Soil respiration as affected by vegetation types in a semiarid region of China

There are variations in soil respiration across vegetation types; however, it is unclear which factors are mainly responsible for the variations. A field experiment was conducted in 2008 and 2009 in a semiarid region of China to investigate the daytime and monthly variation of soil respiration across vegetation types and to determine the factors controlling the variation. An automated portable soil carbon dioxide (CO2) flux measurement system was used to measure the soil respiration in shrubland, grassland, fallow land, and cropland during the growing periods. The results showed that the relative daytime variation amplitude of soil respiration in the fallow land and cropland was as small as that of shrubland and grassland during July, but greater than that of shrubland and grassland during August and October. A hysteresis effect for the relationship between the daytime soil respiration and daytime soil temperature was observed for all four vegetation types. There was also a hysteresis effect for the relationship between the daytime soil respiration and daytime air temperature for the grassland. Over the study period, the monthly soil respiration rates of the fallow land and cropland were statistically comparable and significantly lower than those of the shrubland and grassland, with the exception of August, during which the monthly soil respiration of the cropland was as great as that of shrubland and grassland. The factors responsible for the monthly soil respiration variation across the vegetation types differed from month to month. In general, the soil temperature and soil water content were mainly responsible in August and September; however, the root biomass predominated in July and October. The results are valuable for accurately estimating regional carbon fluxes by considering the temporal variability of the soil respiration variation across vegetation types in the Loess Plateau of China.