Long-term effects of wildfire on available soil nutrient composition and stoichiometry in a Chinese boreal forest.

Wildfire disturbance is a major driver of biogeochemical processes in Eurasian boreal forests, yet little is known about the response of soil nutrient stoichiometry to wildfire in this ecosystem. To fill this gap, we measured the composition of available soil nutrients and their stoichiometric ratios in a Chinese boreal forest along a gradient of fire history. In the 1-year-post-fire site, wildfire increased the relative abundances of element nitrogen (N), phosphorus (P), Sulphur (S), iron (Fe), and aluminum (Al), and reduced the abundances of element calcium (Ca), magnesium (Mg), and potassium (K). Available soil N:K, N:S, P:K, P:S, and S:K ratios were 240%, 70%, 440%, 160%, and 150% higher than the control, but N:P ratio was not significantly different. In the 11-year-post-fire site, the soil nutrient composition recovered to the pre-fire levels. Although most of the soil nutrient stoichiometry returned to pre-fire levels, soil N:P ratios became significantly higher. These results showed immediate wildfire effects on soil nutrient availability and composition were strongly related to fire severity, but such effects could be subdued by soil environment and topographical variations over time. Although wildfire effects on soil nutrients are mostly short-term, it could produce relatively long-term effects on balance between N and P.