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Shizuoka University (2016)

SOIL RESPIRATION IN ARID ECOSYSTEMS OF THE GURBANTŰNGGŰT DESERT REGION IN NORTHWESTERN CHINA

Liu, Gang

Titre : SOIL RESPIRATION IN ARID ECOSYSTEMS OF THE GURBANTŰNGGŰT DESERT REGION IN NORTHWESTERN CHINA

Auteur : Liu, Gang

Université de soutenance : Shizuoka University

Grade : Doctoral Thesis 2016

Résumé partiel
Global climate change has drawn increasingly attentions since it may threaten human being’s existence and further developments. The increasing concentrations of carbon dioxide (CO2) as one of the greenhouse gases, is considered to be a main reason for causing global change. Soil respiration (SR) plays a key role by releasing carbon into atmosphere and hence may influence global carbon cycling considerably. Compared to many terrestrial ecosystems, such as agricultural, grassland or forest ecosystems, arid and semiarid desert ecosystems are relatively less investigated regarding SR studies, due to the low productive characteristics of such ecosystems as well as harsh conditions for carrying out monitoring. However, arid land ecosystems should not be neglected in the global carbon cycling system since they occupy approximately 40% of the global total land surface area. In this study, monitoring and controlling experiments were designed and conducted in the Gurbantünggüt desert ecosystems in Xinjiang province in northwestern China which is featured by typical temperate continental dry climate, for better understanding the SR characteristics and for exploring its potential mechanisms in these ecosystems. The first step of this study was based on continuously measuring the temporal variation and magnitude of the SR, in which the diurnal and seasonal variations of SR of four different land covers (bare soil, crust, under canopy, litter) in the Gurbantünggüt desert ecosystems were mainly focused on. In chapter 2, an automatic chamber system was assembled with a gas analyzer (Li-cor 840) to measure SR throughout the entire growing season of 2013 in Fukang ecological experiment station located just next to the Gurbantünggüt desert. Meanwhile, soil temperature, near-surface temperature, soil moisture and soil electric conductivity (EC) were measured in order to reveal the correlations between SR and environmental factors. Similar experiments were also attempted to be implemented inside the desert site, but due to the absence of sustaining power supply in this savage area, only two or three days of data could have been acquired for every month. The results showed that the average rates of SR in this arid desert ecosystem ranged from about 0.3 to 0.8 μmol/m2/s, which were, as expected, rather lower than forest or grassland ecosystem, and the SR rates of the desert site were lower than those of Fukang site. Furthermore, different surface covers exhibited different SR rates, with higher rates mostly occurred in under-canopy spots compared to those located in the interspaces. Diurnal variations of SR rate displayed an intimate tie with the fluctuation of the soil temperature while seasonal variation was supposed to be complicated by more factors including soil temperature, soil moisture, precipitation events and the activities of soil microorganisms. Moreover, in these drought-stress ecosystems, the abrupt variations of soil moisture tended to change SR rates to greater extents, particularly by dramatic fluctuation of precipitation.

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