Comment on hess-2022-120

Abstract

Understanding the water consumption mechanism of plantations is of great significance for the selection of afforestation trees and ecologically sustainable watershed management in semi-arid areas. In this study, Robinia pseudoacacia and Pinus tabulaeformis plantations, which have been widely planted in Chinese Loess Plateau, were selected to investigate the possible difference in water uptake modes. The spatial and temporal variations in precipitation, xylem and soil water stable isotope compositions (δ2H, δ18O) in 2019–2020 were analyzed, and the water uptake modes of plantations were quantified using the direct inference approach and MixSIAR model, with contrasting soil moisture dynamics. The results showed that δ18O values were positively correlated with air temperature and negatively correlated with precipitation volume. The δ18O content of surface soil (0–40 cm) closely related precipitation input, while those of deep soil layers (100–200 cm) remained stable. When compared with the direct inference approach, the MixSIAR model performed more effectively in quantifying water apportionment, especially in a drought year. In a drought year, R. pseudoacacia showed strong drought resilience to absorb water from deep soil, the soil layers of 0–40 cm and 40–200 cm contributed 32.9 % and 67.1 % to water absorption of R. pseudoacacia, and 62.2 % and 37.8 % to that of P. tabulaeformis, respectively, while there appeared to be minor differences in soil water uptake between the two plantations in a humid year. Generally, R. pseudoacacia consumed more water than P. tabulaeformis, especially in a humid year, and the former inclined to absorb soil layer with enriched soil moisture. The results indicated that R. pseudoacacia plantation may increase transpiration and cause dried deep soil layers when compared with P. tabulaeformis. This study improves our understanding of water uptake mechanisms of plantations and helps with selection of suitable plant species for ecological management in Chinese Loess Plateau.