Effects of fencing on soil respiration rates in the meadow steppes in the northern slope of the Tianshan Mountains

Soil respiration is an important indicator in evaluating soil surface carbon dioxide( CO_2) flux,and carbon cycling in grassland ecosystems is strongly affected by grassland management and implementation. Fencing and grazing are two important grassland management tools in the meadow steppe of the Tianshan Mountains; however,there is limited knowledge of how fencing may influence soil respiration in the arid and semi-arid areas of meadow steppes. In our study,we compared short-term( 9-year fencing) fenced meadow steppes with grazed meadow steppes along the northern slopes of arid and semi-arid areas of the Tianshan Mountains of China. We evaluated daily and seasonal soil respiration dynamics and the correlation between soil respiration rate and environmental factors in both fenced and grazed meadow steppes using a Li-8100 automated soil CO_2 flux system( LI-COR,Lincoln,Nebraska,USA). Significant variations of daily and seasonal soil respiration rate were found as a one-peaked curve at the evaluated fenced and grazing meadow steppe in Tianshan Mountains,and the single peak in the growing season was especially obvious. In June,daily soil respiration rates peaked at17: 00 h for both areas,but soil respiration rates were 33.1% higher in fenced( 5.87 [mu]mol m~(-2)s~(-1)) than grazed( 4.41 [mu]mol m~(-2)s~(-1)) meadow steppes. In October,daily soil respiration rates were lowest at 08: 00 h for both fenced( 0.26 [mu]mol m~(-2)s~(-1)) and grazed( 0.29 [mu]mol m~(-2)s~(-1)) meadow steppes. Annual CO_2 flux is highest in summer,and the contribution of CO_2 flux in June and July to the total annual CO_2 flux was highest during our sampling period. Furthermore,CO_2 flux was 37%higher at fenced than at grazing sites,suggesting that fencing had a more positive effect on CO_2 flux than grazing in arid and semiarid areas of the meadow steppes. Our results are mainly due to the decrease in belowground biomass and root secretion,which reduces root and microbe respiration. The dynamics of soil CO_2 flux were consistent with fluctuations in average daily air and soil temperature,and contrasted with changes in average daily soil moisture content. Our correlation analysis showed that surface soil( 0-5 cm) and near surface air temperature are significantly correlated with soil respiration( P0.05),but there was no significant correlation between soil respiration and soil moisture. Soil respiration and soil temperature were more correlated at surface soil( 0-5 cm) than subsoil( 5