Nitrogen Deposition Shifts Grassland Communities Through Directly Increasing Dominance of Graminoids: A 3-Year Case Study From the Qinghai-Tibetan Plateau.

Hao Shen,Jiannan Xiao,Yangliu Zhi,Wen Lu,Antonio Ditommaso,Shikui Dong

doi:10.3389/fpls.2022.811970

Abstract

Nitrogen (N) deposition has been increasing for decades and has profoundly influenced the structure and function of grassland ecosystems in many regions of the world. However, the impact of N deposition on alpine grasslands is less well documented. We conducted a 3-year field experiment to determine the effects of N deposition on plant species richness, composition, and community productivity in an alpine meadow of the Qinghai-Tibetan Plateau of China. We found that 3 years of N deposition had a profound effect on these plant community parameters. Increasing N rates increased the dominance of graminoids and reduced the presence of non-graminoids. Species richness was inversely associated with aboveground biomass. The shift in plant species and functional group composition was largely responsible for the increase in productivity associated with N deposition. Climatic factors also interacted with N addition to influence productivity. Our findings suggest that short-term N deposition could increase the productivity of alpine meadows through shifts in composition toward a graminoid-dominated community. Longer-term studies are needed to determine if shifts in composition and increased productivity will be maintained. Future work must also evaluate whether decreasing plant diversity will impair the long-term stability and function of sensitive alpine grasslands.

Highlights

There is evidence that long-term N deposition can increase the productivity of grassland ecosystems (Bai et al, 2008; Xia and Wan, 2008; Shen et al, 2019), possibly impacting ecosystem function (Gruber and Galloway, 2008; Stevens et al, 2015)
In plots subjected to the highest N addition rate, the abundance of grass species such as Leymus secalinus, Agropyron cristatum, Poa crymophila, and Stipa purpurea increased substantially during the experimental period while the abundance of forb species such as Aster tataricus and Artemisia scoparia decreased
Species richness was negatively associated with mean annual temperature (1.8◦C in 2015, 3.3◦C in 2016, and 1.8◦C in 2017)

Summary

Introduction

Atmospheric nitrogen (N) deposition has been increasing globally for decades (Phoenix et al, 2006; Galloway et al, 2008a). N deposition rates in terrestrial ecosystems are projected to increase to 200 Tg N yr−1 by 2050 (Galloway et al, 2008b). As N is the principal limiting nutrient for plant growth (Vitousek and Howarth, 1991), N deposition may have positive effects on plant productivity. These effects may be strongest in N-limited ecosystems (Vitousek et al, 1997) such as alpine. There is evidence that long-term N deposition can increase the productivity of grassland ecosystems (Bai et al, 2008; Xia and Wan, 2008; Shen et al, 2019), possibly impacting ecosystem function (Gruber and Galloway, 2008; Stevens et al, 2015). As N deposition rates increase, nitrophilous species become more abundant while N-sensitive species become less abundant (Stevens et al, 2004)

Objectives

Methods

Results

Conclusion