Zinc Absorption by Wheat Seedlings: I. Inhibition by Macronutrient Ions in Short‐Term Experiments and its Relevance to Long‐Term Zinc Nutrition

Short‐term Zn 2+ absorption by intact wheat seedlings ( Triticum aestivum L.) was studied to resolve large discrepancies between Zn 2+ absorption in short‐term experiments with excised roots and in long‐term experiments with whole plants. Excision, pretreatment, and age of seedlings had no effect on short‐term Zn 2+ absorption. Zn 2+ absorption responded to changes in temperatures with Q 10 values of 6.1, 1.8, and 1.9 for the temperature ranges 2 to 10, 10 to 20, and 20 to 29C, respectively. Addition of macronutrient salts to 250µM Ca(NO 3 ) 2 in the absorbing solution decreased Zn 2+ absorption by about 80%. Micronutrient salts had a small additional effect on Zn 2+ absorption. Cations rather than anions inhibited Zn 2+ absorption. Nitrate salts of alkali and alkaline earth cations strongly depressed Zn 2+ absorption. In the presence of 250µM Ca(NO 3 ) 2 , nitrates of alkali cations at 750µ M and of additional Ca 2+ at 250 and 375µ M depressed Zn 2+ absorption from 1µ M ZnCl 2 in the order NH 4 + > Rb + > K + > Cs + > Ca 2+ > Na + > Li + . Nitrates of alkaline earth cations at concentrations of 250µ M depressed Zn 2+ absorption in the order Mg 2+ > Ba 2+ ≥ Sr 2+ = Ca 2+ . Replacing NO 3 ‐ with Cl ‐ , SO 4 2‐ , or H 2 PO 4 ‐ , had no effect on Zn 2+ absorption. The inhibitory effects of alkali and alkaline earth cations appeared to be mutually competitive. Large effects of K + at low concentrations of Ca 2+ decreased and finally disappeared with increasing concentrations of Ca 2+ . The rates of Zn 2+ absorption by 6‐day‐old, intact wheat seedlings closely approximated those reported for long‐term experiments over a wide range of solution Zn 2+ concentrations from 0.05 to 5.0µ M when the temperature and the composition of the absorbing solutions were identical. These results suggest that it may be possible to relate short‐term studies of Zn 2+ absorption to long‐term studies of Zn nutrition.