Reyes-Galindo Verónica, Jaramillo-Correa Juan P, Shishkova Svetlana, Sandoval-Zapotitla Estela, Flores-Ortiz César Mateo, Piñero Daniel, Spurgin Lewis G, Martin Claudia A, Torres-Jardón Ricardo, Zamora-Callejas Claudio, Mastretta-Yanes Alicia
Departamento de Ecología Evolutiva Instituto de Ecología, Universidad Nacional Autónoma de México Mexico City Mexico.
Programa de Maestría en Ciencias Biológicas Universidad Nacional Autónoma de México Mexico City Mexico.
Ecol Evol. 2024 May 13;14(5):e11343. doi: 10.1002/ece3.11343. eCollection 2024 May.
Urbanization modifies ecosystem conditions and evolutionary processes. This includes air pollution, mostly as tropospheric ozone (O), which contributes to the decline of urban and peri-urban forests. A notable case are fir () forests in the peripheral mountains southwest of Mexico City, which have been severely affected by O pollution since the 1970s. Interestingly, some young individuals exhibiting minimal O-related damage have been observed within a zone of significant O exposure. Using this setting as a natural experiment, we compared asymptomatic and symptomatic individuals of similar age (≤15 years old; = 10) using histologic, metabolomic, and transcriptomic approaches. Plants were sampled during days of high (170 ppb) and moderate (87 ppb) O concentration. Given that there have been reforestation efforts in the region, with plants from different source populations, we first confirmed that all analyzed individuals clustered within the local genetic group when compared to a species-wide panel (Admixture analysis with ~1.5K SNPs). We observed thicker epidermis and more collapsed cells in the palisade parenchyma of needles from symptomatic individuals than from their asymptomatic counterparts, with differences increasing with needle age. Furthermore, symptomatic individuals exhibited lower concentrations of various terpenes (ß-pinene, ß-caryophylene oxide, α-caryophylene, and ß-α-cubebene) than asymptomatic trees, as evidenced through GC-MS. Finally, transcriptomic analyses revealed differential expression for 13 genes related to carbohydrate metabolism, plant defense, and gene regulation. Our results indicate a rapid and contrasting phenotypic response among trees, likely influenced by standing genetic variation and/or plastic mechanisms. They open the door to future evolutionary studies for understanding how O tolerance develops in urban environments, and how this knowledge could contribute to forest restoration.
城市化改变了生态系统条件和进化过程。这包括空气污染，主要是对流层臭氧（O），它导致城市和城郊森林的衰退。一个显著的例子是墨西哥城西南部周边山区的冷杉（）森林，自20世纪70年代以来，这些森林受到臭氧污染的严重影响。有趣的是，在臭氧暴露严重的区域内，观察到一些受臭氧相关损害最小的年轻个体。利用这一环境作为自然实验，我们使用组织学、代谢组学和转录组学方法，比较了年龄相似（≤15岁；=10）的无症状和有症状个体。在臭氧浓度高（170 ppb）和中等（87 ppb）的日子里对植物进行采样。鉴于该地区有重新造林的努力，且植物来自不同的源种群，我们首先确认，与全物种样本相比（使用约1.5K个单核苷酸多态性进行混合分析），所有分析个体都聚集在当地遗传群体内。我们观察到，有症状个体针叶的栅栏薄壁组织中的表皮比无症状个体的更厚，细胞塌陷更多，且差异随针叶年龄增加而增大。此外，通过气相色谱 - 质谱法证明，有症状个体中各种萜类化合物（β - 蒎烯、β - 石竹烯氧化物、α - 石竹烯和β - α - 荜澄茄烯）的浓度低于无症状树木。最后，转录组分析揭示了13个与碳水化合物代谢、植物防御和基因调控相关的基因的差异表达。我们的结果表明树木之间存在快速且截然不同的表型反应，这可能受现存遗传变异和/或可塑性机制影响。它们为未来的进化研究打开了大门，有助于理解城市环境中臭氧耐受性是如何发展的，以及这些知识如何有助于森林恢复。
