Chilling Accumulation Is Not an Effective Predictor of Vegetation Green‐Up Date in Inner Mongolian Grasslands

Abstract

As an adaptation strategy, plants shift their phenology in response to environmental variations such as climate change (Richardson et al., 2018). The vegetation green-up date (VGD) during spring indicates the beginning of photosynthetic activity thereby having substantial implications on carbon cycling and energy exchange in global terrestrial ecosystems (Cleland et al., 2007;Piao et al., 2015). In general, satellite-based observations suggested that VGD in the northern hemisphere has been advancing in a warming world (Barichivich et al., 2013;Jeong et al., 2011). A widely recognized mechanism underpinning this phenomenon is that the heat requirement (HR) to break plant ecodormancy can be fulfilled earlier under a warmer climate (Fu et al., 2012;Shi et al., 2017).Prior to beginning of ecodormancy, plants experience a phase of endodormancy, which can be released when a certain low temperature (i.e., chilling) is accumulated (N.K. Dokoozlian, 1999). The absence or inadequate chilling accumulation (CA), however, can lead to a postponed VGD (Meng et al., 2020). In this case, insufficient CA under a warmer condition might potentially offset the warming-induced advancement of VGD (Cook et al., 2012). For example, Yu et al. ( 2010) attributed the delayed VGD of alpline grasslands in Tibetan Plateau (TP) during mid-1990s-2006 to declined CA induced by warming. However, growing evidences have shown that fulfillment of chilling requirement (CR) was not slowed in this region. This is because winter there is long and cold, thus CA is always adequate and has limited effect on release of endodormancy (Chen et al., 2015;Cong et al., 2017).