# Evaluating the Suitability of Four Plant Functional Groups in Green Roofs Under Nitrogen Deposition

## TL;DR

This study evaluates how four types of plants used in green roofs respond to high nitrogen levels, finding that some groups perform poorly under these conditions.

## Contribution

The study introduces a novel evaluation of plant functional groups in green roofs under nitrogen stress.

## Key findings

- Sod-forming graminoids and tall forbs showed reduced growth and aesthetic value under high nitrogen.
- Plant functional traits, not soil properties, mainly determine growth performance.
- High nitrogen deposition challenges the use of certain plant groups in green roofs.

## Abstract

The rapid urban expansion in the past few decades has resulted in a deficit of urban green space, and green roofs have become an effective way to expand urban green spaces. High nitrogen (N) deposition induced by urban development has threatened the health and sustainability of plants. The aim of this study was to evaluate the responses of plant growth performance and aesthetic value to N deposition in green roofs. Eleven species from four plant functional groups were grown under control, low N addition, and high N addition conditions to assess the effects of N addition on their growth performance, aesthetic value, soil properties, and plant functional traits. Different plant functional groups exhibited distinct traits, and their response to N addition was different. Under high N addition, the growth performance of sod-forming graminoids and tall forbs decreased by 47.0% and 23.7%, and their aesthetic value decreased by 24.4% and 16.2%, respectively. Growth performance of plant functional groups was mainly determined by plant functional traits rather than soil properties. The poor growth performance and aesthetic value of sod-forming graminoids and tall forbs challenged their widespread use under high N addition. This study highlighted the importance of selecting environmentally adaptive species from the perspective of plant functional groups, especially in the context of future high N deposition.