Over the past few decades, the pattern of microbial resource limitation has been changing slowly due to elevated deposition of atmospheric nitrogen (N).

Given the N saturation hypothesis, elevated input of N reduces the microbial requirements for additional N, therefore, carbon (C) limitation or phosphorus (P) limitation of soil microbes are expected to be motivated or aggravated.

However, whether such change can be reflected by ecoenzymatic stoichiometry has never been studied. 

Researchers in the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences synthesized data from 36 published studies to evaluate the responses of ecoenzymatic stoichiometry to N addition. 

The team found that that N addition did not change the enzyme ratio (1:1:1) of C, N, and phosphorus (P) acquisition, nor the vector angle of ecoenzymatic stoichiometry, an indicator of microbial P limitation.

However, addition of N increased two indicators of C-limitation significantly (i.e., activity of β-D-glucosidase and vector length of ecoenzymatic stoichiometry), both of which indicated that the addition aggravated microbial C-limitation. "The aggravated C-limitation may be partly due to the reduced decomposition of recalcitrant organic C," said CHEN Hao, a doctoral researcher at ISA. 

These findings extend people’s understanding of the effects of N deposition on C cycling from a new perspective. 

This work was supported by the National Key Research and Development Program of China, the National Science Foundation of Guangxi Province of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences through its One-Hundred Talent Program to LI Dejun, the Chinese Academy of Sciences through its "Light of West China" Program to CHEN Hao, and the Youth Innovation Team Project of ISA, CAS. 

The study entitled "Nitrogen addition aggravates microbial carbon limitation: evidence from ecoenzymatic stoichiometry" was published in Geoderma.