Comparing measurements methods of carbon dioxide fluxes in a soil sequence under land use and cover change in North Eastern Spain

Carbon dioxide measurements from soil surface may indicate the potential for soil respiration and carbon consumption according to microbial biomass and root activity. These processes may be influenced by land use and cover change, and abandonment especially in the upper soil organic layer. Seven environments from cultivation to late abandonment, with the same soil type classified as Lithic Xerorthent, were tested to ascertain the respiration capacity according to the current use and cover, and to establish the ability to preserve and eventually increase the organic matter pools after abandonment. Given the importance of carbon dioxide measurements at soil surface, a comparison between the classic soda lime method (SL) and a rapid method based on infrared sensor analyzer (IR) was performed from autumn 2008 to autumn 2009 in the field. The field measurements of CO2 proved significant correlations between the values from the two techniques under the same natural conditions and along the period of observation. However, the values of CO2 measured by the soda lime method were always higher than those obtained by the infrared analyzer. This pattern was attributed to the difference in time of measurement, larger in the former method, and type of measurement technique. Despite that the trend of measured CO2 values was rather similar along the year. On average, the highest values of CO2 emission in the field were recorded in the warmest periods of the year and with soil surface moisture not lower than 3% independently on the method used. High soil surface temperature with soil moisture below 3% decreased drastically the CO2 production from the dry soil. The cultivated environments and soil under forests have resulted higher CO2 producers than abandoned soils depending on the age of abandonment, climatic conditions, and within abandonment perturbations. Those abandoned soils preserved by perturbations like wildfire showed a higher potential for accumulating organic carbon, as indicated by the lowest emission of CO2 with respect to SOC content, during the period of observation. Results demonstrated the reliability of the methods used to evaluate the soil carbon dioxide production capacity and allowed to classify through environments with increasing potential for carbon sequestration. The classification was rather similar by using both methods indicating a higher susceptibility to carbon loss in the following order: soil under Vines (V)>under Olives (O)> under Pine trees (PI) > under Cork Trees (S)> under Pasture (PR)>under Cistus scrub (MC)>under Erica scrub (MB) by using the SL method and V>O> PI> S>MC>MB> PR by using the IR method. Indications about the need of management of abandoned areas were also considered in order to recover the landscape heterogeneity.