Cluster roots of Embothrium coccineum (Proteaceae) affect enzyme activities and phosphorus lability in rhizosphere soil

© 2015, Springer International Publishing Switzerland. Background and aim: Cluster roots have a profound effect on their rhizosphere. Our aim was to determine the effect of cluster roots of Embothrium coccineum, growing under natural conditions, on soil enzyme activities and phosphorus (P) lability in its rhizosphere. Methods: We determined enzyme activities: acid phosphatase (P-ase), dehydrogenase and β-glucosidase, and the rate of hydrolysis of fluorescein diacetate (FDA), as well as P fractions in the cluster root rhizosphere at different cluster-root developmental stages (juvenile, mature, semi-senescent, senescent), in the non-cluster root rhizosphere, and in bulk soil. In addition, the concentrations of total P and manganese Mn in roots was measured. Results: The rhizosphere of senescing cluster roots presented the highest P-ase, β-glucosidase and dehydrogenase activities, and fastest rate of FDA hydrolysis, being 2.6-, 4.6-, 3.3- and 25.8-fold greater, respectively, than those in the rhizosphere of mature cluster roots. The P fractionation showed that the inorganic P (Pi) fraction was 15 % greater in the rhizosphere of mature cluster roots than in that of other stages. Mature cluster roots showed the highest total [P], suggesting the fastest P uptake. Conclusion: Cluster roots of E. coccineum modified their rhizosphere depending on their developmental stage, presenting lower soil enzyme activities at the mature stage than at other development stages. In addition, mature cluster roots increased the Pi fraction in their rhizosphere, allowing the highest total root [P] at this developmental stage.