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Studying the differences in phenology among plant species is important for understanding their physiological and reproductive responses to climate change and complex inter-species interactions. This study conducted a comparative analysis of the spatio-temporal variation in the phenologies of two herbaceous species ( Plantago asiatica and Taraxacum mongolicum ) and associated climatic driving factors on the Tibetan Plateau (TP) based on ground-observed phenology data during 2000–2012. The results indicated that both spring and autumn phenology of the two species showed strong dependences on altitude, latitude and longitude, although the magnitudes of the variation with geographical factors were different among species. Change in altitude contributed the most to the spatial variation in phenology for both species. In addition, strong dependences on altitude were also observed for the phenological differences between the two species. With the increase of altitude, the same phenophases of the two species tended to occur synchronously at first and then the chronological order of the same phenophases between the two species changed. Spring and autumn phenophases showed significant negative correlations with the growing degree-days (GDD) and the cold degree-days (CDD) ( p 0.001), respectively. Moreover, the phenophases of T. mongolicum were more sensitive than those of P. asiatica in response to GDD or CDD, which explained the spatial variation in the phenological difference between the two species. The divergent phenological responses to climate change and the spatial variation in phenological differences between P. asiatic a and T. mongolicum may alter the inter-species interactions between the two species.

Phylogenetic studies on the leaf unfolding date are expected to improve understanding of phenological change. However, it remains unclear whether the response of leaf unfolding date to temperature is phylogenetically conserved among close relatives across differential and harsh habitats. Meanwhile, the phenological mechanism underlying the role of phylogenetic relationship on plant phenology remains unclear. We used Blomberg's K to assess phylogenetic signal in leaf unfolding date, its sensitivities to daily mean, minimum and maximum temperatures, in growing-degree-days and average level of each of daily mean, minimum and maximum temperatures experienced by plants over a given period prior to leaf unfolding date for eighteen species at seventeen sites in the Tibetan Plateau. We showed that leaf unfolding date and its sensitivities to daily mean, minimum and maximum temperatures did not exhibit overall significant phylogenetic signals. Moreover, the sensitivity of leaf unfolding date to daily minimum temperature exhibited phylogenetic antisignal at species level, which indicated the trait difference among close relatives exceed that among distantly related lineages. However, there were overall significant phylogenetic signals in growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures experienced by plants before leaf unfolding date. The signals were stronger for the growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures in the period closer to leaf unfolding date. Our results imply that close relatives trace similar heat requirements for leaf unfolding date in the harsh and spatially heterogeneous environment of the Tibetan Plateau. However, the time when these lineage-specific heat requirements are met varies spatially depending on local conditions, thereby resulting in phylogenetic non-conservatism of leaf unfolding date and its temperature sensitivities. This provides a phenological explanation, for the first time, for phylogenetic non-conservatism in plant leafing phenology.

Autumn phenology along with spring/summer phenology controls the length of the vegetation growing season and significantly influences ecosystem biogeochemical cycles. Many previous studies have focused on spring/summer phenology. However, fewer studies have addressed autumn phenology because of no available or insufficient observations. Based on a series of long-term and continuous observations of autumn phenological events (8000+ records) on the Qinghai-Tibetan Plateau (QTP), we made a comprehensive assessment of autumn phenological shifts and their responses to climate change during the period from 1981 to 2011. Although a significantly delayed overall trend in autumn phenology was observed across the QTP from 1981 to 2011, the autumn phenologies showed divergent shifting trends and responses to climate change among plant species, phenological events, study periods and thermal conditions. Larger variations were observed for the occurrence dates of fruit-related events than foliar events. Significantly advanced shifts in autumn phenology were observed for woody plants (mostly owing to fruit-related phenological events), while significantly delayed shifts were observed for herbaceous plants (mostly owing to foliar events). The autumn phenology of woody plants varied little among plant species, recording periods and thermal conditions but varied greatly under different temperature change trends. The autumn phenology of herbaceous plants varied greatly among plant species, recording periods, thermal conditions and sites with different temperature change trends. The occurrence dates of most phenological events for herbaceous plants were positively correlated with the preseason temperature and negatively correlated with the preseason precipitation, while opposite relationships were observed for woody plants. Our results provide new field evidence for the dispersive changes in autumn phenology on the QTP and suggest that the dispersive shifts in autumn phenology and their different responses to climate warming should be considered when assessing the impacts of climate change on vegetation dynamics and ecosystem biogeochemical cycles.

The Qinghai-Tibetan Plateau (QTP) is more vulnerable and sensitive to climate change than many other regions worldwide because of its high altitude, permafrost geography, and harsh physical environment. As a sensitive bio-indicator of climate change, plant phenology shift in this region has been intensively studied during the recent decades, primarily based on satellite-retrieved data. However, great controversy still exists regarding the change in direction and magnitudes of spring-summer phenology. Based on a large number (11,000+ records) of long-term and continuous ground observational data for various plant species, our study intended to more comprehensively assess the changing trends of spring-summer phenology and their relationships with climatic change across the QTP. The results indicated a continuous advancement (−2.69 days decade −1 ) in spring-summer phenology from 1981 to 2011, with an even more rapid advancement during 2000–2011 (−3.13 days decade −1 ), which provided new field evidence for continuous advancement in spring-summer phenology across the QTP. However, diverse advancing rates in spring-summer phenology were observed for different vegetation types, thermal conditions, and seasons. The advancing trends matched well with the difference in sensitivity of spring-summer phenology to increasing temperature, implying that the sensitivity of phenology to temperature was one of the major factors influencing spring-summer phenology shifts. Besides, increased precipitation could advance the spring-summer phenology. The response of spring-summer phenology to temperature tended to be stronger from east to west across all species, while the response to precipitation showed no consistent spatial pattern.

Daily temperature data from 1960 to 2013 and field-observed phenology data were used to investigate the spatiotemporal changes in thermal growing season and their relationship with the response of alpine grassland to climate variability in the Three-Rivers Headwater Region (TRHR) during the recent decades. We found a significant extension of the thermal growing season by 8.3 d per decade (p

Phenology is an important indicator of the biological responses to climate change, and previous studies have reported divergent phenological responses of grasslands in Inner Mongolia from the analyses of in-situ measurements and satellite observations; thus, robust phenology models are required to understand and simulate the relationship between ecosystems and climate change. However, phenology models for natural grasslands in which heating accumulation, chilling requirements, precipitation effects and other climate factors are introduced at the same time are relatively deficient; as a result, the accuracy of the herbaceous plant phenology model and its universality across different species and regions are restricted. We proposed an improved phenology model (unified model combined with precipitation driving, UMPD) that reflects the combined effect of temperature and precipitation at the forcing unit level. Green-up evaluation based on satellite observations shows that the UMPD phenology model achieves better accuracy than previous models (RMSE