“…Numerous studies in various ecosystems have been conducted to explore the effects of N deposition on litter decomposition ( Tu et al, 2014 ; Yu et al, 2015 ; Zhu W. Y. et al, 2016 ; Zhu X. M. et al, 2016 ; Wang et al, 2017 ; Ren et al, 2018 ; Yan et al, 2019 ; Pei et al, 2020 ; Zhang et al, 2020 ). However, the responses of litter decomposition to N addition have varied considerably, from positive ( Downs et al, 1996 ; Allison et al, 2009 ; Hobbie et al, 2012 ; Ren et al, 2018 ) or neutral ( Prescott, 1995 ; Hobbie and Vitouesk, 2000 ) to negative ( Micks et al, 2004 ; Hobbie et al, 2012 ; Zhou et al, 2017 ). Some chemical, biological, and biochemical hypotheses have been proposed to explain the possible mechanisms of the different effects of N deposition on litter decomposition, but the effects of N input on litter decomposition are still poorly understood ( Carreiro et al, 2000 ; Knorr et al, 2005 ; Liu et al, 2010 ; Prescott, 2010 ; Sinsabaugh, 2010 ; Lu et al, 2014 ).…”