PS 26-66 - Impact of summer extreme climate events on seed germination of Pinus densiflora

Background/Question/Methods

Extreme climate events have occurred more frequently and intensely compared to the past due to climate change. Temperature and precipitation are the most important environmental factors which affect the speed and percentage of seed germination. Since extreme climate events can induce irreversible damage during the embryo development of seeds, it is highly important to figure out the seed germination responses to extreme abiotic stresses. Pinus densiflora, the most widely distributed coniferous species in South Korea, is known for being vulnerable to climate change. Here, we investigated the impact of experimental extreme climate events on seed germination of P. densiflora. P. densiflora seeds were sowed in April 2021 in the open field. We treated temperature (control, + 3°C, and + 6°C) and precipitation (control, drought, and heavy rainfall) manipulations for P. densiflora seeds from April to June 2021. Germinated seeds were counted every other day during the experimental period to calculate germination percentage, mean daily germination, and germination time.

Results/Conclusions

The extreme heat treatment accelerated the seedling emergence of P. densiflora, whereas the drought treatment delayed the emergence. Thereafter, however, daily germination in the extreme heat treatment was sharply reduced compared to the control. Consequently, germination percentage was highest in TC×PC (86.6% ± 2.7%), and lowest in T6×DR (56.4% ± 5.0%). Mean daily germination (seeds day^-1) was highest in T6×HR (3.66 ± 0.08) and lowest in TC×DR (2.50 ± 0.03), and mean germination time (days) showed the opposite tendency (T6×HR: 27.3 ± 0.6; TC×DR: 40.0 ± 0.4). The high temperature and soil water content could increase the activation of an enzyme, thereby accelerating the dormancy breaking. However, consistent exposure to heat stress may limit embryo development, and thus, germination percentage might be decreased. Lower water potential could inhibit the respiration and energy supply for embryo growth of seeds and may trigger a failure to germinate. Our results showed that extreme heat and drought could reduce the seed germination of P. densiflora. The long-term responses such as survival rate and growth of seedlings under extreme climate events should be further studied.