Soil phosphorus (P) is an essential nutrient element that plant need for growth, which can be affected by the increasing atmospheric nitrogen (N) deposition and the changes in soil microbial biomass. Actually, the atmospheric N deposition consisted of inorganic N and organic N. However, little is known about the changes in soil microbial biomass under mixed inorganic N and organic N addition as well as their relationships with soil P turnover in temperate forest ecosystems.
Researchers in the Institute of Applied Ecology of the Chinese Academy of Sciences determined soil microbial biomass and P forms by phospholipid fatty acid (PLFA) analysis and solution 31P nuclear magnetic resonance (NMR) spectroscopy in the temperate forest ecosystems of Northeast China after a five-year simulated inorganic and organic N addition, respectively.
The team found that mixed inorganic and organic N addition significantly increased the activity of soil alkaline phosphomonoesterase (AlP) and the concentrations of oxalate-extractable aluminum (Al), organic P forms and inorganic orthophosphate. Meanwhile, mixed inorganic and organic N addition also significantly increased soil total microbial biomass, the biomass of bacteria and actinomycetes and enhanced microbial immobilization of soil P, while had no significant effect on soil available P.
The maintaining in soil P availability could be attributed to the hydrolysis of organic P forms catalyzed by AlP, of which the increase in soil microbial biomass and oxalate-extractable Al concentration contributed to the increase of soil organic P forms concentrations, and the increase in bacterial biomass determined the increase of soil AlP activity.
The work revealed the significant effect of bacteria and AlP in maintaining soil P availability by accelerating soil P turnover under increasing atmospheric N deposition, and provided a scientific basis for predicting soil P turnover under increasing atmospheric N deposition in the temperate forest ecosystems of Northeast China in the future.
The study entitled "Soil microbial biomass, phosphatase and their relationships with phosphorus turnover under mixed inorganic and organic nitrogen addition in a Larix gmelinii plantation" was published in August 2018 in Forest Ecology and Management.