Intensified winter precipitation-induced enzymic latch mechanism in moist Arctic tundra may be impeded by an extreme summer drought

Winter precipitation and summer drought in Arctic tundra regions tends to be intensified due to climate change, and these may influence the dynamics of soil carbon stored in the Arctic tundra. Winter precipitation and summer drought are distinct phenomena that appear in separate seasons, but both are linked to a carbon sequestering mechanism called enzymic latch which refers to the inhibition of carbon decomposition by Sphagnum-derived phenolics. An increase in winter precipitation is known to enhance soil moisture and Sphagnum growth which are beneficial to the enzymic latch, while summer drought declines soil moisture and desiccates Sphagnum. Hence, we hypothesized that an increase in winter precipitation may enhance the enzymic latch, but summer drought may compromise it. Besides, the impeded mechanism may not be fully recovered unless the desiccated Sphagnum community will be re-established. The hypothesis is going to be tested in the moist Arctic tundra experimental site with the snow fences to manipulate the winter snow depth near Council, Alaska, United States (64°N, 165°W). The site had been established, and soil temperature, moisture, and visual image of land cover have been monitored since 2017, and abnormally hot and dry summer has been observed in 2022. Pre- and post-drought organic soil and pore water samples from the snow fence plots (control vs. higher snow depth) were collected, and biogeochemistry, the concentration of phenolics, and activity of hydrolases and phenol oxidative enzymes will be measured. Increased winter precipitation is expected to enhance enzymic latch, while the extreme summer drought may eliminate that effect. Drought decreases soil moisture, increases oxygen availability, and dehydrates Sphagnum, resulting in more oxidation of phenolics by phenol oxidative enzymes and less production of phenolics by Sphagnum. Consequently, the stimulation of enzymic latch-involved carbon sequestration by increased winter precipitation may be intervened by extreme summer drought in Arctic tundra soil.