积雪厚度和雪融时间的变化对温带草原植被特征的影响及其生态学机理

The snow cover during winter and early spring is of great importance for the survival and germination/sprouting of plant propagules, plant growth, and even the whole ecosystems. While the snow cover is decreasing and the snow melting is becoming earlier and earlier in high latitude temperate regions in China due to climatic change, the ecological consequences of snow cover and its melting date on grasslands have received far less attention than deserved. In this project, we are to set up a manipulative experiment on typical steppe in the high latitude temperate region, in which the following four experimental treatments are to be established: 1) control; 2) doubling the thickness of snow cover; 3) putting forward the snowmelt; 4) combining 2 and 3. We are to use Two-way ANOVA and multiple range tests to analyze the data acquired by monitoring the soil environment, plant and vegetation. Thereby, we attempt to examine the responses of soil temperature and moisture and nutrient availability to snow cover doubling and earlier snowmelt, and how such responses affect plant phenology, vegetative growth (bud bank) and reproductive growth (seed production and weight), and productivity, species and functional group composition and diversity of vegetation. Through correlation and integrative analysis, we try to uncover the impact of altered snow cover thickness and melting timing on the vegetation of typical steppe and underlying mechanisms. Such declaration will help deepen the understanding of the usefulness of snow cover and the ecological consequences of any changes occurred to the snow cover, more importantly, it will provide more scientific basis for predicting the future vegetation changes under climate change scenario.

冬季和早春积雪覆盖对植物繁殖体的存活、萌发以及植物生长乃至整个生态系统都具有重要意义，但在气候变化影响下，我国温带高纬度地区降雪量有逐年减少和积雪融化时间提前的趋势，然而目前关于积雪厚度和雪融时间对草原的影响尚未引起应有的关注。本项目以温带高纬度地区的典型草原为对象，除对照外，设置积雪厚度倍增、融雪时间提前及二者叠加的实验处理，通过对土壤环境、植物和植被相关参数的观测获取数据，并运用方差分析和多重比较的方法，解析土壤温湿度、养分有效性对积雪厚度倍增、融雪时间提前的响应，及其对植物物候、营养繁殖（芽库）与有性繁殖（种子产量与质量）、植被生产力、植被物种和功能群组成以及多样性特征的影响，并通过对以上参数的关联分析和整合分析，揭示积雪量和雪融时间的变化对典型草原植被的影响机制，有助于加深人们对积雪作用及积雪变化生态后果的认知，而且为更加科学、全面、准确预测植被的未来变化提供重要科学依据。

探究全球变化对生态系统结构和功能的影响是生态学领域普遍关注和广泛研究的内容。但以往研究大多只关注生长季全球变化对陆地生态系统的影响，有关冬季全球变化对季节性积雪覆盖的草原植被特征的影响及其生态学机理尚不清楚。本项目以温带高纬度地区的典型草原为对象，采用野外原位控制试验，研究积雪厚度倍增、融雪时间延迟及二者叠加对植被生产力、植被物种和功能群组成和多样性，以及植被物候等特征的影响。实验结果表明：非生长季积雪厚度倍增和融雪延迟对土壤水分、土壤养分以及净初级生产力和群落组成的影响具有明显的时间动态规律。在积雪融化后的初期，积雪厚度倍增和融雪延迟显著增加土壤水分和土壤养分、提高地下净初级生产力，同时降低植物群落物种多样性。随着时间推移，虽然积雪特征变化对土壤水分和土壤养分的影响逐渐减弱，但积雪厚度倍增和融雪延迟仍显著增加生长季地上净初级生产力，而融雪时间延迟显著降低物种多样性；禾本科相比于杂类草、早花杂类草植物相比于晚花杂类草植物对积雪特征变化更为敏感。积雪厚度倍增和融雪延迟显著增加禾本科植物生物量，融雪延迟显著降低早花杂类草植物生物量，对晚花杂类草和杂类草总生物量影响不显著。积雪厚度增加会导致杂类草植物花期提早，融雪延迟会导致花期推迟；相比于单独积雪厚度倍增和融雪延迟处理，两者同时施加对温带草原植被生产力、多样性和繁殖物候等特征无显著影响，暗示二者存在拮抗作用。本项目研究结果为理解非生长季气候变化对草原生态系统植被的影响提供了重要科学依据。