短期增温对藏北高寒草甸苔藓植物多样性和生长特征的影响

The Tibetan Plateau is one of the most sensitive region to global change.In recent 60 years, the climate of northern Tibet experienced significant warming.Previous studies about warming on plant communities on Tibetan Plateau haven't considered bryophytes, although they are important indicator for climate change,with the growth closely related to water and temperature.To date,few ecological studies on bryophytes on northern Tibet have been reported.The objectives of this study are to answer the following questions: (1)whether bryophytes are sensitive to simulated warming in northern Tibetan alpine grassland, and what are the response characteristics of bryophytes to the warming? (2)what are the relationships between bryophytes and vascular plants? (3)which factors influenced the bryophytes communities under the simulated warming process,and how do they influence? To achieve the above goals, we design a two-year controlled warming experiment by using OTC in Nagqu station,Tibet, where vegetation is dominated by alpine meadowand. We will collect the field data of bryophytes and vascular plants species composition and their quantitative characters, as well as growth response under warming gradient. In addition, abiotic variables including soil surface temperature and humidity, top-soil temperature, humidity, pH, total carbon,total nitrogen, total phosphorus, oganic matter and calcium ions will be also measured. By means of quantitative ecological statistics,the diversity and growth of bryophytes under an increased temperature gradient will be comparatively analyzed, as well as variations of vascular plant communities and abiotic factors. Furthermore, ecological niche analysis will be applied to quantify the relationships between bryophytes and vascular plants, and GAM will be utilized to determine the effect of environmental factors, including biotic and abiotic factors on the diversity of bryophytes. Through this study, we can clarify the response and adaption mechanism of bryophytes to simulated warming, including the species-specific response of bryophyte and their growth characteristics, and internal mechanism. The study will help our understanding of the alpine grassland in response to global change, species interactions in the harsh region, and be of great meaningfulness in using bryophytes to monitor envrionmental changes.

青藏高原是全球变化的敏感区域，在全球气候变暖的背景下，藏北高原增温明显。研究气候变暖对青藏高原植物群落的影响往往忽视苔藓植物这一草地生态系统的重要组成部分。苔藓植物是气候变化的重要指示植物，它们的生长发育与水分、温度等有密切联系。有关藏北高原苔藓植物的生态学研究迄今为止未见报道。本研究以青藏高原那曲站高寒草甸苔藓植物为研究对象，通过短期模拟增温控制实验，借助于数量生态学的研究方法，比较分析不同增温梯度下苔藓植物的多样性和生长的变化，以及维管植物群落和土壤等非生物因子的变化，并用生态位的方法分析苔藓植物与维管植物的种间生态关系，进而用GAM模型分析环境因子，包括生物和非生物因子对苔藓植物组成和多度的影响，以阐明苔藓植物响应和适应全球变化（如温度）的物种特异性和生长特征及其内在机理。该研究对增加高寒草地响应全球变化的理解，丰富严酷地区物种间相互关系，以及利用苔藓植物监测环境变化等具有重要意义。

本研究在藏北典型高寒草甸区采用开顶式生长室(OTC) 构建了模拟增温平台，根据OTC的不同高度设置了四个增温梯度(40 cm、60 cm、80 cm和100 cm)。在增温过程中监测OTC内微气候和土壤性质的变化，并对植物群落的生长、结构、组成和生物量，以及优势物种的物候变化、净生态系统碳交换（NEE）变化等进行了调查，通过回归模型、层次分析法等分析了它们对增温的响应。结果表明：不同高度的OTC作用使得年平均空气温度有了梯度的增加，增幅为1.13–2.72℃；伴随着温度的升高，OTC内空气湿度以及土壤湿度均有所降低，土壤的C、N、P含量也不一致；高山嵩草在所有群落中占有绝对优势，梯度增温作用使得其重要值不断下降，莎草类植物的盖度也在逐渐的下降，温度升高显著影响苔藓植物的生长，导致其难以存活；对整个群落而言，增温幅度较低时，增温对群落的生长和生物量的积累以及多样性都会有明显的促进作用，当温度升高超过一定值，这种促进作用会逐渐减弱甚至变成抑制作用；增温对植物的物候也有明显的影响，但不同物种反应不一致，如增温后高山嵩草返青较晚，花期延迟，提早结束生命周期，而紫花针茅和矮羊茅的开花时间则有所提前；增温还会影响高寒草甸的碳汇能力。该研究表明藏北高寒草甸对增温作用具有敏感而迅速的响应，且温度升高会使得该地区的气候朝着暖干化趋势发展，从而影响植物群落的生长发育，进而导致群落结构的改变，草地生产力下降，草地退化加剧。该研究阐明了植物响应和适应全球变化（如温度）的物种特异性和生长特征及其内在机理。该研究可为青藏高原高寒草甸生态系统应对未来气候变化提供基础数据和理论依据。