Decline of soil nitrogen mineralization and nitrification during forest conversion of evergreen broad-leaved forest to plantations in the subtropical area of Eastern China

Abstract

We examined soil nitrogen (N) mineraliza- tion and nitriWcation rates, and soil and forest Xoor prop- erties in one native forest: evergreen broad-leaved forest (EBLF), one secondary shrubs (SS), and three adjacent plantation forests: Chinese Wr plantation (CFP), bamboo plantation (BP) and waxberry groves (WG) in Tiantong National Forest Park, Eastern China. All forests showed seasonal dynamics of N mineralization and nitriWcation rates. Soil N mineralization rate was highest in EBLF (1.6 § 0.3 mg-N kg i1 yr i1 ) and lowest in CFP (0.4 § 0.1 mg-N kg i1 yr i1 ). Soil nitriWcation rate was also highest in EBLF (0.6 § 0.1 mg-N kg i1 yr i1 ), but low- est in SS (0.02 § 0.01 mg-N kg i1 yr i1 ). During forest conversion of EBLF to SS, CFP, BP and WG, soil N mineralization rate (10.7%, 73%, 40.3% and 69.8%, respectively), soil nitriWcation rate (94.9%, 32.2%, 33.9% and 39%, respectively), and soil N concentration (50%, 65.4%, 78.9% and 51.9%, respectively) declined signiWcantly. Annual soil N mineralization was posi- tively correlated with total C and N concentrations of surface soil and total N concentration of forest Xoor, and negatively correlated with soil bulk density, soil pH and C:N ratio of forest Xoor across the Wve forests. Annual soil nitriWcation was positively correlated with total C concentration of surface soil and N concentration of for- est Xoor, and negatively correlated with soil bulk den- sity and forest Xoor mass. In contrast, annual soil nitriWcation was not correlated to pH value, total N con- centration, C:N ratio of surface soil and total C concen- tration and C:N ratio of forest Xoor.