[Plastic responses of fine root morphological traits of Castanopsis fabri and Castanopsis carlesii to short-term nitrogen addition].

Nitrogen deposition will affect the morphology of fine roots and its absorption of nutrien-ts, resulting in changes nutrient cycling in terrestrial ecosystems. In order to understand the effects of nitrogen deposition on fine root morphological traits of Castanopsis fabri and C. carlesii, two ectomycorrhizas tree species, we carried out in situ experiment using the root bags method in an evergreen broadleaved forest in the subtropical zone. The results showed that the plastic responses of specific root length and specific root surface area of low-order roots (first to third order) to nitrogen addition was higher than that of high-order roots (fourth order). The plastic responses of root tissue density to nitrogen addition increased from the first-order to the fourth-order, while the average root diameter of each order had no significant plastic responses to nitrogen addition. There was a certain synergistic change between the plastic response of specific root length and specific surface area in the low order fine root and the plastic response of tissue density in the high order fine root. The specific root length, specific root surface area and root tissue density of the two species showed opposite plastic responses to nitrogen addition, indicating that different ectomycorrhizal tree species had different nutrient foraging strategies. C. fabri adopted rapid absorption strategy by increasing specific root length, specific root surface area, and proliferation rate of fine root length, while C. carlesii adopted a relatively conservative resource absorption strategy by increasing tissue density of fine roots.