Natural and Synthetic Hydrophilic Polymers Enhance Salt and Drought Tolerance of Metasequoia glyptostroboides Hu and W.C.Cheng Seedlings

We compared the effects of hydrophilic polymer amendments on drought and salt tolerance of Metasequoia glyptostroboides Hu and W.C.Cheng seedlings using commercially available Stockosorb and Luquasorb synthetic hydrogels and a biopolymer, Konjac glucomannan (KGM). Drought, salinity, or the combined stress of both drought and salinity caused growth retardation and leaf injury in M. glyptostroboides. Under a range of simulated stress conditions, biopolymers and synthetic hydrogels alleviated growth inhibition and leaf injury, improved photosynthesis, and enhanced whole-plant and unit transpiration. For plants subjected to drought conditions, Stockosorb hydrogel amendment specifically caused a remarkable increase in water supply to roots due to the water retention capacity of the granular polymer. Under saline stress, hydrophilic polymers restricted Na+ and Cl- concentrations in roots and leaves. Moreover, root K+ uptake resulted from K+ enrichment in Stockosorb and Luquasorb granules. Synthetic polymers and biopolymers increased the ability of M. glyptostroboides to tolerate combined impacts of drought and salt stress due to their water- and salt-bearing capacities. Similar to the synthetic polymers, the biopolymer also enhanced M. glyptostroboides drought and salt stress tolerance.