Effect of Nutrient Addition on the Productivity and Species Richness of Grassland Along With an Elevational Gradient in Tajikistan.

Lian-Lian Fan,Yao-Ming Li,Okhonniyozov Mekrovar,Kai-Hui Li,Jie-Fei Mao,Xue-Xi Ma

doi:10.3389/fpls.2021.765077

Abstract

Grasslands provide key resource for the millions of people who are dependent on livestock in Tajikistan. Productivity and species richness (SR) are important characteristics of grassland ecosystems and are greatly affected by nutrient inputs. The effect that climate change might have on these characteristics remains unclear. Here, an in situ nitrogen (N) and phosphorus (P) fertilization experiment was conducted at four sites along with an elevational gradient (650, 1,100, 1,250, and 2,000 m) in western Tajikistan over 2 years (2018 and 2019) to examine the influences of nutrient availability and climate change on aboveground biomass (AGB) and SR; precipitation and temperature were also considered to analyze the responses. It demonstrated that enrichment with N, P, and their combinations significantly increased AGB along with an elevational gradient (p < 0.05). AGB increased as the concentrations of nutrients added increased. The maximum AGB, which was 2-fold higher compared with control, was observed when 90 kg N ha–1year–1 and 30 kg P ha–1year–1 were added. In addition, nitrogen addition alone stimulated greater AGB than P addition, although no significant difference was observed between these two treatments. Enrichment with N, P, and their combination had no significant effect on SR; however, SR significantly changed at different elevation. Elevation had direct effect on precipitation and temperature, which, in turn, resulted in variation in AGB and SR. Moreover, both nutrient and elevation had significant effect on AGB and SR, but there was no interaction effect of them. AGB and SR interacted with significant negative correlation. In the high-elevation area, plants grew better in the warmer year (2018); this indicates that grasslands in high mountain areas in Tajikistan might have higher productivity as the climate warms, which will positively affect the economic development of the country.

Highlights

Grasslands are important terrestrial ecosystems, accounting for almost 30% of the land area of earth (Bi et al, 2020)
A linear mixed-effects models were used to analyze the effect of different nutrition addition treatments on plant above-ground biomass (AGB) and species richness (SR) along with an elevational gradient, with nutrient and elevation as independent variable and years as a random factor
All the statistical analyses were conducted in R version 3.3.2

Summary

Introduction

Grasslands are important terrestrial ecosystems, accounting for almost 30% of the land area of earth (Bi et al, 2020). Grassland ecosystems have experienced severe changes, for example, the decline of grassland productivity and the loss of species diversity, as both climate change and anthropogenic activities have contributed to dynamic variations in these ecosystems (Jiang et al, 2015; Su et al, 2021). Some studies have shown that nitrogen addition reduced the species diversity, it increased the functional richness (Niu et al, 2014; Mao et al, 2017). Enrichment with phosphorus fertilizer has been shown to have either increased or no effect on ecosystem productivity and species diversity (Menge and Field, 2007; Gao et al, 2021). The effect of phosphorus fertilizer on ecosystems can be regulated by nitrogen fertilizer (Bracken et al, 2015)

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Results

Discussion

Conclusion