Atmospheric deposition of nitrogen (N) compounds have significantly
increased worldwide in the recent decades, mainly in the form of
ammonium (NH4+-N), nitrate
(NO3ā-N) and urea
(CO(NH2)2). Here, we used meta-analysis
to compare the influence of different N types on terrestrial soil
microbial biomass based on 1585 paired observations from 178 articles.
In all N types, NH4+-N addition
displayed the greatest negative affects on soil microbial biomass (-18.9
%) followed by. NH4NO3 (-7.51 %) and
NO3ā-N (-7.26 %).
CO(NH2)2 addition resulted in the
smallest total microbial biomass declines among all N types (-6.99 %).
All the soil microbial characteristics, such as fungi and bacteria,
revealed the same trends across all ecosystems, especially for
arbuscular mycorrhizal fungi, F/B, and G+/Gā ratio. In addition, the
response sizes were significantly correlated with the accumulated N
amount (N addition rate Ć application duration). The results indicated
that the response sizes were significantly N-type dependent.