The impact of drought on sap flow of cooccurring Liquidambar formosana Hance and Quercus variabilis Blume in a temperate forest, Central China

Abstract

AbstractDiffuse‐ and ring‐porous species with different vessel structures exhibited contrasting water use strategies for adapting to water stress. The sap flow rates of two tree species (diffuse‐porous: Liquidambar formosana Hance; and ring‐porous: Quercus variabilis Blume) under different environmental conditions were monitored in a temperate forest in the south of Henan Province, Central China. The mechanisms underlying the contrasting water use strategies in response to drought stress were explored by analysing the correlation of sap flow per unit sapwood area (Fd) with vapour pressure deficit and the contribution of nocturnal Fd to total water use under different soil water contents. The results showed that the Fd of Q. variabilis decreased under drought conditions, whereas that of L. formosana increased. Under drought stress, stronger stomatal control was shown for both tree species. Stomatal regulation and changes of leaf area jointly led to constant sap flow per unit leaf area (JL) across the seasons for Q. variabilis. The seasonal variations in the ratio of nocturnal mean Fd to total Fd were consistent with those in the daytime mean JL for both tree species. Nocturnal sap flow played a critical role in the increased water use of diffuse‐porous species, L. formosana, under drought conditions. Our study highlights the importance of nocturnal sap flow for water use by forest species. This finding provides insights for future studies of the water cycle in forest ecosystems and demonstrates that such studies should take into account the nocturnal physiological processes of plants.