Search Results (3)

In semi-arid regions of Morocco, where the majority of water withdrawals are devoted to irrigation, optimizing irrigation practices in agriculture is a national priority in the face of recurring droughts and growing pressure on groundwater resources. However, the hydrological impacts of different drip-irrigation systems in the soil–plant–atmosphere continuum remain insufficiently understood. We monitored the stable isotope composition (δ²H, δ¹⁸O) across the two agricultural plots in Marrakech (Morocco) with surface drip and subsurface drip irrigation treatments for a complete hydrologic year (June 2022 to June 2023). Weekly to daily samples of rainfall, irrigation water, groundwater, and soil at various depths (5–50 cm) were sampled, and water from branch xylem was extracted using the cryogenic vacuum distillation method. We found that the subsurface irrigation treatment, which delivered water directly to the root zone, maintained narrow isotopic ranges in water of soils beyond 30 cm, as well as in branch xylem and leaf water. By contrast, surface irrigation treatment plots showed pronounced evaporative isotopic enrichment: summer topsoil water δ¹⁸O peaked at −1.1‰ (vs. −8.7‰ in subsurface irrigation treatment), and leaf water reached +13‰ (vs. +8‰ in subsurface). Despite this larger isotopic heterogeneity in surface irrigation site, branch xylem water δ¹⁸O remained within −6 to 2.5‰ across all soil depth, similar to subsurface irrigation treatment, which ranged between −5 and 0‰. This suggests that olive roots accessed soil water uniformly from the upper 50 cm under both irrigation treatments. Seasonal xylem isotopic enrichment in spring and midsummer mirrored shifts towards shallow, evaporatively altered soil water under surface irrigation, but not under the subsurface. The results suggest that subsurface drip irrigation can significantly improve drought resilience and water-use efficiency in the expanding olive sector of the Maghreb, while continuous isotope monitoring serves as a practical approach to enhance sustainable and adaptive water management in water-limited regions. Full article

The direct vapor equilibration-laser spectroscopy (DVE-LS) method can be used to measure the stable isotopes of soil water (δ²H and δ¹⁸O), a technique that is easier to operate and quicker for sampling compared to the traditional cryogenic vacuum distillation (CVD) method. However, the soil water isotope values thus obtained often deviate from the true value, which is affected by the equilibrium temperature during the measurement process. Therefore, this study conducted an indoor experiment on five soil samples of varying textures. The dry soil was wetted by reference water samples to four different soil water content (SWC) values and then equilibrated at five different temperatures. The soil water isotope deviation value (SWIDV) of the DVE-LS method was determined by building a correction equation between SWIDV and the influencing factors (equilibrium temperature, soil clay content (SCC), and SWC, after which the correction equation values were compared to those calculated by the CVD method for the field-collected soil samples to check the accuracy. The results shows that the Δδ²H value increased with increasing equilibrium temperature and soil clay content, but decreased with increasing SWC. The multi-factor variance analysis shows that equilibrium temperature, SCC, and SWC significantly affected the Δδ²H values and deviation values with the DVE-LS method, but insignificantly affected the Δδ¹⁸O values and deviation values. The correction equations (3) was built at different equilibrium temperatures, and the RMSE decreased from 4.07‰ to 1.24‰ and from 8.99‰ to 4.14‰, respectively, as calibrated by the isotope values of soil samples collected in Changwu and Suide counties. The correction equations under various equilibrium temperatures increased the accuracy of the DVE-LS method in obtaining soil water isotope values and promoted the application of the DVE-LS method in soil water isotope analysis. Full article

Stable isotopes of water (δ²H and δ¹⁸O) are reliable tracers for the investigation of plant–soil–water interactions in forest ecosystems. However, variations in isotopic compositions may arise due to differences in analytical instruments and water extraction methods. In this study, we conducted three different experiments to identify isotopic differences caused by analytical and methodological variations. First, we analyzed soil water by using the two most commonly applied methods: isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS). Second, we compared the isotopes in xylem water extracted from the stems of nine tree species using cryogenic vacuum distillation (CVD) with different heating times. Third, we compared the compositions in xylem water extracted with three different methods: mechanical squeezing using a pressure chamber (PC), an induction module (IM), and CVD. The differences in isotopic composition between IRMS and CRDS were significant but minimal. Soil properties were not significant factors contributing to differences between the two instruments. For the xylem water extraction with CVD, each of the nine tree species required heating for more than three hours. Significant differences were observed in δ²H among the three extraction methods for xylem water. Xylem water extracted by CVD showed more depleted values compared to those obtained by PC and IM. Our results highlight the importance of considering analytical and methodological variations in stable isotope analysis. Full article