The effects of nitrogen deposition and invasion on litter fuel quality and decomposition in a Stipa pulchra grassland

Abstract

Fuel loads from invasive annual grasses different from natives can alter the fire regime to one that positively feedbacks to their establishment, known as the grass-fire cycle. Nitrogen (N) deposition can exacerbate the grass-fire cycle by favoring non-native annual grasses and increase their biomass production, generating greater fuel loads. Less studied is how N enrichment can affect the chemical quality of litter as it pertains to the decomposition or accumulation of fuel. Here, we primarily tested how N addition affected the quality and mass loss of litter produced by the native perennial grass, Stipa pulchra, and the non-native annual grass, Bromus hordeaceus. We found that B. hordeaceus litter was significantly lower in quality and decomposed to a lesser extent than S. pulchra litter, even with N addition, which increased litter quality and mass loss overall. In addition, we show that B. hordeaceus sustained dead biomass with lower moisture content for a greater portion of the experimental year. Therefore, we conclude that B. hordeaceus invasion promotes fire by generating litter that decomposes more slowly, leaving a greater source of dry fuel for a longer period of time.