Liming enhances soil priming effect in Chinese fir plantation induced by glycine rather than glucose and oxalic acid

Abstract

Liming is a widely adopted strategy to mitigate soil acidification and enhance forest productivity. However, the extent to which liming modulates forest soil priming effects, particularly those induced by distinct root exudate types, remains poorly understood. To address this, we conducted a 90-day incubation experiment using soils from a three-year field liming experiment in a Cunninghamia lanceolata plantation (treatments: control, soil pH = 4.4; low liming doses, soil pH = 4.7; high liming doses, soil pH = 5.4). We investigated priming effects by adding three major ¹³C-labeled root exudate components - ¹³C-glucose, ¹³C-glycine, and ¹³C-oxalic acid − each at 2 % of soil organic carbon. Results showed that all exudates consistently induced positive priming effects, with glycine eliciting the strongest response (51.6–89.8 μg C g⁻¹ soil), followed by glucose (37.0–41.5 μg C g⁻¹ soil) and oxalic acid (32.9–47.3 μg C g⁻¹ soil). High liming amplified significantly glycine-induced priming effect by 70 % compared to the control, while priming effects induced by glucose and oxalic acid had no change among different doses of liming. This differential response indicates a synergistic effect between liming and glycine additions on the priming effect. Correlation analysis showed that both soil pH and the soil organic carbon mineralization rate (CMR) were positively correlated only with glycine-induced priming, and that glycine addition was the only treatment that increased NAG activity under high liming. These results suggest that liming enhanced soil pH, thereby stimulating microbial activity, and that the combined C and N supplied by glycine further promoted microbial and exoenzyme activity, ultimately intensifying glycine-induced priming in limed soils. Our findings suggested that liming effects on forest soil priming are jointly governed by root exudate type and soil physicochemical properties, advancing our understanding of liming-mediated soil C cycling.