Nutrient availability determines silicon uptake by wetland plants

Date: 20 October 2016

Introduction: The amount of silicon in plant tissue subsequently co-determines how long litter can be stored in the wetlands' soil.

In earlier research of the Global Change Ecology Centre (GCE), it was shown that nutrient enrichment of wetlands (through e.g. fertilization) triggers complex changes in the decomposition of plant litter.

This is important: wetlands often are natural sinks for carbon. Whether this carbon remains stored on longer timescales, or rather decomposes (releasing carbon dioxide), can have important consequences for the atmospheric carbon concentrations, and hence climate change. A new study now shows the important role the element silicon can play here.

Silicon uptake by plants has frequently been associated to plant stress (mainly in agricultural studies): higher Si uptake is observed under more challenging conditions. Willem-Jan Emsens (GCE, research group Ecosystem Management) and his Dutch and Flemish colleagues show that wetland plants that grow under low nitrogen, phosphorus and potassium availability, take up more silicon.

Willem-Jan: “The physiological role of silicon in wetland plants is poorly understood. We observe a consistently higher silicon concentration in plants that grow under low nutrient availability. This has potentially important consequences. Our experiments show that silicon rich plants decompose slower. The durability of the plant litter is a crucial factor in the efficiency of wetlands in retaining carbon.”

Figure 1: Plants rich in nitrogen (N) show consistently lower silicon (BSi) content. As a result, they can decompose faster.

Why the plants take up more silicon under the nutrient poor conditions, could not be answered in this study. It is potentially linked to increased plant stress as a result of low nutrient availability. Willem-Jan: “We did observe a strong interdependence of silicon content in plants, and other factors that determine durability of litter. Silicon rich plants contained more lignin, a molecule that gives strength to plant shoots. The silicon rich biomass is also relatively rich in carbon compared to nitrogen.”

Results were published in the scientific journal Biogeochemistry.

Figure 2: Sedges, often rich in silicon, are important contributors to peat formation (and carbon sequestration) in wetlands.