The ecology of carex flacca schreb and carex panicea L.

Abstract

The effect of pH, calcium and potassium on the performance of Carex flacca and C. panicea is investigated using tillers growing in solution culture. Performance is determined "by changes in fresh weight, dry weight, leaf length and the uptake of mineral nutrients into the plants. Possible age response is taken into consideration by using tillers of two different initial sizes and seeds, as starting material, No differential response due to initial age of the plant parts is detected, pH affects the final fresh and dry weights but not the relative concentrations of the elements present in the plant leaves, Above a certain external calcium concentration (about 50 p.p.m.) uptake of calcium by the plants greatly increases. Performance of both species increases with increase in external calcium concentration until the influx concentration is reached, and then it decreases, The germination and potassium variation experiments show that both species are very efficient in removing potassium from the culture solutions and maintaining a high internal concentration of this element, These observations could have important implications in natural plant communities. There is evidence to suggest that Carex flacca and C. panicea exhibit different responses to calcium and pH which could lead to different ecological tolerances. In a parallel study, the role of calcium and potassium in the nutrient dynamics of the two species is investigated over the two-year growing period. With progressive ageing, percentage potassium content decreases; total potassium increases over the first year, but falls sharply after flowering; both percentage and total calcium content increase steadily over the life span, but tend to decrease after fruiting, Analysis of different plant organs reveals considerable variation in the concentrations of calcium and potassium between adjacent parts of the same plant. There is evidence to suggest that calcium and potassium re-cycle in different ways. Potassium is probably being supplied to the next generation of tillers from the parent plant, either by absorption from the substrate, or by translocation from dying leaves, Calcium, on the other hand, has to be absorbed by the tillers themselves when they have established their own root system