Nutrients uptake and low molecular weight organic acids secretion in the rhizosphere of Cynodon dactylon facilitate mercury activation and migration

Rhizosphere, rich in roots exudates, is the essential zone for pollutants behaviors and plant nutrition. Cynodon dactylon (C. dactylon), dominating in the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR), China, has extensive root systems, probably deeply influencing the mercury (Hg) migration and nutrients assimilation. However, it is unclear whether Hg migration was influenced by the combination of nutrient uptake and the secretion of low molecular weight organic acids (LMWOAs). Therefore, we investigated nutrients and Hg migration trends as well as the distribution of LMWOAs secreted by C. dactylon roots in different distance to rhizosphere through laboratory simulation. The results showed that nutrients diffusion, caused by plants uptake, from bulk soil to the rhizosphere increased Hg mobility. LMWOAs could not only benefit the produce and migration of available nitrogen (AN) and available potassium (AK) but accelerate Hg movement. Meanwhile, the lack supplement of AN and AK for C. dactylon assimilation might provoke Hg translocation from soil to roots. Fortunately, Hg preferred to remain in the roots rather than transferring to shoots during deficient nutrients supplement periods. The study supplemented the research on Hg fate in the WLFZ of the TGR, suggesting that nutrients uptake is also essential in Hg migration.