Study Shows Net Ecosystem CO2 Exchange with Alkaline Soils in Central Asia Following Sinusoidal Pattern during Growing Season

In the last few years, more and more measurements of net ecosystem CO₂ exchange (NEE) have been implemented in some desert and semi-arid ecosystems. The data from these sites indicated that the carbon sequestration capacity by desert and semi-arid ecosystems varies over a wide range.

Central Asia is covered by vast desert ecosystems, and the majority of these ecosystems have alkaline soils. Central Asian desert ecosystems account for a large proportion of global dryland area. Due to the high evaporation–precipitation ratio, most of the soils are alkaline with high pH. This offers a good opportunity to investigate the Central Asian desert ecosystem production and employ their contribution to the global land-atmosphere CO₂ exchange.

To quantify the growing season NEE of two desert ecosystems with alkaline soils in Central Asia and test the hypothesis that desert ecosystem with alkaline soils acts as a carbon sink at night during growing season, Prof. LI Longhui et al. analyzed half-hourly mean NEE data at daytime and nighttime at two alkaline sites (one is close to the Aral Sea and the other is close to the Balkhash Lake) during growing season in Kazakhstan. Researchers also investigated the responses of NEE to meteorological variables and soil moisture to interpret the magnitude of maximum uptake ability of CO₂ absorption by alkaline soil.

Eddy covariance (EC) techniques have commonly been used to measure the NEE between the terrestrial ecosystem and the atmosphere during the past few decades. In order to investigate the NEE of Central Asian desert ecosystems, two EC systems were established to monitor the fluxes of CO₂, H₂O, energy and momentum at two alkaline sites in Kazakhstan in April 2012.

The results showed that 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 but net carbon loss at nighttime and on cloudy and rainy days. Similar to other ecosystems, NEE has strong dependency on PAR and the response of NEE to precipitation resulted in an initial and significant carbon release to the atmosphere.

These findings indicated that biotic processes dominated the carbon processes, and the contribution of abiotic carbon process to NEE may be trivial in alkaline soil desert ecosystems over Central Asia. The study was published in Ecology and Evolution in January 2014.