Impacts of Larix Olgensis Afforestation on Soil Phosphorus Dynamics

In China, landscape had been altered from agricultural land to forest over an area of 219.37 million hectares during the last 50 years. Changes in land use can have significant impacts on soil characteristics, microbial properties and the transformation of soil organic matter, total nitrogen and associated nutrients, including phosphorus (P). P is integrant during the large number elements for plants. P the plants needed is mainly obtained from the soil P pool. In order to assess the impacts of Larch (Larix Olgensis) afforestation on soil P, the authors used Dunhua City in Jilin Province as a case region to investigate the soil P during different afforestation periods(1, 3, 8, 12, 18, 20, 33 years old), with an adjacent 250-year-old natural forest for the possible soil P storing in northeast China. We mainly analyzed the variation of soil P dynamics in different ages. Results showed that total P decreased with stand ages. The content of total P was closed with natural forest in the first years then decreased to a minimum level of 0.4378g/kg in 12 years. In 18 years, the soil total P reached to a level as high as that in the former cropland, i.e. 0.811 g/kg then gradually depleted. Available P accumulated after afforestation. Available P concentration reached the maximum value of 153.96mg/kg in 12 years. Within the short time span of 33 years, the contents of available P was closed to natural forest. The proportion of available P occupied in total P increased with age classes. The ratio was 0.24%-84.33%. Based on this, we made correlation analysis between available P and total P. It showed that there was no significant relation between them. Finally, factors that influenced the availability of P were briefly commented.