Abstract:To investigate the changing trend in plant diversity along the altitude gradient and understand the species replacement rules among communities, the vegetation communities on the southern slope of Nanling National Nature Reserve were selected as the research object. From July to August 2018, plots were established at 100 m intervals along the altitude for individual tree surveys. The vertical distribution characteristics of the species composition, species diversity and species renewal rate of the tree layer vegetation within the altitude range of 300-1 800 m were analyzed. The results showed that with the increase of altitude, the species diversity of the tree layer presented a double-peak curve change, and the dissimilarity among communities also increased, gradually increasing with the expansion of the altitude difference. In the study area, the species renewal rate showed no obvious change along the vertical gradient. The production strategies of communities at different altitudes were different. In the low-altitude area, it was mainly characterized by medium species number + few individuals + high individual biomass; in the medium-altitude area, it was mainly characterized by many species+ medium individuals + medium biomass; and in the high-altitude area, it was mainly characterized by few species + many individuals + low individual biomass. Increasing species diversity can provide more ecological niches and higher resistance stability for the ecosystem, which is beneficial to the protection of rare and endangered plants and key protected plants that are sensitive to environmental changes.

Abstract:The natural variation of nitrogen (N) isotope composition (δ¹⁵N) in leaves has been used to study the N acquisition and utilization strategies of epiphytic vascular plants. However, the ¹⁵N fractionation effect that occurs during N absorption, transport, and assimilation in plants often affects the reliability of research results based on the ¹⁵N natural abundance method. Whether ¹⁵N fractionation occurs in epiphytic plants and leads to δ¹⁵N differences among different organs, as well as whether leaf δ¹⁵N can be used as a reliable proxy for whole-plant δ¹⁵N, remains unclear. This study took epiphytic plants in the subtropical evergreen broad-leaved forest of Ailao Mountain as the research object, analyzed the δ¹⁵N variation characteristics of the whole plant and each organ, and the relationship between the δ¹⁵N difference among organs and other traits. The results showed that the δ¹⁵N of leaves (–3.48‰), stems (–3.47‰), and roots (–2.25‰) of epiphytic plants were all negative, indicating that they mainly relied on ¹⁵N-depleted N sources from atmospheric deposition. Except for Oreocharis longifolia, the other epiphytic plants (Cautleya gracilis, Lepisorus scolopendrium, and Pleione hookeriana) showed N isotope fractionation effects among leaves, stems, and roots (leaf-root: –1.23‰, leaf- stem: –0.62‰, stem-root: –1.10‰), but usually lower than those of terrestrial plants. In addition, the leaf-root ¹⁵N fractionation value of epiphytic plants was significantly negatively correlated with leaf δ¹³C (r=–0.57; P < 0.01) and root δ¹³C (r=–0.57, –0.50; P < 0.05), which may imply their high sensitivity to water deficiency. The δ¹⁵N of epiphytic vascular plant leaves was significantly correlated with whole-plant δ¹⁵N (R_adj.²=0.526, P < 0.01), confirming that leaf δ¹⁵N can be used as a proxy for whole-plant δ¹⁵N. This provides an important basis for using leaf δ¹⁵N to explore the N acquisition strategies and ecological adaptation mechanisms of epiphytic plants.

Abstract:Vegetation is an important part of terrestrial ecosystems, and the study of the spatial and temporal variation characteristics of fractional vegetation cover (FVC) and its influencing factors is of great significance for regional ecological conservation and management. By using the Google Earth Engine (GEE) platform and pixel binary model, the FVC of Hainan Island from 2000 to 2020 was calculated. The spatial and temporal variability of the FVC was analyzed using the Theil-Sen Median trend analysis, the Mann-Kendall test and the Hurst index. Finally, structural equation modelling and geographic detector were used to analyze the response mechanisms of the spatial distribution characteristics of FVC in Hainan Island to climate, topography and human activities. The results showed that FVC in Hainan Island had a significant increasing trend in the past 21 years, with a growth rate of 0.025/10 a. The FVC changes were mainly not significantly improved and extremely significantly improved, accounting for 35.34% and 29.38% of the study area. In the future, the vegetation changes was dominated by weak counter-persistent increase and weak persistent increase. Land use type, elevation, slope, and population density were the dominant factors affecting the spatial distribution of FVC. Interaction type was dominated by bivariate enhancement and nonlinear enhancement. The interaction between land use type ∩ population density and land use type ∩ elevation was stronger, with q values of 49.56% and 48.38%. Therefore, it might provide a theoretical basis for the vegetation restoration policy on Hainan Island.

Abstract:To clarify the adaptability of ferns to environmental changes, thirty typical terrestrial fern species were selected from tropical and subtropical regions, measured their leaf (pinna) morphological structure, mechanical resistance and water relationship traits, and used the corresponding traits of 54 woody angiosperms in the same region as a reference. Combined with phylogenetic and trait network analysis, the correlations of leaf traits in ferns were analyzed. The results showed that compared with woody angiosperms, ferns had lower puncture force (F_p), weaker embolism resistance (P50_leaf), and higher turgor loss point (Ψ_tlp), indicating that ferns had lower resistance to mechanical damage and water stress. The saturated water content (SWC) of fern leaves was significantly positively correlated with Ψ_tlp and P50_leaf, suggesting that ferns balanced their relatively weak drought tolerance by increasing leaf water storage capacity; the SWC of angiosperm leaves was not correlated with P50_leaf. The F_p of angiosperm leaves was significantly positively correlated with leaf mass per area, leaf thickness and maximum leaf hydraulic conductance; the F_p of ferns was only significantly positively correlated with leaf thickness, and the two evolved in concert. Therefore, different plant groups have diverse strategies for adapting to the environment.

Abstract:To deeply understand the effects of different moisture and straw addition on the composition, structure and diversity of soil microbial phosphorus cycling functional gene communities in paddy fields, typical paddy soil in Jianghan Plain was selected as the research object. Four treatments were set up including simulated dry land, dry land with straw addition, paddy field and paddy field with straw addition. The samples were incubated at a constant temperature of 25 ℃ for 30 days. The community composition and diversity of soil bacteria and fungi and the responses of dominant bacterial groups to changes in soil moisture and straw addition were analyzed by using Illumina Miseq high-throughput sequencing technology. The results showed that the richness and diversity of bacterial communities in simulated dry land were higher than those in paddy fields; while the richness and diversity of fungal communities in simulated paddy fields were higher than those in dry land. Straw addition was conducive to increasing the richness of soil phoD gene communities, while moisture had a relatively weak effect on its richness. Redundancy analysis indicated that moisture had a greater impact on the structure of soil bacterial communities; while straw addition had a greater impact on the structure of soil fungal communities. At the phylum level, soil bacteria and fungi were not affected by moisture and straw addition. The dominant bacteria in the soil bacterial communities of each treatment were Proteobacteria and Acidobacteria (relative abundance > 15.0%); the dominant fungi in the soil fungal communities were Ascomycota and Basidiobolomycota (relative abundance > 5.0%). Therefore, soil moisture and straw addition have significant effects on the composition and structure of soil phosphorus cycling microbial communities in paddy fields.

Abstract:To further understand the growth strategies of semi-parasitic species and their interactions with their host species, the leaf functional traits of two common Loranthaceae species in the Chengdu Plain, China, Taxillus nigrans and Scurrula parasitica, were examined with their four primary host species, Chimonanthus praecox, Magnolia grandiflora, Osmanthus fragrans, and Ligustrum lucidum, in the urban areas of Chengdu to identify variations in leaf functional traits among the mistletoe species across different categories and types of hosts. Furthermore, a comparative assessment of these traits was conducted under diverse parasitism scenarios, encompassing both parasitized and non-parasitized host branches. Among mature mistletoe plants, there were significant differences in flavonoid content, leaf nitrogen content, leaf thickness, specific leaf area, and leaf dry matter content among different host plants. The nitrogen content in the leaves of mature mistletoe individuals parasitizing on the nitrogen-fixing host species, Robinia pseudoacacia, was significantly lower than that parasitizing on the non-nitrogen-fixing host species, M. grandiflora. However, except for the flavonoid content in mistletoe leaves parasitizing on shrubs being significantly higher than those on trees, host type (evergreen or deciduous, broadleaved or coniferous, tree or shrub) did not significantly affect leaf functional traits of the mistletoe plants, including leaf nitrogen content, chlorophyll content, specific leaf area, dry matter content, and leaf thickness. Mistletoe leaves on different host plants exhibited diverse leaf economic spectrum characteristics. Those on M. grandiflora displayed a "quick investment-return" strategy, whereas those on Prunus cerasifera 'Atropurpurea' and Chaenomeles speciosa followed a "slow investment-return" strategy. Meanwhile, mistletoes on other host plants did not exhibit typical leaf economic spectrum traits. For the juvenile individuals, the leaf chlorophyll and leaf nitrogen contents of T. nigrans were significantly higher than those of mature individuals. The responses of leaf chlorophyll content, nitrogen content, thickness, and the specific leaf area of proximal and distal leaves infected on host plants O. fragrans, M. grandiflora, and C. praecox to the mistletoe infection were not influenced by the relative position of the mistletoes. Therefore, it would be essential to understand the survival strategies of semi-parasitic plants and their interactions with host species.

Abstract:To grasp the application status of tree species in the green spaces of the central urban area of Guangzhou, The composition and structural characteristics of the trees in 200 sample points selected from six types of green spaces through ArcGIS, including park and greenbelt, Land for square, Unit and residential area attached green space, regional green land, green area for environmental protection and Road planting in the central urban area of Guangzhou were systematically analyzed. The results showed that a total of 3 238 trees were recorded in these green spaces, belonging to 191 species of 136 genera and 60 families. Among them, more than 30 species such as Ficus microcarpa and Terminalia neotaliala were dominant tree species. The species richness of regional green spaces was the highest, while that of square green spaces and road green spaces was the lowest. The application of native tree species was generally insufficient, with the proportion of regional green spaces being relatively high and that of square green spaces being the lowest. The age and diameter structure of the trees were relatively reasonable, with mature trees being the most common, followed by old trees; large trees were the least. The average diameter of square green spaces was the largest, while that of regional green spaces was the smallest. The tree height structure was distinct, with medium-sized trees being the most common. The average height of regional green spaces was the highest, while that of park green spaces was the lowest. The crown width structure was dominated by medium-sized trees, with protective green spaces and road green spaces having the largest average crown width and park green spaces having the smallest. The overall health of the trees was good, with grade Ⅰ and grade Ⅱ healthy trees being the most common. Square green spaces had the best condition, while regional green spaces were relatively poor. Therefore, it is suggested that in future planning, the application of native plants should be increased, the selection of tree species should be enriched, the structure of tree communities should be optimized, and green space management should be strengthened. At the same time, attention should be paid to the protection of large trees and ancient and famous trees to improve and optimize the construction quality of urban green spaces in Guangzhou.

Abstract:The seeds of Polygonatum cyrtonema have a comprehensive dormancy, which seriously restricts its production and industrial development. The seed dormancy was broken by using warm sand storage treatment, and the changes in metabolomics, transcriptomics at six stages of dormancy release and germination were analyzed. The results showed that amino acid metabolism and synthesis played a key role in the process of dormancy release and germination of P. cyrtonema seeds. The correlation between five metabolites (l-threonine, l-glutamic acid, indole, S-adenosylmethionine and choline) and ten differentially expressed genes in the amino acid metabolism and synthesis related pathways was analyzed. Adenosine diphosphate, alanine-tryptophan, coumarin 151, loniceroside, N-methylthreonine and sedoheptulose-7-phosphate were identified as important characteristic molecules for the germination of P. cyrtonema seeds, and ten related genes were also identified. The expression trends of some genes were verified by qPCR. The key metabolic pathways and gene regulatory networks were revealed for the release of seed dormancy of P. cyrtonema from the levels of metabolite changes and molecular mechanisms, which would provide a theoretical basis for further understanding the molecular mechanism of seed dormancy release and optimizing the germination conditions of P. cyrtonema seeds.

Abstract:By using the published genome of Begonia peltatifolia and the transcriptome data of different tissues, the miniature inverted repeat transposable elements (MITEs) in the genome were identified and classified, and their distribution characteristics, insertion preferences and expression states in the genome were analyzed. The results showed that a total of 925 MITEs copies were identified, belonging to four superfamilies: hAT, Mutator, PIF/Harbinger and Tc1/Mariner, among which the hAT family accounted for the highest proportion, reaching 70.49%. The analysis of insertion positions revealed that 59.5% of the MITEs elements were located in the flanking regions (upstream and downstream 5 kb, respectively) or within genes, while the other approximately 40% of the MITEs were located in telomeres, centromeres or other gene-sparse regions; moreover, the number of MITEs copies located in the 5′ flanking region of genes was approximately twice that in the 3′ flanking region, and the insertion hotspots were within 1000 to 3000 base pairs. These co-transcribed genes were mainly related to secondary metabolism, energy synthesis and transport functions; those inserted into the genes were mainly distributed in non-coding regions (UTRs and introns), and no MITEs insertions were observed in exons. The functional enrichment of the genes with MITEs insertions was mainly related to functions, protein synthesis and the expression of genetic information. A total of 68 MITEs co-transcriptions were detected in the transcriptome data of different tissues of B. peltatifolia, with very little expression in vegetative organs such as pedicels and leaves. They were expressed more in reproductive organs such as flowers and active meristems of roots. Among the transcripts containing MITEs, 80.8% had lower expression levels or no significant difference compared with their isoforms, while only 19.1% had increased expression levels. Therefore, these would lay the foundation for studying the epigenetic regulation mechanism of transposons in drought tolerance and provides genetic resources for the breeding of drought-tolerant Begonia varieties.

Abstract:To screen the suitable cultivation substrate for the high-quality seedling production of Cyclocarya paliurus, container seedling cultivation was adopted to determine the effects of four cultivation substrates (J1, J2, J3 and J4) on the survival rate, growth indicators and physiological indicators of seedlings. The results showed that the survival of seedlings cultivated in J1 was 100%, which was 2.25 times that of J2. Moreover, the seedlings cultivated in J1 had better growth indicators, such as plant height, leaf area and ground diameter than those in the other three substrates. The water content of seedlings cultivated in J2 reached 67.25%, and the content of soluble sugar was only 2.33%. The content of Ca in the seedlings was the highest, while the content of Na was the lowest. The content of K and Mg in the leaf of seedlings cultivated in J4 was the highest. The translocate factor of four mineral elements in the leaves cultivated in J1 was significantly lower than that in the other three substrates. Compared with J2, the activities of SOD, POD and CAT and the content of MDA in the leaves of seedlings cultivated in J1 decreased by 92.36%, 80.98%, 87.21% and 81.51%, respectively, while the activity of PPO was 13.30 times that of J2. Through the membership function and principal component analysis, the function values were in the order of J1 > J4 > J3 > J2, and the contribution rate of J1 to the seedling cultivation was 89.71%. Mantel's analysis showed that the survival and growth indicators of seedlings were significantly correlated with water content and SOD activity. Therefore, the substrate mixed with peat soil and perlite at a volume ratio of 10:1 is a suitable cultivation substrate for C. paliurus seedlings, which has a high survival rate and vigorous plant growth.

Abstract:Soil fertility is a comprehensive indicator of soil physical, chemical and biological properties and is an important factor determining forest productivity. Michelia macclurei is an important native tree species in southern China. Due to its fast growth, excellent wood quality and good soil improvement effect, it is often used as an associate tree species to mix with timber tree species such as Pinus massoniana, Cunninghamia lanceolata and Eucalyptus to improve soil fertility and increase forest productivity in artificial forests. However, the impact of M. macclurei on soil physical, chemical and biological properties in artificial forests is still unclear, and the mechanism of its improvement of soil fertility is still lacking. The current research status of M. macclurei in improving soil fertility in artificial forests from three aspects were systematically reviewed: soil physical and chemical properties, soil microbial community characteristics and soil nutrient cycling, and preliminarily clarifies the key pathways for improving soil fertility. At the same time, through integration and quantitative analysis methods, the effects of pure forests and M. macclurei mixed forests on soil fertility in artificial forests at two soil depths of 0-20 cm and 20-40 cm are studied. It was believed that M. macclurei had the potential to be a soil improvement tree species, and the potential mechanism of its improvement of soil fertility is revealed.

Abstract:Flower induction is an important physiological process in fruit trees. Tropical fruit trees, which grow in the tropical regions as evergreen species, exhibit different growth habits compared to temperate deciduous species and are more stimulated to flower by environmental. The recent advances in the field of tropical fruit tree flowering, including the effects of genetic, exogenous and endogenous factors were summarized. It focuses on the regulation of flowering events by key genes, microRNAs (miRNAs), long non-coding RNAs (lncRNAs), alternative splicing, and epigenetic modifications. The review also discusses the differences and similarities of flower formation in the tropical fruit trees relative to temperate fruit trees, considering factors such as temperature, water, light, endogenous hormones, carbohydrates, and mineral nutrition. Finally, drawing on the relevant cutting-edge research from around the world, this review offers outlooks aimed at providing valuable references for further understanding of the flowering mechanism of tropical fruit tree.