Plant Functional Diversity Can Be Independent of Species Diversity: Observations Based on the Impact of 4-Yrs of Nitrogen and Phosphorus Additions in an Alpine Meadow.

Wei Li,Liang Guo,Guang-Hua Jing,Kai-Liang Yu,Howard E. Epstein,Ji-Min Cheng,Jie Zhao,Guo-Zhen Du,Takeshi Miki

doi:10.1371/journal.pone.0136040

Abstract

Past studies have widely documented the decrease in species diversity in response to addition of nutrients, however functional diversity is often independent from species diversity. In this study, we conducted a field experiment to examine the effect of nitrogen and phosphorus fertilization ((NH4)2 HPO4) at 0, 15, 30 and 60 g m-2 yr-1 (F0, F15, F30 and F60) after 4 years of continuous fertilization on functional diversity and species diversity, and its relationship with productivity in an alpine meadow community on the Tibetan Plateau. To this purpose, three community-weighted mean trait values (specific leaf area, SLA; mature plant height, MPH; and seed size, SS) for 30 common species in each fertilization level were determined; three components of functional diversity (functional richness, FRic; functional evenness, FEve; and Rao’s index of quadratic entropy, FRao) were quantified. Our results showed that: (i) species diversity sharply decreased, but functional diversity remained stable with fertilization; (ii) community-weighted mean traits (SLA and MPH) had a significant increase along the fertilization level; (iii) aboveground biomass was not correlated with functional diversity, but it was significantly correlated with species diversity and MPH. Our results suggest that decreases in species diversity due to fertilization do not result in corresponding changes in functional diversity. Functional identity of species may be more important than functional diversity in influencing aboveground productivity in this alpine meadow community, and our results also support the mass ratio hypothesis; that is, the traits of the dominant species influenced the community biomass production.

Highlights

In terrestrial plant communities, fertilization via nutrient deposition and agricultural inputs often leads to decreases in plant diversity and shifts in community composition [1, 2]
The experimental site has been overgrazed in the past, but has been fenced by wire netting during the growing season since May 2007, with grazing limited to the non-productive winter months (October to April in the following year) [34].The average soil organic C(%), available N(kg−1), available P(kg−1) and PH is 1.6, 16.2, 2.1 and 7.1, respectively before applying fertilizers
Our results emphasized that community productivity is linked to the functional traits of the dominant species rather than functional diversity, and supported the mass ratio hypothesis

Summary

Introduction

Fertilization via nutrient deposition and agricultural inputs often leads to decreases in plant diversity and shifts in community composition [1, 2]. Numerous experiments of nutrients addition, in grasslands, reported nearly ubiquitous negative productivity–diversity relationships [1,2,3,4]. This pattern is well documented [5], attempts to link biodiversity to aboveground productivity following fertilization are rare (but see [6, 7]). Examining functional diversity has been proposed as a promising method to identify the effects of species loss on ecosystem functioning following fertilization [16, 18]. We use aboveground productivity as a proxy of ecosystem functioning, and the other functions of ecosystems such as biogeochemical cycles, invasion resistance, stability in the face of disturbance are not being taken into consideration in this study

Methods

Findings

Discussion

Conclusion