Biochemical and physiological studies on races of Festuca rubra (L.) from a serpentine and non serpentine soil

Abstract

Soil solutions were extracted, using a centrifugation method, from a Scottish serpentine soil from Meikle Kilrannoch, Angus. Analyses showed that the soil was outstanding for its very high ratio of magnesium to calcium and it also contained relatively high levels of nickel. The suitability of the centrifugation method of extracting soil solutions from a range of serpentine soils from Britain and Rhodesia was assessed. Whilst the technique seemed successful for the Meikle Kilrannoch soil, the validity of its application to other soils was not proven. The levels of elements in Meikle Kilrannoch soil solutions were used as the basis for the composition of the solutions for water culture experiments. These experiments showed large differences between serpentine and non-serpentine Festuca rubra in response to a number of elements. Increasing solution nickel and magnesium reduced the dry weights of the non-serpentine plants and caused them to absorb large quantities of potentially toxic metals. However, Increasing calcium supply appeared to ameliorate much of the toxic influences of nickel and magnesium in the non-serpentine race. By contrast, high calcium supply, particularly when micronutrient levels were high, depressed the growth of the serpentine race. In both races, increasing calcium supply promoted the absorption of magnesium; conversely, increasing magnesium supply depressed calcium uptake. The serpentine race maintained a lower tissue Mg/Ca ratio than the non-serpentine race in all treatments. Non-serpentine plants seemed unable to maintain high tissue potassium levels in serpentine-simulated conditions. Chromium was shown to have some effect in determining growth rates of both races in the experimental conditions but at concentrations which were not related to those in the soil solution. Assays were carried out of the activity of root- surface acid phosphatase in different culture media. In the serpentine race, when micronutrients were absent or in short supply, nickel specifically enhanced the enzyme activity. This suggests that the serpentine race has evolved a use for, if not a strict requirement for, nickel. Increasing micronutrients removed the enzyme-activity enhancement of nickel and appeared to inhibit enzyme activity in the serpentine race. No root-surface phosphatase activity enhancement by nickel was noted for the non-serpentine race. The serpentine race also apparently required higher levels of magnesium for optimum enzyme activity. Carbohydrates accumulated in the non-serpentine race when nickel and magnesium supply were high, indicating a generally unfavourable metabolic response to these conditions. This high-carbohydrate effect was dependent on the supply of micronutrients and calcium. The serpentine race appeared able to synthesize and use carbohydrate in all the experimental treatments. A short investigation was undertaken into the chemical form of nickel in MK1 and Rhodesian soil solutions. Finally, the data derived from the water culture experiments were used to construct a computer model of the MK1 soil/Festuca rubra interrelationship.