Li Yulin, Ning Zhiying, Cui Duo, Mao Wei, Bi Jingdong, Zhao Xueyong
Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Donggang West Road, Lanzhou 730000, China.
PLoS One. 2016 Sep 12;11(9):e0162663. doi: 10.1371/journal.pone.0162663. eCollection 2016.
The decomposition of plant material in arid ecosystems is considered to be substantially controlled by water and N availability. The responses of litter decomposition to external N and water, however, remain controversial, and the interactive effects of supplementary N and water also have been largely unexamined.
METHODOLOGY/PRINCIPAL FINDINGS: A 3.5-year field experiment with supplementary nitrogen and water was conducted to assess the effects of N and water addition on mass loss and nitrogen release in leaves and fine roots of three dominant plant species (i.e., Artemisia halondendron, Setaria viridis, and Phragmites australis) with contrasting substrate chemistry (e.g. N concentration, lignin content in this study) in a desertified dune grassland of Inner Mongolia, China. The treatments included N addition, water addition, combination of N and water, and an untreated control. The decomposition rate in both leaves and roots was related to the initial litter N and lignin concentrations of the three species. However, litter quality did not explain the slower mass loss in roots than in leaves in the present study, and thus warrant further research. Nitrogen addition, either alone or in combination with water, significantly inhibited dry mass loss and N release in the leaves and roots of the three species, whereas water input had little effect on the decomposition of leaf litter and fine roots, suggesting that there was no interactive effect of supplementary N and water on litter decomposition in this system. Furthermore, our results clearly indicate that the inhibitory effects of external N on dry mass loss and nitrogen release are relatively strong in high-lignin litter compared with low-lignin litter.
CONCLUSION/SIGNIFICANCE: These findings suggest that increasing precipitation hardly facilitates ecosystem carbon turnover but atmospheric N deposition can enhance carbon sequestration and nitrogen retention in desertified dune grasslands of northern China. Additionally, litter quality of plant species should be considered when modelling the carbon cycle and nutrient dynamics of this system.
干旱生态系统中植物材料的分解被认为主要受水分和氮素有效性的控制。然而，凋落物分解对外部氮和水的响应仍存在争议，补充氮和水的交互作用也基本未被研究。
方法/主要发现：在中国内蒙古的一个荒漠化沙丘草地进行了一项为期3.5年的补充氮和水的田间试验，以评估添加氮和水对三种优势植物物种（即冷蒿、狗尾草和芦苇）的叶片和细根质量损失和氮释放的影响，这三种植物具有不同的底物化学性质（如本研究中的氮浓度、木质素含量）。处理包括添加氮、添加水、氮和水组合以及未处理的对照。叶片和根中的分解速率与这三种物种凋落物的初始氮和木质素浓度有关。然而，在本研究中，凋落物质量并不能解释根中质量损失比叶片中慢的原因，因此值得进一步研究。单独添加氮或与水组合添加氮，均显著抑制了这三种物种叶片和根中的干质量损失和氮释放，而水分输入对落叶和细根的分解影响很小，这表明在该系统中补充氮和水对凋落物分解没有交互作用。此外，我们的结果清楚地表明，与低木质素凋落物相比，外部氮对高木质素凋落物干质量损失和氮释放的抑制作用相对较强。
结论/意义：这些发现表明，增加降水几乎无助于生态系统碳周转，但大气氮沉降可以增强中国北方荒漠化沙丘草地的碳固存和氮保留。此外，在模拟该系统的碳循环和养分动态时，应考虑植物物种的凋落物质量。
