Differential Responses of Plant Primary Productivity to Nutrient Addition in Natural and Restored Alpine Grasslands in the Qinghai Lake Basin.

Chunli Li,Yuanming Xiao,Li Ma,Xinwei Li,Yonghui Li,Chunhui Zhang

doi:10.3389/fpls.2021.792123

Abstract

Climate, land-use changes, and nitrogen (N) deposition strongly impact plant primary productivity, particularly in alpine grassland ecosystems. In this study, the differential responses of plant community primary productivity to N and phosphorus (P) nutrient application were investigated in the natural (NG) and “Grain for Green” restored (RG) alpine grasslands by a continuous 3-year experiment in the Qinghai Lake Basin. N addition only significantly promoted plant aboveground biomass (AGB) by 42% and had no significant effect on belowground biomass (BGB) and total biomass (TB) in NG. In comparison with NG, N addition elevated AGB and BGB concurrently in RG by 138% and 24%, respectively, which further significantly increased TB by 41% in RG. Meanwhile, N addition significantly decreased BGB and the AGB ratio (R/S) both in NG and RG. Compared with N addition, P addition did not perform an evident effect on plant biomass parameters. Additionally, AGB was merely negatively influenced by growing season temperatures (GST) under the N addition treatment in NG. AGB was negatively associated with GST but positively related to growing season precipitation (GSP) in RG. By contrast, changes in the R/S ratio in RG were positively correlated with GST and negatively related to GSP. In sum, the results revealed that plant community biomass exhibited convergent (AGB and R/S) and divergent (BGB and TB) responses to N addition between NG and RG. In addition, the outcomes suggested that climate warming would enhance plant biomass allocation to belowground under ongoing N deposition, and indicated the significance of precipitation for plant growth and AGB accumulation in this restored alpine grassland ecosystem.

Highlights

The plant community biomass of the alpine grassland was affected by N addition (Table 1)
N addition significantly increased belowground biomass (BGB) and total biomass (TB) in RG by 24 and 41% (p < 0.01, Table 1; Figures 1B,C), respectively; it showed no evident effects on BGB and TB in natural alpine grassland (NG) (p > 0.05, Table 1; Figures 1B,C)
Combined with the preceding analyses, our results indicated that climate change could affect plant community biomass accumulation and allocation mainly by regulating soil moisture in the alpine grasslands around Qinghai Lake Basin (QLB)

Summary

Introduction

As a representation of primary productivity and carbon (C)uptake by plants, biomass is a foundational measure that can be used to infer aspects of nutrient cycling and energy flow in terrestrial ecosystems (Borer et al, 2014; Fay et al, 2015; Grace et al, 2016; Kohli et al, 2019). The availability of N has been deemed an essential determinant of the aboveground net primary productivity (ANPP) across terrestrial ecosystems, and N fertilization could promote plant N uptake and improve plant biomass production (Elser et al, 2007; LeBauer and Treseder, 2008; Borer et al, 2014; Fay et al, 2015; Wang et al, 2020). Nutrient co-limitation of grassland productivity is common and more widely recognized (Ågren et al, 2012; Borer et al, 2014; Fay et al, 2015; Wang et al, 2020)

Methods

Results

Conclusion