Rhizosphere priming effects on the decomposition of soil organic matter in C4 and C3 grassland soils

Abstract

Using a natural abundance 13 C method, soil organic matter (SOM) decomposition was studied in a C3 plant – ‘C4 soil’ (C3 plant grown in a soil obtained from a grassland dominated by C4 grasses) system and a C4 plant – ‘C3 soil’ (C4 plant grown in a soil taken from a pasture dominated by C3 grasses) system. In C3 plant – ‘C4 soil’ system, cumulative soil-derived CO2–C were higher in the soils planted with soybean (5499 mg pot −1 ) and sunflower (4484 mg pot −1 ) than that in ‘C4 soil’ control (3237 mg pot −1 ) without plants. In other words, the decomposition of SOM in soils planted with soybean and sunflower were 69.9% and 38.5% faster than ‘C4 soil’ control. In C4 plant – ‘C3 soil’ system, there was an overall negative priming effect of live roots on the decomposition of SOM. The cumulative soil-derived CO2–C were lower in the soils planted with sorghum (2308 mg pot −1 )a nd amaranthus (2413 mg pot −1 ) than that in ‘C3 soil’ control (2541 mg pot −1 ). The decomposition of SOM in soils planted with sorghum and amaranthus were 9.2% and 5.1% slower than ‘C3 soil’ control. Our results also showed that rhizosphere priming effects on SOM decomposition were positive at all developmental stages in C3 plant – ‘C4 soil’ system, but the direction of the rhizosphere priming effect changed at different developmental stages in the C4 plant – ‘C3 soil’ system. Implications of rhizosphere priming effects on SOM decomposition were discussed.