Soil Water Use Strategy Of Dominant Species In Typical Natural And Planted Shrubs In Loess Hilly Region

Artemisia gmelinii is a dominant specie naturally established after abandonment of cultivated lands in the Loess Plateau,and Caragana korshinskii is one of the main planted shrub species to control soil erosion.Improved understanding of water use strategies of these two species is of great significance to evaluate the sustainable development of the Loess Plateau under the trend of climate warming and increasing drought events.Stable oxygen-18 isotope was used to determine seasonal variations in the water sources of native A.gmelinii communities established after abandonment of cultivated lands for 7 and 30 years and planted C.korshinskii after 30 years.The contributions of soil water from different depths to water uptake were estimated by the MixSIR Bayesian mixing model.The results show that:?1?On the one hand,the change of soil water content was affected by climate,such as rainfall and evaporation.On the one hand,it was affected by the growth of plants.Soil water content?SWC?of shrub ecosystem varied under different site conditions.SWC of planted C.korshinskii established after abandonment of cultivated lands for 30 years were generally lower than that of native A.gmelinii communities after 7 and 30 years.Overall,soil moisture in above 0–40 cm soil layer changed greatly.?2?A strong evaporation effect generally takes place in shallow soil layers and decreases with depth.During the sampling periods,monthly ?¹⁸O values of soil water in deep soil layers were relatively uniform across depths and was approaching up the stable value-7.47‰.Differences in surface oxygen-18 isotopic composition were observed among various sampling dates,which suggest that those are greatly influenced by evaporation.The ?¹⁸O values from xylem water changed with the sampling date and plant species.?3?The native A.gmelinii communities established after abandonment of cultivated lands for 7 and planted C.korshinskii after 30 years showed plasticity in switching water sources from different soil layers,extracting water from shallow soil?0–40 cm?when soil water was available,but deeper soil?40–80 cm?when shallow soil water was dry.In contrast,A.gmelinii growing in site after cultivation abandonment for 30 years mainly relied on water from the surface soil?0–10 cm?throughout the growing season.Our results suggest that the ability of A.gmelinii to compete for soil water reduces with aging of the community while the plantedC.korshinskii will have competitive advantage under the condition of increasing frequency of drought events in the future.?4?Compared with the IsoSource model,the MixSIR model taked into account the uncertainty analysis.The heterogeneity of soil water in arid and semi-arid areas was big,so the results are more accurate used the MixSIR model.Accounting for uncertainty in mixing model inputs can change the variability,magnitude and rank order of estimates of source contributions to the mixture.Increasing sampling repetition and sampling frequency are also beneficial to fully account for uncertainty in order to accurately estimate source contributions.