Effect of K+ on the growth, ion absorption and distribution of Apocynum venetum under salt stress

The effects of two K+ levels(0.01 and 2.5 mmolL-1)on the growth,ion absorption and distribution of Apocynum venetum under NaCl stress were investigated by the pot experiment. The results indicated that the biomass and plant height of A. venetum decreased with the increase of external NaCl concentration, however, there was no significant difference between 0.01 and 2.5 mmolL-1 K+ under the same salt treatment(P0.05). Na+ contents in all tissues of A. venetum increased significantly (P0.05) with the increase of external NaCl concentration and the increase rate in leaf was greater than that in root and stem. In contrast to Na+,K+ contents decreased significantly but still maintained at a high level in leaf and stem and maintained stable in root with the increase of external NaCl concentration. Furthermore, compared with the control, K+ contents in leaf did not significantly change when A. venetum was exposed to 50 mmolL-1 NaCl. Moreover,A. venetum accumulated high contents of K+ in the absence of salt stress, especially in leaf where K+ contents were 15 times higher than that of Na+. In conclusion, enhancing the capacity of selective absorption and transport for K+, and hence maintaining high K+ contents and K+/Na+ ratio in leaf are the key adaptive mechanisms of salt-tolerance in A. venetum.