Abstract:

Ecological processes occurred in the ecotone from shifting sand desert to oasis cropland are by far important for desertification development and oasis sustainability. Carbon fixation and emission, the principal ecosystem process along a desertification gradient in the ecotone in Minqin Oasis, Gansu Province was studied. Net photosynthetic rate, leaf dark respiration rate and water use efficiency of Tamarix ledeb and Nitraria tongutorum, the dominant species in the sucessional plant communities were examined. Leaf and soil respiration were also measured in the gradient. Although the two species had similar leaf dry weight based photosynthetic rate,T. ledeb plant and its dominated plant community had higher rate of photosynthesis and soil respiration, therefore, its intensity of carbon biogeochemical cycling was higher than that of N. tongutorum community. During the desertification process from T.ledeb community to N. tongutorum community and further to mobile sand, local and regional carbon cycling and nutrient turnover changed dramatically. The strength of cycling as well as temporal and spatial variation decreased.

Key words: Desertification, Photosynthesis, Respiration, Carbon balance, Plant community, Ecotone