Seasonal and interannual variability of carbon dioxide and water balances of a grassland

Abstract

There is great international concern over the increase of atmospheric carbon dioxide and its effect on vegetation and climate, and vice versa. Many studies on this issue are based on climate model calculations or indirect satellite observations. In contrast we present a 12-year study (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) on the net ecosystem exchange of carbon dioxide (NEE ) and precipitation surplus (i.e., precipitation-evaporation) of a grassland area in the centre of the Netherlands. On basis of direct flux observations and a process-based model we study and quantify the carbon uptake via assimilation and carbon release via soil and plant respiration. It appears that nearly year-round the assimilation term dominates, which indicates an accumulation of carbon dioxide. The mean net carbon uptake for the 12-year period is about 3 tonnes C per hectare, but with a strong seasonal and interannual variability depending on the weather and water budget. This variability may severely hamper the accurate quantification of carbon storage by vegetation in our present climates and its projection for future climates.

Net ecosystem productivity of temperate grasslands in northern China: An upscaling study

“…Site-level studies have shown that the annual amount and timing of precipitation is the major factor affecting gross primary productivity and respiration (Xu and Baldocchi, 2004;Jacobs et al, 2007;Craine et al, 2012), and thus, the NEP in the arid and semi-arid ecosystems. In our study, we found the northern China's grasslands were sensitive to precipitation.…”

The effect of introducing a winter forage rotation on CO2 fluxes at a temperate grassland

“…Some established grasslands are believed to have a net uptake of atmospheric CO 2 at annual timescales (Byrne et al, 2007;Jacobs et al, 2007), but temperate, managed grasslands tend to have a net emission of CO 2 over the winter months (Jaksič et al, 2006;. A growing body of evidence suggests that long-term carbon sequestration in grassland is largely controlled by management practices (Soussana et al, 2004;Ammann et al, 2007;Skinner, 2008;Wohlfahrt et al, 2008).…”

“…The eddy covariance (EC) technique has become well-established as a method of measuring surface-atmosphere fluxes of energy and trace gases, with several sites now observing continuously for five years or longer (Jacobs et al, 2007;Wohlfahrt et al, 2008;Haslwanter et al, 2009). The technique is suitable for measuring fluxes in the area adjacent to the sensor, but extended networks of flux observation sites together with satellite remote sensing have helped to address the issue of quantifying CO 2 exchange at the continental scale (Xiao et al, 2008).…”

Modeling the coupled exchange of water and CO2 over croplands

“…• C, E a the ecosystem sensitivity coeafficient in K, R * the universal gas constant, and T s the upper soil layer temperature in K. In contrast to Jacobs et al (2007a) and for practicality, we assume here no dependance of soil respiration on water stress. We use an R 10 of 0.08 mg CO 2 m −2 s −1 , and an E a of 53 kJ kmol −1 , two reasonable values measured over grassland sites in the Netherlands (Jacobs et al, 2007b).…”

“…The soil moisture index (SMI, see Eq. 3.13) obtained with MXL-GECROS is very low, which suggests a heavy drought situation that was not observed: Jacobs et al, 2007a).…”