Heterotrophic Soil Respiration and Temperature Sensitivity of a Bromus erectus-dominated Grassland (Central Apennines).

Secondary origin grasslands are among the most investigated ecosystems as they provide a wide array of ecosystem services, including carbon sequestration. Their conservation requires management practices (e.g., mowing, grazing or their combination) that could play a key role on terrestrial carbon dynamics which in turn affect atmospheric CO2 concentrations and global warming. Defined as the release of CO2 from the soil into the atmosphere, soil respiration includes respiration of plant roots, rhizosphere, microbes and pedo-fauna. Many studies have argued that grasslands have a huge potential in climate change mitigation but research still lacks extensive assessments on carbon dynamics, especially under different management. For these reasons, it is crucial to broaden research on grasslands soil respiration, particularly on its heterotrophic component (RH), since it strongly relates to soil organic carbon decomposition. This study reports the results of one year (May 2016-April 2017) of RH monitoring in a Bromus erectus-dominated grassland (Central Apennines, 900 m a.s.l.), carried out within MACSUR 2 project (Award Number: 24064/7303/2015), under different management. A randomized block design experiment was established to test three different treatments: i) customary management (mowing in end of June followed by a second utilization in October) (MN0), ii) customary management with 100 kg ha-1 yr-1 N-fertilization (MN100), iii) abandonment (C). Exponential regression modelling was used to examine the relationship between RH and soil temperature. Subsequently, the sensitivity of soil respiration (Q10) was calculated from the differences in the respiration rate of RH at 10 °C interval using the previous exponential regression model. No differences were detected in annual cumulative values, which accounted for 4.77, 5.47 and 5.42 t C ha-1 in MN100, MN0 and C, respectively. Soil temperature at 5 cm depth explains between 67 and 76% of the annual variation of RH. Soil respiration sensitivity was lowest in MN0 (2.38) and highest in C (2.70), while MN100 registered an intermediate value (2.58). Results suggest that management practices do not significantly influence the annual cumulative RH of Bromus erectus-dominated grasslands, which was largely controlled by soil temperature. Despite this, the Q10 values suggest that MN0 is the best for permanent grasslands concerning global warming, while abandonment may be detrimental to soil organic carbon stock.