Nitrogen addition increases root biomass allocation and changes functional traits of two dominant tree species in North China

Abstract

AbstractAims Nitrogen (N) is one of the limiting nutrients for plant growth in terrestrial ecosystems. Numerous studies that have explored the effects of N addition on the eco-physiological traits and biomass production of plants, but the underlying mechanism of N deposition on biomass allocation has not been clarified, especially for urban greening trees. Methods A greenhouse simulated experiment was conducted by two dominating urban street trees in North China, including coniferPinus tabuliformisand broadleavedFraxinus chinensis. We set up three levels of N addition: ambient, low N addition, and high N addition (0, 3.5, and 10.5 gN m− 2year− 1) and determined the biomass distribution, plant functional traits, and soil nutrient traits of the two trees. Results Our results showed that N addition had positive effects on the aboveground and belowground biomass ofP. tabuliformis, which also shifted its functional traits to fast. WhileF. chinensisonly increased root biomass distribution and root acquisitive traits as N increased. Furthermore, N addition increased the soil N and phosphorus contents of both two trees and improved the root nutrient uptake capacity, resulting in the increase of root-shoot ratio. We found that optimal partitioning theory could better explain that trees would invest more resources in roots in the poor-resource area. Conclusion Trees changed their root structure and increased root biomass allocation to adapt to the high N deposition environment. Our findings highlight the importance of plant functional traits in driving the responses of biomass allocation to environmental factors for urban greening-dominated tree species.