Nitrogen cycling is a critical component in plantations, yet the spatial and temporal variations of N transformations in different stages of afforestation are poorly known so far.

Dr. WANG Faming, led by Prof. LI Zhian and Prof. Hanping Xia, from the Key Lab of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, CAS, has conducted a study on soil N cycling in five young plantations (two monocultures of exotic species: Eucalyptus urophylla and Acacia crassicarpa, a native species monoculture, a 10-species mixture and a 30-species mixture) and a shrubland (without experimental planting) in in Heshan Forest Ecology Research Station, CAS. The results show that net N mineralization and nitrification rates in the E. urophylla monoculture (13.5 and 9.98 kg N ha-1 yr-1, respectively) were the lowest among six planting treatments, less than 1/3 of those in the 10-species and 30-species mixtures (Fig.1). Two exotic fast-growing monocultures had 10%-60% lower soil extractable nitrate concentrations than the native plantations and shrubland, and had the lowest nitrogen leaching losses. The leguminous A. crassicarpa monoculture did not have higher soil N availability in comparison with non-leguminous species. Both N mineralization and nitrification varied seasonally; soil moisture seemed to be important in controlling these temporal variations. This study highlights that，in the early stages of afforestaion, a better understanding of plant species effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing restoration practices.

This research was published on line in internal journal Restoration Ecology (DOI: 10.1111/j.1526-100X.2009. 00642.x)