Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Allemagne → 2015 → Carbon dioxide and water fluxes over semi-arid grassland in Inner Mongolia (China)

Technische Universität Dresden (2015)

Carbon dioxide and water fluxes over semi-arid grassland in Inner Mongolia (China)

Vetter Sylvia

Titre : Carbon dioxide and water fluxes over semi-arid grassland in Inner Mongolia (China)

Kohlendioxid- und Wasserflüsse über semiarider Steppe in der Inneren Mongolei (China)

Auteur : Vetter Sylvia

Université de soutenance : Technische Universität Dresden

Grade : Doctor rerum naturalium (Dr. rer. nat.) 2015

Résumé partiel
Semiarid grasslands in Inner Mongolia (China) are degrading. The change from the traditional Nomadic lifestyle to conventional agriculture stresses the semiarid grasslands and increases desertification. In particular, intense grazing of the semiarid grasslands reduces their potential of storing carbon (C) in the soil. In the project Matter fluxes in grasslands of Inner Mongolia as influenced by stocking rate (MAGIM) a team of scientists researched the catchment area of the Xilin River to investigate impacts of different grazing intensities on semiarid grasslands. Meteorological and eddy covariance measurements took place from 2004 to 2009. The aim of the measurements was to examine the energy balance and the exchange of the carbon dioxide (CO2) and water (H2O) fluxes of the dominant grasslands in Inner Mongolia under different grazing intensities. The energy balance could be closed by 70 – 90% depending on the driving factors. The energy balance shows a smaller gap for moist conditions. The CO2 und H2O fluxes in the study area are much smaller than in temperate grasslands and show a high sensitivity towards the driving factors. Evapotranspiration (ET) is closely connected to the precipitation (P) and over longer periods of a year or more, ET nearly matches P (ET : 185.7 mm a-1 to 242 mm a-1 ; P : 138 mm a-1 to 332 mm a-1). The annual net ecosystem exchange (NEE) of ungrazed grassland ranges from -10.7 g C m-2 a-1 (2005) to -67.5 g C m-2 a-1 (2007), which makes the grassland a small CO2-sink. Overall, ungrazed grassland shows higher C sequestration (averaged maximum -0.06 g C m-2 s-1) than grazed grassland (averaged maximum -0.02 g C m-2 s-1). The measurements show the semiarid grassland as a CO2-source under dry conditions and as a CO2-sink under moist conditions, while grazing decreases the C sequestration for both climatic conditions. A comparison of the two dominant steppe types (Leymus chinensis and Stipa grandis) showed a higher tolerance for Leymus chinensis under dry conditions, which resulted in higher C sequestration for this vegetation. Besides the steppe type, the main driving factors are P, temperature (T) and grazing. These factors can not only be considered in isolation, but cross correlation needs to get considered as well. Grazing affects the sustainability of the ecosystem, with an increasing impact due to grazing intensity and duration (years). The impact of grazing influences the vegetation directly and shows indirect impacts for the soil properties. Simulations with the models BROOK90 and DAILYDAYCENT (DDC) enable a sensitivity analysis of CO2 and H2O fluxes of the semiarid grassland. Both models performed well, but BROOK90 showed a better fit to observed ET (r2 = 0.7) than DDC (r2= 0.34). Both models simulated the dynamics of the measured ET well. The sensitivity analysis showed a close relationship between P und ET and a smaller impact on ET due to a change in T. DDC performs well in the simulation of CO2 exchange dynamics of the semiarid grassland. The results show for high grazing intensities a decreasing influence of the other driving factors.

Mots clés : Kohlenstoff, Verdunstung, semiaride Steppe, Beweidung, Eddykovarianz — carbon dioxide, evapotranspiration, semi-arid grassland, grazed, eddy covarianz

Présentation (QUCOSA)

Version intégrale (7,62 Mb)

Page publiée le 26 novembre 2016, mise à jour le 2 décembre 2018