PS 26-60 - Growth and Physiological Responses of Pinus densiflora Seedlings to Extreme Climate Events and Subsequent Recovery

Background/Question/Methods

According to the IPCC Fifth Assessment Report, the frequency and intensity of extreme climate events have increased since 1950, and the trend is expected to further increase in the 21^st century. Since most meteorological disasters are caused by extreme climate events, the severity of the climate crisis has been greatly emphasized, yet the responses of plants to extreme climate events have not been fully understood. This study aimed to observe the impact of extreme climate events on the physiological and growth responses and subsequent recovery of two-year-old Pinus densiflora seedlings. The 90th percentile of the warm spell and consecutive dry days were used to define extreme warming and extreme drought, respectively. The extreme warming treatment was designed to increase the air temperature by 4 ℃ compared to the temperature control plots and was carried out for six weeks. The drought treatment was designed to block precipitation for four weeks completely.

Results/Conclusions

The extreme drought treatment reduced transpiration rate, stomatal conductance, net photosynthetic rate, and leaf water content by 49.0%, 49.3%, 27.2%, and 44.9%, respectively, and resulted in the decrease of biomass and seedling quality. Additionally, a decrease in leaf water content induced an increase in specific leaf area by 64.6%, resulting in an elevating total chlorophyll content per unit weight by 20.9%. The extreme warming treatment reduced transpiration rate, stomatal conductance, and net photosynthetic rate by 34.7%, 35.0%, and 19.4%, respectively. During the recovery, P. densiflora seedlings in extreme warming and drought treatments showed a more significant increase in leaf gas exchange rates and biomass growth rates. The increased leaf gas exchange rates were likely to offset the differences in biomass growth between extreme climate events treatments plots and control plots. In conclusion, environmental stresses caused by extreme climate events throughout May–June can impair leaf gas exchange mechanisms and result in biomass reduction, although the effect could be mitigated in autumn if temperature and precipitation remain at average year levels. Additionally, four weeks of the extreme drought treatment had a more significant negative impact on P. densiflora seedlings than six weeks of the extreme warming treatment.