Effects of Field Simulation of Precipitation Changes on Soil Nitrogen Availability under a Mongolian Pine Plantation at Horqin Sandy Lands in Northeast China

Rainout shelters and irrigation systems were manipulated in a Mongolian pine plantations to simulate changes in precipitation amount and to explore how it would affect soil N availability in in Keerqin Sandy lands. Both reduced (RP) and increased (IP) precipitation treatments significantly affected soil inorganic N concentration, increasing it through the growing season except in September under RP treatment, and decreasing it in June, July, and October but not in August and September under IP treatment. Soil microbial biomass N in each month was significantly reduced by RP and raised by IP. IP and RP treatments had no significant effect on height and basal diameter growth of Mongolian pine trees. Above ground net primary productivity (ANPP) of understorey was more than two times greater in the IP than in the RP treatment, and was intermediate in the control treatment. Results indicated the asynchrony of soil moisture and soil nutrient availability in Mongolian pine plantations. Water availability is the overriding limiting factor on grass growth in Horqin Sandy Lands when precipitation decrease, and nitrogen limitation became increasingly important when precipitation increase.