Research on seasonal water use strategy of artificial Haloxylon ammodendron in the lower reaches of the Shiyang River

As the main sand-fixing afforestation tree species, artificial Haloxylon ammodendron has strong stress resistance and ecological adaptability, which are also the first lines of defense against wind-sand hazards in the lower reaches of the Shiyang River. Based on the methods of in-situ observation and isotope tracing, we studied the seasonal patterns of the water source of artificial H. ammodendron, which has important practical guiding significance for the restoration of the degraded protection system in the Minqin oasis. In the growing season, the average soil moisture in the 0－200 cm vertical soil layer of the rhizosphere of artificial H. ammodendron was 0.87%, and the soil moisture content in the 120 cm depth was relatively high. Soil moisture content seasonally showed the pattern: May (1.22%) > April (1.05%) > June (0.83%) > July (0.80%) > October (0.67%) > August (0.65%). Soil moisture δ¹⁸O in the 0 − 60 cm surface layer showed obvious enrichment, with drastic changes being observed, whereas that in the middle and lower layers was decreased and relatively stable. In spring, the proportions of soil water in the deep layer of 120 − 200 cm, the middle layer of 60 − 120 cm, and 20 − 60 cm shallow layer were 45.15%, 20.6%, and 20.6%, respectively. In summer, the soil water utilization ratios of 0 − 20 cm surface layer, 60 − 120 cm middle layer, and 120 − 200 cm deep layer were 32.5%, 24.75%, and 22.1%, respectively. In autumn, the soil water utilization ratios in the 0 − 20 cm surface layer and the 120 − 200 cm deep layer were relatively high, accounting for 44.4% and 48.75%, respectively. Soil water at different depths is an important seasonal water source of artificial H. ammodendron. It has been suggested that the methods of artificial supplementary rainfall infiltration were optimal to maintain the soil water balance of forestland in tending management.