Partitioning tree water usage into storage and transpiration in a mixed forest

Background Water migration and use are important processes in trees. However, it is possible to overestimate transpiration by equating the water absorbed through the plant roots to that diffused back to the atmosphere through stomatal transpiration. Therefore, it is necessary to quantify the water transpired and stored in plants. Method The delta H-2/delta O-18 technique and heat ratio method were used to explore the water usage of coniferous and broad-leaved tree species, including the proportions of water used for transpiration and water storage. Results Platycladus orientalis and Quercus variabilis had strong plasticity in their water usage from different sources. Platycladus orientalis primarily used groundwater (30.5%) and the 60-100-cm soil layer (21.6%) throughout the experimental period and was sensitive to precipitation, absorbing water from the 0-20-cm layer (26.6%) during the rainy season. Quercus variabilis absorbed water from all sources (15.7%-36.5%) except from the 40-60-cm soil layer during the dry season. In addition, it did not change its water source but increased its groundwater uptake during the rainy season. The annual mean water fluxes of P. orientalis and Q. variabilis were 374.69 and 469.50 mm center dot year(- 1), with 93.49% and 93.91% of the water used for transpiration, respectively. However, nocturnal sap flow in P. orientalis and Q. variabilis was mainly used for water storage in the trunk rather than transpiration, which effectively alleviated drought stress and facilitated the transport of nutrients. Conclusions The water stored in both species comprised 6%-7% of the total water fluxes and, therefore, should be considered in water balance models.

Automated summary

The study investigated the water usage of coniferous and broad-leaved tree species using different methods, revealing that Platycladus orientalis and Quercus variabilis have different preferences for water sources, with the majority of water fluxes used for transpiration being 93.49% and 93.91% respectively. Additionally, nocturnal sap flow in both species was found to be primarily used for water storage, aiding in drought resistance and nutrient transport.