Zhiping Fan

Effect of Land Cover Change on Soil Phosphorus Fractions in Southeastern Horqin Sandy Land, Northern China

In the past 50 years, large areas of the Horqin sandy land were afforested to prevent desertification. Although the afforestation policy appears successful, many people now doubt whether it is suitable to plant trees with high density on the poor soils in semiarid regions. Little is known about the impacts of afforestation on the sandy soil properties, although the evaluation of these impacts is fundamental to judge the rationality of afforestation policy. Soil phosphorus (P) fractions, acid phosphomonoesterase activities, and other soil chemical properties were compared among five adjoining typical ecosystems on poor sandy soils in southeastern Horqin sandy land. The ecosystems studied are natural elm savanna, degraded grassland, Mongolian pine (Pinus sylvestris var. mongolica) plantation, Chinese pine (Pinus tabulaeformis) plantation, and mixed plantation of Mongolian pine and poplar (Populus simonii). The results showed that organic P dominated soil P (47%-65%) was the principal source of available P. The degradation of elm savanna to grassland significantly reduced soil pH and resulted in an overall reduction in soil fertility, although slightly increased labile inorganic P. Grassland afforestation had no significant influence on soil pH, organic carbon, and total N but significantly reduced total P. Impacts of grassland afforestation on soil P fractions depended on tree species. Natural elm savanna had higher soil P conserving ability than artificial plantations. Therefore, with the aim of developing a sustainable ecosystem, we suggested that vegetations with low nutrient demand (particularly P) and efficient nutrient cycling would be more suitable for ecosystem restoration in the semiarid region.

Effects of freeze-thaw on soil nitrogen and phosphorus availability at the Keerqin Sandy Lands, China

A laboratory simulated freeze-thaw was conducted to determine the effects of freeze-thaw on soil nutrient availability in temperate semi-arid regions. Soil samples were collected from sandy soils (0–20 cm) of three typical ecosystems (grassland, Mongolian pine plantation and poplar plantation) in southeastern Keerqin Sandy Lands of China and subjected to freeze-thaw treatment (−12°C for 10 days, then 20°C for 10 days) or incubated at constant temperature (20°C for 20 days). Concentrations of the soil NO3−-N, NH4+-N, NaHCO3 extractable inorganic P (LPi) and microbial biomass P (MBP) were determined on three occasions: at the start of the incubation, immediate post-thawing and at the 10th day post-thawing. The results showed that soil net nitrification and N mineralization rates at three sites were negatively affected by freeze-thaw treatment, and decreased by 50%–85% as compared to the control, of which the greatest decline occurred in the soil collected from poplar plantation. In contrast, the concentration of soil NH4+-N, NaHCO3 extractable inorganic P (LPi) and microbial biomass P were insignificantly influenced by freeze-thaw except that LPi and NH4+-N showed a slight increase immediate post-thawing. The effects of freeze-thaw on soil N transformation were related to soil biological processes and the relatively constant available P was ascribed to severe soil aridity.