Sphagnum mosses--masters of efficient N-uptake while avoiding intoxication.

Area of Science:

• Ecology
• Biogeochemistry
• Plant Physiology

Background:

• Sphagnum mosses are crucial for ombrotrophic peatlands, preventing vascular plant dominance by scavenging atmospheric nitrogen (N).
• Understanding N-uptake kinetics in Sphagnum is vital for predicting N availability, plant competition, and carbon sequestration.
• The combined effects of nitrogen concentration, form, and exposure duration on Sphagnum N-uptake remain poorly understood.

Purpose of the Study:

• To investigate the effects of varying nitrogen concentrations, forms (ammonium vs. nitrate), and exposure times on Sphagnum magellanicum N-uptake kinetics.
• To compare N-uptake in Sphagnum from a pristine Patagonian bog versus a N-polluted Dutch bog.
• To assess the implications of N-uptake dynamics for peatland ecosystem functioning under changing environmental conditions.

Main Methods:

• Experimentally manipulated nitrogen concentrations (1–500 µM) and forms ((15)N-ammonium or nitrate).
• Measured N-uptake rates over different exposure times (0.5, 2, and 72 hours).
• Utilized Sphagnum magellanicum samples from both a pristine Patagonian bog and a long-term N-polluted Dutch bog.

Main Results:

• Ammonium uptake was significantly faster than nitrate uptake, especially over short durations (8x faster at 0.5h vs. 2x faster at 72h).
• N-uptake rates decreased substantially with longer exposure times, suggesting overestimation in short-term studies.
• Sphagnum from the polluted site exhibited lower N-uptake rates than from the pristine site, indicating adaptive N-pollution responses.

Conclusions:

• Sphagnum mosses are highly adapted to utilize short N pulses, a strategy potentially compromised by chronic N pollution.
• Reduced long-term N-uptake capacity in polluted Sphagnum may alter competitive advantages over vascular plants and reduce carbon sequestration.
• Interactions between nitrogen deposition and climate change-induced rainfall alterations pose significant risks to Sphagnum peatland functioning.