General conceptions imply that the below-ground tissue of plant is the most important part in nature because most essential nutrients for life, such as mineral elements, enter biosphere and food chains through the roots of higher plants. Specific to submerged macrophytes, multitudinous nutrients exist in both water column and sediments. They uptake nutrients not only from the sediments but also from the overlying water through their leaves.

The role of the above-ground part of plants has recently been recognized more important than previously thought. However, there are still no direct evidences for the importance of the above-ground part on nutrient utilization. One of the existing bottlenecks is the difficulty to separate nutrients for the above- and below-ground parts of the submerged macrophytes at whole plant level.

A research team at Wuhan Botanical Garden used hermetic bags made by natural emulsion to successfully divide the nutrients for the above- and below-ground parts of macrophytes, and explored the characteristics of ammonium utilization in two representative species of submerged macrophytes (Myriophyllum spicatum L. and Potamogeton lucens L. w).

The results showed that both the above- and below- ground parts of the two species could uptake ammonium from the environment, the acropetal and basipetal translocation of nitrogen were exhibited in both the species.

However, ammonium uptake through the above-ground part and the acropetal translocation were dominant in both species when ammonium was in excess. M. spicatum exhibited higher plasticity in photosynthesis under various ammonium concentrations in comparison with P. lucens. Moreover, the pathway catalyzed by GDH (glutamate dehydrogenase) in the above-ground part of M. spicatum contributed more in ammonium detoxification.

This study identifies ammonium utilization strategy of submerged macrophytes and gives the first direct evidence that the above-ground part plays a much bigger role in nutrient utilization and provides theoretical support for practical water restoration by aquatic plants.

This work was supported by the National Natural Science Foundation of China and the Ministry of Science & Technology of China. It has been published in Frontiers in Plant Science with the title of "The above-ground part of submerged macrophytes plays an important role in ammonium utilization".

Characteristics of ¹⁵N uptake and translocation in plants (Image by WBG)