## 1 Introduction
For example, a cross-biome analysis of belowground R\({}_{\rm aut}\) observations suggests that abiotic factors do not directly control R\({}_{\rm aut}\), but rather GPP, which when reduced, leads to lower plant respiration [19]. Following this line of logic, GPP could be considered a major driver of R\({}_{\rm aut}\). Analysis of C-fluxes from different biomes (from boreal forests to tropical) shows that R\({}_{\rm aut}\) varies from 40 to 65% of GPP, with the lower values in the Mediterranean biome [20]. Soil heterotrophic respiration (R\({}_{\rm het}\) g C m\({}^{-2}\) s\({}^{-1}\)), which is the outcome of microbial and fungal activity, is mainly controlled by temperature and soil water content [21]. Temperature can directly affect microbial activity by changing the activation energy of their enzymes, as well as indirectly by limiting other factors, such as soil moisture [22]. When soil water content (\(\theta\) cm\({}^{3}\) cm\({}^{-3}\)) is low, R\({}_{\rm het}\) is limited due to microorganisms' reduced conductivity to substrate that damages the organisms [23] and limited diffusion of the extracellular enzymes that break down the organic C [24]. However, in Mediterranean ecosystems that frequently experience a pronounced inter- and intra-annual climate variability, a linear reduction of R\({}_{\rm het}\) due to low \(\theta\) may not occur, as rapid adaptations of the microbial community have been reported [25]. Although there is limited information on the response and recovery time of the soil microbial community after rehydration, a R\({}_{\rm het}\) pulse after rainfall events has been frequently reported in Mediterranean ecosystems [26; 27]. On the other hand, excessive soil water content seems to inhibit soil respiration due to limitations in soil aeration [28; 29]. Empirical soil respiration models developed for temperate and Mediterranean forests [26] often identify temperature, temperature variability, soil C and water content as the primary drivers of soil respiration. However, these parameters illustrate significant site to site variability and thus local studies and site-specific models could provide more accurate performance [30; 31]. Pine forests are an important element of natural vegetation in areas surrounding the Mediterranean basin. At lower elevations (up to 600 m above sea level--asl), the two pine species _Pinus halepensis_ and _Pinus brutiia_ are distributed in around 7 million hectares along the Mediterranean coastline [32]. At higher elevations (up to 2000 m asl), _Pinus nigra_ covers 3.5 million hectares of the forested area [33]. Both forest types provide a range of ecosystem services and are estimated to absorb ca. 1586 and 1169 g C m\({}^{-2}\) year\({}^{-1}\), respectively [34; 35]. However, under current climate change conditions and shifting fire regimes, the C sinks of these ecosystems might be at risk [36; 37] and thus it is important to understand how shifting climate conditions might affect their C dynamics. According to the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment emission scenarios [38], the Mediterranean region is expected to experience rising average air temperatures (from 0.9 to 5.6 \({}^{\circ}\)C), reduced annual precipitation (from 4 to 22%) and more frequent drought events [39]. For example, climate projections based on the IPCC's moderate RCP4.5 scenario suggest an average temperature increase of 2-2.5 \({}^{\circ}\)C for the eastern part of the Mediterranean, followed by up to 20% annual precipitation reductions until the end of the 21 st century [40]. Projections based on the more pessimistic RCP8.5 scenario lead to a drier future, with 10-20% less precipitation and higher (5-6 \({}^{\circ}\)C) average temperatures by the end of the century [41]. In this latter trajectory, apart from the expected overall precipitation decrease, the frequency of extreme events is also projected to increase, leading to an overall rise in the number of dry days in the area [42].