Carbon Sequestration by Glomeral Fungi in Soil Is Influenced by Phosphorus and Nitrogen Fertilization

Abstract

Glomalin is the most abundant gylcoprotein in soil which produces by glomeral fungi in symbiosis with plant roots. It improves soil physical, chemical and biological properties. Assimilated plant C which is allocated to the mycorrhizal fungus, appears as a recalcitrant glycoprotein (glomalin) in cell walls of hyphae and spores. Considering global warming due to increasing greenhouse gases, this phenomenon could be important in carbon sequestration and reducing CO₂ in atmosphere. Chemical fertilizers could affect symbiotic relations of these fungi, which in turn affect glomalin production. In a pot culture experiment, the sterile soil was treated with 0, 100, 200 mg N kg^-1 soil as urea  or 0, 20, 40 mg P kg^-1 soil as triple superphosphate, in two separate factorial experiment based on completely randomized design with three replications. Corn plant (Zea mays L.) was inoculated with Rhizophagus clarus (formerly, Glomus clarum) or Rhizophagus intraradices (formerly, Glomus intraradices) in each set of experiment. Easley extractable glomalin (EEG) and total glomalin (TG) in soil were determined by Bradford method at the end of experiment. Root colonization by both fungi increased EEG and TG compared to the non-mycorrhizal control (p<0.05). Nitrogen levels of 100, 200 increased EEG by 75 and 112% and TG by 59 and 76%, respectively, compared to the no nitrogen treatment. P levels of 20, 40 caused 27% increase and 6% decrease in EEG, and 24% increase and 13% decrease in TG, respectively, compared to the zero addition of phosphorus. Regarding glomalin production in this condition, R. clarus was more efficient than R. intraradices. Application of 20 mg P kg^-1 increased root colonization, dry weights of shoot and root, chlorophyll index, leaf area, amount of shoot and  root nitrogen and potassium compared to the 40 mgP. kg^-1 and control. Thus, application of 100 mg N kg^-1 increased root colonization, dry weights of shoot and root, chlorophyll index, leaf area, amount of shoot and root phosphorus and potassium compared to the 200 mg N kg^-1 and control.