| Long-term atmospheric nitrogen(N)deposition can change the amount of litter input by affecting the growth of forest vegetation,and then affect the rate of litter decomposition through mechanisms such as excitation effects,but it has not been verified.In order to explore the effects of increased N deposition and changes in litter input on the decomposition of litter,a two-factor experiment with N addition and changes in litter input was set for the evergreen broad-leaved forest.Three levels of N addition including N control(CN,ambient N input),low N(LN,+50 kg N ha-1 year-1)and high N(HN,+150 kg N ha-1 year-1),and three levels of litterfall manipulation including intact litter input(L0,no litter alteration),litter reduction(L-,reduced by50%)and litter addition(L+,added by 50%)were conducted monthly.A three–year litter decomposition test was conducted in an evergreen broadleaf forest on the western edge of the Sichuan Basin in China by using the litter bag method,and the results showed that:(1)Forest litter production has a distinct seasonal dynamic with?double–peak?,which occurring in May and November,respectivily.The annual productions for four consecutive years were 5.97,4.81,5.75,and 5.04 t ha-1,with significant annual phenomena.Cumulative total litter yields in CN,LN,and HN over the four years were21.8,20.5,and 22.4 t hm-2,respectively.Six–year nitrogen addition did not significantly change forest litter yields.(2)The litter decomposition rate is fast-slow alternate:the fastest decomposition in summer and the slowest decomposition in winter.Throughout the decomposition process,the early stage is faster than the later stage.N addition significantly inhibited litter decomposition while litter treatment had no effect on litter decomposition.Moreover,C remaining and dynamics were similar to mass remaining,and N addition significantly inhibited it at the later decomposition period.(3)N,P,K concentration increased with decomposition time increased.Mn concentration increased first and then decreased.During the decomposition process,the N remaining first increased and then decreased.Litter treatment delayed the N accumulation stage in litter and nitrogen treatment significantly increased the N remaining in the later period.The remaining of P,K,and Mn have the same release dynamics:they are firstly decreased sharply,then increased,and finally decreased again.The difference is that the remaining of P and K elements were significantly reduced by litter treatment in the early stage of decomposition,and significantly increased by nitrogen addition treatment in the later stage.Conversely,the remaining of Mn element was significantly increased by litter treatment in the early stage of decomposition,and decreased significantly by nitrogen treatment in the later stage.(4)The interaction effects of N addition and litter treatment on the quality and nutrient remaining rate of litter decomposition are not significant.The above results indicate that the N addition treatment for many years has not significantly changed the amount of forest litter returned.Combined with N addition to suppress the decomposition of litter leaves,it is inferred that long-term N deposition may increase soil C storage.In addition,N addition significantly inhibited litter decomposition,while litter treatment did not significantly change litter decomposition,indicating that the impact of N deposition on litter decomposition was more from direct effects.N addition treatment significantly increased the remaining rate of N,P and K,and significantly reduced the remaining rate of Mn,which may not be beneficial to the nutrient cycle of the ecosystem in the long term. |
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