Long-term reactive nitrogen loading alters soil carbon and microbial community properties in a subalpine forest ecosystem

• Published in: Soil biology & biochemistry 2016-01, Vol.92, p.211-220
• Main Authors: Boot, Claudia M., Hall, Ed K., Denef, Karolien, Baron, Jill S.
• Format: Article
• Language: English
• Subjects: Enzymes; Microbial biomass; Microbial community; Nitrogen deposition; Soil carbon cycling
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2015.10.002

Elevated nitrogen (N) deposition due to increased fossil fuel combustion and agricultural practices has altered global carbon (C) cycling. Additions of reactive N to N-limited environments are typically accompanied by increases in plant biomass. Soil C dynamics, however, have shown a range of different responses to the addition of reactive N that seem to be ecosystem dependent. We evaluated the effect of N amendments on biogeochemical characteristics and microbial responses of subalpine forest organic soils in order to develop a mechanistic understanding of how soils are affected by N amendments in subalpine ecosystems. We measured a suite of responses across three years (2011–2013) during two seasons (spring and fall). Following 17 years of N amendments, fertilized soils were more acidic (control mean 5.09, fertilized mean 4.68), and had lower %C (control mean 33.7% C, fertilized mean 29.8% C) and microbial biomass C by 22% relative to control plots. Shifts in biogeochemical properties in fertilized plots were associated with an altered microbial community driven by reduced arbuscular mycorrhizal (control mean 3.2 mol%, fertilized mean 2.5 mol%) and saprotrophic fungal groups (control mean 17.0 mol%, fertilized mean 15.2 mol%), as well as a decrease in N degrading microbial enzyme activity. Our results suggest that decreases in soil C in subalpine forests were in part driven by increased microbial degradation of soil organic matter and reduced inputs to soil organic matter in the form of microbial biomass. •N amendments decreased organic soil pH, microbial biomass C and % C.•N amendments altered microbial community structure.•Fertilization decreased arbuscular mycorrhizal and saprotrophic fungal abundance.•Spring, but not fall bacterial abundance was reduced by N amendments.•N degrading enzymes activities were elevated in N amendment plots.