Large annual net ecosystem CO₂ uptake of a Mojave Desert ecosystem

Abstract

The net ecosystem CO 2 exchange (NEE) between a Mojave Desert ecosystem and the atmosphere was measured over the course of 2 years at the Mojave Global Change Facility (MGCF, Nevada, USA) using the eddy covariance method. The investigated desert ecosystem was a sink for CO 2 , taking up 102 AE 67 and 110 AE 70 g C m À2 during 2005 and 2006, respectively. A comprehensive uncertainty analysis showed that most of the uncertainty of the inferred sink strength was due to the need to account for the effects of air density fluctuations on CO 2 densities measured with an open-path infrared gas analyser. In order to keep this uncertainty within acceptable bounds, highest standards with regard to maintenance of instrumentation and flux measurement postprocessing have to be met. Most of the variability in half-hourly NEE was explained by the amount of incident photosynthetically active radiation (PAR). On a seasonal scale, PAR and soil water content were the most important determinants of NEE. Precipitation events resulted in an initial pulse of CO 2 to the atmosphere, temporarily reducing NEE or even causing it to switch sign. During summer, when soil moisture was low, a lag of 3-4 days was observed before the correlation between NEE and precipitation switched from positive to negative, as opposed to conditions of high soil water availability in spring, when this transition occurred within the same day the rain took place. Our results indicate that desert ecosystem CO 2 exchange may be playing a much larger role in global carbon cycling and in modulating atmospheric CO 2 levels than previously assumedespecially since arid and semiarid biomes make up 430% of Earth's land surface.

Controls on winter ecosystem respiration in temperate and boreal ecosystems

“…The effects of self-heating can be corrected for in post-processing (Burba et al, 2008), however while some studies found these corrections to improve the correspondence with concurrent closed-path CO 2 flux measurements (Burba et al, 2006(Burba et al, , 2008Grelle and Burba, 2007;Järvi et al, 2009), others did not (Wohlfahrt et al, 2008a;Haslwanter et al, 2009). The reasons for these mixed results are unclear at present; they may be partly attributed to differences in environmental conditions (Haslwanter et al, 2009), partly to the deployment of the open-path analyser.…”

Hidden carbon sink beneath desert

“…Often the downward flux of CO 2 is not equal to carbon accumulation in plants or soils [Jasoni et al, 2005;Luo et al, 2007;Wohlfahrt et al, 2008]. For instance, in European grasslands DIC leaching out of the ecosystem can account for a large portion (22% or 24 g C m À2 yr À1 ) of the net ecosystem exchange of carbon (NEE) [Kindler et al, 2011].…”

Comparison between eddy covariance and automatic chamber techniques for measuring net ecosystem exchange of carbon dioxide in cotton and wheat fields

“…Unfortunately, the techniques currently available for correcting the surface heating effect are only suitable for vertical sensors, and thus would overestimate the bias for the titled sensors. Besides, directly applying this correction seems unwarranted at present because the results of the correction varied greatly among different experimental sites (Burba et al, 2008;Wohlfahrt et al, 2008;Haslwanter et al, 2009). For these reasons, we assumed that the self-heating effect was of minimal importance in our case.…”