Mulches assist degraded soil recovery via stimulating biogeochemical cycling: metagenomic analysis

Soil degradation of urban greening has caused soil fertility loss and soil organic carbon depletion. Organic mulches are made from natural origin materials, and represent a cost-effective and environment-friendly remediation method for urban greening. To reveal the effects of organic mulch on soil physicochemical characteristics and fertility, we selected a site that was covered with organic mulch for 6 years and a nearby lawn-covered site. The results showed that soil organic matter, total nitrogen, and available phosphorus levels were improved, especially at a depth of 0–20 cm. The activities of cellulase, invertase, and dehydrogenase in soil covered with organic mulch were 17.46%, 78.98%, and 283.19% higher than those under lawn, respectively. The marker genes of fermentation, aerobic respiration, methanogenesis, and methane oxidation were also enriched in the soil under organic mulch. Nitrogen cycling was generally repressed by the organic mulch, but the assimilatory nitrate and nitrite reduction processes were enhanced. The activity of alkaline phosphatase was 12.63% higher in the mulch-covered soil, and functional genes involved in phosphorus cycling were also enriched. This study presents a comprehensive investigation of the influence of organic mulch on soil microbes and provides a deeper insight into the recovery strategy for soil degradation following urban greening. Key points • Long-term cover with organic mulches assists soil recovery from degradation • Soil physical and chemical properties were changed by organic mulches • Organic mulches enhanced genes involved in microbially mediated C and P cycling • Soil organic matter was derived from decomposition of organic mulch and carbon fixation • N cycling was repressed by mulches, except for assimilatory NO 2 − and NO 3 − reductions