Ecosystem-atmosphere exchange of carbon dioxide and water vapour in typical East-Asian croplands

Agricultural areas comprise a large portion of the land surface of the earth. Under the current climate and environmental changes, the role of cropland ecosystems in the surface-atmosphere energy and matter exchange has drawn a lot of attention. This thesis investigated the potential change on ecosystem-atmosphere exchange of heat, water vapour and carbon dioxide if crop species planted or irrigation management is changed in croplands. Improvement of the Penman-Monteith model to simulate evapotranspiration and light-response model to simulate carbon dioxide flux for croplands is studied. Field campaigns were carried out in an irrigated rice field and a non-irrigated potato field in an intensively managed agricultural area in Korea Peninsula in 2010 and 2011. The eddy-covariance technique was used to observe net ecosystem carbon dioxide exchange and energy fluxes of sensible and latent heat with additional measurements of meteorological variables and biomass change. Results show that the conventional Penman-Monteith approach which estimates the stomatal resistance as a function of single leaf stomatal resistance and leaf area index performs well for the estimation of evapotranspiration when the vegetation is fully developed in the potato field. In the case of evaporation-dominated croplands, i.e. the rice field with standing water or the potato field with small leaf area index in this study, it is shown that the stomatal resistance should be estimated as a function of meteorological variables rather than leaf area index. The study on the light response function indicates that the primary cause of seasonal change in gross primary productivity was the change in leaf area index during the whole growing season under the summer monsoonal condition. Thus, a site-specific time window approach could significantly improve the model performance. In its standard form, however, the light response function does not account for leaf area index changes. In order to simulate longer time series, which is needed for filling large gaps in the observations, a new leaf-light response function is proposed. A significant change in ecosystem-atmosphere exchange of heat, water vapour and carbon dioxide is found if irrigation management is changed. The non-irrigated potato field had 140% more sensible heat and 30% less latent heat than the nearby irrigated rice field. The difference in evapotranspiration between these two fields was mostly attributed to less evaporation (rather than transpiration) in the potato field than in the rice field. The seasonal sum of carbon dioxide flux was 12% less for gross primary productivity, 7% less for ecosystem respiration, and 20% less for net ecosystem exchange in the potato field than in the rice field. The rice field acted as a sink of carbon dioxide through the whole season, while the potato field turned from a sink to a slight source at the late growing stage when the above-ground green biomass disappeared. Besides the decline in solar radiation and the warm conditions in summer monsoon, the enhancement of ecosystem respiration caused by the large amount and the rapid growth rate of the biomass is suggested to be a cause of the mid-season depression in net ecosystem exchange.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Bayreuth

Year

2014

Author dc:creator

• Zhao, Peng

Contributors dc:contributor

• Lüers, Johannes

Repository record source_url

https://epub.uni-bayreuth.de/id/eprint/1720/

OAI identifier oai:identifier

oai:epub.uni-bayreuth.de:1720