Simulating soil CO2 emissions under present and climate change conditions in selected vegetation covers of a semiarid region

Changes in soil organic carbon (SOC) can lead to increased concentration of carbon dioxide (CO2) in the atmosphere and eventually contribute to climate change. Simulation models are useful tools to evaluate the effect of future scenarios of climate change on soil CO2 emission in the long term; this study aimed to: (1) evaluate the performance of RothC model using SOC data measured from five different vegetation covers in a semiarid region (southern Iran); (2) assess the impacts of present climate and climate change scenarios on cumulative CO2 emissions from soil; and (3) assess the net effect of climate change on soil CO2 emissions by comparing the two scenarios. The following vegetation covers were studied: rangeland, cypress trees, almond trees, cypress understory and almond understory. Model validation indicated that RothC accurately simulated SOC measured data (R-2 = 0.97; Pearson correlation = 0.98; performance efficiency = 0.96). Results showed that climate change effect on soil cumulative CO2 emissions increased by 2050 under all vegetation covers, although not significantly in each vegetation cover in comparison with the present climate scenario. The extent of soil cumulative CO2 emissions may be related to the different decomposability of plant materials and soil carbon input (plant material quantity) in tree covers and rangeland/understory covers, respectively. However, vegetation covers with the highest and lowest soil cumulative CO2 emissions did not correspond with the highest and the lowest values of soil CO2 emissions under the net effect of climate change. In addition, trends of the soil CO2 emissions were decreasing in all vegetation covers during the 2014-2050 period. We argue that under the net effect of climate change SOC will be resistant against further decomposition over time. In fact, easily decomposable materials are fully or partially depleted, and microbial population and decomposition rate of litter materials will decline. This also implies a chemical change of organic matter and the formation of humus complex compounds showing a high resistance to decomposition. Therefore, the study of organo-mineral complex and humus complex compounds in the soils of this region is recommended for future researches.