| Popis: |
By automatically scheduling irrigation according to soil moisture thresholds, this work aims to understand how over-irrigation (applying 50 % more than full water requirements) affect soil properties (volumetric water content, soil oxygen and temperature) and plant physiological responses. Four weeks of over-irrigation significantly decreased shoot fresh weight and total leaf area of tomato plants (Solanum lycopersicum Mill. cv. Ailsa Craig) compared to well-drained plants. Since over-irrigation did not alter leaf water potential, stomatal conductance or foliar concentrations of the plant hormone abscisic acid (ABA), it seems unlikely that ABA accumulation or leaf water status mediate growth. In contrast, over-irrigation significantly increased foliar ethylene evolution. Over-irrigating the partial ethylene-insensitivite genotype Never ripe did not lead to such a dramatic growth inhibition as in the wild type, suggesting that partial ethylene-insensitivity can ameliorate over-irrigation induced growth-inhibition to a degree. Although the ethylene precursor ACC was not detected in root xylem sap, over-irrigation increased leaf xylem sap ACC concentration. Shoot fresh weight correlated with increased tZ, GA3, ABA and JA leaf xylem sap concentration, but was not correlated with concentrations of any root xylem sap phytohormone. Over-irrigation significantly decreased foliar nitrogen concentrations by 32 % and daily additions of 10 mM Ca(NO3)2 to over-irrigated soil did not significantly change leaf water potential, stomatal conductance or foliar ABA concentration, but restored foliar nitrogen concentrations, ethylene emission and growth of over-irrigated plants to control levels. Thus, over-irrigation-introduced foliar nitrogen deficiency may be key to limiting growth of over-irrigated tomato plants. |
