Mycorrhiza-released glomalin-related soil protein fractions contribute to soil total nitrogen in trifoliate orange

Glomalin released from arbuscular mycorrhizal fungi (AMF) has important roles in soil nutrient cycles, whereas contributing to glomalin-related soil protein (GRSP) fractions to soil nitrogen (N) is unknown. In this study, a two-chambered root-box that was divided into root chamber (root and mycorrhizal fungi hypha) and hypha chamber (free of the root) was used, and three AMF species including Diversispora epigaea, Paraglomus occultum, and Rhizoglomus intraradices were separately inoculated into the root chamber. Plant growth, soil total N, N content of purified GRSP fractions, and its contribution to soil total N, and leaf and root N contents were analysed. After four months, total biomass and root total length, surface area, and volume were improved by all AMF inoculations. AMF inoculations dramatically increased soil total N content in two chambers. The N content of purified easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 0.10 +/- 0.01 mg/g and 0.16 +/- 0.02 mg/g, respectively, accounted for 15.6 +/- 1.6% and 18.1 +/- 1.8% of soil total N, respectively. AMF inoculations stimulated the N accumulation in EE-GRSP and DE-GRSP, especially in the hypha chamber. It concluded that GRSP, especially DE-GRSP, acts as a soil N pool accounting for 33.8 +/- 1.9% of soil total N in orchards.