Background and aims

Understanding of the influences of soil moisture changes on plant phenological shifts on the Qinghai–Tibetan Plateau (QTP) is insufficient mainly because previous studies focused on the climatic factors. We explored the role of soil moisture in regulating plant autumn phenology on the QTP.

Methods

Based on long-term ground observations of soil moisture, plant phenology, and meteorology, temporal and spatial changes in soil moisture and leaf senescence dates (LSD) were analyzed using ordinary least squares regression and a meta-analysis procedure. Influences of soil moisture changes on the LSD shifts were assessed through correlation analysis and support vector machine, and also compared with those of air temperature and precipitation.

Results

Nonsignificant interannual changes in soil moisture were observed, and LSD significantly delayed at a rate of 2.7 days/decade. Spatial changes of LSD were more correlated with site elevation and air temperature, and soil moisture and precipitation showed insignificant negative impacts. However, correlations between annual LSD and average soil moisture were mainly positive. Soil moisture and precipitation showed greater importance in regulating the LSD of sedges and grasses, whereas temperature exerted a larger influence on the LSD of forbs. Precipitation showed higher importance in regulating the interannual shifts in LSD, while temperature played a more important role in determining the spatial variations.

Conclusion

Soil moisture had divergent influences on the temporal and spatial shifts in LSD of different plant functional groups on the QTP. Overall, soil moisture was outweighed by temperature and precipitation in regulating autumn phenological shifts. However, soil moisture may become increasingly important in the future and forbs are expected to be more competitive if the QTP becomes warmer and drier, which will bring challenges in grassland management and utilization on the QTP.

中文翻译：

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土壤水分变化对青藏高原草本植物叶片衰老日期的不同影响

 背景和目标

对青藏高原 （QTP） 土壤水分变化对植物物候变化影响的认识不足，主要是因为以前的研究集中在气候因素上。我们探讨了土壤水分在高原种子中对植物秋季物候的调控作用。

 方法

基于对土壤水分、植物物候和气象的长期地面观察，使用普通最小二乘回归和荟萃分析程序分析土壤水分和叶片衰老日期 （LSD） 的时空变化。通过相关性分析和支持向量机评估土壤水分变化对 LSD 变化的影响，并与气温和降水进行比较。

 结果

观察到土壤水分的年际变化不显著，LSD 以 2.7 d/decade 的速度显着延迟。LSD 的空间变化与立地海拔和气温的相关性更强，土壤水分和降水表现出不显著的负面影响。然而，年际 LSD 与平均土壤水分之间的相关性主要是正相关。土壤水分和降水在调节莎草和禾本科植物的 LSD 中表现出更大的重要性，而温度对杂草的 LSD 影响更大。降水在调节 LSD 的年际变化中表现出更高的重要性，而温度在决定空间变化中起着更重要的作用。

 结论

土壤水分对 QTP 上不同植物功能群 LSD 的时空变化存在不同的影响。总体而言，在调节秋季物候变化方面，温度和降水超过了土壤水分。然而，如果 QTP 变得更温暖和更干燥，预计未来土壤水分可能会变得越来越重要，杂草将更具竞争力，这将给 QTP 上的草地管理和利用带来挑战。