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不同形态氮沉降对杉木凋落叶分解和碳氮磷释放的影响

Effects of Different Forms of Nitrogen Deposition on the Decomposition of Chinese Fir Leaf Litter and the Release of Carbon, Nitrogen, and Phosphorus

    摘要
  • 摘要:
    目的 凋落物分解是森林生态系统养分归还的重要途径，探究氮沉降对杉木凋落叶分解及养分释放的影响，有助于揭示杉木林生态系统养分循环对全球变化的响应机制。
    方法 选取15年生杉木人工林凋落叶为研究对象，以硝态氮（NaNO3）、铵态氮（NH4Cl）和有机氮（CO(NH2)2）3种形态氮为氮源，设置低氮（N1, 50 kg N·hm−2·a−1）、中氮（N2, 100 kg N·hm−2·a−1）、高氮（N3, 200 kg N·hm−2·a−1）和对照（CK, 0 kg N·hm−2·a−1）4个浓度水平。采用网袋分解法进行模拟不同形态氮沉降下杉木凋落叶野外分解试验，定期测定不同氮沉降处理凋落叶分解过程中干质量残留率和碳（C）、氮（N）、磷（P）释放动态。
    结果 不同形态氮沉降处理均表现为低氮促进凋落叶分解，中、高氮抑制。在硝态氮和有机氮沉降下，凋落叶分解速率（K）表现为KN1> KCK> KN2> KN3，铵态氮沉降下则表现为KN1> KCK> KN3> KN2。低氮浓度处理下，凋落叶在硝态氮、铵态氮和有机氮沉降下的周转期分别比对照缩短了1.40%、6.59%和5.61%。在不同形态氮沉降处理下，凋落叶C呈净释放模式，P呈释放-富集模式，氮沉降将N的净释放模式转变为淋溶-富集-释放模式。经360 d分解，在硝态氮和铵态氮沉降下，低氮处理C释放率分别比对照提高了25.98%和10.88%，N释放率分别比对照提高了30.35%和0.92%，中、高氮处理均抑制凋落叶C、N释放。不同浓度有机氮沉降处理对凋落叶C释放影响不显著，但抑制了N释放。在分解前期不同形态氮沉降处理均表现为促进凋落叶P释放，在分解后期则显著抑制P释放。
    结论 短期低浓度氮沉降处理显著促进了杉木凋落叶分解及其养分释放，长期高浓度氮沉降处理表现为明显的抑制作用，随着氮沉降持续加剧，P可能成为限制杉木凋落叶分解的关键因子。

     

    Abstract:
    Objective Litter decomposition is a crucial pathway for nutrient return in forest ecosystems. This study aimed to explore how nitrogen (N) deposition affects the decomposition of Chinese fir litter, thereby providing a better understanding of the response mechanisms of nutrient cycling in Chinese fir ecosystems to global change.
    Method Based on leaf litter from a 15-year-old Chinese fir plantation, three N forms were applied: nitrate N (NaNO3), ammonium N (NH4Cl), and organic N (CO(NH2)2). Four N addition levels were established: low-N (N1, 50 kg N·hm−2·a−1), medium-N (N2, 100 kg N·hm−2·a−1), high-N (N3, 200 kg N·hm−2·a−1), and the control (CK, 0 kg N·hm−2·a−1). A field decomposition experiment of Chinese fir leaf litter under different forms of N deposition was conducted by using the nylon mesh bag method. The dry mass remaining and the release dynamics of carbon (C), N, and phosphorus (P) during litter decomposition were measured.
    Results Under different nitrogen deposition treatments, low-N addition promoted the leaf litter decomposition, whereas medium-N and high-N additions inhibited decomposition. Under nitrate and organic N deposition, the litter decomposition rate (K) were ranked in the following order: KN1> KCK> KN2> KN3, whereas under ammonium N deposition, the change pattern as follows: KN1> KCK> KN3> KN2. Under low-N treatment, the turnover periods for leaf litter under nitrate N, ammonium N, and organic N deposition were shortened by 1.40%, 6.59%, and 5.61%, respectively, compared with CK. Under all the N deposition treatment, the C exhibited a net release pattern, while P exhibited a release-enrichment pattern N deposition transformed the net release pattern of N into a leaching-enrichment-release pattern. After 360 days of decomposition, under nitrate N and ammonium N deposition, the low-N treatment increased C release rate by 25.98% and 10.88%, respectively, compared to the CK, while N release rates increased by 30.35% and 0.92%, respectively. In contrast, both medium-N and high-N treatments inhibited C and N release. Organic N deposition had no significant effect on C release, but inhibited N release. During the early decomposition stage, all N deposition treatments promoted P release from leaf litter, whereas P release was significantly inhibited during the late decomposition stage.
    Conclusion Short-term low-concentration N deposition significantly promoted the decomposition and nutrient release of Chinese fir leaf litter, whereas higher levels of N deposition exerted a pronounced inhibitory effect. As N deposition intensifies, P is likely to become a key limiting factor controlling the decomposition of Chinese fir leaf litter.

     

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