Fu Yongshuo H, Piao Shilong, Vitasse Yann, Zhao Hongfang, De Boeck Hans J, Liu Qiang, Yang Hui, Weber Ulrich, Hänninen Heikki, Janssens Ivan A
College of Urban and Environmental Sciences, Peking University, Yiheyuan Road 5, 100871, Beijing, China.
Department of Biology, Centre of Excellence PLECO (Plant and Vegetation Ecology), University of Antwerp, Universiteitsplein 1, B-2610, Wilrijk, Belgium.
Glob Chang Biol. 2015 Jul;21(7):2687-2697. doi: 10.1111/gcb.12863. Epub 2015 Mar 6.
Recent studies have revealed large unexplained variation in heat requirement-based phenology models, resulting in large uncertainty when predicting ecosystem carbon and water balance responses to climate variability. Improving our understanding of the heat requirement for spring phenology is thus urgently needed. In this study, we estimated the species-specific heat requirement for leaf flushing of 13 temperate woody species using long-term phenological observations from Europe and North America. The species were defined as early and late flushing species according to the mean date of leaf flushing across all sites. Partial correlation analyses were applied to determine the temporal correlations between heat requirement and chilling accumulation, precipitation and insolation sum during dormancy. We found that the heat requirement for leaf flushing increased by almost 50% over the study period 1980-2012, with an average of 30 heat units per decade. This temporal increase in heat requirement was observed in all species, but was much larger for late than for early flushing species. Consistent with previous studies, we found that the heat requirement negatively correlates with chilling accumulation. Interestingly, after removing the variation induced by chilling accumulation, a predominantly positive partial correlation exists between heat requirement and precipitation sum, and a predominantly negative correlation between heat requirement and insolation sum. This suggests that besides the well-known effect of chilling, the heat requirement for leaf flushing is also influenced by precipitation and insolation sum during dormancy. However, we hypothesize that the observed precipitation and insolation effects might be artefacts attributable to the inappropriate use of air temperature in the heat requirement quantification. Rather than air temperature, meristem temperature is probably the prominent driver of the leaf flushing process, but these data are not available. Further experimental research is thus needed to verify whether insolation and precipitation sums directly affect the heat requirement for leaf flushing.
近期研究发现，基于热量需求的物候模型存在大量无法解释的差异，这导致在预测生态系统碳和水平衡对气候变化的响应时存在很大的不确定性。因此，迫切需要增进我们对春季物候热量需求的理解。在本研究中，我们利用欧洲和北美的长期物候观测数据，估算了13种温带木本植物叶片萌发的物种特异性热量需求。根据所有观测点叶片萌发的平均日期，将这些物种定义为早萌物种和晚萌物种。应用偏相关分析来确定热量需求与休眠期冷积累、降水量和日照总量之间的时间相关性。我们发现，在1980 - 2012年的研究期间，叶片萌发的热量需求增加了近50%，平均每十年增加30个热量单位。所有物种都出现了这种热量需求随时间的增加，但晚萌物种的增加幅度远大于早萌物种。与之前的研究一致，我们发现热量需求与冷积累呈负相关。有趣的是，在去除冷积累引起的变化后，热量需求与降水总量之间主要呈正偏相关，与日照总量之间主要呈负相关。这表明，除了众所周知的冷效应外，叶片萌发的热量需求还受到休眠期降水量和日照总量的影响。然而，我们推测，观测到的降水和日照效应可能是由于在热量需求量化中不恰当地使用气温而产生的假象。分生组织温度可能才是叶片萌发过程的主要驱动因素，而非气温，但目前尚无这些数据。因此，需要进一步开展实验研究，以验证日照和降水总量是否直接影响叶片萌发的热量需求。
