Spatial heterogeneity of soil organic carbon and total nitrogen in a monsoon evergreen broadleaf forest in Dinghushan, Guangdong, China. Effects of simulated N deposition on free amino acids and soluble protein of three dominant understory species in a monsoon evergreen broad-leaved forest of subtropical China ASSESSING SOIL NITROGEN AVAILABILITY IN DINGHUSHAN MONSOON EVERGREEN BROADLEAF FOREST BY ION EXCHANGE RESIN BAG METHOD