11 January, 2020 (Piao, GCB, Phenology)

Piao S, Liu Q, Chen A, et al. Plant phenology and global climate change: Current progresses and challenges. Global Change Biology, 2019;00:1–19. https://doi.org/10.1111/gcb.14619

Piao et al. (2019) reviewed the current understanding of leaf phenological processes. They suggested that four key factors are driving the phenological processes: 1) temperature, 2) photoperiod, 3) nutrient and water availability, and 4) interseasonal phenological correlations (i.e. the positive spring and autumn phenological intercorrelation).

Temperature regulates periods of endo- and eco-dormancy of leaves. Low temperature stimulates the endodormancy to break; the required amount of accumulated low temperature is numerically represented as a chilling requirement. By the same token, warming is needed to break the ecodormancy before the spring leaf-out. It seems that the amount of the temperature effect differs by circumstances. For example, the warming effect on spring phenology is larger during the daytime than nighttime (Rossi and Isabel, 2017). Also, the spring leaf-out responds less to further warming due to the insufficient chilling accumulation during warmer winters (Fu et al., 2015).

The major effect of photoperiod on leaf phenology is to induce bud set and leaf senescence. However, its effect on spring phenology is still poorly understood. A longer photoperiod with the warmer climate may compensate for the reduced chilling accumulation (Way and Montgomery, 2015), thereby stimulating the spring leaf-out (Chuine et al., 2010). On the other hand, it is also possible that the photoperiod prevents too early leaf-out in spring by reducing sensitivity to warming (Flynn and Wolkovich, 2018).

Sufficient nutrients during the growing season prepare trees well for the freezing stress, postponing the autumn senescence (Sakai and Larcher, 1987). Elevated atmospheric CO2 concentration may also delay the timing of leaf senescence because it enhances water use efficiency of trees and prevents the water stress that causes earlier leaf fall (Reyes-Fox et al., 2014). Water availability also influences leaf phenology.

Precipitation may be a key factor determining the spring and autumn phenology (Fu et al., 2014, Liu et al., 2016). The snowmelt stimulates root development in spring, leading to leaf flushing (Yun et al., 2018). Water availability may also be linked with the effect of a nutrient on phenology because plants uptake nutrients and water at the same time by their roots.