Analysis of Córdoba's urban trees identifies which species best tolerate heat
The orange tree emerges as one of the most heat-vulnerable trees, according to a University of Córdoba (UCO) study that analyzed 17 tree species found in Córdoba's urban environment
Global warming is transforming ecosystems around the world. Urban trees are also affected by these changes, especially in cities like Córdoba, where summers are growing longer and more intense. These trees also play a key role in regulating urban climate through shade and evapotranspiration. But do trees keep performing this function as temperatures rise?
Taking up this question, researchers Cristina C. Bastias and Sonia Vega, at the Department of Botany, Ecology and Plant Physiology, analyzed the heat tolerance of 17 tree species found on the streets of Córdoba to see how they respond to rising temperatures. Mediterranean hackberry, carob, olive, holm oak, cork oak, ash, poplar, elm, privet, jacaranda, and orange are among the species selected, both because they are some of the most widespread in the city and because they represent a range of biogeographic origins, climatic provenances, and characteristics: native or exotic; evergreen or deciduous; and Mediterranean, subtropical, or temperate in bioclimatic origin.
"We measured how the efficiency of the photosynthetic apparatus in the leaves of these 17 species declines, using chlorophyll fluorescence. This allowed us to identify the temperature thresholds at which the photosynthetic performance of these species begins to be impaired, which could compromise their ability to 'cool their surroundings,'" explained researcher Sonia Vega.
The results show that not all urban tree species respond in the same way to high temperatures. Overall, native species from Mediterranean and temperate climates showed greater heat tolerance than exotic species of subtropical origin. However, subtropical species like orange, chinaberry, catalpa, and tipu are commonly planted in Córdoba's parks and streets, often chosen on cultural or aesthetic grounds, among others. Although one might assume at first glance that species from warm climates would cope well with Córdoba's temperatures, it is worth remembering that their climate of origin features a combination of temperature, humidity, and water availability, the latter two being scarce in southern Spanish cities such as Córdoba. As a result, these species' functioning and their role in cooling the environment could be compromised. Native Mediterranean species such as holm oak and olive were by far the most heat-tolerant compared with the other species analyzed.
What are the most heat-adapted trees like?
Greater heat tolerance correlated with structural traits that conserve resources such as water, including higher wood density, leaf mass per area, and leaf thickness, all of which are characteristic of native Mediterranean species. Leaf habit (whether a tree is evergreen or deciduous), on the other hand, was not a determining factor in greater or lesser tolerance in this study.
These results provide the keys to selecting the tree species best suited to an urban environment with rising temperatures, as is the case in Córdoba. Incorporating these criteria into urban planning can help create more resilient green infrastructure capable of coping with the rise in temperatures associated with climate change.
Reference:
Vega-Rosete, Sonia & Bastias, Cristina C. (2026). "Biogeographic status, climate-origin and functional traits predict heat tolerance of urban trees under climate warming." Urban Forestry & Urban Greening. 126. 129728. 10.1016/j.ufug.2026.129728
Journal
Urban Forestry & Urban Greening
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Biogeographic status, climate-origin and functional traits predict heat tolerance of urban trees under climate warming
Passion fruit’s cold survival secrets revealed in metabolic reprogramming study
Nanjing Agricultural University The Academy of Science
image:
Silencing cold-tolerance genes weakened cold tolerance in H1, and overexpression of cold-tolerance genes enhanced the cold tolerance of QM9 and H1
view moreCredit: Horticulture Research
Passion fruit, a tropical crop of growing economic importance, suffers devastating yield losses when unexpected cold snaps hit. Now, researchers have uncovered the molecular strategies that allow some varieties to withstand low temperatures while others wither. By integrating transcriptomic and metabolomic analyses of cold-tolerant and cold-sensitive cultivars, the team identified three key metabolic pathways—sphingolipid, phenylpropanoid, and terpene metabolism—that are dramatically reprogrammed under cold stress. The findings reveal that cold tolerance in passion fruit does not rely on the well-known ICE-CBF-COR pathway found in Arabidopsis and other plants, but instead employs a distinct set of protective mechanisms.
Low-temperature stress is a growing threat to global agriculture, and tropical crops like passion fruit are especially vulnerable. Originating in warm climates, passion fruit lacks innate freezing tolerance—damage can begin below 8°C, and temperatures near 0°C are often lethal. Even in traditional growing regions, sporadic cold events can slash production. While the molecular basis of cold acclimation is well characterized in model plants like Arabidopsis thaliana, centered on the conserved ICE-CBF-COR transcription regulatory module, these pathways appear poorly developed in tropical species. Previous studies in passion fruit have been largely phenomenological, documenting physiological markers without uncovering causal mechanisms. Given these challenges, a systems-level understanding of the regulatory and metabolic networks that confer cold adaptation in passion fruit is urgently needed.
A research team from Guangxi University and the State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, in collaboration with the Guangxi Academy of Agricultural Sciences, published (DOI: 10.1093/hr/uhag164) their findings in Horticulture Research in 2026. The open-access study, licensed under Creative Commons Attribution 4.0, provides the first comprehensive multi-omics dissection of cold tolerance mechanisms in this high-value horticultural crop.
The team compared two cold-tolerant varieties (H1 and G15) with two cold-sensitive ones (QM9 and TN1) across stem, leaf, pericarp, and pulp tissues. Using liquid chromatography-mass spectrometry (LC-MS), gas chromatography-mass spectrometry (GC-MS), and RNA sequencing (RNA-Seq), they identified 1,236 metabolites and thousands of differentially expressed genes. Surprisingly, the canonical ICE-CBF-COR cold-signaling pathway showed no significant differential expression in tolerant varieties—suggesting passion fruit evolved alternative cold-defense strategies. Instead, three pathways emerged as central: sphingolipid metabolism, where genes like PesSPT and PesKDSR drive accumulation of sphinganine to stabilize cell membranes; phenylpropanoid metabolism, producing chlorogenic acid via PesHCT; and flavonoid biosynthesis, generating rutin through PesFG2. Exogenous application of sphinganine, chlorogenic acid, rutin, and three terpenoids significantly boosted cold tolerance in sensitive cultivars. Conversely, virus-induced gene silencing (VIGS) of core biosynthetic genes compromised cold resistance, leading to increased oxidative damage and severe wilting. Overexpression of these genes in cold-sensitive plants reversed the effect, confirming their protective roles. The study also revealed that the protective effects of chlorogenic acid and rutin were not simply due to reactive oxygen species (ROS) scavenging, suggesting alternative mechanisms such as osmotic adjustment or metabolic feedback regulation are at play.
“We were quite surprised to find that the classical ICE-CBF-COR pathway—the gold-standard cold response in model plants—barely registers in passion fruit,” the authors said. “Instead, cold-tolerant varieties rely on a sophisticated metabolic rewiring across sphingolipid, phenylpropanoid and terpene networks. These pathways don’t just passively respond to cold—they actively build a protective shield, from stabilizing membranes to deploying antioxidant metabolites. What excites us most is that we’ve moved beyond correlation to causation: we can now spray these compounds onto sensitive plants and watch them survive the cold.”
The findings open multiple avenues for improving cold tolerance in passion fruit and other tropical crops. Exogenous spraying of key metabolites—sphinganine, chlorogenic acid, rutin, or specific terpenoids—offers a practical, immediate strategy for protecting crops when cold snaps are forecast. For long-term solutions, the identified genes (PesSPT, PesKDSR, PesHCT, PesFG2) provide precise targets for molecular breeding or genetic engineering. The study also challenges the assumption that cold tolerance mechanisms are universally conserved across plant species, urging researchers to look beyond model-organism paradigms when studying tropical crops. As climate variability intensifies, these insights could help secure sustainable cultivation of passion fruit and guide similar efforts in other cold-sensitive, high-value horticultural species.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhag164
Funding information
National Natural Science Foundation of China (32270712); Guangxi Science and Technology Major Program (guikeAA23062085); State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources (SKLCUSA-a202306, SKLCUSA2024-a04); Innovation Project of Guangxi Graduate Education (YCSW2025080); Guangxi University High-level Talents research grant.
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.
Journal
Horticulture Research
Subject of Research
Not applicable
Article Title
Integrated transcriptomic and metabolomic analysis reveals key pathways and metabolites underlying cold tolerance in passion fruit
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