5. Dr. Yongjiang Zhang

Extreme drought events are becoming increasingly frequent globally, resulting in widespread plant mortality and forest dieback. Although covering approximately 20% of the land area, responses of savanna plants to extreme drought have been less studied compared to forests. The savannas in Southwest China experienced extreme drought events in 2015, 2019 and 2020. Both evergreen and deciduous species showed high drought resistance and limited mortality, while semi-deciduous species had the highest branch dieback and mortality. Branch dieback and mortality were well-explained by hydraulic traits like embolism resistance and hydraulic safety margins, but the prediction power is affected by leaf habit and growth form. For evergreen shrubs, although they showed high branch dieback, individual mortality was low. They showed high resistance to xylem embolism. The low water potentials (-7.6 MPa to -10.0 MPa) during the drought caused embolism levels from 23% to 65% in terminal branches, and the remaining stems maintained 15% to 35% xylem embolism at the end of the drought. Large within-individual variations in stem vulnerability to embolism were detected, and the shedding of vulnerable branches could be a mechanism for shrubs to reduce water and carbon consumption. Our results suggest that both evergreen species with strong drought tolerance and deciduous plants with drought avoidance can resist extreme drought, while those with an intermediate strategy showed high sensitivity.  Additionally, high embolism resistance, shedding of vulnerable branches, and resprouting after drought allow high resilience of evergreen shrubs under extreme drought.