Fine-Root Responses of Two Maple and Two Magnolia Species to Waterlogging

Abstract Background Urban trees provide many environmental benefits but often face challenging growing conditions like waterlogged soils. How tree root systems respond to waterlogging impacts tree performance and survival, yet this has received little attention. Our goal was to identify how the roots of temperate urban tree species respond and recover to waterlogging. Methods We monitored the responses and recovery of 2 contrasting maple and magnolia species pairs that differ in their reported waterlogging tolerance to a 2-week waterlogging period, measuring belowground stress indicators, fine-root mortality, and aboveground responses including leaf-level photosynthesis, leaf loss, and stem growth. Results Though silver maple experienced a temporary reduction in photosynthetic activity during waterlogging, it exhibited no fine-root mortality, and photosynthetic activity recovered after a 10-day recovery period. In contrast, sugar maple showed high fine-root mortality, decreased photosynthetic activity, and significant leaf loss, with no recovery in fine-root growth or photosynthetic activity after the recovery period. Both magnolia species showed high fine-root mortality and reduced photosynthesis during the waterlogging period. However, after the 10-day recovery period, both magnolias also showed new fine-root growth and increased photosynthetic activity. Conclusion The species studied here showed a wide range of fine-root response and recovery strategies to waterlogging, and this was mirrored in their aboveground performance. Future work clarifying the mechanisms driving these different strategies, such as silver maple’s ability to maintain fine roots and mitigate internal tissue damage, will help us to further understand species differences in waterlogging tolerance and better inform urban tree selection for repeatedly flooded soils.