Perennial cereal grain cultivation: Implication on soil organic matter and related soil microbial parameters

Novel perennial grains in agriculture have the potential of providing soil ecosystem services and boosting plantsoil microbial relationships via increasing soil organic matter (SOM). Hence, we evaluated the implication of perennial intermediate wheatgrass agroecosystems (+/- alfalfa intercrop) in contrast to organic and conventional rotation systems on SOM and related soil microbial parameters. Soil samples were obtained from perennial intermediate wheatgrass (IWG), sole (IWG-SC) or intercropped with alfalfa (IWG-IC), as well as organic (ORG-A) and conventional (CON-A) rotation systems of annual wheat. Soil samples were taken in two depths (0-30 cm and 30-60 cm) and analyzed for total and fractionated soil organic C (SOC), microbial biomass C and N (MBC and MBN), basal microbial respiration (Rb), potential enzyme activities related to C and N cycling (Cellobiohydrolase (CBH), Leucine-aminopeptidase (LAP)), and abundance of functional genes related to N cycling (amoA, nifH) and 16S rRNA genes. Despite the lack of fertilization in the IWG systems, SOC concentration and the amount of C in the particulate organic matter were higher in the 30-60 cm depth of IWG systems than ORG-A and CON-A. Higher MBN and LAP activities were observed in the 0-30 cm depth of ORG-A than both IWG and CON-A. Mass specific CBH activities and metabolic quotient qCO(2) were lower in the 30-60 cm depth of IWG systems, implying reduced C losses and high C use efficiency in these systems. Similarly, we observed higher amounts of 16S rRNA in the 30-60 cm depth of IWGs than ORG-A and CON-A. Hence, IWG systems increased SOC and microbial biomass and activities in the 30-60 cm depth than ORG-A and CON-A. However, the more diverse IWG (+ alfalfa intercrop) did not increase microbial biomass and activities than IWG monoculture. Our study provides a reflection of how perennial grain agroecosystems, in conjunction with organic rotation systems, induce a positive influence on SOC and microbial activities than CON-A. It further suggested that perennial grain cultivation goes beyond the reach of organic farming dominated by annual crops to induce SOC and support relevant soil microbial functions in subsoils.