Litter Quality Modulates Effects of Dissolved Nitrogen on Leaf Decomposition by Stream Microbial Communities

Area of Science:

• Aquatic Ecology
• Biogeochemistry
• Environmental Science

Background:

• Stream decomposition is influenced by dissolved nutrients and litter traits like lignin, nitrogen (N), and phosphorus (P).
• Contrasting responses of leaf litter decomposition to nutrient enrichment are observed in streams, but the cause is unclear.
• Interspecific variation in litter nutrient or lignin concentrations may explain differing responses to stream nutrient enrichment.

Purpose of the Study:

• To determine if litter nutrient or lignin concentrations are the primary drivers of differing decomposition rates across leaf species.
• To quantify the effect of nitrogen (N) enrichment on decomposition rates for various leaf litter types.
• To model the relationship between N enrichment and decomposition using Monod kinetics.

Main Methods:

• A controlled laboratory experiment was conducted using 38 leaf species with varying litter traits (N, P, lignin).
• Litter was exposed to 8 levels of dissolved N concentrations (0.07 to 8.96 mg N L⁻¹).
• Decomposition rates were measured and modeled using Monod kinetics to assess N effects.

Main Results:

• Lignin concentration was the most significant litter trait influencing decomposition rates and their response to N enrichment.
• Increasing dissolved N accelerated decomposition of lignin-poor litter (e.g., <10% lignin) more than lignin-rich litter (e.g., >15% lignin).
• Litter P concentration had a slight positive effect, while litter N concentration had no significant effect on decomposition.

Conclusions:

• Litter lignin concentration is a key factor mediating the impact of stream nutrient enrichment on decomposition.
• Shifts in riparian vegetation to species with high litter lignin could reduce accelerated carbon turnover caused by stream nutrient enrichment.
• Understanding litter traits is crucial for predicting ecosystem responses to anthropogenic nutrient inputs in streams.