Influence of green manuring on soil properties, abundance and expression of key denitrification genes in a greenhouse Anthrosol

Intercropping with green manure is a valuable agronomic practice for promoting sustainability agricultural systems. The aim of this study was to evaluate the effects of green manure (GM) – based on a mixture of vetch (Vicia sativa L.), forage turnip (Brassica rapa L. subsp. rapa), and oats (Avena sativa L.) – on the physicochemical properties of a greenhouse Anthrosol and its impact on the abundance and expression of denitrifying genes (nirK, nirS, and nosZ (clade I and II)) using real-time PCR. The cultivated crop throughout the three-year experiment was eggplant (Solanum melongena L. subs. Telma) fertilized with manure and crop residues from the previous growing season. A linear mixed model (LMM) was used to assess the effect of GM on both the physicochemical variables and the target-gene and transcript copy number in the soil. After three years of GM coverage, moderate changes in soil physicochemical properties were observed, with the exception of a significant decrease in soil temperature (<6 %) and ammonium ion concentration (<14 %) with GM application. Gene copy numbers remained largely unchanged between treatments, however transcripts levels decreased for all target genes under GM, with particularly pronounced reduction for nirK (p < 0.0001) and nosZ II (p < 0.05), suggesting partial suppression of gene transcription within the denitrification pathway. In addition, potassium (K⁺) and soil moisture were found to correlate with DNA and RNA abundances, indicating a complex interaction between salinity and soil moisture in the regulation of the denitrification process.