Responses of fine root mass, length, production and turnover to soil nitrogen fertilization in Larix gmelinii and Fraxinus mandshurica forests in Northeastern China

The responses of fine root mass, length, production and turnover to the increase in soil N availability are not well understood in forest ecosystems. In this study, sequential soil core and ingrowth core methods were employed to examine the responses of fine root (≤1 mm) standing biomass, root length density (RLD), specific root length (SRL), biomass production and turnover rate to soil N fertilization (10 g N m⁻² year⁻¹) in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations. N fertilization significantly reduced fine root standing biomass from 130.7 to 103.4 g m⁻² in ash, but had no significant influence in larch (81.5 g m⁻² in the control and 81.9 g m⁻² in the fertilized plots). Similarly, N fertilization reduced mean RLD from 6,857 to 5,822 m m⁻² in ash, but did not influence RLD in larch (1,875 m m⁻² in the control and 1,858 m m⁻² in the fertilized plots). In both species, N fertilization did not alter SRL. Additionally, N fertilization did not significantly alter root production and turnover rate estimated from sequential soil cores, but did reduce root production and turnover rate estimated from the ingrowth core method. These results suggested that N fertilization had a substantial influence on fine root standing biomass, RLD, biomass production and turnover rate, but the direction and magnitude of the influence depended on species and methods.