Juncus Bulbosus Tissue Nutrient Concentrations and Stoichiometry in Oligotrophic Ecosystems: Variability with Seasons, Growth Forms, Organs and Habitats.

Therese F Moe,Benoît O L Demars,Dag O Hessen

doi:10.3390/plants10030441

Therese F Moe, Benoît O L Demars + Show 1 more

Open Access

https://doi.org/10.3390/plants10030441

Copy DOI

Abstract

Aquatic plant nutrient concentrations provide important information to characterise their role in nutrient retention and turnover in aquatic ecosystems. While large standing biomass of aquatic plants is typically found in nutrient-rich localities, it may also occur in oligotrophic ecosystems. Juncus bulbosus is able to form massive stands even in very nutrient-dilute waters. Here we show that this may be achieved by tissues with very high carbon-to-nutrient ratios combined with perennial (slow) growth and a poor food source for grazers inferred from plant stoichiometry and tissue nutrient thresholds. We also show that the C, N, P and C:N:P stoichiometric ratios of Juncus bulbosus vary with the time of year, habitats (lakes versus rivers) and organs (roots versus shoots). We found no differences between growth forms (notably in P, inferred as the most limiting nutrient) corresponding to small and large plant stands. The mass development of J. bulbosus requires C, N and P, whatever the ecosystem (lake or river), and not just CO2 and NH4, as suggested in previous studies. Since macrophytes inhabiting oligotrophic aquatic ecosystems are dominated by isoetids (perennial plants with a high root/shoot ratio), attention should be paid to quantifying the role of roots in aquatic plant stoichiometry, nutrient turnover and nutrient retention.

Highlights

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Standing biomasses of freshwater macrophyte meadows are equivalent to those of grassland ecosystems [1]; aquatic plants can actively contribute to nutrient cycling [4,5,6], as well as through the uptake, retention and release of nutrients from the sediment to the water column via decomposition and herbivory [7,8]
There were, no significant differences in C, N, P and C:N:P between large growth forms and rosette leaves or new shoots

Summary

Introduction

Aquatic plants tend to have higher N and P and lower C:N and C:P ratios than terrestrial plants [1,2]. This generally corresponds to higher growth rates and decomposition rates, as well as higher herbivory [1,2,3]. Standing biomasses of freshwater macrophyte meadows are equivalent to those of grassland ecosystems [1]; aquatic plants can actively contribute to nutrient cycling [4,5,6], as well as through the uptake, retention and release of nutrients from the sediment to the water column via decomposition and herbivory [7,8]

Objectives

Methods

Results

Discussion

Conclusion