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Asymmetric daytime and nighttime warming broadly affects terrestrial ecosystem carbon cycling in the Northern Hemisphere. Photosynthesis mostly occurs in the daytime and respiration occurs during the whole day. Then AW D-N will certainly affect the ratio between net primary productivity (NPP) against gross primary productivity (GPP), i.e. vegetation carbon use efficiency (CUE). However, how night and daytime warming differentially affects CUE remains unclear on a global scale. Using long-term productivity datasets from MODIS and terrestrial biosphere models, we investigated spatiotemporal patterns of CUE response to daytime (Tmax) and nighttime (Tmin) temperature changes across the Northern Hemisphere (>30°N) spanning 2000–2019. Regions exhibiting a negative correlation between Tmax and CUE were extensive throughout the growing season in most northern ecosystems, with a stronger correlation magnitude in summer than in spring and autumn. Tmin warming tended to cause a positive impact on CUE in spring and autumn, while being correlated negatively with summer CUE, resulting in an overall weak positive relationship between CUE and Tmin. Divergences in the strength and direction of productivity and respiratory responses to AW D-N lead to spatial and seasonal patterns between CUE and Tmax or Tmin, and this pattern is regulated by soil moisture. Our findings provide an in-depth understanding on how the interactions between AW D-N and water limitations regulate the spatiotemporal variations of vegetation gross primary product allocation, which is vital for improving model performance. • Daytime warming has decreased CUE, while night warming has weakly increased CUE. • The net effect is a modest CUE decreasing in response to asymmetric diurnal warming. • The response pattern is regulated by regional moisture conditions. [ABSTRACT FROM AUTHOR]

The alpine ecosystems on the Qinghai-Tibetan Plateau are quite sensitive to climate change. The increasing temperature and changing precipitation patterns greatly affect the gross primary productivity (GPP) and disturb the carbon balances of these alpine ecosystems. To clarify the impacts of future climate change across the Qinghai-Tibetan Plateau, it is important to address the scientific issue "Which factor would dominate interannual variability (IAV) in GPP and through which path does it work?" To clarify this issue, two key processes, growing season length (GSL) and maximum photosynthetic capacity (GPP max), were introduced to reveal the underlying mechanisms, and which of the environmental factors dominated their variations were studied specifically based on the flux and corresponding environmental observation data obtained in different types of alpine ecosystems across the Qinghai-Tibetan Plateau in this study. The results indicated that across the temperature- and water-limited alpine ecosystems, the temperature controlled the GSL, but the water conditions dominated the variations in GPP max. The soil water content (SWC) dominated GPP max , which could explain 89% of the variation in GPP max. The GSL alone was incapable of explaining IAV in GPP. Conversely, GPP max is robust in explaining IAV in GPP, which could explain 94% of the annual GPP. Therefore, climate change would probably drive IAV in GPP through the path of "SWC → GPP max → annual GPP" on the Qinghai-Tibetan Plateau. In addition, GPP max together with GSL (GSL × GPP max) could explain 99% of IAV in GPP, as they indicated the length of the carbon uptake time and the capacity of carbon sequestration, respectively. This study provides a new perspective on the predominant causes of IAV in GPP in alpine ecosystems, indicating that the changing precipitation patterns under future climate change will play a dominant role in affecting the carbon sink function of the Qinghai-Tibetan Plateau. [Display omitted] • Temperature dominated the growing season length (GSL) in alpine ecosystems. • Soil water content (SWC) dominated the maximum photosynthetic capacity (GPP max). • GPP max rather than GSL dominated the annual GPP. • GSL and GPP max coexplained 99% of the interannual variability in annual GPP. • Climate change drove GPP through two key underlying processes: GSL and GPP max. [ABSTRACT FROM AUTHOR]

Greening of the Earth is among the world's most important ecological changes in recent decades, but its effects and triggers are multifaceted and varied across the globe. Climate change is the primary driver for greening of the Tibetan Plateau (TP), where vegetation is of great significance for resident survival, carbon sequestration and climate feedbacks. However, the spatial variability of greening and its drivers are not well-understood on the TP. Here, we compiled multi-source vegetation indices, climate and atmospheric data to investigate the greenness spatiotemporal variability and its linkage with large-scale climate oscillations. We found that greening dominated the TP during 1980s–2010s and positive trends in satellite-based vegetation indices account for >70% of the TP. Specifically, the arid and semi-arid TP experienced a significant and higher greening rate due to the remarkable increase in precipitation. We further clarified the domains of the South Asian monsoon (SAMI1 and SAMI2), the westerly wind (WI) and the plateau monsoon (TPMI) on the TP, and realized that the wetness increase in the arid and semi-arid was correlated with a weakening WI. Detecting the linkage between WI with large-scale climate oscillations, we suggested that the decadal weakening WI was induced by a warmer North Atlantic SST (positive AMO phase), which triggered wave train anomalies and regulated zonal and meridional vapor transport across Eurasia. Generally, during the weak/negative WI phase, anticyclone anomalies centered over Mongolia may strongly reduce vapor output across the east boundaries, while cyclone anomalies centered over the northwest outside the TP likely enhance meridional vapor transport into the western TP from the south ocean. Eventually, precipitation over the arid and semi-arid TP increased significantly in the past four decades, that stimulated plant growth and greening pattern on the TP. Our results established the linkage among climate oscillations, regional climate alteration and vegetation greening, providing a more thorough understanding in terrestrial greening. • Approximately 70% areas of Tibetan Plateau (TP) were greening at the past four decades. • The greening of TP was dominated by the wetting in arid and semi-arid areas. • The decadal weakening of westerly wind dominated wetting over the TP, thus actuated the greening of TP. [ABSTRACT FROM AUTHOR]