristics of the rhizosphere /bulk soils of the taproot system alfalfa (MR/MNR) and the fibrous-root system pisum sativum (PR/PNR). Furthermore, we explored the relationship between soil physicochemical properties, enzyme activities and organic carbon fractions Important findings Our results showed that: (1) Phragmites was more able than alfalfa to significantly enhance the quick-acting nutrient content of the disposal site reconstructed soil and provide a suitable microenvironment for carbon transformation; (2) the rhizosphere effects of Phragmites on TOC and DOC were 50.36% and 78.60%, respectively, which were significantly higher than those of alfalfa (13.38%, -7.10%) (P<0.05); and (3) the enzyme activities of rhizosphere soils of the two plant species were significantly higher than those of the bulk soils, with PR cellulase activity 28.66% higher than MR (P<0.05), indicating that Phytolacca promotes rapid conversion of organic carbon; (4) the relative abundance of PR Ascomycetes phylum (41.09%) was higher than that of MR (37.85%) (P<0.05), and the abundance of Acidobacterium phylum (10.25%) was lower than that of MR (10.51%).Ammonium nitrogen, effective phosphorus, organic matter and cellulase activity were significantly and positively correlated with organic carbon fractions. The fibrous rooted Phytolacca drove organic carbon accumulation in granite spoil reconstituted soils through the synergistic effects of fast-acting nutrient enhancement, cellulase activity enhancement, and enrichment of functional flora of Acidobacterium phylum. The results of this study provide theoretical support for the stabilisation of organic carbon pools in granite dumps, and the screening and community allocation of ecological restoration plants.

Key words: root architecture, rhizosphere effect, active organic carbon, granite spoil dump, ecological restoration