Field-based observations of regional-scale, temporal variation in net primary production in Tibetan alpine grasslands

Y Shi,D F B Flynn,Y Ma,B Schmid,J.-S He,W Ma,C Liang,J Fang,Y Wang

doi:10.5194/bg-11-2003-2014

Abstract

Abstract. Net primary production (NPP) is a fundamental process of natural ecosystems. Temporal variation of NPP not only reflects how communities respond to environmental fluctuations, but it also has important implications for regional carbon assessment. Unfortunately, studies based on field measurements to directly address this issue in the extreme environment of alpine grasslands are rare. In this study, we measured aboveground NPP (ANPP) and species richness in 40 sites across the Tibetan alpine grasslands from 2006 to 2009 to investigate the regional pattern of temporal variation in ANPP and to quantify the effects of climate fluctuation and biodiversity on this variation. The results showed that, during the 4-year period, the average ANPP varied 1.5-fold, from 83.9 to 125.7 g m−2, with a mean coefficient of variation of temporal variation of 36.6% across the 40 sites. Compared with other studies, alpine grasslands are not more sensitive to climate fluctuations than other grassland types. Aboveground NPP exhibited synchronous temporal variation and consistent spatial patterns over the 4-year period due to the regionally similar climatic fluctuations caused by monsoon-dominated plateau climate. Surprisingly, rainfall fluctuation had a more profound effect on the ANPP dynamics than temperature variation, which suggests that production in the Tibetan alpine grasslands is primarily driven by precipitation. Therefore, ANPP in the Tibetan alpine grasslands are mainly constrained by water availability. Finally, we found a reduction in interannual variation (i.e., CV) in ANPP with increasing species richness of plant communities, suggesting that diversity can stabilize community production in high-altitude grasslands.

Highlights

Net primary production (NPP) is the fundamental component and the most variable part of the carbon biogeochemical cycle (McNaughton et al, 1989; Field et al, 1998; Huston and Wolverton, 2009; Zhao and Running, 2010)
aboveground NPP (ANPP) values in 2006 and 2009 were significantly higher than those in 2007 and 2008 (P < 0.05). This pattern was evident for alpine meadows, but ANPP in 2009 was highest in alpine steppes (Table 2)
As our analysis showed, production in Tibetan alpine grassland ecosystems would be quite constrained by rainfall, especially growing season precipitation, and the temporal variation in precipitation surpasses that of temperature in determining the spatial patterns of NPP

Summary

Introduction

Net primary production (NPP) is the fundamental component and the most variable part of the carbon biogeochemical cycle (McNaughton et al, 1989; Field et al, 1998; Huston and Wolverton, 2009; Zhao and Running, 2010). Investigating and quantifying the interannual dynamics of NPP will provide insight into the processes by which plant communities respond to external variations (Knapp and Smith, 2001; Oesterheld et al, 2001; Weber et al, 2009) and improve predictions of the potential responses of ecosystem function to global change (Ma et al, 2010b; La Pierre et al, 2011). Highly productive communities may be susceptible to climatic fluctuations and experience lower production in response to drought or cold damage. Even if such incidents affect only a subset of sites during a 1-year transect survey, biased conclusions might be reached. It is necessary to use methods, such as multi-year surveys, which incorporate temporal variation into investigations of large-scale patterns of ecosystem productivity

Objectives

Methods

Results

Discussion

Conclusion