Response of carbon fluxes to water relations in a savanna ecosystem in South Africa

Abstract

Abstract. The principal mechanisms that connect carbon fluxes with water relations in savanna ecosystems were studied by using eddy covariance method in a savanna ecosystem at Kruger National Park, South Africa. Since the annual drought and rewetting cycle is a major factor influencing the function of savanna ecosystems, this work focused on the close inter-connection between water relations and carbon fluxes. Data from a nine-month measuring campaign lasting from the early wet season to the late dry season were used.Total ecosystem respiration showed highest values at the onset of the growing season, a slightly lower plateau during the main part of the growing season and a continuous decrease during the transition towards the dry season.The regulation of canopy conductance was changed in two ways: changes due to phenology during the course of the growing season and short-term acclimation to soil water conditions.The most constant parameter was water use efficiency that was influenced by VPD during the day but the VPD response curve of water usage did change only slightly during the course of the growing season and decreased by about 30% during the transition from wet to dry season.The regulation of canopy conductance and photosynthetic capacity were closely related. This observation meets recent leaf-level findings that stomatal closure triggers downregulation of Rubisco during drought. Our results may show the effects of these processes on the ecosystem scale.

Evaluating Water Controls on Vegetation Growth in the Semi-Arid Sahel Using Field and Earth Observation Data

“…Growing season EC GPP was attained across all sites when PAW was generally above 25 mm (~0.04 m 3 m −3 ) and when VPD was below 2 kPa, which is comparable to studies conducted in similar environments [22,66]. The decline in PAW and the onset of high VPD during times of drought reduces plant photosynthetic capacity by causing closure of stomata to prevent moisture loss [67]. Thus, a decrease in moisture during the growing season, as happened in Dahra in 2011, where there was 42% decrease in rainfall and 46% decrease in soil moisture from the previous year, could cause a reduction in GPP.…”

Long term observations of carbon dioxide exchange over cultivated savanna under a Sudanian climate in Benin (West Africa)

“…Night CO 2 fluxes. Total ecosystem respiration (TER) is generally expected to depend heavily on temperature (Brümmer et al, 2008;LIoyd and Taylor, 1994) and on soil water content Merbold et al, 2009;Williams et al, 2008;Kutsch et al, 2008;Hanan et al, 1998). However, as the daily temperature variability at our site is relatively low and the seasonality of dry periods clearly marked, the ecosystem respiration was not found to vary significantly with temperature but depended strongly on the soil moisture (Liu et al, 2006).…”

Water and energy fluxes from a woodland savanna (cerrado) in southeast Brazil

“…8 for wet and dry months. The increase in ET with D in the rainy-season and the nearly constant lower ET observed during the dry-season indicate that the bulk canopy conductance declined towards the dry-season (Eamus et al, 2001;Kutsch et al, 2008).…”