Response ofKobresia pygmaeaandStipa purpureaGrassland Communities in Northern Tibet to Nitrogen and Phosphate Addition

Jingsheng Wang,Baoxiong Chen,Yangjian Zhang,Bingsong Zhang,Xianzhou Zhang,Zhikai Wang,Junlong Zhang,Congqian Ran

doi:10.1659/mrd-journal-d-11-00104.1

Abstract

The Tibetan Plateau is of fundamental ecological significance to China, Asia, and the world. In recent years, Tibetan grasslands have suffered from severe degradation due to climate change and anthropogenic disturbance. In this study, nitrogen (N) and phosphate were applied to a moderately degraded Kobresia pygmaea meadow and Stipa purpurea steppe in the arid alpine northern Tibetan Plateau. The results showed that with increasing nitrogenous fertilizer, the height, coverage, biomass, and importance value of the K. pygmaea population decreased whereas the population of S. purpurea exhibited the opposite trend. Application of a mixed fertilizer with the same amount of N and phosphorus (P) (5 g each per m2) doubled the biomass of the K. pygmaea meadow and increased the aboveground biomass of the S. purpurea steppe by 72.3%. The nitrogenous fertilizer increased the total biomass and belowground biomass of the S. purpurea steppe, whereas the mixed fertilizer was beneficial to aboveground grass recovery. Application of 10 g N 5 g P m−2 fertilizer increased aboveground biomass by 164.8%, whereas the belowground biomass was less than the control by 4.7%. The N and P fertilizer did not affect soil pH, except for some changes in soil N and P contents.

Highlights

The Tibetan Plateau, known as the world’s ‘‘third pole,’’ is of fundamental ecological significance for China, Asia, and even the world (Qiu 2008)
Study site Unique climate conditions on the northern Tibetan Plateau have generated several ecosystems (Gao et al 2010), including K. pygmaea meadow and S. purpurea steppe, which are widely distributed in the Nagqu and Ngari regions of Tibet, an alpine zone in the upper reaches of the Brahmaputra river and the lake basin region in the northern Tibetan Plateau (Figure 1)
When the fertilizer amount was 10 g N, the height, coverage, and importance value decreased to 2.1 cm, 20%, and 0.2, respectively

Summary

Introduction

The Tibetan Plateau, known as the world’s ‘‘third pole,’’ is of fundamental ecological significance for China, Asia, and even the world (Qiu 2008). The vegetation on the Tibetan Plateau has undergone severe degradation due to intensified grazing, urbanization, population growth, burgeoning tourism, and climate change (Zhang et al 2008; Harris 2010). Fencing and fertilization are currently the main measures applied to rehabilitate the degraded grassland ecosystem (Smith et al 2000). Fertilization can provide the necessary nutrition for plants and increase grass yield. Previous studies have shown that fertilization, especially nitrogen (N) fertilization (William et al 1995), is one of the most important and cost-effective measures to improve grass productivity in various climatic zones and soils. N has been found to be the predominant factor limiting the primary productivity of most land ecosystems (Vitousek and Howarth 1991; LeBauer and Treseder 2008)

Objectives

Methods

Results

Discussion

Conclusion