Growing season net ecosystem CO2 exchange of two desert ecosystems with alkaline soils in Kazakhstan

Longhui Li,Xi Chen,Christiaan Van Der Tol,Zhongbo Su,Geping Luo

doi:10.1002/ece3.910

Abstract

Central Asia is covered by vast desert ecosystems, and the majority of these ecosystems have alkaline soils. Their contribution to global net ecosystem CO2 exchange (NEE) is of significance simply because of their immense spatial extent. Some of the latest research reported considerable abiotic CO2 absorption by alkaline soil, but the rate of CO2 absorption has been questioned by peer communities. To investigate the issue of carbon cycle in Central Asian desert ecosystems with alkaline soils, we have measured the NEE using eddy covariance (EC) method at two alkaline sites during growing season in Kazakhstan. The diurnal course of mean monthly NEE followed a clear sinusoidal pattern during growing season at both sites. Both sites showed significant net carbon uptake during daytime on sunny days with high photosynthetically active radiation (PAR) but net carbon loss at nighttime and on cloudy and rainy days. NEE has strong dependency on PAR and the response of NEE to precipitation resulted in an initial and significant carbon release to the atmosphere, similar to other ecosystems. These findings indicate that biotic processes dominated the carbon processes, and the contribution of abiotic carbon process to net ecosystem CO2 exchange may be trivial in alkaline soil desert ecosystems over Central Asia.

Highlights

Worldwide paucity of measurements of net ecosystem CO2 exchange (NEE) in desert and semi-arid ecosystems limits our understanding on their contributions to global atmospheric carbon cycle (Falge et al 2002)
Ecology and Evolution published by John Wiley & Sons Ltd
One site is close to Aral Sea and the other is close to Balkhash Lake (Fig. 1). Both sites are representative of Central Asian desert ecosystems, and both are dominated by alkaline soils, as one can be visually recognized from satellite images (Fig. 1)

Summary

Introduction

Worldwide paucity of measurements of net ecosystem CO2 exchange (NEE) in desert and semi-arid ecosystems limits our understanding on their contributions to global atmospheric carbon cycle (Falge et al 2002). In the last few years, more and more measurements of NEE have been implemented in some desert and semi-arid ecosystems, including Mojave Desert in the USA (Wohlfahrt et al 2008), Baja California desert shrub ecosystem in Mexico (Hastings et al 2005; Bell et al 2012), Burkina Faso shrub savanna in West Africa (Bruemmer et al 2008), temperate desert steppe (Yang et al 2011; Shao et al 2013), and desert shrub ecosystems (Gao et al 2012; Liu et al 2012a,b) in China.

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Conclusion