The role of different tree species of plantations on soil nutrient cycling is of great importance for restoration of degraded lands. In southern China, both N-fixing and non-N-fixing tree species were widely used in forest restoration.

To evaluate the potential of N-fixing and non-N-fixing tree species to recuperate degraded land, Dr. WANG Faming, guided by Prof. LI Zhian and Prof. XIA Hanping, from the Key Lab of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, CAS, conducted a study which compared soil properties and N transformations in six forest types (two N-fixing plantations, three non-N-fixing plantations and a secondary shrubland) established in 1984. They found that the N-fixing forests had 40%-50% higher soil organic matter and 20%-50% higher total nitrogen concentration in the 0-5 cm soils than non-N-fixing forests. Soil inorganic N was the highest under the secondary shrubland. N-fixing Acacia auriculiformis plantation had the highest soil available P. There were no significant differences in soil N mineralization and nitrification among forest types, but seasonal variation of these N processes was highly significant. In the rainy season, the rates of N mineralization (7.41-11.3 kg N ha-1 mo-1) were similar to the values found in regional climax forests, indicating soil N availability has been well recovered in these forest types. These results suggest that N-fixing species, especially A. mangium, were more efficient in re-establishing the C and N cycling processes in the degraded land of southern China. Moreover, N-fixing A. auriculiformis performed better than others in improving soil P availability.

This research was published on line in internal journal Soil Science and Plant Nutrition (2010, 56: 297-306).