Soil biogenic volatile organic compounds (VOCs) play an important role in soil ecology and function and may affect atmospheric chemistry. While previous studies of soil VOCs have predominantly measured surface flux exchange rates, VOC concentrations within the surface soil layer are largely unknown, especially in Mediterranean ecosystems. In this study, we measured seasonal and annual concentrations of soil VOCs in a Mediterranean shrubland and a holm oak forest over the period 2014–2016. Soil CO₂ efflux, and soil enzyme and plant activities were measured as explanatory variables of soil VOC concentrations. There were greater total soil VOC concentrations in the shrubland (3.66 ± 1.01 ppb) than the holm oak forest (2.23 ± 0.51 ppb) across the study period. There were the greatest concentrations of monoterpenes (0.85 ± 0.43 ppb) and methanol (0.81 ± 0.20 ppb) in the shrubland and forest, respectively, and concentrations of methanol, acetic acid, formaldehyde, ethanol, and acetaldehyde were the dominant compounds in both ecosystems (>0.1 ppb). Although concentrations of some VOCs in both ecosystems were highest and lowest in spring and winter, respectively, the variability of other VOCs depended on compound and ecosystem. Soil temperature and water content, CO₂ efflux, and enzyme activity were the best explanatory variables for variation in soil VOC concentrations in the two ecosystems: there was a stronger association between concentration of dominant compounds, except formaldehyde, with soil temperature and/or CO₂ efflux than with soil water content. Activity of C- and N-degrading enzymes was positively associated with the concentration of VOCs, depending on ecosystem, and consistently correlated with high soil water content. In the holm oak forest soils, net photosynthetic rate (A) was positively correlated with soil concentration of monoterpenes. These results show that soil VOC concentrations in these Mediterranean ecosystems are driven by soil temperature and water content, and microbial activity, in combination with ecosystem plant activity. It is thus likely that projected climate change increases in temperature increase soil VOC concentrations and lead to increases in emissions to the atmosphere; however, microbial production and consumption of soil VOCs may be modulated by soil water content.

土壤生物源挥发性有机化合物 (VOC) 在土壤生态和功能中起着重要作用，并可能影响大气化学。虽然之前对土壤 VOC 的研究主要测量地表通量交换率，但表层土壤层内的 VOC 浓度在很大程度上是未知的，尤其是在地中海生态系统中。在这项研究中，我们测量了 2014 年至 2016 年期间地中海灌木丛和圣栎林中土壤 VOC 的季节性和年度浓度。土壤 CO ₂外排、土壤酶和植物活性被测量为土壤 VOC 浓度的解释变量。在整个研究期间，灌木丛中的土壤 VOC 总浓度 (3.66 ± 1.01 ppb) 高于圣栎林 (2.23 ± 0.51 ppb)。灌丛和森林中单萜（0.85±0.43 ppb）和甲醇（0.81±0.20 ppb）的浓度最大，甲醇、乙酸、甲醛、乙醇和乙醛的浓度是两个生态系统中的主要化合物(>0.1 ppb)。虽然两个生态系统中部分 VOCs 的浓度分别在春季和冬季最高和最低，但其他 VOCs 的变化取决于化合物和生态系统。土壤温度和含水量，CO ₂外排和酶活性是两个生态系统中土壤 VOC 浓度变化的最佳解释变量：除甲醛外，主要化合物的浓度与土壤温度和/或 CO ₂外排之间的相关性强于与土壤含水量的相关性。C 和 N 降解酶的活性与 VOC 的浓度呈正相关，这取决于生态系统，并始终与高土壤含水量相关。在圣栎林土壤中，净光合速率 ( A) 与土壤单萜浓度呈正相关。这些结果表明，这些地中海生态系统中的土壤 VOC 浓度受土壤温度和含水量、微生物活动以及生态系统植物活动的影响。因此，预计的气候变化可能会增加温度，从而增加土壤 VOC 浓度并导致向大气中的排放量增加；然而，土壤 VOC 的微生物产生和消耗可能受土壤含水量的调节。