Trade-off relationship of leaf functional traits of desert halophyte Lycium ruthenicum in the lower reaches of Heihe River, Northwest China: response to soil moisture and salinity

Abstract

Background: Soil salinization affects plant growth and causes changes in leaf traits. Lycium ruthenicum Murr. is one of the dominant shrubs and halophytes in the lower reaches of the Heihe River in Northwest China. We analyzed the trade-off relationship of fourteen leaf functional traits of eight L.ruthenicum populations growing at varying distances from the Heihe River, and discussed the effects that soil moisture and salinity have on leaf functional traits. Results: Lower nitrogen (N) contents indicated that L.ruthenicum was located at the slow investment-return axis of the species resource utilization graph. Compared with non-saline and very slightly saline sites, populations of slightly saline sites showed higher carbon to nitrogen ratio (C:N). Redundancy analysis (RDA) revealed a relatively strong relationship between leaf functional traits and soil properties, the first RDA axis accounted for 70.99 % and 71.09 % of the variation in 0-40 cm and 40-80 cm of soil moisture and salinity. Populations in non-saline and very slightly saline habitats tended to have higher leaf C content, whereas populations in slightly saline habitats tended to have lower leaf C content, and the discrepancy was evident. Relative importance analysis found that in the 0-40 cm soil layer, leaf traits variations were mainly influenced by soil moisture (SWC), HCO3- and CO32- ions content, while leaf trait variations in the 40-80 cm soil layer were mainly influenced by HCO3- and SO42-. Conclusions: The leaf functional traits of L. ruthenicum in this region are mainly restricted by soil N content. The L.ruthenicum populations formed a pattern of increased C:N ratios and C content, reduced nitrogen to phosphorus ratio (N:P) and N content from very slightly saline soil to slightly saline. L.ruthenicum has a foliar resource acquisition method and a resource conservation trade-off with a flexible life history strategy in habitats with drought and salinity stress. In the shallow soil layers, water affects greater than salt on leaf traits variation; in both shallow and deep soil layers, HCO3- plays a dominant role on leaf traits. We believe that these findings will provide some baseline information to facilitate the management and restoration of arid-saline desert ecosystems.