摘要:植物物候是植物为适应其生长环境而呈现的规律性变化，是气候变化的指示器。为了解高寒植物物候对温度变化的响应，利用1997-2010年青海湖海北高寒草原生态监测站群落优势种矮嵩草物候观测资料和同时段的气象资料，应用偏最小二乘（PLS）回归定量分析了植物物候期变化特征、趋势及其与气温间的相互关系。结果表明：①1997-2010年青海湖地区年均温度总体上升，倾向率为0.5℃/10a，其中年均最高温度和最低温度呈现出非对称型变化，最低温度显著升高且高于年均温升幅，倾向率为0.7℃/10a（P < 0.05），而年均最高温度无明显变化。②1997-2010年间，矮嵩草平均返青期和枯黄期分别为4月18日和10月2日，矮嵩草返青期推迟，枯黄期提前，生长季长度缩短。③影响矮嵩草返青的关键时期为每年的1月和3-4月，1月温度升高影响植物休眠进程进而延迟返青，而3-4月温度升高有利于热量积累使返青提前；影响矮嵩草枯黄的关键时期为7月上中旬和8月，期间温度升高使枯黄期提前。④根据PLS分析和相关分析，最低温度在各关键时期内显著影响植物物候，而最高温度仅在8月对枯黄期影响通过显著性检验，因此最低温度是影响高寒草地矮嵩草物候期的关键因子。



Abstract:Vegetation phenology, considered as an ideal indicator of climate change, is a key aspect of plant life strategy that determines the ability to capture seasonally variable resources. As an important climatic factor, temperature substantially impacts vegetation phenology in many parts of the world and shows dominant effects in the plateau area particularly. During the past few decades, warming in Tibetan Plateau is believed to have been higher than that for the rest of the globe, particularly in the trend that daily minimum temperature (T_min) increased significantly faster than daily maximum temperature (T_max). However, the alpine vegetation phenological response to asymmetric increases in T_min and T_max is unknown. The underlying mechanism provides the novel insight that asymmetric changes in T_min and T_max should be explicitly considered in dynamic global vegetation models to elucidate the effects of climate change on vegetation phenology. Owing to the lack of in-situ observations, assessments of vegetation phenological changes in the Tibetan Plateau are mainly dependent on remote sensing data. However, because of relatively coarse spatial and temporal resolutions, as well as many other factors (data sources, retrieval methods), remote sensing information introduces great uncertainty to vegetation phenology determinations. Great controversy has arisen about the satellite-based delayed trend of spring phenology induced by current global warming in the Tibetan Plateau, as there is an absence of adequate field observations. Hence, based on in-situ observations of the dominant species Kobresia humilis in the Qinghai Lake region, the largest inlet lake in the northeastern part of the Tibetan Plateau, we use partial least squares (PLS) regression to reveal the characteristics of plants phenology and their variations, as well as the potential response mechanisms of alpine plants to asymmetric increases in T_min and T_max on a daily scale. The results indicated that (1) from 1997 to 2010, the mean temperature increased in the Qinghai Lake area at a rate of 0.5℃/10 a, the mean minimum temperature also significantly increased at a rate of 0.7℃/10 a (P < 0.05), and the mean maximum temperature showed no obvious change. (2) From 1997 to 2010, the average green-up and leaf coloring dates of Kobresia humilis were April 18th and October 2^nd, respectively. With delayed green-up date and early coloring date, the length of the growing season decreased. (3) The critical periods of temperature for the green-up dates of Kobresia humilis were January and March-April. To be specific, warming in January postponed the fulfillment of chilling requirement during the dormant period and consequently delayed the vegetation green-up date. In contrast, temperature increases in March-April accelerated the accumulation of heat and thus resulted in an early onset of spring green-up. In terms of the end of growing season, the critical periods of temperature for coloring dates were early-to mid-July and August. Specifically, warming in these periods shifted the vegetation coloring date to occur earlier. (4) Based on the results of PLS regression and correlation analysis, T_min significantly impacted plants phenology during each critical period; however, T_max only showed a significant impact on the coloring dates in August. Conclusively, T_min played a dominant role in controlling the phenology of Kobresia humilis in the Tibetan Plateau.





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