Evaluation of water use of Caragana korshinskii and Hippophae rhamnoides in the Chinese Loess Plateau

Understanding the water-use strategy of trees and shrubs is crucial for developing effective vegetation restoration in regions that are subjected to water scarcity. We studied the water-use strategy of Caragana korshinskii Kom. and Hippophae rhamnoides L. in the Chinese Loess Plateau to evaluate the adaption strategies of these two shrubs, which are both commonly used in the restoration programs in this region. We extrapolated the measurements of water use by individual plants to determine the area-averaged transpiration of the shrublands. There was a good agreement between transpiration estimated by the Penman–Monteith method and by the sap-flow method, which suggests that that the sap-flow method can provide reliable estimates of shrub transpiration at the stand level. Stand transpiration was mainly influenced by environmental factors such as photosynthetically active radiation, vapor pressure deficit, and soil water content. When the soil water content was sufficient, photosynthetically active radiation and vapor pressure deficit were the dominant factors; however, soil water content was the primary factor under low soil moisture levels. Stand transpiration ranged from 0.52 to 4.21 mm·day −1 with a mean of 1.42 mm·day −1 for C. korshinskii and ranged from 0.57 to 3.99 mm·day −1 with a mean of 1.94 mm·day −1 for H. rhamnoides. During the experimental period (from June to September 2013), cumulative transpirations were 173.4 and 236.6 mm for C. korshinskii and H. rhamnoides, respectively, which accounted for up to 88.2% of the rainfall registered during this period. We calculated the soil water balance and measured the water potential of stems and leaves for C. korshinskii and H. rhamnoides. Hippophae rhamnoides had a lower net soil water storage, indicating that it consumed more soil water than C. korshinskii. There were some negative water potential drops between stems and leaves for H. rhamnoides, suggesting the lack of a safety margin for H. rhamnoides. Our results indicated that C. korshinskii is more suitable for afforestation than H. rhamnoides in the Loess Plateau.