Relationships between glomalin-related soil protein in water-stable aggregate fractions and aggregate stability in citrus rhizosphere

Despite glomalin-related soil protein (GRSP) as a stable and persistent glycoprotein liked to arbuscular mycorrhizal fungi is highly correlated with aggregate stability of various soils, its characteristics in water-stable aggregate fractions and function with aggregate stability are not known. GRSP at 0-15 and 15-30 cm depth in a yellow-brown soil was determined from rhizosphere of 23-year-old Citrus unshiu trees grafted on Poncirus trifoliata in central China. Easily extractable-GRSP (EE-GRSP) ranged 0.45-0.62 mg/g and total-GRSP (T-GRSP) 0.61-1.07 mg/g dry soil within all water-stable aggregate fractions (0.25, 0.50, 1.00, 2.00 and 4.00 mm). GRSP significantly decreased with the decrease of water-stable aggregate size and soil depth, and significantly negatively linearly correlated with percentage of 0.50-1.00 mm size water-stable aggregate. Mean weight diameter (an indicator to aggregate stability) was significantly higher at 15-30 cm than at 0-15 cm depth. Mean weight diameter at 0-30 cm depth was significantly negatively linearly correlated with EE-GRSP in 0.50-1.00 mm size water-stable aggregate and T-GRSP in 2.00-4.00 mm size water-stable aggregate, but positively with EE-GRSP in 0.25-0.50 mm size water-stableaggregate. These results suggested that GRSP exhibited a certain distributive characteristic in water-stable aggregate fractions as EE-GRSP mainly localized in 0.25-1.00 mm size water-stable aggregate fraction, while T-GRSP in 2.00-4.00 mm size water-stable aggregate fraction.©2013 Friends Science Publishers.