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25 October 2019, Volume 41 Issue 05
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  • Articles
    Phytosociology of stratification in a lowland tropical rainforest occurring north of the Tropic of Cancer in Meghalaya, India
    Uma Shankar
    2019, 41(05):  285-299.  doi:10.1016/j.pld.2019.08.001
    Abstract ( 35 )   HTML ( )   PDF (4829KB) ( 52 )   Save
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    Stratification in lowland rainforests of Meghalaya, India, which represent the westernmost limit of the rainforests north of the Tropic of Cancer, was studied in horizontal and vertical planes to elucidate the patterns in stacking of species diversity and community attributes, and to draw comparisons with rainforests of ‘Indo-Malaya’ ecozone (biogeographical realm). All individuals 10 cm GBH (girth at breast height) were enumerated in six transects of 10 m width and up to 500 m length covering 2.45 ha area. The stratification of whole assemblage of species in vertical plane is referred to as ‘storey structure’ (=height class distribution), which explains structural complexity. In horizontal plane, it is typically referred to as ‘stand structure’ (=girth class distribution), which explains structural heterogeneity. The stratification of an individual species in vertical plane is referred to as ‘loftiness’ and in horizontal plane, it is frequently referred to as ‘population structure’. The stand structure was characterized by a negative exponential relationship or a reverse J-shaped curve, which is typical of a well regenerating forest stand. The storey structure was characterized by the low stature of the rainforest (<30 m), subtle layering in the canopy with dearth of discrete multi-stories, narrower widths of the stories and a thick understory. The cluster analysis and ‘candlestick charts’ showed that the dominant species spatially segregated in canopy height to profile three strata, viz., an understory of juveniles and shrubs below 5 m, a middle-storey of intermediate trees between 5 and 15 m, and an overstory of large trees between 15 and 25 m. Emergent trees of a few species may reach up to 30 m. The individuals tended to scatter in increasingly wider range of height classes from a lower to the next higher girth class, creating a ‘torchlight scatter’ pattern, with a tendency to concentrate towards smaller height classes due to stochastic factors, which potentially influence vertical growth proportionate to diametric growth. In comparison to equatorial rainforests of Malaysia and seasonal rainforests of southwestern China, the rainforests of Meghalaya are short-statured at the geographic extremity of the occurrence of rainforest biome in AsiaePacific region, owing to floristic composition, site quality factors, excessively higher quantities of rainfall and high differential of precipitation and potential evapotranspiration. Despite limited diversity of megaphanerophytes, these rainforests deserve concerted conservation efforts as they stack high diversity of meso-, micro- and nano-phanerophytes.
    Genetic diversity and population structure of Hibiscus aridicola, an endangered ornamental species in dry-hot valleys of Jinsha River
    Xin Zhang, Le Zhang, Johann Schinnerl, Wei-Bang Sun, Gao Chen
    2019, 41(05):  300-306.  doi:10.1016/j.pld.2019.07.001
    Abstract ( 61 )   HTML ( )   PDF (1815KB) ( 75 )   Save
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    Hibiscus aridicola is an endangered ornamental shrub of the family Malvaceae that is endemic to the dryhot valleys of Jinsha River in southwestern China. This species is a typical plant species with extremely small populations (PSESP). To support and monitor future conservation, develop management measures, and genotype this species, we performed extensive field studies together with genetic analyses. Specifically, we screened eleven microsatellite loci of 69 individuals of H. aridicola from four accessions. The population genetics analyses indicated that H. aridicola possesses high genetic diversity at both the population (0.6962-0.7293) and species level (0.7837) compared to other endemic/endangered species in China. The low differentiation of populations (Fst=0.0971) and the high gene flow between populations of H. aridicola (Nm=2.3236) could be due to its distribution along rivers in the hot-valleys of the Jinsha River and the wind-mediated dispersal of its seeds. Furthermore, the genetic diversity of H. aridicola is slightly positively correlated with geographic distance. Two populations are undergoing a genetic bottleneck, and require more specific attention from conservationists. Additionally, our analyses of the population genetics of H. aridicola demonstrate that the declines in populations are not the result of the internal genetics of these populations but due to external human activities over the past decades.
    Cell number explains the intraspecific spur-length variation in an Aquilegia species
    Zhi-Li Zhou, Yuan-Wen Duan, Yan Luo, Yong-Ping Yang, Zhi-Qiang Zhang
    2019, 41(05):  307-314.  doi:10.1016/j.pld.2019.06.001
    Abstract ( 44 )   HTML ( )   PDF (2007KB) ( 13 )   Save
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    Variations of nectar spur length allow pollinators to utilize resources in novel ways, leading to the different selective pressures on spurs and allowing taxa to diversify. However, the mechanisms underlying spur length variation remain unclear. Interspecific comparisons of spur length suggest that both cell division and anisotropic expansion could explain the changes of spur length, and that hormone-related genes contribute to the process of spur formation. In contrast, little is known about intraspecific spur length variation. In Aquilegia rockii, spur length varies strikingly, ranging from 1 mm to 18 mm. To examine the potential mechanisms underlying spur length variation in A. rockii, we observed cell morphology and analyzed RNA-seq of short- and long-spurred flowers. Scanning electron microscopy revealed that at two positions on spurs there were no differences in either cell density or cell anisotropy between short- and long-spurred flowers, suggesting that in A. rockii changes in cell number may explain variations in spur length. In addition, we screened transcriptomes of short- and long-spurred flowers for differentially expressed genes; this screen identified several genes linked to cell division (e.g., F-box, CDKB2-2, and LST8), a finding which is consistent with our analysis of the cellular morphology of spurs. However, we did not find any highly expressed genes involved in the hormone pathway in long-spurred flowers. In contrast to previous hypotheses that anisotropic cell expansion leads to interspecific spur variation in Aquilegia, our results suggest that cell number changes and related genes are mainly responsible for spur length variations of A. rockii. Furthermore, the underlying mechanisms of similar floral traits in morphology may be quite different, enriching our understanding of the mechanisms of flower diversity in angiosperms.
    Plastome sequencing of Myripnois dioica and comparison within Asteraceae
    Nan Lin, Xu Zhang, Tao Deng, Jianwen Zhang, Aiping Meng, Hengchang Wang, Hang Sun, Yanxia Sun
    2019, 41(05):  315-322.  doi:10.1016/j.pld.2019.07.003
    Abstract ( 59 )   HTML ( )   PDF (8214KB) ( 24 )   Save
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    Myripnois is a monotypic shrub genus in the daisy family constricted to northern China. Although wild populations of Myripnois dioica are relatively rare, this plant may potentially be cultured as a fine ornamental. In the present study, we sequenced the complete plastome of M. dioica, generating the first plastome sequences of the subfamily Pertyoideae. The plastome of M. dioica has a typical quadripartite circular structure. A large~20-kb and a small~3-kb inversion were detected in the large single copy (LSC) region and shared by other Asteraceae species. Plastome phylogenomic analyses based on 78 Asteraceae species and three outgroups revealed four groups, corresponding to four Asteraceae subfamilies:Asteroideae, Cichorioideae, Pertyoideae and Carduoideae. Among these four subfamilies, Pertyoideae is sister to Asteroideae + Cichorioideae; Carduoideae is the most basal clade. In addition, we characterized 13 simple sequence repeats (SSRs) that may be useful in future studies on population genetics.
    The coexistence of hermaphroditic and dioecious plants is associated with polyploidy and gender dimorphism in Dasiphora fruticosa
    Lin-Lin Wang, Zhi-Qiang Zhang, Yong-Ping Yang, Yuan-Wen Duan
    2019, 41(05):  323-329.  doi:10.1016/j.pld.2019.06.002
    Abstract ( 50 )   HTML ( )   PDF (24028KB) ( 22 )   Save
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    Dasiphora fruticosa comprises male, female and hermaphrodite plants, which are distributed sympatrically in some populations on the Qinghai-Tibet Plateau. To explore what governs the coexistence of these three sexual phenotypes, we investigated the DNA contents, pollen and ovule production, pollen deposition, and performed hand-pollination in both hermaphroditic and dioecious individuals of D. fruticosa. Flow cytometry confirmed that the DNA content of males and females were almost twice as much as that of the hermaphrodites. Male and female flowers produced more pollen grains and ovules than hermaphroditic flowers. Hand-pollinated treatments showed that unisexual flowers were sterile in one sexual function and bisexual flowers were fertile for both functions, but no sterile seeds were produced between unisexual and bisexual flowers. Our findings imply that polyploidy is related to gender dimorphism, and both are likely to play a strong role in the coexistence of two cryptic biological species of D. fruticosa (low ploidy hermaphroditic species and high ploidy dioecious species) in the Qinghai-Tibet Plateau.
    Phoenix phylogeny, and analysis of genetic variation in a diverse collection of date palm (Phoenix dactylifera) and related species
    Srinivasa R. Chaluvadi, Porter Young, Kentrez Thompson, Bochra Amina Bahri, Bhavesh Gajera, Subhash Narayanan, Robert Krueger, Jeffrey L. Bennetzen
    2019, 41(05):  330-339.  doi:10.1016/j.pld.2018.11.005
    Abstract ( 27 )   HTML ( )   PDF (5647KB) ( 19 )   Save
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    Date palm (Phoenix dactylifera), one of the most ancient crops, is grown commercially in>30 countries. Using whole plastome assemblies, phylogenetic analyses revealed that cultivated date palm accessions share the same clade with Phoenix sylvestris, Phoenix pusilla and Phoenix acaulis, which are native to the Indian subcontinent, and Phoenix caespitosa that is native to the Arabian Peninsula and the deserts of Somalia. Analysis of genetic diversity and genetic relationships among date palm accessions from 13 producing countries involved 195 date palm accessions that were genotyped at 19 microsatellite loci. Extensive genetic diversity was observed, with many accessions heterozygous for most markers in this clonally propagated crop. The average number of alleles per locus (42.1), expected heterozygosity (0.8), observed heterozygosity (0.47) and fixation indices (FST=0.42) demonstrated substantial genetic diversity and population structure. Iraqi accessions were found to have the richest allelic diversity, and the most private alleles. The model-based Bayesian method indicated that these accessions could be broadly divided into two structure groups, one group with predominantly African accessions and another predominantly Asian. Some germplasm, especially from Tunisia and Iraq, deviated from this generalization. Many accessions in the STRUCTURE-derived groups were found to be genetic admixtures, with gene flow between Asian and African groups. Indian and Pakistani date palms were found to be most closely related to North African germplasm.
    Effects of soil properties on accumulation characteristics of copper, manganese, zinc, and cadmium in Chinese turnip
    Boqun Li, Di Chen, Yongping Yang, Xiong Li
    2019, 41(05):  340-346.  doi:10.1016/j.pld.2019.06.006
    Abstract ( 43 )   HTML ( )   PDF (654KB) ( 16 )   Save
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    Clarifying the mechanisms of heavy metal (HM) accumulation and translocation from soil-root-leaf is crucial to coping with soil HM pollution. In this study, we analysed copper (Cu), manganese (Mn), zinc (Zn) and cadmium (Cd) accumulation characteristics in Chinese turnips and the effect of soil physicochemical properties on both HM accumulation and translocation. Our results indicate that Chinese turnips absorb and translocate Mn, Zn, and Cd at much higher levels than they do Cu. When we measured bioconcentration factors in Chinese turnips for different HMs in the same soil, we found Chinese turnip capacities for HM accumulation decrease from Zn > Mn > Cd > Cu. In addition, the translocation factor for these HMs decreases from Mn > Cd > Zn > Cu. Correlation analysis indicates that soil pH and various soil components are either negatively or positively correlated with Mn, Zn, and Cd accumulation; also, soil properties are correlated with Mn translocation from root to leaf. These findings may help evaluate HM accumulation and translocation mechanisms as well as artificially regulate HM uptake levels from soils to turnips.
    Root hemiparasitism in Malania oleifera (Olacaceae), a neglected aspect in research of the highly valued tree species
    Ai-Rong Li, Ping Mao, Yun-Ju Li
    2019, 41(05):  347-351.  doi:10.1016/j.pld.2019.09.003
    Abstract ( 86 )   HTML ( )   PDF (8995KB) ( 19 )   Save
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    Malania oleifera (Olacaceae) is a valued tree species, mostly because its seeds have high precious fatty acid content (particularly nervonic acid). However, seedling mortality rates are often high and regeneration of this tree has been problematic, which greatly hinders its utilization at a large scale. Cultivation difficulties of some tree species in the family Olacaceae have been attributed to their root hemiparasitic habit. Prompted by field observations and the taxonomic proximity of M. oleifera to root hemiparasites in Olacaceae, we hypothesized that tuberous structures observed on the roots of M. oleifera are parasitic organs known as haustoria. To test this hypothesis, we collected root samples from M. oleifera plants of various ages and growth conditions, investigated the morphological and anatomical features of tuberous structures and their connections to neighboring roots. Our analyses confirmed that M. oleifera are root hemiparasites. To the best of our knowledge, this is the first empirical report on root hemiparasitism in M. oleifera. Because life strategies of root hemiparasitic plants differ greatly from autotrophic plants, the root hemiparasitic habit needs to be taken into account for successful seedling regeneration of M. oleifera. This study establishes the foundation for investigations into a long-neglected but essential aspect in research of these highly valued tree species.