Cork Oak Research Articles

Predicting the climatic suitability of non-native drought resistant trees in the face of desertification – A case study with Argania spinosa in the Iberian Peninsula

Climate change is driving a poleward shift in the optimal distributions of terrestrial organisms, including trees. Consequently, trees are expected to decrease in climatically unfavourable areas as their optimal climatic conditions shift poleward. This is the case of Mediterranean High Nature Value agroforestry systems in Iberian Peninsula, dominated by holm oaks (Quercus rotundifolia) and cork oaks (Quercus suber), which are expected to shift their future distribution northward. Failure to keep pace with climate warming poses a heightened risk of extinction for these tree species, as well as the loss of crucial ecosystem services they provide. A similar situation is found for argan trees (Argania spinosa) in the southwestern region of Morocco, where it also supports an agroforestry system. The optimum climate for these trees is also shifting northward, toward the Iberian Peninsula. As the argan tree thrives in more arid conditions with irregular precipitation, the future climatic conditions in the Iberian Peninsula may become favourable for the persistence of this tree. In light of this situation, the assisted colonization of the argan tree could potentially contribute to protecting and preserving the tree-associated ecosystem services in Iberian Peninsula. We conducted climate suitability modelling using maximum entropy approach, for both the current and future timeframes, for North of Morocco and Algeria (native range) and the whole Iberian Peninsula (non-native range). Accordingly, there appears to be a significant area with highly suitable climatic conditions (>80 %) for argan tree occurrence, covering approximately 6.7 % of the territory, over 38,000 km2. This area is projected to increase significantly in the future, covering 9–22 % of the territory, or about 55,000 and 127,000 km2. With this study, we aim to contribute to the discussion on the benefits of assisted colonization of argan trees into Iberian Peninsula, as well as potential drawbacks such as the risk of this species becoming invasive.

Characteristic of epicotyl dormancy and its hormonal regulation in Chinese cork oak (Quercus variabilis)

Emergence heterogeneity caused by epicotyl dormancy contributes to variations in seedling quality during large-scale breeding. However, the mechanism of epicotyl dormancy release remains obscure. We first categorized the emergence stages of Chinese cork oak (Quercus variabilis) using the BBCH-scale. Subsequently, we identified the key stage of the epicotyl dormancy process. Our findings indicated that cold stratification significantly released epicotyl dormancy by increasing the levels of gibberellic acid 3 (GA3) and GA4. Genes associated with GA biosynthesis and signaling also exhibited altered expression patterns. Inhibition of GA biosynthesis by paclobutrazol (PAC) treatment severely inhibited emergence, with no effect on seed germination. Different concentrations (50 μM, 100 μM, and 200 μM) of GA3 and GA4+7 treatments of germinated seeds demonstrated that both can promote the emergence, with GA4 exhibiting a more pronounced effect. In conclusion, this study provides valuable insights into the characterization of epicotyl dormancy in Chinese cork oak and highlights the critical role of GA biosynthesis in seedling emergence. These findings serve as a basis for further investigations on epicotyl dormancy and advancing large-scale breeding techniques.

Genome-wide identification of TCP transcription factors and their potential roles in hydrolyzable tannin production in Quercus variabilis cupule.

Hydrolyzable tannins (HTs) have garnered significant attention due to their proven beneficial effects in the clinical treatment of various diseases. The cupule of Chinese cork oak (Quercus variabilis Blume) has been used as raw material of traditional medicine for centuries for its high content of HTs. Previous studies have identified UGT84A13 as a key enzyme in the HT biosynthesis pathway in Q. variabilis, but the transcriptional regulation network of UGT84A13 remains obscure. Here, we performed a comprehensive genome-wide identification of the TCP transcription factors in Q. variabilis, elucidating their molecular evolution and gene structure. Gene expression analysis showed that TCP3 from the CIN subfamily and TCP6 from the PCF subfamily were co-expressed with UGT84A13 in cupule. Further functional characterization using dual-luciferase assays confirmed that TCP3, rather than TCP6, played a role in the transcriptional regulation of UGT84A13, thus promoting HT biosynthesis in the cupule of Q. variabilis. Our work identified TCP family members in Q. variabilis for the first time, and provided novel insights into the transcriptional regulatory network of UGT84A13 and HT biosynthesis in Q. variabilis, explaining the reason why the cupule enriches HTs that could be used for traditional medicine.

The protective role of canopy cover against cork oak decline in the face of climate change

Abstract Cork oak (Quercus suber L.) mortality has reached alarming proportions in the last decades, exacerbated by climate change. Understanding this phenomenon is crucial in finding mitigation or adaptation strategies. This study conducts a diachronic analysis of cork oak mortality over 10 years using GIS (Geographic Information Systems) tools, focusing on Portugal’s Tagus Lezíria region. Topographic, edaphic and climatic variables were employed to create maps of edaphoclimatic aptitude for cork oaks. Dead trees were identified using remote sensing techniques and crown coverage was determined to calculate the trees’ mortality index. The diachronic analysis aimed the exploration of climate change effects on cork oak mortality. A decrease in precipitation was observed, significantly impacting stands with canopy cover below 40%. Furthermore, a negative effect of solar radiation identified only in stands with canopy cover of 40% suggested its role in cork oak decline. This study introduces a novel perspective, highlighting the protective effect of denser canopy cover against excessive solar radiation and the impact of reduced precipitation. The integrated and diachronic approach provides valuable information for adapting management strategies to climate change challenges.

Small molecule inhibitors of human LRRK2 enhance in vitro embryogenesis and microcallus formation for plant regeneration of crop and model species

In vitro plant embryogenesis and microcallus formation are systems which are required for plant regeneration, a process during which cell reprogramming and proliferation are critical. These systems offer many advantages in breeding programmes, such as doubled-haploid production, clonal propagation of selected genotypes, and recovery of successfully gene-edited or transformed plants. However, the low proportion of reprogrammed cells in many plant species makes these processes highly inefficient. Here we report a new strategy to improve in vitro plant cell reprogramming using small molecule inhibitors of mammalian leucine rich repeat kinase 2 (LRRK2), which are used in pharmaceutical applications for cell reprogramming, but never used in plants before. LRRK2 inhibitors increased in vitro embryo production in three different systems and species, microspore embryogenesis of oilseed rape and barley, and somatic embryogenesis in cork oak. These inhibitors also promoted plant cell reprogramming and proliferation in Arabidopsis protoplast cultures. The benzothiazole derivative JZ1.24, a representative compound of the tested molecules, modified the expression of the brassinosteroid (BR)-related genes BIN2, CPD, and BAS1, correlating with an activation of BR signaling. Additionally, the LRRK2 inhibitor JZ1.24 induced the expression of the embryogenesis marker gene SERK1-like. The results suggest that the use of small molecules from the pharmaceutical field could be extended to promote in vitro reprogramming of plant cells towards embryogenesis or microcallus formation in a wider range of plant species and in vitro systems. This technological innovation would help to develop new strategies to improve the efficiency of in vitro plant regeneration, a major bottleneck in plant breeding.

Exploring the Bioactive Properties of Hydroethanolic Cork Extracts of Quercus cerris and Quercus suber

Exploring the Bioactive Properties of Hydroethanolic Cork Extracts of Quercus cerris and Quercus suber

Irrigation is an effective strategy to assist cork oak (Quercus suber L.) regeneration in a semi-arid climate

ABSTRACT Irrigation can be a strategy to overcome the high mortality and declining vigour of cork oak trees facing increasing drought stress in the Mediterranean basin. Through a three-year irrigation experiment in a semi-arid Mediterranean region, which encompassed two sets of 100 planted individuals that had a 24-year age gap and the direct seeding of 100 acorns, we tested the influence of water irrigation on distinct stages of cork oak establishment and development, namely (1) acorn germination, (2) emerged seedling survival, (3) growth of planted seedlings, (4) vertical and (5) radial growth, and (6) the vigour of 28-year-old trees. Water irrigation significantly improved acorn germination and the growth of both cork oak seedlings and trees but did not affect the survival of emerged seedlings to the dry season. The vigour of 28-year-old trees (height-to-diameter ratio) showed no significant differences between the plants growing in watered and in controlled conditions.

Analysis of Land Use Changes in the Sado Estuary (Portugal) from the 19th to the 21st Century, Based on Historical Maps, Fieldwork, and Remote Sensing

This study analyses land use changes in the Sado Estuary (West-Central Portugal) based on a multi-temporal analysis of 19th century cartographic data and 21st century remote sensing land use maps, updated by fieldwork. A GIS plot of land use evolution is summarized in a quantitative table. The comparison shows the changes in land use, with increasing occupation by human economic activities, including extensive agriculture and forestry, as well as localized urbanization and industrialization. The main elements of the landscape impacted by anthropogenic uses were (i) hydrography—river dams affected the flow dynamics and sedimentary processes in the estuary; (ii) vegetation—increasing agriculture and forestry reduced the area of native vegetation, which is now mostly occupied by vineyards, pine forests and cork oaks; (iii) wetlands—tidal and alluvial plains are being occupied by rice cultivation, aquaculture, industries, and ports; (iv) coastal dunes—new developments are occupying large areas of Holocene coastal dunes; and (v) natural environment—mining and dredging have affected some habitats and biodiversity. This analysis is intended to help the territorial organization of present and future economic activities, as well as to reduce environmental and social problems, thus promoting the long-term sustainability of this rapidly evolving region.

Analysis of land-use change in Mandrolisai 1860 to 2016: a case study from Sardinia (Italy)

ABSTRACT The focus on rural landscapes, already present in ‘Agenda 2000’, is reconfirmed for the CAP 2023–2027 (Green Deal). The CAP programmes have, however, often turned out to be generic and unsuited to the multifaceted reality of Mediterranean Europe, while FAO-GIAHS and UNESCO World Heritage programmes suit large territories. Both, as well as the CAP, support the conservation or renaturalisation of rural landscapes but cannot apply prescriptions at the planning stage. In Italy, the ‘Code of Cultural Heritage and Landscape’ contains prescriptive measures that the regions must include in their Landscape Plan (RLP); the municipalities must then adopt Urban Plans in accordance with the RLP. In Sardinia, RLP has protected the coastal areas (49.6 per cent of the 24,000 km2 surface area of the island) since 2006 but does not provide detailed guidelines for inland areas. We therefore tested the methodology proposed by the Ministry of Agriculture for recovering Historic Rural Landscapes in a study area of 23.63 km2 located in the heart of the island (in Mandrolisai region), where the two rural villages of Atzara and Sorgono border a system of traditional vineyards. Comparison of the 1860–1880 Land Register data, images from the first (1954) and last air flight (2016) shows that the agro-silvo-pastoral system has not changed structurally. In 2016, 53 per cent of the analysed area retains the same land-use macrocategories as the 1954 aerial photographs. Despite wide fluctuations in some agricultural crops, the most characteristic ones tend to occupy the same places, e.g., 72 per cent of 2016 vineyards compared to 1954. The biggest changes have been the transformation of natural pastures into cork oak wooded pastures, due to the sustained demand for cork.

Climate Change-Induced Growth Decline in Planted Forests of Quercus variabilis Blume near Beijing, China

A progressive decline in tree growth may be induced by global warming, affecting tree health and eventually resulting in death, particularly for trees growing in rocky mountainous regions where seasonal droughts have become more pronounced. However, tree growth dynamics in areas experiencing pronounced climate change have received little attention. In this study, a total of 100 (10 m × 10 m) grid plots were investigated in planted forests of Chinese cork oak (Quercus variabilis Blume), which were established in the 1960s and 1970s in a rocky mountainous area near Beijing, northern China. Furthermore, the radial growth of Q. variabilis (a total of 843 trees sampled from the dominant [D], co-dominant [CD], and suppressed [S] crown classes) was analyzed using retrospective dendrochronology and generalized additive models. The effects of meteorological changes between 1962 and 2020 on radial growth across the three crown classes were examined using correlation analysis. The results indicated that the growth of Q. variabilis initially increased and then decreased after 2010 at the regional level, and these trends varied according to crown class. The radial growth of the D trees responded more positively to an increase in temperature and drought severity index (<0 for dry and >0 for wet conditions) compared with that of the CD and S trees. The growth of the D and CD trees continuously increased under higher temperatures during the rainy seasons (June to September); however, the increases were higher for D than for CD trees. In contrast, the radial growth of S trees declined. We confirmed the historical effects of rising temperatures on tree growth and health, which are linked to water availability. Our data suggested that Q. variabilis trees will be considerably affected by intensified droughts. This study furthers our knowledge regarding the impact of climate change on tree and forest growth and provides management strategies for afforestation projects in rocky mountainous areas that are facing climate change.

Storing cork oak (Quercus suber) seeds under different temperatures and the effect of storage treatments on the germination and growth of stored seeds

Storing cork oak (Quercus suber) seeds under different temperatures and the effect of storage treatments on the germination and growth of stored seeds

Natural regeneration of cork oak forests under climate change: a case study in Portugal

The sustainability of forest species is directly related to the success of stand regeneration. Assuring success is particularly critical in stands where perpetuity relies on natural regeneration, as is often the case with cork oak forests. However, 59% of the stand in Portugal have no natural regeneration, and climate change could further worsen the sustainability of the system. The study summarizes the factors that affect the natural regeneration of cork oak (Quercus suber L.) based on current knowledge and presents a case study on a forest in Northeast Portugal, where the natural regeneration of Quercus suber under the effect of climate change have been monitored and analyzed. The present work focuses on the effect of stand density, i.e., tree cover, on the production of acorns, the establishment and survival of seedlings, and the impact of the summer season on seedling mortality. The monitoring was carried out in February, June, September 2022, and January 2023 in two stands with distinct stand canopy cover, when the region was under extreme drought. Data analysis was performed using the analysis of variance for repeated measures and the Mann–Whitney-Wilcoxon test. The study showed that cork oak regeneration is influenced by stand density, which promoted the establishment success and survival of natural regeneration in a period of reduced precipitation, despite possible competition for water resources. The mean number of seedlings differed significantly between the two stands. However, there were no significant differences in the mean number of seedlings throughout the field measurements. Additionally, the percentage of dead seedlings was low even after the summer season (9.5% of the total seedlings) in the denser stand. These results indicate that high canopy cover can have a protective effect for extreme climatic events and should be considered in forestry management to promote regeneration of the cork oak forests.

An improved method to study Phytophthora cinnamomi Rands zoospores interactions with host

Phytophthora cinnamomi Rands is a highly prevalent phytopathogen worldwide, ranking among the top ten in terms of distribution. It inflicts crown rot, canker, and root rot on numerous plant species, significantly impacting the biodiversity of both flora and fauna within affected environments. With a host range spanning over 5,000 species, including important plants like Quercus suber, Quercus ilex, Castanea sativa, and commercially significant crops such as avocado (Persea americana), maize (Zea mays), and tomato (Solanum lycopersicum), Phytophthora cinnamomi poses a substantial threat to agriculture and ecosystems. The efficient dissemination of the oomycete relies on its short-lived asexually motile zoospores, which depend on water currents to infect host roots. However, managing these zoospores in the laboratory has long been challenging due to the complexity of the life cycle. Current protocols involve intricate procedures, including alternating cycles of growth, drought, and flooding. Unfortunately, these artificial conditions often result in a rapid decline in virulence, necessitating additional steps to maintain infectivity during cultivation. In our research, we sought to address this challenge by investigating zoospore survival under various conditions. Our goal was to develop a stable stock of zoospores that is both easily deployable and highly infective. Through direct freezing in liquid nitrogen, we have successfully preserved their virulence. This breakthrough eliminates the need for repeated culture transfers, simplifying the process of plant inoculation. Moreover, it enables more comprehensive studies of Phytophthora cinnamomi and its interactions with host plants.

Insights into haplotype distribution and population dynamics of Biscogniauxia mediterranea in cork oak forests in Tunisia

Biscogniauxia mediterranea is a pathogenic fungus associated with Quercus species causing charcoal canker disease in forests. Its phenotypic and genetic variability has been well studied in Tunisia but little is known about its demographic history. Population dynamic of B. mediterranea was evaluated among 30 isolates from different cork oak forests in Northwestern Tunisia. The genetic structure analyzed with two DNA markers (ITS and tef-1α) showed low genetic differentiation associated with high genetic flow among populations. The polymorphism analysis showed low nucleotide diversity but high haplotypic diversity among and within B. mediterranea populations which could be due to rapid growth from a small ancestral population. This hints at recent population growth after a period of decline likely due to a catastrophic event involving fires and human-induced tree cutting. The resulting genetic diversity within populations primarily arises from the emergence of new haplotypes. Overall, this study provides insights into the polymorphism of B. mediterranea and its potential adaptive strategy.

Rhytidome- and cork-type barks of holm oak, cork oak and their hybrids highlight processes leading to cork formation

BackgroundThe periderm is basic for land plants due to its protective role during radial growth, which is achieved by the polymers deposited in the cell walls. In most trees, like holm oak, the first periderm is frequently replaced by subsequent internal periderms yielding a heterogeneous outer bark made of a mixture of periderms and phloem tissues, known as rhytidome. Exceptionally, cork oak forms a persistent or long-lived periderm which results in a homogeneous outer bark of thick phellem cell layers known as cork. Cork oak and holm oak distribution ranges overlap to a great extent, and they often share stands, where they can hybridize and produce offspring showing a rhytidome-type bark.ResultsHere we use the outer bark of cork oak, holm oak, and their natural hybrids to analyse the chemical composition, the anatomy and the transcriptome, and further understand the mechanisms underlying periderm development. We also include a unique natural hybrid individual corresponding to a backcross with cork oak that, interestingly, shows a cork-type bark. The inclusion of hybrid samples showing rhytidome-type and cork-type barks is valuable to approach cork and rhytidome development, allowing an accurate identification of candidate genes and processes. The present study underscores that abiotic stress and cell death are enhanced in rhytidome-type barks whereas lipid metabolism and cell cycle are enriched in cork-type barks. Development-related DEGs showing the highest expression, highlight cell division, cell expansion, and cell differentiation as key processes leading to cork or rhytidome-type barks.ConclusionTranscriptome results, in agreement with anatomical and chemical analyses, show that rhytidome and cork-type barks are active in periderm development, and suberin and lignin deposition. Development and cell wall-related DEGs suggest that cell division and expansion are upregulated in cork-type barks whereas cell differentiation is enhanced in rhytidome-type barks.

Post-fire dynamics of recolonization by Cistus plants in the Aleppo pine and Cork oak forests in Bejaia region, central north Algeria

Abstract In August 2021, very intense fires swept through various forested areas in northern Algeria, particularly in Kabylia. The population dynamics of Cistus salviifolius and Cistus monspeliensis were studied along a post-fire successional gradient during the first nine months (September 2021 – May 2022), in two forest communities: the Cork oak (Quercus suber) and the Aleppo pine (Pinus halepensis) forests in the coastal zone of Bejaia province. The Cistus spp. germinations were counted monthly in each forest on 10 plots of 1 m2, evenly distributed along 2 transects of 45 m each. The results showed that the majority of germinations occur in December with 207.5 ± 24.2 seedlings in the Cork oak forest and 171.3 ± 18.0 seedlings in the Aleppo pine forest. Student's t-test does not reveal significant differences for December between the two communities. During the first months following the fire (September and October 2021), germinations were almost absent. The monthly rainfall in September 2021 was estimated at 16.25 mm, an insufficient amount for effective germination. Late germination results in an extension of its period, showed a high rate in January 2022 with 42.2 ± 2.1 and 11.5 ± 0.8 seedlings, respectively, in the Cork oak forest and the pine forest. Beyond January, germination was practically nonexistent in both communities. Therefore, the majority of the seed germination was concentrated in November, December, and January with a unimodal germination pattern.

Breeding ecology of the endangered Algerian Nuthatch (Sitta ledanti) endemic to the Babors′ Kabylia (Northeastern Algeria): Implications of conservation

Abstract The endemic Algerian Nuthatch Sitta ledanti, is classified as an endangered species by the IUCN and protected species by Algerian law. Available information on its nesting and breeding biology is sporadic and incomplete, the purpose of which is to provide additional data on the different aspects of multi-site nesting of the species. 22 nests are monitored across five forests, during the nesting season of 2021. An endoscopic camera was used to monitor eggs and nestlings in the nests during the whole study. Most of the nests (n = 20) were constructed in different parts of the dead trees such as trunks or branches of the Atlas cedar Cedrus atlantica, the Algerian oak Quercus canariensis, the African oak Quercus afares or Cork oak Quercus suber. The laying dates were from early April to the end of May when April 28 (± 13 days) is the laying season’s median start date. The average clutch size was 4.6 (n = 21). The mean hatching success was 89.2%, while mean fledging success was 88.2%. The nestling sex ratio was 14 males versus 18 females. Data on clutch dates and fecundity of breeding pairs should be considered in any conservation approach and strategy in the context of habitat management and preservation.

Assessing Carbon Storage and Biomass in Moroccan Cork Oak Forests

Assessing Carbon Storage and Biomass in Moroccan Cork Oak Forests

Resilience of Bird Communities After Wildfires in Algerian Cork Oak Forests

Resilience of Bird Communities After Wildfires in Algerian Cork Oak Forests

The Afternoon/Morning Ratio of Tower-Based Solar-Induced Chlorophyll Fluorescence Can Be Used to Monitor Drought in a Chinese Cork Oak Plantation

Monitoring drought stress is crucial for estimating productivity and assessing the health status of forest ecosystems under global climate change. Solar-induced chlorophyll fluorescence (SIF) is mechanistically coupled to photosynthesis and has advantages over greenness-based vegetation indices in detecting drought. In recent years, SIF has commonly been used in monitoring drought stress in crop ecosystems. However, the response of tower-based SIF to drought stress in forest ecosystems remains unclear. In this study, we investigated the potential of tower-based SIF to monitor drought, which was quantified using the plant water stress index (PWSI) in a Chinese cork oak plantation. The results show the negative effect of drought on SIF, and afternoon depression of SIF emission under drought stress was observed. Canopy SIF (F) exhibited a nonlinear relationship with PWSI, while the quantum yield of SIF (ΦF) exhibited a significant linear relationship with PWSI at 687 nm and 760 nm (ΦF687: R2 = 0.90; ΦF760: R2 = 0.85). Incident radiation (PAR) and canopy structure affected the response of SIF to drought stress, with PAR as the main factor causing the nonlinear relationship between F and PWSI. Afternoon depression was described as the afternoon/morning ratio (AMR). AMRF and AMRΦF exhibited a negative linear response to PWSI. AMRF was less affected than F by PAR and canopy structures, and AMRΦF was more physiologically representative than ΦF. Moreover, AMRΦF was sensitive to VPD and REW, and it might be a good indicator of drought. Red SIF was more sensitive to drought than far-red SIF, as the R2 of PWSI with AMRΦF687 (R2 = 0.89) was higher than that with AMRΦF687 (R2 = 0.84). These results highlight the potential of tower-based SIF, especially red SIF, for drought monitoring in a plantation, and consideration of the physiological diurnal variation in SIF under drought stress is crucial for improving the accuracy of drought stress monitoring.