**3.4 Contribution of different depth of soil water to the water source of four shrubs in sandy land**

Iso-source analysis showed that *S. vulgaris* mainly used 25 cm soil water on May 13, which accounted for 78.5% of its total water source. On July 17, it mainly used 10–25 cm and 100–200 cm soil water and rainwater, which accounted for 50.8% and 40.7% of its total water source. On September 22, it mainly used 10–25 cm and 100–200 cm soil water, which accounted for 51.2% and 39.8% of its total water source (**Table 4**).

Iso-source analysis showed that *A. ordosica* and *H. fruticosum* var. *laeve* mainly used 10 cm soil water on May 13, which accounted for 72.9% and 66.5% of their total water source, respectively. On July 17, they mainly used 10 cm and 150 cm soil water, which accounted for 65.8% and 54.9% of their total water source, respectively. On September 22, they mainly used 10–25 cm soil water, which accounted for 46.1% and 49.0% of their total water source, respectively (**Table 5**).

Iso-source analysis showed that *S. psammophila* and *H. fruticosum* var. *laeve* mainly used 10–25 cm soil water on May 13, which accounted for 59.0% and 37.9% of their total water source. On July 17, they mainly used 50–200 cm soil water and 10–25 cm and 100–200 cm soil water, which accounted for 71.0% and 91.8% of their total water source, respectively. On September 22, they mainly used 10–100 cm soil water, which accounted for 73.8% and 72.5% of their total water source, respectively (**Table 6**).

Four shrubs in sandy land have a resource-dependent water use strategy, e.g. used different depths of soil water based on their availability in the growing season. *Sabina vulgaris* mainly used 25 cm shallow soil water in spring; however, it mainly

*Water Source of Six Woody Plants in Different Habitats on Desertified Land of Ordos Plateau… DOI: http://dx.doi.org/10.5772/intechopen.99658*

#### **Figure 4.**

*Stable oxygen isotope ratio of xylem water, soil water and rainwater of Sabina vulgaris (A), Artemisia ordosica (B) and Salix psammophila (C) in sandy land. Dark symbol is soil water, white symbol is xylem water of three shrubs, and gray symbol is xylem water of Hedysarum fruticosum var. laeve.*


#### **Table 4.**

*Contribution of different depths of soil water and rainwater to the water source of Sabina vulgaris in sandy land (%, mean ± SD).*


#### **Table 5.**

*Contribution of different depths of soil water and rainwater to the water source of Artemisia ordosica (Ao) and Hedysarum fruticosum var. laeve (Hf) in sandy land (%, mean ± SD).*


#### **Table 6.**

*Contribution of different depths of soil water and rainwater to the water source of and Salix psammophila (Sp) and Hedysarum fruticosum var. laeve (Hf) in sandy land (%, mean ± SD).*

used both of 10–25 cm shallow and 100–200 cm deep soil water in summer and autumn. *Artemisia ordosica* and the accompany plant *H. fruticosum* var. *laeve* always used the same water source, e.g. 10 cm surface soil water in spring, 10 cm surface soil water and 150 cm deep soil water in summer, and 10–150 cm soil water in autumn. *Salix psammophila* mainly used 10–25 cm shallow soil water whereas *H. fruticosum* var. *leave* mainly used 50–200 cm soil water in spring. However, they both mainly used 10–25 cm shallow soil water and 100–200 cm deep soil water in summer, and 25–200 cm soil water in autumn. Soil water recharged by rainwater

*Water Source of Six Woody Plants in Different Habitats on Desertified Land of Ordos Plateau… DOI: http://dx.doi.org/10.5772/intechopen.99658*

is the main water source for vegetation in sandy land since shallow groundwater was depleted by coal mining. However, in the habitat with shallow groundwater in the sandy land, woody species still could use groundwater. For example, *Salix matsudana* and *S. vulgaris* mainly used deep soil water and groundwater, whereas *A. ordosica* mainly used groundwater in Mu Us Sandy Land. The groundwater table were 1.0 m for *S. matsudana* in interdune, 1.5 m and 1.3 m for *S. vulgaris* and *A. ordosica* on sand dune, respectively [5].

The water source of the company shrub *H. fruticosum* var. *leave* were similar to the dominant shrub *A. ordosica* or *S. psammophila*, which indicated water competition between them. Water source of shrubs was closely related to their root type in sandy land, especially fine root. The root length of *H. fruticosum* var. *laeve* was 80 cm, with the biomass concentrated within 40 cm [31]. The distribution of its root system is partly overlap with two dominant shrubs. The root depth of *A. ordosica* was 200 cm, with the fine root concentrated within 40 cm [32]. The root system of *S. psammophila* was as deep as 150 cm, with fine root concentrated within 50 cm [33]. Similar phenomenon occurred in other sandy land vegetation. For example, *Salix gordejevii* mainly used soil water, whereas *Artemisia halodendron* mainly used 10–150 cm soil water in Horqin Sandy Land [11]. Their root biomass concentrated within 40 cm in the mixed community [34]. Therefore, the distribution of deep-rooted species should be arranged appropriately to avoid excessive water competition in the restoration of degraded vegetation in sandy land. It was suggested to keep reasonable afforestation density in the ecological engineering in Mu Us Sandy Land and other area of semi-arid region.
