放牧和模拟增温对藏北高寒草地植物群落特征及生产力的影响

气候变化和放牧活动对草地植物物种多样性和生产力具有重要影响。为探索藏北高寒草地植物物种多样性和生产力对增温、放牧及其交互作用的响应, 于2011年在藏北高原开始建立增温实验平台, 2016年起增设放牧、增温+放牧实验, 连续2年(2016-2017年)观测了植物群落特征、群落组成、生产力和物种多样性。结果表明, 增温和放牧对高寒草地植物高度和净初级生产力具有显著交互作用。在放牧条件下, 增温对植物高度无显著影响; 但在不放牧条件下, 增温却显著增加了植物高度。在放牧条件下, 增温对净初级生产力的影响存在年际差异, 2016年增温对生产力无显著影响, 2017年增温显著降低了植物净初级生产力; 但在不放牧条件下, 增温对植物净初级生产力无显著影响。增温和放牧对高寒草地植物物种丰富度、盖度、重要值及多样性均无显著交互作用。植物盖度在增温和放牧条件下显著降低, 杂类草物种比例显著增加, 但物种多样性均无显著变化。研究表明, 增温和放牧显著改变高寒草地群落结构。未来气候变化条件下, 放牧活动加剧有可能导致高寒草地生产力降低。

Effects of grazing and simulated warming on plant community structure and productivity of alpine grassland in Northern Xizang,China

Aims Climate change and grazing activities have important effects on species diversity and productivity of grassland ecosystems. The aim of this study is to reveal the differences in responses of species diversity and productivity to warming, grazing and their interactions in an alpine meadow ecosystem. Methods Warming experiment was established in 2011. In 2016, the grazing experiment and the combination of warming and grazing experiment were added. A two-year continuous field experiment was conducted (from 2016 to 2017) and plant community structure, community composition, productivity and species diversity were monitored. Twelve sites were sampled, and were divided into four treatments: control, warming, grazing and the combination of warming and grazing. All sampled species were classified into three functional groups: sedges, grasses and forbs. The species diversity and productivity were sampled in three different treatments. Important findings Results showed that warming and grazing had significant interaction on vegetation height and net primary productivity in alpine grassland. Under grazing treatment, warming had no significant effect on plant height, while warming significantly increased plant height without grazing. Under grazing treatment, the warming effect on net primary productivity significantly differed between 2016 and 2017. In 2016, warming had no significant effect on net primary productivity, while in 2017, warming significantly decreased net primary productivity. Warming and grazing had no significant interaction on species richness, coverage, species important value and species diversity in the alpine meadow. Under the treatments of warming and grazing, the total vegetation coverage decreased, and the proportion of forbs significantly increased. However, no significant effect of warming or grazing was found on species diversity. This study showed that warming and grazing significantly changed the community structure of alpine grassland. Therefore, with the projected climate change in the future, the intensification of grazing activities may lead to the decrease of alpine meadow productivity.