Water use strategies of Robinia pseudoacacia and Quercus acutissima vary among seasons and planting methods

Aims Forests with various mixed patterns often show large differences in water use strategies. However, mixed planting may enhance the drought resistance of the whole forest community. We evaluated whether mixed planting could enhance the drought resistance of Robinia pseudoacacia and Quercus acutissima under different seasons in the warm temperate zone of North China. Methods Shallow-rooted R. pseudoacacia and deep-rooted Q. acutissima were studied to determine plant water use strategies under different seasons and planting methods. We measured hydrogen and oxygen isotope ratios of two species grown under pure and mixed planting methods, as well as those of the environment, including rainwater, soil water, and groundwater in spring, summer, and autumn. Results Hydrogen and oxygen isotopic contents of soil water were significantly less than groundwater and significantly more than rainwater irrespective of the season. However, season was the key factor influencing the plant water use strategies. In spring and autumn, Q. acutissima used more groundwater while R. pseudoacacia used more soil water; in summer, both of the two species took more use of rainwater and soil water. Mixed planting significantly increased the proportion of groundwater use and the diversity of plant water use strategies of two species. Conclusion Diversity of plant water use strategies facilitate the coexistence of two species with the same ecosystem irrespective of the changes in water availability in their respective root zones. Besides, mixed planting can enhance the drought resistance of the whole forest community via reducing competition for the seasonal changes in water resources.

Automated summary

Forests with mixed planting patterns show differences in water use strategies. This study found that mixed planting can increase the proportion of groundwater use and enhance the diversity of plant water use strategies. It also improves the drought resistance of the whole forest community.