Net primary productivity and its partitioning in response to precipitation gradient in an alpine meadow

Fangyue Zhang,Jian Sun,Quan Quan,Qingping Zhou,Shuli Niu,Bing Song,Youjun Chen

doi:10.1038/s41598-017-15580-6

Abstract

The dynamics of net primary productivity (NPP) and its partitioning to the aboveground versus belowground are of fundamental importance to understand carbon cycling and its feedback to climate change. However, the responses of NPP and its partitioning to precipitation gradient are poorly understood. We conducted a manipulative field experiment with six precipitation treatments (1/12 P, 1/4 P, 1/2 P, 3/4 P, P, and 5/4 P, P is annual precipitation) in an alpine meadow to examine aboveground and belowground NPP (ANPP and BNPP) in response to precipitation gradient in 2015 and 2016. We found that changes in precipitation had no significant impact on ANPP or belowground biomass in 2015. Compared with control, only the extremely drought treatment (1/12 P) significantly reduced ANPP by 37.68% and increased BNPP at the depth of 20–40 cm by 80.59% in 2016. Across the gradient, ANPP showed a nonlinear response to precipitation amount in 2016. Neither BNPP nor NPP had significant relationship with precipitation changes. The variance in ANPP were mostly due to forbs production, which was ultimately caused by altering soil water content and soil inorganic nitrogen concentration. The nonlinear precipitation-ANPP relationship indicates that future precipitation changes especially extreme drought will dramatically decrease ANPP and push this ecosystem beyond threshold.

Highlights

The terrestrial ecosystem has experienced frequent and extreme precipitation events during the last five decades[1,2,3,4,5], which is projected to become even more frequent and severe during the remainder of the 21st century[6,7]
Some manipulative experiments have been set up to examine the relationship between precipitation and aboveground NPP (ANPP), the relationship is restricted by the limited range of rainfall that mostly have two or three
We addressed the following questions: (1) How does ANPP, belowground NPP (BNPP) and fBNPP respond to changes in precipitation gradient in an alpine meadow? (2) What are the key factors controlling the responses of net primary productivity (NPP) and its partitioning to precipitation changes?

Summary

Introduction

The terrestrial ecosystem has experienced frequent and extreme precipitation events during the last five decades[1,2,3,4,5], which is projected to become even more frequent and severe during the remainder of the 21st century[6,7]. The precipitation-NPP relationship has been studied by spatial approach, temporal approach, and manipulative experiments. The temporal studies relate time series of ANPP and annual precipitation in a single site and find linear relationship between them but with lower slopes and regression coefficients than spatial models[14,15]. To gain empirical evidence of ANPP responses to large variations in precipitation, it is imperative to conduct field precipitation gradient experiments, with multiple levels of precipitation, especially the extreme precipitation condition. There are a few studies on the responses of belowground biomass (BGB) to precipitation change, but generate large debates. A few manipulative experiments were conducted to examine belowground NPP (BNPP) response to precipitation changes[24,25,26], but none of them studied the response to a precipitation gradient. Due to the limited studies on BNPP, how fBNPP would respond to precipitation gradient is highly uncertain

Methods

Results

Conclusion