To explore the water sources of riparian forests and their response to the water level of the Yellow River in the Ulan Buh desert section of the Yellow River basin, reveal the water use strategies of Salix matsudana, understand their adaptability under drought conditions, and to provide a theoretical basis for ecological protection and restoration in the desert area of the Yellow River basin.

Salix matsudana was selected from the river bank of the Ulan Buh desert of Yellow River “Jizi bend”. In the growing season of 2022-2023, plant stems were collected, as well as forest soil, groundwater, Yellow River water and other potential water sources of plants. Water was extracted from plant and soil samples by a freeze-vacuum water extraction device, and the stable hydrogen and oxygen isotopes of each water sample were determined and analyzed. The contribution ratio of different potential water sources to plants was calculated using MixSIAR model.

The water source of Salix matsudana had obvious seasonal changes. In May 2022, Salix matsudana mainly absorbed deep soil water, accounting for 84.1%. In June, July, August and September, the absorption proportion of deep soil water decreased (44.6%, 36.9%, 26.0%, 54.1%). Concurrently, the proportion of water absorbed from the middle soil increased by 24.3%, 13.7%, 8.6% and 7.2%, respectively. Additionally, the proportion of groundwater absorption increased by 6.9%, 21.5%, 38.3% and 19.1% respectively during these months. From May to September 2023, Salix matsudana mainly absorbed deep soil water and groundwater. The proportion of deep soil water absorption was 65.6%, 38.9%, 63.3%, 52.3% and 30.2%, and the proportion of groundwater absorption was 14.3%, 31.6%, 18.6%, 29.1% and 48.2%, respectively. There was no significant difference between 2022 and 2023 in the contribution ratio of different potential water sources (P>0.05). The proportion of groundwater absorbed by Salix matsudana increased with the water level of the Yellow River, and the proportion of Yellow River water to the water source of Salix matsudana decreased.

The main water source of Salix matsudana is relatively reliable deep soil water and groundwater. The water level of the Yellow River will affect the water source of Salix matsudana to a certain extent, especially the absorption ratio of groundwater and Yellow River water, which reflects the adaptability of Salix matsudana to drought.

Understanding the photosynthetic characteristics, water use efficiency (WUE) and their differences of Haloxylon ammodendron under different stubble treatments is helpful to understand the adaptation strategies of Haloxylon ammodendron to the environment under different stubble treatments. It provides a theoretical basis for the tending management of shrubs in arid areas and is of great significance for ecological restoration in arid areas.

The light response curves of Haloxylon ammodendron (0%, 25%, 50%, 75%) under different light intensities were measured by Li-6800 portable photosynthesis instrument, and water use efficiency of different stubble Haloxylon ammodendron were analyzed.

In the range of photosynthetically active radiation (PAR)0-2 000 μmol·m^-2·s^-1, the net photosynthetic rate, transpiration rate and stomatal conductance of different stubble Haloxylon ammodendron increased with the increase of photosynthetically active radiation, and the intercellular CO₂ concentration decreased with the increase of photosynthetically active radiation. When photosynthetically active radiation was greater than 600 μmol·m^-2·s^-1, the net photosynthetic rate values showed stubble 75% > stubble 0% > stubble 25% > stubble 50% > no stubble, and the difference was significant (P < 0.05). The light saturation rate (A_max) and light compensation point (LCP) of stubble 75% were the highest, the apparent quantum efficiency (AQY) of stubble 25% was the highest. When the photosynthetically active radiation was less than 600 μmol·m^-2·s^-1, the water use efficiency of different stubble Haloxylon ammodendron increased rapidly. When it was greater than 600 μmol·m^-2·s^-1, it continued to rise slowly with the increase of light intensity. Stubble 25% increased water use efficiency by reducing transpiration rate. The water use efficiency of different stubble Haloxylon ammodendron was stubble 25% > stubble 75% > stubble 50% > no stubble > stubble 0%.

The water use efficiency of stubble 25% is the highest. The most suitable management of Haloxylon ammodendron is stubble 25%. This study reflects that after different degrees of stubble of Haloxylon ammodendron, its own drought resistance mechanism and water regulation strategy are formed in arid environment.

To reveal the adaptation strategies of Haloxylon ammodendron leaves to the environment at different stubble strength and provide scientific basis for better nurturing degraded artificial H. ammodendron forests.

Taking a 20 year old artificial H. ammodendron forest near the northeast edge of the Ulanbuhe desert as the research object, a total of 9 indicators of leaf functional traits were measured after different proportions of flat cropping. The changes in leaf functional traits of H. ammodendron were explored and the differences between different growth periods after flat cropping were analyzed, aiming to reveal the adaptation strategies of H. ammodendron to arid desert environments after flat cropping.

Different proportions of flat stubble H. ammodendron showed varying degrees of compensatory growth, with the most obvious phenomenon of over compensatory growth observed in 0% of stubble; The 9 leaf traits tested showed significant differences between different growth stages under the same proportion of flat cropping treatment; During the same growth period, there were significant differences (P<0.05) in leaf fresh mass, saturated fresh mass, dry mass, and leaf area between 0% stubble and other (25%, 50%, 75%) stubble strength and CK. Except for 0% stubble, the coefficient of variation of leaf traits under other treatments and CK was less than 50%, belonging to moderate variation. The leaf traits with 0% stubble were most prone to strong variation. There was a certain correlation between the functional traits of various leaves of H. ammodendron, and flat cropping increased the correlation between leaf traits to a certain extent; Principal component analysis showed that fresh leaf mass and saturated fresh leaf mass could be used as the main indicators for evaluating the functional traits of flat cut H. ammodendron leaves.

Research has shown that it is necessary to carry out appropriate and reasonable pruning for degraded, withered and aging H. ammodendron. Ulanbuhe desert artificial H. ammodendron forests can adopt pruning with a height of 0% to promote forest growth and sustainable development, which is conducive to restoring their functions in desert ecosystems.