Soil respiration is a critical ecological process and is a hierarchical component of ecosystem respiration that regulates the global carbon cycle. But there is scarce knowledge on respiration dynamics in water-stressed ecosystems and the influence of biocrusts. Soil respiration-values varied from 0.099 to 0.828 mu mol s(-1) m(-2) after extraordinary rains; after this period, recorded values were null or negative at the most (0.000 to -0.055 mu mol s(-1) m(-2)). Shrubland soil with and without biocrusts showed the highest net CO2 exchange values and in disturbed soil with and without biocrusts (0.067; 0.059; 0.048, and 0.023 mu mol s(-1) m(-2)). The results showed that shrubland soil with BSC absorbed more CO2 than the rest of the experimental variants. Accordingly, the observed low precipitation combined with high temperatures and evapotranspiration could not activate the BSC respiration process. Such an event seemed to occur under specific temperature and moisture conditions, anyhow related to extraordinary rain events to emit CO2 to the atmosphere. Reports of negative soil respiration values in drylands are very scarce, so we discuss the possible processes that could cause this phenomenon for our study area.