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Background and aims: Potassium (K), Calcium (Ca), and magnesium (Mg) are essential nutrients for plant and animal growth. The ratio of K/(Ca + Mg) in forage is considered as an indicator of grass tetany. While atmospheric nitrogen (N) deposition is declining or projected to decline in many countries, it remains unknown whether historical N inputs would have legacy effects on K, Ca, and Mg nutrition in soil and plants. Methods: After the cessation of 6-yr N addition with wide-ranging rates, we measured the concentrations of K, Ca, and Mg in soil and plants in a temperate steppe of northern China during three successive years from 2016 to 2018. Results: Soil K/(Ca + Mg) ratios were increased by historical N addition across the three years. Soil K/(Ca + Mg) ratios were higher than 0.08, indicating potential occurrence of grass tetany for ruminants. Plant mineral concentrations and K/(Ca + Mg) ratios at the plant community level showed no variation with increasing historical N addition rates in all the three years, except for the increasing K and Ca concentrations in 2017. All plant functional types showed strong stoichiometric homeostasis with respect to nutrient concentrations, which contributed to the stable forage K/(Ca + Mg) ratio under the N-induced increasing soil K/(Ca + Mg) ratio. Conclusion: Our results highlight the critical role of stoichiometric homeostasis in maintaining forage non-N mineral nutrition of natural grasslands under the background of soil nutritional alterations. [ABSTRACT FROM AUTHOR]

Langevin dynamics simulations are employed to explore the effects of chain stiffness and electrostatic interaction (EI) on the conformational behavior of a circular semiflexible polyelectrolyte (CSPE) in presence of trivalent counterions. We investigate the effect of bending energy b and the dimensionless Bjerrum length A on the conformational behaviour of the CSPE with a fixed chain length. The competition among the EIs, chain stiffness and entropy of the system leads to rich conformations for the CSPE. As the b is less than or equal to 50, The shape of the CSPE changes from a oblate ring to a rod at small A, then to a toroid at intermediate A, and finally to a globule at very large A. However, the globular conformation is not observed for large b. In addition, we find that the number of torus ring increases with A increase, while decreases with b increase. This study should be helpful in gaining insight into the conformational behaviour of charged biopolymer. [ABSTRACT FROM AUTHOR]