Plant residues play an important role in soil organic matter (SOM) assimilation, and the 'fresh' organic matter inputted to soils might change the mineralization of native SOM, which is commonly known as the priming effect (PE).

Nutrient application critically affects the soil carbon (C) turnover via modifying the microbial composition and activities. Moreover, soil nutrient availability and C:N:P stoichiometric ratios basically regulate the 'fresh' organic matter decomposition and PE. This process has been widely investigated in upland ecosystems. However, there are relatively few studies linking the soil C cycling with element stoichiometry in paddy soils.

Researchers in the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences investigated the effect of N and P additions on straw mineralization and the subsequent PE in a 100-day incubation experiment in flooded paddy soil.

The team found that the straw mineralization increased exponentially with soil DOC:NH₄⁺-N and DOC:Olsen P until reaching a maximum rate. The input of straw combined with N and P fertilizers promoted microbial growth and enzyme activity, thereby, strongly increased straw mineralization and PE for CO₂. However, N and P application could stimulate microbes to use more readily available straw-C and induce negative PE for CH₄.

This study also showed that soil microorganisms generally have conservative stoichiometric responses to the frequent artificial perturbation in paddy soil.

The acquisition of C, N, and P constrain both individual microbe and microbial community responses to straw and inorganic fertilizer application. Alternatively, soil microbes may be flexible and shift their elemental balance in response to such perturbation.

"Our findings provide information regarding the stoichiometry of soil nutrient elements and their interactions with residue decomposition to help interpret the mechanisms of PE in an anaerobic paddy soil," said ZHU Zhenke, an associate researcher in ISA.

This research was funded by the National Key Research and Development Program, the National Natural Science Foundation of China, the Youth Innovation Team Project of the Institute of Subtropical Agriculture, Chinese Academy of Sciences, and Chinese Academy of Sciences President's International Fellowship Initiative to Georg Guggenberger.

The study entitled "Microbial stoichiometric flexibility regulates rice straw mineralization and its priming effect in paddy soil" was published in Soil Biology and Biochemistry.

Contact: Tida Ge

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences