| Over the last several decades, human activities have increased the nitrogen input in terrestrial ecosystem, and the alteration of the N cycle has profoundly affected the cycles of many other elements, especially carbon (C). Litter decomposition is an important ecosystem process that plays a key role in the balance of global carbon and nitrogen cycles. To investigate the effects of simulated nitrogen (N) deposition on litter decomposition and nutrient release, a one-year field experiment on litter decomposition following N addition treatments was conducted in a natural evergreen broad-leaved forest in a rainy area of Western China. Beginning November 2013, we conducted a field experiment using the litterbag method that included four treatments:0,5,15, and 30 g N·m-2·a-1 as the control (CK), low (L), medium (M), and high (H) nitrogen deposition, respectively. Every 15 days, NH4NO3 was added to the N-treated plots. The results indicated that:(1) Foliar litter decomposed faster in the summer of 2014, obviously faster than other seasons, the contribution rates of mass loss of CK, L, M and H were 37.78%?29.76%? 34.31% and 37.27%; while decomposed slower in the spring of 2014, the contribution rates of mass were 14.65%?14.00%?12.61% and 10.76%, respectively.(2) N deposition significantly inhibited the decomposition of foliar litter in this evergreen broad-leaved forest. As N deposition increased, the inhibition effects were enhanced. The time of 95% mass loss(T95%) of foliar litter due to simulated N deposition was increased by 0.53-1.88 years compared with 4.81 years for T95% of control.(3) The decomposition coefficient of C and N were all in the order k(CK)>k(L)>k(M)> k(H), while N released faster. The time of 95% C decomposition of foliar litter increased by 0.92-2.20 a from 4.09a (T95% of CK) caused by N addition, and the N decomposition was increased by 0.64-1.22 a from 3.73 a. After decomposing for 1 a, the C remaining rate of L, M and H were 6.00%,9.89% and 14.11% higher than CK, while N remaining rate were 4.13%,6.75% and 10.08%, nitrogen addition significantly increased the C, N remaining rate, inhibited the release of carbon and nitrogen significantly. N deposition significantly inhibited the degradation of lignin and cellulose.(4) The mass remaining after one year of decomposition of lignin and cellulose in medium nitrogen and high nitrogen treatments were significantly higher than that in control. N deposition significantly inhibited the degradation of lignin and cellulose. The inhibiting effects of inorganic N on degradation of lignin and cellulose explained the inhibitory effect of N on foliar litter decomposition.(5) N deposition significantly influenced the litter substrate quality, the concentrations of carbon, nitrogen and cellulose in leaf litter were found to increase significantly with the doses of nitrogen additions. N deposition also affected the C/P and C/N of leaf litter, all N deposition treatments significantly increased the C/P wherein medium nitrogen and high nitrogen treatments significantly increased the C/N. N deposition exacerbated the litter decomposition process P restrictions inhibited the growth and activity of microorganisms, thereby delaying the litter decomposition process.(6) The correlation coefficient of mass remaining with C/N, lignin/N and cellulose/N were increased by N deposition, while the C, N, cellulose remaining and C/P was reduced. In the context of simulated N deposition, compared with the N, lignin and P remaining, C/N and cellulose/N, the C and cellulose remaining, C/P and lignin/N are still good indicator of litter decomposition characteristic. |
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