中国北方典型灌丛的分布特征及气候限制

Distribution patterns and climate limitations of typical shrublands in northern China

灌丛是中国北方常见的植被类型,随着全球变化进程加剧,全球和中国灌丛面积正逐年上升,成为陆地生态系统碳循环中愈加重要的组分.研究灌丛的分布规律及其驱动因子有助于了解植物对自然胁迫的适应机制以及环境变化对植被动态的影响.本研究基于2400个灌丛群落的野外调查数据,利用k均值聚类以及典范对应分析(canonical correspondence analysis,CCA)排序研究了中国北方灌丛类型与分布及其与气候的关系.结果表明,中国北方灌丛可以划分为分布区间、生境和结构差异显著的29种典型的灌丛群系,各群系平均物种丰富度、盖度随其分布区的平均年降水量增加而增加;CCA排序显示,第一、第二排序轴分别对应水分和热量因子,中国北方灌丛的分布体现了两个更替梯度:沿湿冷-干热梯度以及在较湿润条件下沿冷-热梯度的变化.水分可利用性调控了灌木的叶属性权衡,随水分可利用性增加,各灌丛类型指示种的叶厚度减小,而比叶面积增加.上述结果表明,相比于热量,水分条件在决定中国北方灌丛分布格局中具有更重要的作用,它不但影响灌丛群落结构,还通过筛选位于叶经济谱上的不同灌木来决定灌丛群系.本研究揭示了气候对中国北方灌丛的塑造过程,对中国北方灌丛的分类结果可以成为更广泛、全面的灌丛分类体系的基础.

Shrublands are typical vegetation types in northern China. Their areas are continuing to increase each year not only in China but also worldwide owing to the intensification of global change, and they are becoming increasingly important components of terrestrial ecosystem carbon cycle. Exploring the distribution patterns of shrublands and the underlying driving factors is necessary to understand the adaptive mechanisms of plants to habitat stresses as well as the influences of environmental changes on vegetation dynamics. In this study, we classified vegetation types with k-means clustering, explored the factors governing their distribution through canonical correspondence analysis(CCA), and analyzed the relationships between climate and functional traits of indicator species, based on the field data of 2,400 shrubland communities across northern China. We classified 29 typical shrubland alliances with considerable differences in geographic distributions, habitat conditions, and community structures. The mean annual precipitation was positively correlated with average species richness and plant coverage of each alliance. The first two CCA ordination axes(CCA1 and CCA2) represented water and energy availabilities, respectively. Shrublands from northern China exhibited two gradients, namely, along the wet-cold to dry-hot gradient and along the cold to hot gradient when water availability was relatively high. The leaf thickness and specific leaf area of indicator species were negatively and positively correlated with water availability, respectively, indicating that water conditions regulated the trade-off between leaf functional traits. These results suggest that water availability is a more important constraint on the distribution pattern of shrublands in northern China than the energy availability. The water availability could not only affect community structures but also select for adaptive dominant shrubs along the leaf economics spectrum to determine shrubland alliances. This study reveals an ecological process that shapes shrubland distribution,and our classification of shrublands could serve as the foundation for a more comprehensive classification system for shrublands in China.