Contribution of arbuscular mycorrhizas to glomalin-related soil protein, soil organic carbon and aggregate stability in citrus rhizosphere

Low soil organic matter (SOM) (5-15 g kg-1) and poor physical and chemical soil properties in most of the citrus orchards in the southern regions of China lead to reduce yield and fruit quality. To investigate the contribution of arbuscular mycorrhizas (AMs) to soil carbon pools and aggregate stability, a pot study was designed to analyze glomalin-related soil protein (GRSP), soil organic carbon (SOC), and proportion of different water-stable aggregate (WSA) fractions in rhizosphere of Citrus tangerina, Fortunella margarita and Poncirus trifoliata inoculated with or without an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae. The AM colonization significantly improved all tested plant growth and root morphological traits of five-month-old C. tangerina and F. margarita, than P. trifoliata. Mycorrhizosphere of these three citrus plants showed 19-26% higher easily extractable GRSP (EE-GRSP), 13-20% higher total GRSP (T-GRSP), and 39-325% higher SOC, and 18-72% lower T-GRSP/SOC ratio. Compared with their non-mycorrhizosphere, the mycorrhizosphere of these three citrus plants had significantly higher proportion of WSA at 2.00-4.00, 1.00-2.00, 0.50-1.00, and >0.25 mm size fractions, and 119-217% higher mean weight diameter (MWD, an indicator of aggregate stability). Both EE-GRSP and T-GRSP fractions were significantly positively correlated with SOC, WSA fractions and MWD. The present study indicated a positive contribution of GRSPs to SOC and soil aggregate stability in rhizosphere, irrespectively of citrus genotypes and/or mycorrhization. These results would provide important information on better understanding the contribution of GRSPs to soil organic C dynamics and structure stability. © 2014 friends science publishers.