Soil drought increases the retention time of plant water in Pinus thunbergii saplings

Aim Efficient fog water utilization under soil drought conditions is important for improving the water status and growth of forest trees. However, importance of fog water retention for trees during drought is yet to be completely examined. The aim of this study was to examine changes in fog water retention in different organs of Japanese black pine ( Pinus thunbergii ) saplings under well-watered and drought conditions. Methods P. thunbergii saplings were grown under well-watered and drought conditions in a glasshouse for 19 days and exposed to 2 H-enriched water vapor under a high relative humidity (~ 95%) for 1 h in a growth chamber under a uniform light condition. The exposed trees were harvested 48 h after the fog exposure experiment and the 2 H concentration of water in current needles, old needles, current branches, old branches, roots, and soil was determined. Results Absorbed fog water was detected in the needles, branches, and roots 48 h after exposure to fog. The amount of water in the current needles, old needles, and current branches contributed by fog water was significantly higher in drought-stressed trees than in well-irrigated trees. Small amount of absorbed fog water was redistributed to the soil, irrespective of soil water conditions. Conclusion We found that larger amount of absorbed fog water was retained in drought-stressed trees than that in well-watered trees, which may improve the water status of plants under drought. Our results also suggest that hydraulic redistribution from the roots to the soil may occur irrespective of soil drought conditions.