Soil microbial respiration responses of nitrogen addition: Evidence from a long-time semi-arid grassland soil incubation

Nitrogen is essential for the synthesis of key cellular compounds such as proteins and nucleic acids in all organisms, and it is one of the limiting elements in most terrestrial ecosystems. During past decades, terrestrial ecosystems nutrients availability have altered with nitrogen deposition increases rapidly so that under the soil microbial metabolism activities terrestrial ecosystem biogeochemical cycles are strongly affected. Therefore, maintaining the stability of soil carbon pools, especially microbial carbon pools has great importance for studying global carbon cycle and global climate change processes. Depending on whether soil microbial has already adapted to the environment nitrogen concentration, there exists different results, such as promotion, inhibition, and no impact. To date, how nitrogen will affect soil microbial respiration still has controversy. To determine the effects, we performed a 59 weeks incubation with the soil which has already treated with Urea for 9 years. The soil has been treated with four N addition levels in a semi-arid grassland where located in North-west part of China. We measured CO₂ effluxion under different treatments within the same temperature. Our results showed that during the first 8 weeks, soil microbial had strong responses about N addition and N9.2 showed greatest influence with soil microbial respiration. With the time passing, in the time of 9-59 weeks, N0 had highest soil microbial respiration rate while N2.3 was the lowest, this illustrated N2.3 had highest N use efficient (NUE), in order to meet soil microbial stoichiometry, microbial growth became strong C-limitation under the N2.3 treatment. What’s more, comparing with other studies which we shared same study area, we also found that the time of nitrogen application also had strong effect on soil microbial respiration. These results highlight the importance of microbial respiration and may also help us to have a better understand about how N deposition controls terrestrial C flows.