Reciprocal interactions between plants and their local environment, commonly referred to as ‘plant-soil feedback’ (PSF), have been a focal component of plant population and community ecology over the past two decades. Non-native, perennial forage grasses can have tremendous effects on abiotic properties and biotic communities of native ecosystems; however, very few studies have explored PSF between native and non-native perennial prairie grasses, and how PSF between the two are affected by biomass removal. Here, we present a standard two-phase PSF experiment conducted in a greenhouse, pairing one non-native and one native grass of both C3 and C4 photosynthetic pathways. Plant–soil feedback was measured through plant productivity, arbuscular mycorrhizal (AM) fungal colonization, and neutral lipid fatty acids (NLFAs). Defoliation generally neutralized PSF, regardless of whether the PSF was being measured through biomass production, intra-radical AM fungal colonization, or NLFAs. Second, responses of AM fungi to defoliation, conditioning species, and feedback species were complex, with significant two- and three-way interactions for cool- and warm-season pairings, respectively. Both cool- and warm-season grass pairs displayed strong positive PSF for AM fungal colonization, though intra-radical colonization in the two functional groups was differentially affected by defoliation. Through alterations to abundance, and perhaps even composition, of soil microbial communities, defoliation was demonstrated to neutralize, and even completely shift direction of, PSFs between native and non-native grasses. Overall, these results highlight the differential effects of defoliation on plant productivity and AM fungal abundances of native and non-native cool- and warm-season grasses, and how these alterations influence PSF dynamics between these often-interacting grass species, thus shedding light onto complex coexistence dynamics.
The Anacardiaceae is a diverse family of flowering plants of considerable ecological and economic importance, with a rich fossil record that provides valuable insights into its evolutionary and biogeographic history. This review synthesizes fossil, molecular phylogenetic, geological, and distributional evidence to reconstruct the historical biogeography of the family and critically evaluate current hypotheses of its origin and diversification. Fossil records including leaves, wood, fruits, endocarps, flowers, and pollen reveal a complex history of diversification and dispersal across the Northern and Southern Hemispheres. While molecular biogeographic studies generally support a Laurasian origin of Anacardiaceae, the fossil record—particularly the abundance of early Cenozoic fossils from the Indian subcontinent—highlights important gaps and uncertainties that warrant further investigation. The review also examines the role of major palaeogeographic events and dispersal corridors, including the North Atlantic Land Bridge, Bering Land Bridge, Isthmus of Panama, Sunda and Sahul shelves, and transoceanic dispersal, in shaping the present-day distribution of major lineages. Tribe-wise synthesis of the fossil evidence reveals distinct temporal and spatial patterns of diversification, range expansion, and regional extinction driven by tectonic movements and climatic fluctuations. By integrating multiple lines of evidence and critically assessing the reliability of published fossil records, this review provides a comprehensive framework for understanding the evolutionary history of Anacardiaceae and identifies key priorities for future research, including improved fossil documentation, broader phylogenetic sampling, robust fossil calibrations, and the incorporation of palaeogeographic history into ancestral-area reconstructions.
Endemic plant species often belong to taxonomically complex groups arising by processes such as hybridization and polyploidy, and thus represent a particular challenge for conservation. Information on species’ delimitation, genetic diversity, and population structure of these species is therefore essential to guide effective management practices, including both in situ and ex situ programs. These practices shall also be properly based on prior knowledge of species’ reproductive modes, which are often associated with the occurrence of polyploidy in plants. Using cytogenetic and genotyping-by-sequencing (GBS) data, we characterized the ploidy level and tested interspecific boundaries of three species of Paspalum subgenus Harpostachys (Poaceae) — the broadly distributed Paspalum axillare, and the endemics P. sp. nov. and P. carajasense — which co-occur on the cangas in southeastern Amazon, Brazil. In addition, we investigated clonality, and characterized patterns of genetic diversity and population structure, as well as estimated the effective population size of the endemics P. carajasense and P. sp. nov. Our results indicated that P. axillare and P. sp. nov. are diploid (2 n = 2x=20), while P. carajasense has a chromosome count compatible with triploidy (2 n = 3x=30). Genomic data indicated that the three taxa are genetically distinct and support a non-recurrent origin of the triploid P. carajasense, followed by limited clonal propagation. Analyses also support the existence of a single Evolutionary Significant Unit for both the endemics P. carajasense and P. sp. nov. across their entire distribution. Our data also showed that P. carajasense exhibits higher heterozygosity than P. sp. nov. and a negative inbreeding coefficient, coherent with the expected for alloploids. In addition, our data revealed a small effective population size (NE < 50) for both endemics, with lower values for the diploid P. sp. nov. than for the triploid P. carajasense. Based on these results, we suggest that mixing individuals from different localities during in situ and ex situ management of both endemic species poses no genetic risks and highlights the potential of seed banking as a conservation strategy.
The relative roles of local and regional processes in determining community assembly in heterogeneous landscapes are poorly understood. Generally, local floras encompass much fewer species than their corresponding regional flora. Such reduction partly results from the local action of environmental filtering, so that only some species from the regional pool can successfully establish in a particular habitat, based on their ability to survive and thrive under certain conditions. We hypothesized that filtering power varies across vegetation types, as these represent different habitats, and that lineages are filtered more effectively than species in more restrictive habitats. We assessed reductions in lineage and species richness from the regional pool to habitat-specific pools using floristic information gathered over three decades in a tropical landscape encompassing seven vegetation types with differing environmental constraints. We constructed the phylogeny for the regional flora based on a mega-phylogeny for seed plants and pteridophytes, and calculated three α-phylogenetic metrics (ses.MPD, ses.MNTD, and ses.PD). Vegetation types differed in taxonomic (range: 94–666 species) and phylogenetic (range: 5410–21,661 Ma) α-diversities. Most habitat-specific floras were phylogenetically under-dispersed. By artificially creating increasingly smaller reference species pools, we showed that the most speciose floras do not necessarily possess the highest phylogenetic diversity. Stronger filtering of lineages than of species in harsher habitats results in differential filtering power across heterogeneous landscapes and may underlie the decoupling of taxonomic and phylogenetic diversities.
The Chapada Diamantina (CD) clade (Asteraceae, Eupatorieae) comprises 26 species distributed among six genera (Agrianthus, Arrojadocharis, Bishopiella, Lasiolaena, Semiria, and Stylotrichium) endemic to the high elevations of the Espinha & ccedil;o Range in Brazil. We aimed to clarify phylogenetic relationships within the CD clade, which shows low genetic differentiation, high morphological variation, and unclear species delimitation. The DNA sequences of four plastid (psbA-trnH, trnC-petN, trnY-rpoB, and trnL-trnF with trnL intron) and three nuclear markers (ITS and low-copy regions gsh1 and shmt) allowed the construction of a dataset with 96% of the species described for the clade. Our results confirm that the CD clade is monophyletic and originated during the Pliocene (5.1 Mya), with subsequent diversification in the Pleistocene (2.5 Mya). Phylogenetic analysis also confirmed Bishopiella and Semiria as monotypic genera, a broader circumscription of Agrianthus including Arrojadocharis and two species of Lasiolaena, and that Lasiolaena and Stylotrichium are sister groups. In addition, four potential hybrids were detected, possibly providing evidence that reticulate evolution has occurred in the CD clade. Further studies with endemic and sympatric species with recent radiation could benefit from approaches combining phylogenetic trees and non-tree-like results, as well as nuclear markers, to propose improved explanations for the underlying evolutionary mechanisms generating diversity.
To conserve threatened species effectively, it is necessary to integrate ecological and population genetic data, identify drivers of population decline, and define protection priorities. We studied the rare and endangered annual plant species Omphalodes scorpioides at its northwestern range margin in central Germany. Genetic diversity, germination ecology, and environmental associations were assessed across multiple populations and years. We found strong genetic variation among populations (39.7%), and significant isolation by distance, yet consistently moderate within-population genetic diversity (mean uHe = 0.23, mean FIS =-0.23). Low variation in genetic diversity between years suggests genetic stability despite annual fluctuations in population size. In the laboratory, seed germination was low (5.6%), with seed viability declining rapidly during storage. No germination occurred in the soil seed bank samples over two years, indicating that recruitment may require specific or disturbed environmental conditions. Population size was not related to genetic diversity or environmental factors. Larger populations showed a higher reproductive performance but produced smaller seeds, whereas vegetative performance was associated with environmental conditions. An assessment of herbarium specimens revealed a phenological deceleration over the last 200 years, accompanied by a reduction in leaf area, both of which may result from increasing environmental stress over time. Our results highlight the ecological vulnerability of O. scorpioides, whose survival is closely linked to narrow environmental niches. Successful conservation measures require maintaining habitat quality and conditions that promote recruitment to ensure the long-term survival of peripheral populations.
Positive plant-plant interactions are important drivers of community assembly in environmentally stressful ecosystems, yet the ecological role of bromeliads as potential nurse plants in semi-arid rocky outcrops remains poorly understood. We investigated patterns of vascular plant richness associated with clumps of Encholirium spectabile, a rupicolous bromeliad endemic to the Brazilian Caatinga. Specifically, we evaluated how bromeliad clump size, plant growth form, seasonality, and cacti presence were associated with variation in plant assemblages occurring within bromeliad clumps. We sampled 155 bromeliad clumps distributed across 22 semi-arid rocky outcrops in northeastern Brazil during dry and rainy seasons. Generalized linear models and hierarchical partitioning analyses were used to evaluate the relative importance of ecological predictors associated with vascular plant richness. Associated plant richness increased consistently with bromeliad clump size, indicating that structural complexity strongly influenced plant assemblages within bromeliad microsites. Climbing and woody species exhibited higher richness than herbaceous taxa, suggesting functionally structured associations linked to bromeliad architecture. Cacti presence contributed to richness variation in isolated analyses but showed no independent conditional effect in the full multivariate model. Seasonal variation exerted comparatively little influence on total richness, although growth-form composition differed between dry and rainy periods. Our findings are consistent with the interpretation that Encholirium spectabile may contribute to the formation of structurally buffered microsites capable of supporting diverse vascular plant assemblages in environmentally restrictive rocky outcrop ecosystems. Given the increasing anthropogenic pressures affecting semi-arid rocky outcrops, preserving structurally complex bromeliad clumps may contribute to biodiversity maintenance and ecological resilience in these threatened landscapes.
The structure of meadow communities is determined by the abiotic environment and biotic interactions (mostly competition). Yet, both the environment and species identity affect the final balance (symmetry) and strength of competition. Here, we aimed to disentangle the mutual competitive effects and the symmetry of competition between a potential grass dominant and four closely related sedges (Carex). We asked whether the dominant experienced competition effects from subordinates (and vice versa), and how the magnitude and dynamics of these interactions are shaped by contrasting water regimes. We experimentally planted four sedge species, all with a grass competitor or alone, and under low or high water regimes. Both the dominant and subordinate species exerted significant competitive effects. The grass affected the final biomass of all sedges similarly, while their growth dynamics differed among species. Nevertheless, the strength of competitive effects exerted on the grass depended largely on the identity of the neighbouring sedge. The magnitude of competitive interaction was unequal resulting often in asymmetric competition favouring the grass. However, in several species, the interaction strength was context-dependent as sedges exhibited mostly symmetric competition with the grass dominant under the high water regime. The overall competitive strength of sedge species corresponded to their soil moisture requirements, with drought-tolerant species being weaker competitors, while more water-demanding species being stronger competitors, and the effects were even more pronounced under high water regime. Our results shed light on the abiotic and biotic drivers of plant-plant interactions, and the mechanisms maintaining balance precluding competitive exclusion in meadows.
Environmental filtering is widely associated with plant community structure in harsh ecosystems, such as Neotropical inselbergs. In these systems, leaf functional traits provide insights into patterns of community assembly and variation in ecological strategies. Here, we investigated how fine-scale edaphic and topographic heterogeneity is associated with variation in plant functional strategies across vegetation patches on eight Brazilian inselbergs. We measured key leaf economic traits and classified species strategies using the Competitive, Stress-tolerant and Ruderal (CSR) framework. Community-weighted means (CWMs) of traits and CSR components were calculated for each vegetation plot. Associations between environmental variables (soil depth, patch area, slope, and soil properties summarized by PCA) and CWM traits were assessed using linear mixed-effects models. Plant communities were predominantly characterized by conservative trait syndromes and stress-tolerant strategies, with several functional traits and CSR components showing significant associations with fine-scale environmental variation. Soil depth was positively associated with higher leaf dry matter content and greater expression of stress-tolerant strategies, while showing negative associations with leaf area and competitive strategy components. In contrast, patch area was positively associated with plant height and competitive strategies, and negatively associated with specific leaf area and ruderal strategies. Together, these results indicate a consistent functional trade-off between patch area and soil depth across inselberg vegetation islands, with contrasting associations along the CSR spectrum. Fine-scale habitat heterogeneity was associated with the coexistence of conservative and acquisitive strategies, contributing to functional differentiation in resource-poor environments. Our findings highlight the importance of maintaining microhabitat heterogeneity for understanding and conserving the functional structure of inselberg plant communities, while emphasizing the need for experimental approaches to disentangle correlation from causation in future studies.
Climate change is expected to profoundly reshape the composition and diversity of temperate ecosystems worldwide, yet its effects on the South American Temperate Grasslands, Savannas, and Shrublands (STG) biome remain poorly quantified at a biome-wide scale. Here, we assess the potential impacts of future climate scenarios on the angiosperm flora of the STG, which includes the Espinal, Humid Pampas, Low Monte, and Patagonian Steppe ecoregions. Using species distribution models, we generated current and future projections for 2116 species (representing 76% of the biome's angiosperm flora) and analyzed changes in species ranges and taxonomic and phylogenetic diversity. Projections were based on five global circulation models under SSP3-7.0 and SSP5-8.5 for 2071-2100. Results indicate a pronounced but spatially heterogeneous decline in biodiversity, with 70-75% of species projected to experience range contractions and up to 5% lost from the biome. The northern Espinal and Humid Pampas exhibited the greatest biodiversity reductions, whereas the central-southeastern Humid Pampas and southwestern Patagonian Steppe showed lower declines, potentially functioning as climatic refugia. Shifts in phylogenetic structure revealed both clustering and overdispersion, reflecting lineage-specific and spatially variable responses to climate change. Projected changes in beta diversity showed a predominance of nestedness-driven patterns associated to biodiversity loss, indicating that climate change will primarily promote non-random species loss and the reduction of assemblage diversity rather than compositional turnover. Floristic units captured spatial variation in biodiversity loss more effectively than ecoregions, underscoring the need for finer-scale bioregionalization to guide conservation planning across southern South America's temperate ecosystems.
The flowers of Anacardiaceae are known to produce nectar, in most cases secreted by a nectary disk, which may have an intra- or more rarely extrastaminal position. Exceptions include species that produce nectar via secretory trichomes on the petals and/or base of the stamens. To evaluate whether differences in nectary morphology and position result from independent ontogenetic trajectories, we investigated the development of floral nectaries differing in morphology and position in three phylogenetically unrelated species of Anacardiaceae: Anacardium humile A.St.-Hil. (corolline nectariferous trichomes), Schinus mole L. (intrastaminal nectary disk) and Mangifera indica L. (extrastaminal nectaries), using light and scanning electron microscopy. Additionally, we examined the evolution of floral nectaries using the Maximum Likelihood method to infer transitions between nectar gain and loss within the family and to assess potential correlations with pollination mode. In Schinus, the nectary disk develops from an intercalary growth of the receptacle, leading to the formation of a continuous disk in an intrastaminal position. In contrast, the nectaries of Mangifera develop from five individual primordia located at the base of the filaments, indicating a positional shift due to heterotopic meristem displacement. In Anacardium, each nectariferous trichome originates from successive divisions of a single protodermal cell, and the suppression of the disk is linked to functional replacement by the secretory trichomes. Ancestral state reconstructions indicate that the intrastaminal disk represents the most likely ancestral condition, but occasional positional shifts and developmental divergence indicate that this structure is homoplastic within the family, reflecting the interplay between developmental flexibility and evolutionary innovation.
Although larch (Larix spp.) trees dominate the Siberian boreal forest, the species' genetic structure within the world's largest forest biome is still poorly understood. Here, we compile and analyze genetic data from six boreal populations of three putative larch species (Larix sibirica Ledeb., Larix gmelinii (Rupr.) Rupr., and Larix cajanderi Mayr) from disjunct sites distributed across much of the Russian northern taiga between 60 and 170 degrees E. Using nine nuclear microsatellite markers (nSSR), we find high genetic diversity (mean HE = 0.757) and allelic richness (mean AR = 9.289) within all populations. Our analyses reveal two main genetic lineages: a western lineage corresponding to L. sibirica and an eastern lineage comprising L. gmelinii and L. cajanderi. Active hybridization connects these lineages across their contact zone. Our findings not only provide insights into the biogeographic structure and evolution of Eurasia's boreal forest, but also highlight the need for spatially explicit and better replicated genetic studies to resolve remaining taxonomic uncertainties.
Prunus serotina (Ehrh.) is a deciduous tree that has spread quickly across Europe in recent decades, raising concern due to its negative ecological and socioeconomic impacts. Although recognised as an invasive species in many European countries, it is not included among the European Union’s invasive alien species of concern. This review summarises current knowledge on taxonomy, biology and management. To prevent misidentifications, we present taxonomic challenges and key morphological characteristics.Prunus serotina grows best on nutrient-rich, well-drained substrates and benefits from canopy disturbances or forest management. Key traits contributing to its invasion success include rapid juvenile growth, high and early seed production, vegetative reproduction, sapling bank formation, and allelopathy. High herbivory and pathogen pressure on native tree species also enhance P. serotina establishment and spread.Management strategies include mechanical, chemical and biological control methods, as well as management aimed at reducing forest susceptibility to invasion by enhancing resilience and, in some cases, accepting P. serotina in the forest. Across Europe, management is context-dependent: eradication is prioritised in the Czech Republic due to its limited distribution, while in Germany, Belgium, Poland, and the Netherlands, integration into structurally diverse forests and resilience enhancement are emphasised, often combined with targeted control in protected areas.Overall, P. serotina is an invasive species with negative impacts. In isolated populations of P. serotina, the aim should be to eradicate the species in order to limit further spread. In valuable ecosystems where complete eradication is unfeasible, the goal is to suppress P. serotina.
Interactions are fundamental pillars of ecosystem functions, and plants often host a multitude of organisms both above- and belowground. However, plant populations of the same species may be visited by different communities depending on their size or local environment. Here we thoroughly surveyed the aboveground arthropod and belowground bacteria communities interacting with six Pyrenean rare plant species. We compared the patterns of alpha and beta diversity between patches of similar size located in small and large plant populations, and explored the relationship between aboveground arthropod and belowground bacterial diversities. Alpha diversity of arthropod visitors did not differ between plant patches, but belowground bacterial diversity was higher in small populations. In addition, significant differences were observed in the composition of arthropod communities, with patches in small populations having communities that differed from those in large populations. Finally, above- and belowground patterns of beta, but not alpha diversity were positively correlated. Our results suggest that isolated small plant populations may sustain communities of similar diversity as similar sized patches located within large populations, although with different taxonomic composition. This highlights the importance of small plant populations, often regarded as having lower ecological value, as hosts to a wide range of species both above- and belowground.
The Leguminosae (Fabaceae) is one of the largest and most evolutionary diverse plant families that comprises emblematic examples of symbiotic nitrogen fixation. This striking diversity is reflected across research areas ranging from taxonomy and phylogenomics to symbiosis, microbiology, biogeography, and functional traits. Insights into the genetic and molecular bases of root nodule symbiosis (RNS) are rapidly accumulating, enabling advances in agriculture and the engineering of biological nitrogen fixation (BNF). Nevertheless, substantial gaps remain, particularly regarding non-model species and the ecological and evolutionary drivers of RNS. This review summarises current knowledge on legume RNS and highlights that while the trait has likely contributed to legume diversification, the evolutionary trajectory of nodulation is complex, involving multiple gains, losses, and variations in symbiotic strategies across lineages. Nodule morphology and organogenesis, including determinate and indeterminate types, reveal structural and functional differences that may influence adaptability and BNF efficiency, although direct comparisons under varying environmental conditions remain limited. Ecological traits, such as drought tolerance, seed dormancy, and specialised pollination and defence mechanisms, interact with RNS to facilitate survival across diverse habitats. Case studies on Lebeckia ambigua and soybean wild relatives demonstrate how insights from non-model legumes can contribute to sustainable agriculture by improving stress resilience, expanding symbiotic partnerships, and broadening the genetic base for crop improvement. Future research should expand to non-model species and systematically assess nodulation, symbiotic efficiency, and environmental responsiveness to fully harness the potential of legumes for ecological and agricultural applications.
Accurate taxonomic treatment and classification is essential for advanced genomic research, but not always straightforward. Here, we address the long-standing taxonomic confusion regarding the names Cardamine rivularis Schur and C. rivularis auct. non Schur, which refer to different entities involved in allopolyploidization events. A number of studies from the 1970s to the present have misclassified the parental species of the Alpine neopolyploids C. insueta and C. schulzii, disregarding morphological and genetic evidence. This prompted us to search for an appropriate taxonomic solution, which has remained problematic for decades. Here, we apply whole-genome resequencing, ddRADseq, and morphometrics to support C. rivularis Schur and C. rivularis auct. non Schur as separate species and, in particular, to distinguish the latter from the widespread C. pratensis s.str. Despite the evidence of introgression, we demonstrate their genetic distinction with subtle morphological differentiation, indicating cryptic speciation. The Alpine populations hitherto provisionally treated as C. rivularis auct. non Schur are described as the new species C. pseudorivularis Landolt ex Marhold & Lihova; those from the Eastern Carpathians are assigned to C. marholdii Tzvelev, and the adjacent Eastern Carpathian foothill populations are described as C. ucranica Marhold & Lihova. We emphasize that C. pseudorivularis, not C. rivularis, was involved in the polyploidization events in the Alps that have attracted the attention of many researchers, and we appeal for the correct taxonomic classification. Notably, populations of C. rivularis Schur from the Rhodopes also produce allotriploids, which should not be confused with the well-studied triploid C. insueta in the Alps.
Climbing plants are found in numerous plant families and play a key role in the community and ecosystem dynamics of forests worldwide. The climbing habit is often understood as allowing plants to reach better lit layers and enhance light capture. Therefore, it should be nearly absent in environments with abundant light and canopies rarely imposing significant shade on lower layers. Arid ecosystems fit the latter description, yet climbing plants are consistently present there. To address this issue, I considered their climbing mechanism. First, I explored the distribution of climbing plants in arid environments vs their climbing mechanism in Chile, a country with a marked latitudinal gradient in aridity. Results showed that root climbers are excluded -and scramblers are nearly excluded- from the desert, while both tendril-bearing and twining vines increase their relative presence in the desert compared to the forest. Second, to test whether stem twiners and tendril bearers are intrinsically more resistant to drought than scramblers, I compiled data from studies measuring physiological resistance to drought-induced embolism. Results showed that there was no difference in this trait among species with different climbing mechanisms. Finally, I discuss that twining and tendril-bearing climbers could be favored in arid environments because of their higher efficiency in finding (and attaching to) shrubs, which will grant them substantial benefits in terms of abiotic conditions and/or herbivory protection. Although there is surely no single explanation for the presence of climbing plants in deserts, I would suggest that the role of climbing mechanisms deserves further exploration.
Resource sharing in ramets located in heterogeneous environments is an important regeneration strategy for clonal plants. Primarily clonal herbs have been used as model systems in studying eco-physiological integration of clonal plants that often maintain dominance by sharing resources among ramets. Many forest understorey shrubs are clonal and their rapid expansion after canopy removing disturbance may impede forest regeneration. Such is the case with Kalmia angustifolia L. (hereafter called Kalmia), in the boreal forest of eastern Canada. Kalmia is known for its ability to establish a persistent heath within 6-8 years after fire. We asked if the persistent dominance of Kalmia is related to its resource sharing in ramets and shade tolerance. More specifically we asked if i) rhizome severing (by trenching) and shade would affect above-and belowground traits of Kalmia by breaking resource sharing among ramets, ii) Kalmia being shade-tolerant, low shade may not affect these traits, but high shade would, and iii) trenching and high shade together would have the strongest negative effect than either trenching or high shade alone. With a five-year field experiment we tested resource sharing of Kalmia in ramets subjected to trenching and 0, 34, 62, 79 and 98 % shade treatment in an established heath. We hypothesized that i) trenching alone and in combination with high shade will result in lower cover, stem density, and biomass of Kalmia ramets due to breakdown in resource sharing, ii) low shade (<= 62 %) may not affect it's above-and below ground traits but high shade (>= 62 %) will, and iii) trenching and high shading together will have a strong interactive effect resulting lower cover, stem density, and biomass. We found that overall, trenching had no significant effect on individual response variables whereas only the highest shade dramatically decreased cover (82 %), number of live stems (92 %), aboveground biomass (93 %) and belowground biomass (80 %). We conclude that Kalmia is a very shade tolerant shrub, and it does not rely on rhizomatous resource sharing among ramets in established heath.
Mixed-ploidy species, which contain individuals with different numbers of chromosome sets (e.g., diploids and polyploids), serve as exceptional natural laboratories for studying evolution in action. Previous studies have revealed that the Enkianthus chinensis species complex comprises tetraploid and hexaploid populations. However, whether diploid populations exist within this complex and how ploidy types are geographically distributed remain unclear. It also remains uncertain whether polyploids in this complex exhibited distinct responses to Quaternary climate changes compared to diploids in subtropical China, if they exist in subtropical China. Here, we first employed flow cytometry to assess cytotype distribution and then investigated the phylogeographic structure and demographic history of the complex using two chloroplast intergenic spacers (psbA-trnH and rpl32-trnL). The results revealed that the complex was composed solely of tetraploid and hexaploid populations with no diploid populations being detected, implying either diploid ancestor extinction or ancient polyploidization outside subtropical China. Tetraploids and hexaploids exhibited largely non-overlapping distributions possibly due to their divergent ecological tolerances. Twenty-seven chloroplast haplotypes were identified, forming six allopatric clades (Clades I-VI). N-ST (population differentiation based on ordered haplotypes) was significantly large than G(ST) (differentiation based on unordered haplotypes) in this complex, indicative of significant phylogeographic structure. Molecular dating suggested the six clades diverged in the late Pliocene (similar to 2.74 million years ago, Ma), suggesting the E. chinensis complex could have diversified prior to the Quaternary and persisting in multiple glacial refugia. Demographic analyses revealed recent range expansions in two clades (IV and VI) during the Last Glaciation (ca. 0.019 Ma and 0.049 Ma, respectively). Range expansions in these clades may correlate with cooler, wetter conditions during the Last Glaciation, aligning with patterns observed in sky island organisms (high elevation organisms on isolated mountains). Phylogenetic analyses indicated that hexaploids likely originated via multiple independent events, while the absence of extant diploids complicates tracing tetraploid evolution, necessitating future genomic work. Overall, this study advances understanding of polyploid evolution in subtropical China and provides insights for conservation strategies and germplasm utilization under ongoing climate change.
