A biogeographic perspective on the evolution of fire syndromes in pine trees (Pinus: Pinaceae)

Fire in the tree: The origin and distribution of fire-adapted traits within conifers and their influence on speciation rates across the conifer phylogeny

PREMISE

Considering rapidly changing fire regimes due to anthropogenic disturbances to climate and fuel loads, it is crucial to understand the underpinnings driving fire-adapted trait evolution. Among the oldest lineages affected by fire is Coniferae. This lineage occupies a variety of fire prone and non-fire prone habitats across all hemispheres and has four fire-adapted traits: (1) thick bark; (2) serotiny; (3) seedling grass stage; and (4) resprouting ability. We seek to determine the historic origins of these traits, the degree of convergent evolution among species, how fire adaptations affect diversification rates in conifers, and if there is a link between climate and the evolution of fire adaptations.

METHODS

To investigate these questions, we use a combination of ancestral state reconstructions, multiple diversification analyses, and Pagel trait correlations.

RESULTS

Our results point to multiple evolutionary origins of fire adaptations. We find certain climates, particularly Subtropical and Mediterranean, are highly correlated with species possessing fire adaptations. Several lineages evolved fire adaptations after the Mid-Miocene Climactic Optimum, which coincides with the expansion of the then novel Mediterranean Climate type. Generally possessing a fire adaptation does not increase diversification rates, with the possible exceptions of Pinus subsections Australes and Ponderosae.

CONCLUSIONS

The appearance of novel climates and associated fire regimes seem to have been the primary drivers of fire adaptation evolution in conifers. However, most increases in diversification rates are within clades that responded favorably to cooler drier climates post Mid-Miocene Climactic Optimum, regardless of whether the clade is fire adapted.

Antimicrobial Activities of Essential Oils of Different Pinus Species from Bosnia and Herzegovina

BACKGROUND/OBJECTIVES

The emergence of antimicrobial resistance has urged researchers to explore new antimicrobial agents, such as essential oils (EOs). The aim of this study was to examine chemical composition and antimicrobial activity of the EOs from the needles and green cones of four Pinus species (Pinus mugo Turra., P. nigra J.F., P. syilvestris L., and P. halepensis Miller) from Bosnia and Herzegovina.

METHODS

Chemical profiles of EOs were assessed by gas chromatography, while microdilution method was used to test their antimicrobial activity. A synergistic action of EOs and gentamicin was investigated by the checkerboard assay.

RESULTS

The chemical composition of the tested EOs showed a high percentage of α-pinene, (E)-caryophyllene, limonene, germacrene D, myrcene, and δ-3-carene. EO from green cones of P. sylvestris showed high efficiency against S. aureus and E. faecalis. The MIC of P. nigra cones' EO was 100 μg/mL against E. coli. The EO of P. halepensis green cones demonstrated the strongest activity against E. faecalis. EOs of P. halepensis needles and green cones exhibited the highest activity against C. albicans. Further, synergistic interaction was detected in combination of the selected EOs/gentamicin toward S. aureus and K. pneumoniae.

CONCLUSIONS

Among the tested EOs, oils of P. sylvestris cones and P. halepensis cones and needles showed the greatest antimicrobial activity. The same EOs and EO from P. nigra cones displayed synergistic potential in combination with gentamicin, supporting their utilization as antimicrobial agents alone or in combination with antibiotics, which is in line with their ethnopharmacological usage and circular bioeconomy principles.

Gymnosperm Resprouting—A Review

Gymnosperms are generally regarded as poor resprouters, especially when compared to angiosperms and particularly following major disturbance. However, is it this clear-cut? This review investigates two main aspects of gymnosperm resprouting: (i) various papers have provided exceptions to the above generalization—how frequent are these exceptions and are there any taxonomic trends?; and (ii) assuming gymnosperms are poor resprouters are there any anatomical or physiological reasons why this is the case? Five of six non-coniferous gymnosperm genera and 24 of 80 conifer genera had at least one species with a well-developed resprouting capability. This was a wider range than would be expected from the usual observation ‘gymnosperms are poor resprouters’. All conifer families had at least three resprouting genera, except the monospecific Sciadopityaceae. Apart from the aboveground stem, buds were also recorded arising from more specialised structures (e.g., lignotubers, tubers, burls and underground stems). In some larger genera it appeared that only a relatively small proportion of species were resprouters and often only when young. The poor resprouting performance of mature plants may stem from a high proportion of apparently ‘blank’ leaf axils. Axillary meristems have been recorded in a wide range of conifer species, but they often did not form an apical dome, leaf primordia or vascular connections. Buds or meristems that did form often abscised at an early stage. While this review has confirmed that conifers do not resprout to the same degree as angiosperms, it was found that a wide diversity of gymnosperm genera can recover vegetatively after substantial disturbance. Further structural studies are needed, especially of: (i) apparently blank leaf axils and the initial development of axillary meristems; (ii) specialised regeneration structures; and (iii) why high variability can occur in the resprouting capacity within species of a single genus and within genera of the same family.

On tree longevity

Large, majestic trees are iconic symbols of great age among living organisms. Published evidence suggests that trees do not die because of genetically programmed senescence in their meristems, but rather are killed by an external agent or a disturbance event. Long tree lifespans are therefore allowed by specific combinations of life history traits within realized niches that support resistance to, or avoidance of, extrinsic mortality. Another requirement for trees to achieve their maximum longevity is either sustained growth over extended periods of time or at least the capacity to increase their growth rates when conditions allow it. The growth plasticity and modularity of trees can then be viewed as an evolutionary advantage that allows them to survive and reproduce for centuries and millennia. As more and more scientific information is systematically collected on tree ages under various ecological settings, it is becoming clear that tree longevity is a key trait for global syntheses of life history strategies, especially in connection with disturbance regimes and their possible future modifications. In addition, we challenge the long-held notion that shade-tolerant, late-successional species have longer lifespans than early-successional species by pointing out that tree species with extreme longevity do not fit this paradigm. Identifying extremely old trees is therefore the groundwork not only for protecting and/or restoring entire landscapes, but also to revisit and update classic ecological theories that shape our understanding of environmental change.

Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines

How coniferous forests evolved in the Northern Hemisphere remains largely unknown. Unlike most groups of organisms that generally follow a latitudinal diversity gradient, most conifer species in the Northern Hemisphere are distributed in mountainous areas at middle latitudes. It is of great interest to know whether the midlatitude region has been an evolutionary cradle or museum for conifers and how evolutionary and ecological factors have driven their spatiotemporal evolution. Here, we investigated the macroevolution of Pinus, the largest conifer genus and characteristic of northern temperate coniferous forests, based on nearly complete species sampling. Using 1,662 genes from transcriptome sequences, we reconstructed a robust species phylogeny and reestimated divergence times of global pines. We found that ∼90% of extant pine species originated in the Miocene in sharp contrast to the ancient origin of Pinus, indicating a Neogene rediversification. Surprisingly, species at middle latitudes are much older than those at other latitudes. This finding, coupled with net diversification rate analysis, indicates that the midlatitude region has provided an evolutionary museum for global pines. Analyses of 31 environmental variables, together with a comparison of evolutionary rates of niche and phenotypic traits with a net diversification rate, found that topography played a primary role in pine diversification, and the aridity index was decisive for the niche rate shift. Moreover, fire has forced diversification and adaptive evolution of Pinus Our study highlights the importance of integrating phylogenomic and ecological approaches to address evolution of biological groups at the global scale.

Genome-wide RAD sequencing resolves the evolutionary history of serrate leaf Juniperus and reveals discordance with chloroplast phylogeny

Juniper (Juniperus) is an ecologically important conifer genus of the Northern Hemisphere, the members of which are often foundational tree species of arid regions. The serrate leaf margin clade is native to topologically variable regions in North America, where hybridization has likely played a prominent role in their diversification. Here we use a reduced-representation sequencing approach (ddRADseq) to generate a phylogenomic data set for 68 accessions representing all 22 species in the serrate leaf margin clade, as well as a number of close and distant relatives, to improve understanding of diversification in this group. Phylogenetic analyses using three methods (SVDquartets, maximum likelihood, and Bayesian) yielded highly congruent and well-resolved topologies. These phylogenies provided improved resolution relative to past analyses based on Sanger sequencing of nuclear and chloroplast DNA, and were largely consistent with taxonomic expectations based on geography and morphology. Calibration of a Bayesian phylogeny with fossil evidence produced divergence time estimates for the clade consistent with a late Oligocene origin in North America, followed by a period of elevated diversification between 12 and 5 Mya. Comparison of the ddRADseq phylogenies with a phylogeny based on Sanger-sequenced chloroplast DNA revealed five instances of pronounced discordance, illustrating the potential for chloroplast introgression, chloroplast transfer, or incomplete lineage sorting to influence organellar phylogeny. Our results improve understanding of the pattern and tempo of diversification in Juniperus, and highlight the utility of reduced-representation sequencing for resolving phylogenetic relationships in non-model organisms with reticulation and recent divergence.

Seed release by a serotinous pine in the absence of fire: implications for invasion into temperate regions

In pines, the release of seeds from serotinous cones is primarily considered a response to the high temperatures of a fire. However, the naturalization of serotinous pines in regions where fires are rare highlights the need to quantify environmental conditions that determine seed release to allow accurate prediction of dispersal and spread risk. We investigated the conditions that break cone serotiny in Pinus radiata, a widely planted forestry species that has naturalized in temperate regions worldwide. We quantified the cone temperatures at which cones open in this species, while also assessing potential confounding effects of cone moisture and age on these temperature requirements. We compared our laboratory results with cone opening behaviour under typical field conditions during summer in Canterbury, New Zealand. Cones opened at a mean temperature of 45 °C, much higher than maximum ambient air temperatures recorded in New Zealand. We found no influence of cone age or moisture content on opening temperature. Under field conditions, cones opened upon reaching similar temperatures to those determined in the laboratory; however, passive solar heating caused cones to reach temperatures up to 15 °C higher than ambient conditions. This resulted in 50 % of cones opening in field conditions where maximum air temperatures never exceeded 30 °C. Our results highlight the need for complementary laboratory and field experiments for understanding seed release from serotinous cones. Our findings have important implications for weed risk assessments, showing that serotinous pines can release seed in temperate climates without fire.