A study of the root surface phosphatase activities of three species of higher plants: Juncus effusus, Phragnutes australis, and Typha latifolia

Abstract

The aim of this project was to investigate a possible link between environmental phosphorus status and the root surface phosphatase activities of three species of emergent macrophytes, with a view to assessing their potential for use as "biondicators". Analyses of water phosphorus concentrations and rates of surface phosphatase activities of Juncus effusus, Phragmites australis and Typha latifolia were carried out on samples from Bakethin Reservoir, Northumberland and Durham University Botanic Garden. Differences were found in water phosphorus concentrations at the sites. Water from Bakethin Reservoir was found to have lower levels of P than water from the Botanic Garden. Interspecific differences at p = 0.0002 were discovered in rates of phosphatase activity between Juncus, Phragmites and Typha. Juncus and Typha were found to exhibit significantly lower rates of phosphatase activity at the Botanic Garden than at Bakethin reservoir (p = 0.026 for Juncus, p = 0.037 for Typha). High rates of phosphatase activity in Juncus and Typha at Bakethin Reservoir corresponded with low concenfrations of environmental phosphorus, so it is possible that root surface phosphatases of both species are inducible in conditions of P- limitation. Juncus and Typha may therefore have the potential for use as bioindicators of environmental phosphorus status. Several practical problems were encountered, and may be of general significance. Rates of phosphatase activity declined rapidly in 100 μM pNPP assays. As a consequence, assays were terminated after 10 min. It was also observed that roots removed after assays had been terminated often showed a yellow coloration, presumably due to the retention of pNP. The accuracy of the pNPP assay relies upon all the pNP produced by the hydrolysis of pNPP being released into solution. The apparent retention of pNP by roots therefore brings the use of the pNPP assay, as a method for determining rates of phosphatase activity in eukaryotes, under scrutiny. One preliminary experiment carried out showed that more pNP was retained by roots under conditions of low pH.