Phosphorus uptake and root anatomical traits of Typha domingensis Pers. grown on nutrient solution

Abstract

The increase of anthropic activities has caused eutrophication, characterized by the excess of nutrients and the excessive, permanent and continuous fertilization of bodies of water, which may result the massive and unwanted algae and aquatic macrophytes development. Phosphorus is one of the main elements responsible for this process, and may be involved in the excessive growth of macrophytes populations. This paper evaluates the effects of Phosphorus on root growth and the anatomical features related to the absorption of this nutrient in Typha domingensis macrophyte, worldwide spread. The plants were cultivated during 60 days in nutrient solution containing different levels of phosphorus: 0, 0.2, 0.4, 0.6 and 0.8mM. At the end of the experiment, root elongation, the anatomy of the Maturation and the tip of the root were evaluated. The experimental design was completely randomized with five treatments and six replicates. Phosphorus absorption from the root increased proportionally to its levels in the nutrient solution showing 8 g Kg-1 in the treatment with 0.8 mM. Root elongation was reduced by higher levels of phosphorus and all treatments showed an increase in root length from 30 to 60 days. Phosphorus promoted a greater proportion of the root cap, while reducing the proportion of procambium at its tip. In addition, treatments of 0.2 and 0.8 mM improved the fundamental meristem ratio. Higher phosphorus levels reduced the diameter of the xylem vessels and the proportion in the vascular cylinder, while increasing the proportion of phloem. The endoderm and the exoderme were reduced by higher levels of phosphorus. The cortical aerenchyma of the root was reduced both by the absence and by 0.6 and 0.8 mM of phosphorus. Therefore, the absorption of phosphorus in the roots of T. domingensis is favored by reduced apoplastic barriers, but the higher levels of nutrients cause a limitation in root growth and tissue development.