Phosphorus is a limiting nutrient affecting the primary productivity of terrestrial ecosystems. In semi-arid grasslands, soil phosphorus mainly exists in the form of mineral-bound inorganic phosphorus (up to 75% of total phosphorus in calcium-rich soil), which is an important soil phosphorus pool but is difficult to be directly used by plants. In response to increased global nitrogen deposition and changes in precipitation patterns, however, plant productivity may increase significantly, and the activation of this phosphorus pool will play a vital role in alleviating the limitation of phosphorus on plants. 

On semi-arid grasslands with different land-use history (natural vs. abandoned grasslands) in North China, Associate Prof. Wang Ruzhen and Research Assistant Liu Heyong from the research team of the Soil Chemistry Group of the Institute of Applied Ecology, Chinese Academy of Sciences, studied how nitrogen and water addition drive the activation of inorganic phosphorus components and regulate the availability of phosphorus. The researchers found that the historic farming on the abandoned grasslands promoted the mineralization of soil organic matter, resulting in higher contents of total inorganic phosphorus compared to the natural grasslands. Furthermore, the responses of different soil inorganic phosphorus components to experimental treatments were similar in the natural and abandoned grasslands: nitrogen addition resulted in soil acidification and thus promoted the conversion of poorly soluble inorganic phosphorus (e.g., calcium phosphate) to low-activity inorganic phosphorus (e.g., iron phosphate and aluminum phosphate), thereby increased the availability of soil phosphorus. In addition, water addition reduced the contents of soil available phosphorus, mainly by alleviating soil acidification, reducing the availability of iron and aluminum, and through increasing phosphorus absorption by plants.  

This study was funded by the National Natural Science Foundation of China and the Youth Promotion Association of the Chinese Academy of Sciences. The paper titled "Interacting effects of urea and water addition on soil mineral-bound phosphorus dynamics in semi-arid grasslands with different land-use history" has been published in European Journal of Soil Science.