The Effects of Warming-Shifted Plant Phenology on Ecosystem Carbon Exchange Are Regulated by Precipitation in a Semi-Arid Grassland

BackgroundThe longer growing season under climate warming has served as a crucial mechanism for the enhancement of terrestrial carbon (C) sink over the past decades. A better understanding of this mechanism is critical for projection of changes in C cycling of terrestrial ecosystems.
Methodology/Principal FindingsA 4-year field experiment with day and night warming was conducted to examine the responses of plant phenology and their influences on plant coverage and ecosystem C cycling in a temperate steppe in northern China. Greater phenological responses were observed under night than day warming. Both day and night warming prolonged the growing season by advancing phenology of early-blooming species but without changing that of late-blooming species. However, no warming response of vegetation coverage was found for any of the eight species. The variances in species-level coverage and ecosystem C fluxes under different treatments were positively dependent upon the accumulated precipitation within phenological duration but not the length of phenological duration.
Conclusions/SignificanceThese plants' phenology is more sensitive to night than day warming, and the warming effects on ecosystem C exchange via shifting plant phenology could be mediated by precipitation patterns in semi-arid grasslands.

研究背景：近几十年来，气候变暖背景下更长的生长季是增强陆地碳汇（terrestrial carbon (C) sink）的关键机制。深入理解该机制，对预测陆地生态系统碳循环变化至关重要。研究方法与主要发现：本研究在中国北方温带草原开展了为期4年的野外增温实验，设置日间增温和夜间增温处理，旨在探究植物物候（phenology）的响应特征，及其对植物盖度与生态系统碳循环的影响。结果显示，夜间增温下植物物候的响应幅度高于日间增温。日间与夜间增温均通过提前早开花物种的物候期延长了生长季，但未改变晚开花物种的物候期。然而，8个受试物种均未表现出植被盖度对增温的响应。不同处理下，物种水平盖度与生态系统碳通量的变异，与物候期内的累积降水量呈正相关，而与物候期长度无显著关联。研究结论与意义：本研究表明，植物物候对夜间增温的敏感性高于日间增温；在半干旱草原生态系统中，增温通过改变植物物候对生态系统碳交换产生的影响，可由降水格局所介导。