Fig. 1

Changes of activities of studied enzymes (µmol·g^− 1 SOC·h^− 1) after two years of N addition. (a) BG (β-D-glucosidase) and (b) POX (polyphenol oxidase) are two C-acqusition enzymes; (c) LAP (L-leucine aminopeptidase) and (d) NAG (β-N-acetylglucosaminidase) are two N-acquisition enzymes; (e) AP (acid phosphatase) is a P-acqusition enzyme. CT: control; LN: low-N addition; HN: high-N addition. Error bars denote the standard error (n = 3). Different letters indicate significant difference (P < 0.05) between treatments