Spatial heterogeneity of soil respiration of Nitraria tangutorum nebkhas in the desert-oasis ecotone of Minqin

Applying Li-8100 soil respiration measurement system, we made field observations on the soil respiration rate of Nitraria tangutorum nebkhas, which is at the stable stage and is largely located in the oasis-desert ecotone at the southern fringe of the Badanjara Desert. The daily change and the spatial heterogeneity of soil respiration at different positions of the nebkhas in different growing periods were analysed and studied. The results showed: 1) The daily change of the soil respiration rate of N. tangutorum nebkhas at different positions and at different growing periods were different. It exhibited a “one-peak curve” at the beginning of the growing period and at the dormancy period; but the “one-peak curve” and “double-peak curve” were overlapped in the flourishing period. 2) The peaks of soil respiration in different growth periods were different: the peaks of each observed position occurred around 11:00 in the morning at the beginning of the growth period, the peaks of the flourishing period were concentrated around 09:00 and 17:00, and the peaks in the dormancy period occurred between 13:00-15:00 in the afternoon. 3) The soil respiration rate of N. tangutorum at different observation points showed a strong sensitivity to water content, the correlation between them was higher at lower water content (<1%) than at higher water content (>1%). 4) There was spatial heterogeneity of soil respiration rate at different positions on the nebkhas: there was a non-significant difference (P>0.05) between the soil respiration rate at the beginning of the growing period and in the dormancy period; whereas there was a significant difference (P<0.01) in the flourishing period. The average soil respiration rate at different growing periods varied significantly, which was ranked as follows: flourishing period 0.53 μmol·(m2·s)-1>at the beginning of the growing period 0.24 μmol·(m2·s)-1>dormancy period 0.12μmol·(m2·s)-1. The regression analysis showed that the significant spatial heterogeneity in the soil respiration rate was the result of the interaction between the near-surface water condition at different positions, the temperature, and humidity at the depth of 5-20 cm of N. tangutorum.