Abstract
Despite the importance of nitrogen (N) deposition for soil biogeochemical cycle, how N addition affects the accumulation of humic substances in decomposing litter still remains poorly understood. A litterbag experiment was conducted to assess the potential effects of N addition (0 kg·N·ha−1·year−1, 20 kg·N·ha−1·year−1 and 40 kg·N·ha−1·year−1) on mass remaining and humification of two leaf litter (Michelia wilsonii and Camptotheca acuminata) in a subtropical forest of southwestern China. After one year of decomposition, litter mass was lost by 38.1–46.5% for M. wilsonii and 61.7–74.5% for C. acuminata, respectively. Humic substances were declined by 12.1–23.8% in M. wilsonii and 29.1–35.5% in C. acuminata, respectively. Nitrogen additions tended to reduce mass loss over the experimental period. Moreover, N additions did not affect the concentrations of humic substances and humic acid in the early stage but often increased them in the late stage. The effect of N addition on the accumulation of humic substances was stronger for C. acuminate litter than in M. wilsonii litter. Litter N and P contents showed positive correlations with concentrations of humic substances and fulvic acid. Our results suggest that both litter quality and season-driven environmental changes interactively mediate N impacts on litter humification. Such findings have important implications for carbon sequestration via litter humification in the subtropical forest ecosystems experiencing significant N deposition.
Highlights
Organic matter accumulated at the surface of forest soils as humus is of primary importance to long-term site fertility and productivity in forest ecosystems[1]
N additions tended to increase litter mass remaining over the experimental period (Fig. 1)
analysis of variance (ANOVA) analysis showed that the effect of N treatment on mass remaining was dependent on deposition period (Table 1)
Summary
Organic matter accumulated at the surface of forest soils as humus is of primary importance to long-term site fertility and productivity in forest ecosystems[1]. The annual wet N deposition in this study site is 36.2 kg N·ha−1 16, which is much higher than the average value of atmospheric N deposition in China (18.0 kg N ha−1)[17]. This region is considered as a special natural laboratory for N deposition studies of N-rich ecosystem. Understand the effects of rising N deposition on soil organic matter, a field experiment was conducted to explore the potential influences of N additions on the humification of two foliar litter with contrasting quality (Michelia wilsonii and Camptotheca acuminata) in the high-N deposition subtropical ecosystem. We hypothesize that (1) N additions would stimulate litter humification and such effect could be greater in high-quality litter; (2) season-associated conditions could mediate the response of litter humification to N additions
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