Seasonal and diurnal variations of mineral concentrations in the branch xylem sap of Cornus controversaa

Abstract

The seasonal variation of the nocturnal concentrations of the major inorganic ions in the branch xylem sap of 11-year-old Cornus controversa HENSL. was studied by vacuum extraction using an attached branch. The diurnal change of inorganic ion concentrations was studied by vacuum extraction using a detached branch in connection with the heat pulse velocity of the stem and the xylem pressure potential of the leaves on a clear summer day. There were increases in the concentrations of most ions just prior to leaf emergence followed by rapid decreases as the leaves expanded. The concentration peaks of the cations were K⁺: 175 and Call: 265 ppm, while those of the anions were C1-: 51, NO₂ NO₂^--N: 4, NO₃^--N: 6, and SO₄^2--S: 25 ppm both before leaf emergence at the beginning of March, but the Mg²⁺ peak was 25 ppm in late May. The coefficient of correlation, using a simple equation between the K⁺ and Ca²⁺ or Cl^- nocturnal concentrations, was above 0. 80, and that between the Ca²⁺ and Cl^- or NO^3--N concentrations was above 0.7. The coefficients of correlation between total cations (K⁺+Ca²⁺+Mg²⁺) or total anions (Cl^-+NO₂^--N+NO₃^--N+SO₄^2--S) were 0.91, and those between total cations or total anions and K⁺, Ca²⁺, and Cl^- concentrations were above 0.7. On a clear summer day, the inorganic ion concentrations of branch xylem sap were maximum at noon and minimum at night. The time and duration of sampling need to be considered when sampling branch xylem sap in investigating nutrient concentrations.