Mediterranean shrublands adjacent to urbanization experience nitrogen deposition and exotic grass invasions which likely have downstream consequences for carbon and nitrogen emissions from soils. We tested a hypothesis that soil wetting produces trace gas pulses modified by seasonal wetting history, grass litter availability, and cover type in these systems. Over two seasons, we conducted 48-h wetting experiments and measured CO2, N2O, and NO pulses at an invaded, polluted California shrubland following grass litter addition to sites dominated by either an invasive grass (Schismus barbatus) or a native shrub (Erioginum fasciculatum). CO2 and N2O pulses consistently appeared 15 min post-wetting and diminished within 12 h; NO peaked later and remained elevated at 24 h. All pulses were stronger in the dry season than wet season. Grass litter amendments increased CO2 and dry-season N2O pulses without significantly modifying NO pulses. Grass cover reduced CO2 pulses compared to shrub cover. Our results support the hypothesis that shrubland soils produce stronger pulses of CO2, N2O, and NO during the dry season when wetting is less frequent. We show that invasive grass litter can provide a labile C source that stimulates CO2 and N2O, but not NO, emissions from shrubland soils.

中文翻译：

---

在荒地-城市界面的地中海型沿海鼠尾草灌木丛中，异国情调的草屑调节 CO2 和 N2O 的季节性脉冲动态，但不调节 NO

与城市化相邻的地中海灌木地经历了氮沉积和外来草入侵，这可能会对土壤中的碳和氮排放产生下游影响。我们测试了一个假设，即土壤润湿会产生微量气体脉冲，这些脉冲会受到季节性润湿历史、草屑可用性和这些系统中覆盖类型的影响。在两个季节里，我们进行了 48 小时的润湿实验，并测量了受侵染、受污染的加州灌木丛中的 CO2、N2O 和 NO 脉冲，随后向以入侵草（Schismus barbatus）或原生灌木（Erioginum fasciculatum）为主的地点添加了草屑）。CO2 和 N2O 脉冲始终在润湿后 15 分钟出现并在 12 小时内减少；NO 峰值较晚，并在 24 小时保持升高。所有豆类在旱季都比雨季强。草屑改良增加了 CO2 和旱季 N2O 脉冲，而没有显着改变 NO 脉冲。与灌木覆盖相比，草覆盖减少了 CO2 脉冲。我们的结果支持这样的假设，即灌木地土壤在湿润较少的旱季产生更强的 CO2、N2O 和 NO 脉冲。我们表明，侵入性草屑可以提供一种不稳定的碳源，刺激灌木丛土壤中的 CO2 和 N2O，但不会刺激 NO 排放。