Abstract
BackgroundWater 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.MethodThe δ2H/δ18O 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.ResultsPlatycladus 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·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.ConclusionsThe water stored in both species comprised 6%–7% of the total water fluxes and, therefore, should be considered in water balance models.
Highlights
Water is a key factor affecting the circulation of materials and plant growth in forest ecosystems (Nadezhdina et al 2020)
In contrast to P. orientalis, 79.2% of the main root system of Q. variabilis is highly developed and uniformly distributed in different soil layers (Liu et al 2019); it can use multiple water sources. It uses a higher surface soil water ratio during the dry season, possibly owing to the short transport distance of surface soil water and the lower energy consumption. This suggests that Q. variabilis prefers surface soil water during the dry season, consistent with previous findings, which established that plants with uniform root distributions preferentially absorb water from surface soil layers (Fan et al 2017; Cai et al 2018; Cuneo et al 2018)
We used an isotope technique and the heat ratio method to quantify the utilization ratio of water source and sap flow and determine the proportion of water used in transpiration and storage
Summary
Water is a key factor affecting the circulation of materials and plant growth in forest ecosystems (Nadezhdina et al 2020). Plants absorb water from the soil through their roots and store it in their xylem, use it during photosynthesis, or lose it through evaporation through the stomata in their leaves (Weatherley 1982; Buckley et al 2020; Barbeta et al 2015; Huang et al 2017; Molina et al 2019). Very few studies have focused on the water usage and symbiotic mechanism in coniferous and broad-leaved mixed forests under seasonal drought in rocky mountainous regions characterized by thin soils and high gravel content. Method: The δ2H/δ18O 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
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