Whole-Plant Water Use and Hydraulics of Populus euphratica and Tamarix ramosissima Seedlings in Adaption to Groundwater Variation

Riparian phreatophytes in hyperarid areas face selection pressure from limiting groundwater availability and high transpiration demand. We examined whole-plant water use and hydraulic traits in Populus euphratica and Tamarix ramosissima seedlings to understand how they adapt to groundwater variations. These species coexist in the Tarim River floodplain of western China. Measurements were performed on 3-year-old seedlings grown in lysimeters simulating various groundwater depths. P. euphratica had relatively greater leaf area-specific water use due to its comparatively higher sapwood area to leaf area ratio (H-v). A high H-v indicates that its sapwood has a limited capacity to support its leaf area. P. euphratica also showed significantly higher leaf-specific conductivity (k(sl)) than T. ramosissima but both had similar sapwood-specific conductivities (k(ss)). Therefore, it was H-v rather than k(ss) which accounted for the interspecific difference in k(sl). When groundwater was not directly available, k(sl) and H-v in P. euphratica were increased. This response favors water loss control, but limits plant growth. In contrast, T. ramosissima is more capable of using deep groundwater. Stomatal sensitivity to increasing leaf-to-area vapor pressure deficit was also higher in P. euphratica. Overall, P. euphratica is less effective than T. ramosissima at compensating for transpirational water loss at a whole-plant level. For this reason, P. euphratica is restricted to riverbanks, whereas T. ramosissima occurs over a wide range of groundwater depths.

Automated summary

This study examined how Populus euphratica and Tamarix ramosissima seedlings adapt to groundwater variations. It was found that P. euphratica had a greater leaf area-specific water use and higher leaf-specific conductivity, while T. ramosissima was more capable of using deep groundwater.