降水变化和氮沉降对荒漠草原两种多年生禾草凋落物分解的影响

凋落物分解是陆地生态系统养分循环的重要过程，在生物地球化学循环过程中发挥着重要作用。全球变化是影响凋落物分解的重要因子，其对生态系统养分循环的影响存在诸多不确定性。研究荒漠草原凋落物分解对氮沉降和降水变化及其二者交互作用的响应，是揭示这些不确定性、保护草原生态系统结构和功能的科学基础。以内蒙古四子王旗短花针茅荒漠草原为研究对象，选取建群种短花针茅和优势种无芒隐子草两种植物凋落物，开展为期4年的长期分解实验，探究两种植物凋落物分解特征及养分释放规律。实验采用裂区设计，主区为自然降水（C）、增雨30%（W）和减雨30%（R）3个水分梯度，副区为0（N0）、30（N30）、50（N50）和100（N100） kg hm^-2 a^-1 4个氮素梯度。结果表明：（1）增雨和氮沉降促进荒漠草原凋落物分解，减雨反之，降水对两种凋落物影响具有差异，而氮沉降的作用不依赖于物种；（2）氮沉降缩短凋落物分解周期5.12%-14.82%，增雨与氮沉降交互缩短凋落物分解周期3.69%-28.75%；（3）降水始终有利于凋落物中碳、纤维素和木质素释放，而分解后期氮沉降对其影响不显著，凋落物分解后期主要受木质素分解速率控制。综上所述，影响荒漠草原凋落物分解的主要因素为降水，其次是氮素，二者对凋落物分解具有协同作用。

Effects of precipitation and nitrogen deposition on litter decomposition of two perennial grasses in a desert steppe

Abstract:Litter decomposition is an important process of ecosystem nutrient cycling, which plays an important role in biogeochemical cycling. Global change is an important factor affecting litter decomposition, but there are many uncertainties in its impact on ecosystem nutrient cycling. Studies on the response and feedback of litter decomposition of desert steppe to the increased nitrogen deposition and precipitation change will provide the scientific basis for revealing these uncertainties and protecting the structure and function of grassland ecosystem. In this study, taking S. breviflora desert steppe in Siziwang Banner, Inner Mongolia as the research object, two kinds of plant litter, the dominant species S. breviflora and C. songorica, were selected to carry out a 4-year decomposition experiment, to explore the litter decomposition characteristics and nutrient release patterns of the two kinds of plants. The experiment used split-pot design, with precipitation as the whole-plot factor and N as the split-pot factor. Precipitation treatments include addition 30% (W), removal 30% (R), and ambient precipitation(C). Nitrogen was added at 0 (N0), 30 (N30), 50 (N50) and 100 (N100) kg hm^-2 a^-1. The results show that:(1) Increased precipitation and nitrogen deposition promoted litter decomposition in the desert steppe. Furthermore, the precipitation effects were different between the two kinds of litter, while the effect of nitrogen deposition does not depend on species; (2) Nitrogen deposition shortened the litter decomposition duration by 5.12%-14.82%, and the interaction between precipitation enhancement and nitrogen deposition shortened the litter decomposition duration by 3.69%-28.75%; (3) Precipitation was always beneficial to the release of carbon, cellulose and lignin from litter, but nitrogen deposition had no significant effect on it in the later stage of litter decomposition, and the late stage of litter decomposition is mainly controlled by the decomposition rate of lignin. In conclusion, the main factor affecting the decomposition of litter in the desert steppe is precipitation, followed by nitrogen, and the two factors have a synergistic effect on decomposition of litter.