Synergistic Effect of Arbuscular Mycorrhizal Fungi and Rhizobium on Glomalin Related Soil Protein and Biochemical Properties of Blackgram Rhizosphere Soil

Purpose: Arbuscular mycorrhizal (AM) fungi and Rhizobium co-inoculation can improve the growth and health of crop plants, including blackgram, although understanding the synergistic impact of this co-inoculation on the biochemical properties of rhizosphere soil and glomalin-related soil protein (GRSP) is crucial for sustainable soil fertility. Methods: GRSP and the biochemical properties of blackgram rhizosphere soil were assessed after two successive crop cycles of blackgram co-inoculated with AM, Rhizophagus intraradices, and Rhizobium. Moreover, AM colonization, nodulation, growth, and yield of blackgram were recorded in both successive crops. Results: Root mycorrhizal colonization, nodulation efficiency, plant dry biomass, number of pods per plant, and grain legume yield of blackgram were improved with the co-inoculation of AM and Rhizobium compared to single inoculations of either AM or Rhizobium, regardless of successive cropping. Notably, AM inoculation alone significantly improved GRSP and its fraction, soil organic carbon (SOC), and the contribution of GRSP carbon to SOC pool in the rhizosphere soil, and this improvement was further enhanced when AM and Rhizobium co-inoculation. Additionally, available soil nutrients such as nitrogen, phosphorus, and potassium in the rhizosphere soil were higher in the AM and Rhizobium co-inoculated treatment compared to single inoculations of AM or Rhizobium. Moreover, soil dehydrogenase activity increased with the inoculation of either microbial symbionts or the co-inoculation of AM and Rhizobium compared to the microbial un-inoculated control. Conclusions: Our results demonstrate that co-inoculating AM fungi and Rhizobium can synergistically enhance GRSP and the biochemical properties of the blackgram rhizosphere soil, in addition to improving plant growth and yield.