Dominant role of plant physiology in trend and variability of gross primary productivity in North America

Sha Zhou (1) , Yao Zhang (2) , Philippe Ciais (3) , Xiangming Xiao (2) , Yiqi Luo (2) , Kelly Caylor (4) , Yuefei Huang (1) , Guangqian Wang (1)

1 THU - Tsinghua University [Beijing]
2 OU - University of Oklahoma
3 ICOS-ATC - ICOS-ATC
4 Princeton University

Annual gross primary productivity (GPP) varies considerably due to climate-induced changes in plant phenology and physiology. However, the relative importance of plant phenology and physiology on annual GPP variation is not clear. In this study, a Statistical Model of Integrated Phenology and Physiology (SMIPP) was used to evaluate the relative contributions of maximum daily GPP (GPP max) and the start and end of growing season (GS start and GS end) to annual GPP variability, using a regional GPP product in North America during 2000-2014 and GPP data from 24 AmeriFlux sites. Climatic sensitivity of the three indicators was assessed to investigate the climate impacts on plant phenology and physiology. The SMIPP can explain 98% of inter-annual variability of GPP over mid-and high latitudes in North America. The long-term trend and inter-annual variability of GPP are dominated by GPP max both at the ecosystem and regional scales. During warmer spring and autumn, GS start is advanced and GS end delayed, respectively. GPP max responds positively to summer temperature over high latitudes (40-80°N), but negatively in mid-latitudes (25-40°N). This study demonstrates that plant physiology, rather than phenology, plays a dominant role in annual GPP variability, indicating more attention should be paid to physiological change under futher climate change. The importance of plant phenology shifts and physiology change on annual GPP variability is evident 1-4. Warming-induced earlier leaf emergence enhances terrestrial carbon uptake in spring, whereas later leaf senescence in autumn also leads to a smaller increase in carbon uptake in North American temperate forests 5. However, drought events associated with high temperature and low water availability can decrease plant photo-synthetic uptake 6-8. In regions exposed to summer drought, an increase of leaf area in earlier spring can accelerate soil drying, and lead to increased vulnerability of GPP in summer 9,10. In terms of net carbon balance, carbon loss during summer drought can negate increased uptake in warmer springs and autumns 11-13 , related to the negative covariance between increased spring productivity and decreased yearly productivity. The different responses of plant phenology and physiology to climate anomalies, and the contributions of phenological and physiological changes to annual GPP variability must thus be disentangled. The joint control of plant phenology and physiology on annual GPP can be expressed by constructing a statistical model 4,14 , which uses indicators to represent plant phenological and physiological changes. Phenology is about the time and duration of a process or event. The length of carbon uptake period (CUP), and the start (GS start) and the end (GS end) of the growing season, can be used as indicators of plant phenology. Plant pho-tosynthesis is an important process of plant physiology, and can reflect the responses of plant physiology to

Mots clés: Carbon cycle; Climate-change impacts

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Sha Zhou, Yao Zhang, Philippe Ciais, Xiangming Xiao, Yiqi Luo, et al.. Dominant role of plant physiology in trend and variability of gross primary productivity in North America. Scientific Reports, 2017, 7 (1), pp.41366. ⟨10.1038/srep41366⟩. ⟨hal-02903491⟩