Response of Root Biomass and Root Morphology to Long-term Nitrogen Application in Subtropical Evergreen Broad-leaved Forest

Abstract:

In order to explore the survival strategies of forest ecosystems under environmental change and predict the response mode of roots under the background of long-term nitrogen (N) deposition, two treatments, including control and N addition [80 kg N/(hm²·a)], were set up in subtropical natural evergreen broad-leaved forest to study the effects of long-term N addition on root biomass, specific root length, specific surface area and tissue density. The results showed that long-term N addition had no significant effect on root biomass and its root biomass reduction coefficient β (P>0.05), the vertical distribution characteristics of root biomass did not change significantly (there was no significant difference between biomass accumulated in different soil layers). The root biomass density of different diameter classes under control and N addition showed the same trend with soil layer, but the interaction between soil layer and diameter class had a significant effect on root biomass. Long-term N addition significantly increased 0-1 mm fine specific root length. However, long-term N addition significantly decreased the tissue density and was not affected by diameter class. However, N addition had no significant effect on the specific surface area of roots, and this change was an overall trend at the community level. At the community level, long-term N addition had no significant effect on the root biomass and vertical distribution of subtropical evergreen broad-leaved forest, which was consistent with the changes in total carbon (C), N and phosphorus (P) contents in soil with soil layer. However, N addition for 11 years increased the specific root length and decrease the tissue density, and the root resource acquisition strategy of some species changed to a rapid acquisition strategy. Therefore, under the background of long-term N deposition, roots would respond to nutrient changes by increasing specific root length and decreasing tissue density.

Key words:N addition;Root biomass;Regression coefficient β;Root morphology;Nutrient absorption strategy