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 plant-soil 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 qCO2 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.