College of Environmental Science and Engineering, Qilu University of Technology (Shandong Academy of Science), Jinan, 250353, People's Republic of China.
Laboratory of Nutrients Recycling, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, People's Republic of China.
Environ Sci Pollut Res Int. 2019 Mar;26(7):6791-6800. doi: 10.1007/s11356-019-04135-z. Epub 2019 Jan 10.
External nitrogen (N) supply has been testified to exert important impacts on plant residue decomposition. The influence of N may be interactive with soil contact in terrestrial ecosystems. However, the joint mechanisms of decomposition of plant residues driven by soil contact and N addition remain incomplete. Using contrasting residues, including needles of Chinese fir (Cuninghamia lanceolata) (Cl) (relatively hard to degrade) vs. leaves of eucalyptus (Eucalyptus urophylla) (Eu) (relatively easy to degrade), a full factorial experiment was conducted by 360-day experiment to investigate the combined effect of N addition and soil contact on residue decay. As the microbe-manipulated decomposition could leave an imprint on the residue carbon (C) and N stable isotope, variations of the two signatures (δC and δN) were synchronously monitored. Our results firstly showed that added N sped up initial decomposition, while it played an opposite role in subsequent stage, and soil contact always stimulated decay. Under soil contact condition, we found a markedly more accelerating effect of N addition on decay of Cl than without soil contact. Linking with residue N dynamics, we thought that although N immobilized from soil could not completely meet microbial needs for decay of Cl, this N limitation was just relieved by added N, leading to this synergistic effect. At late decay stage, the N inhibiting influence was partly offset under soil contact condition, and this phenomenon was more dramatic for Eu. Our results lastly revealed that the C and N signatures mirrored and explained the underlying mechanisms of the above interactions. Overall, we concluded that external N and soil contact could interactively affect decay, depending on plant residue decomposability. These results would be used to accurately predict C sequestration for terrestrial ecosystems under heightened N scenario in the future.
外源氮（N）供应已被证明对植物残体分解有重要影响。N 的影响可能与陆地生态系统中的土壤接触相互作用。然而，由土壤接触和 N 添加驱动的植物残体分解的联合机制仍不完整。本研究使用具有对比性的凋落物（包括相对难降解的杉木（Cunninghamia lanceolata）针叶（Cl）和相对易降解的尾巨桉（Eucalyptus urophylla）叶片（Eu）），通过为期 360 天的实验，采用完全析因实验设计，研究了 N 添加和土壤接触对凋落物分解的联合效应。由于微生物操纵的分解可能会在凋落物碳（C）和 N 稳定同位素上留下印记，因此同步监测了这两个特征（δC 和 δN）的变化。我们的研究结果首先表明，添加的 N 加速了凋落物的初始分解，但在随后的阶段中则起到了相反的作用，而土壤接触总是刺激分解。在土壤接触条件下，我们发现 N 添加对 Cl 分解的促进作用明显大于没有土壤接触的情况。结合凋落物 N 动态，我们认为，虽然从土壤中固定的 N 不能完全满足微生物对 Cl 分解的需求，但这种 N 限制只是被添加的 N 缓解了，从而导致了这种协同效应。在分解的后期阶段，土壤接触条件下的 N 抑制作用在一定程度上被抵消了，而这种现象在 Eu 中更为明显。我们的研究结果最后揭示了 C 和 N 特征反映并解释了上述相互作用的潜在机制。总体而言，我们得出结论，外源 N 和土壤接触可以相互作用影响分解，这取决于植物残体的可分解性。这些结果将用于在未来准确预测陆地生态系统在高氮情景下的碳固存。
