Bioconcentration and translocation of elements regulate plant responses to water-salt conditions in saline-alkaline wetlands

Abstract

Water level and salinity are important abiotic factors in saline-alkaline wetlands, which have been altered due to climate change and human activities. For saline-alkaline wetland plants, it remains to be revealed whether the most important abiotic factor is water or salt. Therefore, it is valuable to examine plant responses and adaptive strategies to water-salt conditions in saline-alkaline wetlands. We performed a simulation experiment using soil and plants from a typical saline-alkaline wetland. The responses and adaptive strategies of plants, the relationship between abiotic factors and the causal relationships between plant functional traits under the combined effects of water level and salinity of NaHCO3 and NaCl were studied, taking Scirpus planiculmis as the plant model. The results showed that water level had stronger effects on plant functional traits than salinity and their combined effects, and there was an antagonistic relationship between water level and salinity. The salinity effects disappeared with rising water level. Different plant functional traits among organs showed similar changes with increasing water levels: highest at stressed and suitable conditions and lowest at middle condition, including stem diameter, chlorophyll fluorescence parameters, total sulphur (TS) and total nitrogen (TN) in leaf and the bioconcentration factor (BCF) of TS and TN in leaf, which indicated that environmental stresses force plants to improve their performance to remain similar to the performance in a suitable environment. Based on the structural equation model (SEM), water-salt conditions and photosynthesis influenced the TN, TS, total phosphorus (TP), and N:P ratio of S. planiculmis, stem diameter, root:shoot ratio (R:S ratio) and stem:leaf ratio (S:L ratio) by regulating the BCF and the translocation index (TI) of elements. Therefore, element bioconcentration and translocation are crucial for plant responses to altered water-salt conditions. This study is beneficial for understanding plant response mechanisms and adaptive strategies in saline-alkaline wetlands under climate change and may provide new theoretical evidence for the restoration of degraded wetlands.