Mixing of tree species with the same water use strategy might lead to deep soil water deficit

Abstract

Water is a crucial factor limiting artificial vegetation growth in arid and semi-arid regions. The water availability and plant utilization patterns reflect the ecosystem's response to environmental water conditions. In arid and semi-arid areas, it was considered that mixed-species plantations, particularly arbors mixed with shrubs, were conducive to enhancing drought resistance. However, inappropriate artificial vegetation and exorbitant productivity could have accelerated soil desiccation in range and intensity, demonstrating adverse effects on soil water cycle and further influencing vegetation's growth and natural succession. In this study, we investigated the water use strategies of mixed tree planting (Elaeagnus angustifolia) with shrubs (Caragana korshinskii) in the sandy land of the east Yellow River, China. Our findings demonstrated that Elaeagnus angustifolia consumed more than 1.2 times more water than Caragana korshinskii. Elaeagnus angustifolia and Caragana korshinskii primarily used the middle and deep layer soil water during high water consumption. During the lower water consumption season, Elaeagnus angustifolia and Caragana korshinskii utilized the shallow layer soil water. In most cases, the two species have overlapping niches in space and time and compete while sharing water resources. In very few cases, the two species responded to seasonal droughts primarily through spatial differences in water use. The soil water deficit and water consumption rate in deep layers of the mixed plantation of Elaeagnus angustifolia and Caragana korshinskii were 260 mm and 19 mm/year, which were significantly higher than those in the pure plantation of Elaeagnus angustifolia and Caragana korshinskii. The mixed forest of Elaeagnus angustifolia and Caragana korshinskii might lead to the soil moisture environment in the study area to show a drought trend, resulting in soil desiccation. These findings could provide the scientific basis for restoring regional vegetation and stand structure optimization allocation of shelter forests.