Abstract:Plant hydraulic traits can reflect the adaptability of plants to different water conditions. It is important to study the hydraulic traits of dominant plants in the special habitat of tropical coral islands for a deep understanding of the hydraulic adaptation strategies of tropical coral island plants, and for selecting suitable tree species for tropical coral island vegetation construction and restoration. Thus, the leaf and branch hydraulic traits of two representative dominant tree species in the habitat of tropical coral islands of China, i.e., Pisonia grandis and Scaevola sericea, were measured, and their hydraulic adaptation strategies were compared and analyzed. The results showed that the leaf embolism resistance, leaf turgor point and branch specific xylem conductivity of P. grandis were significantly higher than those of S. sericea, but the values of branch embolism resistance, leaf hydraulic conductance, sapwood density and leaf to stem area ratio were significantly lower than those of S. sericea. Furthermore, leaves of P. grandis were more resistant to embolism than branches, and were sensitive to water stress. Meanwhile, high water transport efficiency in branches of P. grandis provided sufficient water to ensure the high transpiration of the leaves. On the other hand, there was a significant hydraulic vulnerability segmentation between leaves and branches of S. sericea. The leaves of S. sericea could act as “safety valves” to protect branch hydraulic pathway from dysfunction. Pisonia grandis and S. sericea could adapt to the special habitats of tropical coral islands by coordinating the water transport efficiency and safety of leaves and branches and adopting different hydraulic strategies.

Abstract:The adaptability of plant growth in soil conditions on Chinese tropical coral islands is severely limited by the alkaline environment and soil nutrient deficiencies. Improving coral sand is essential to facilitate the rejuvenation of coral island vegetation and maintain the healthy development of the coral island ecosystem. In this study, we investigated the effects of four common soil amendment materials (vermiculite, perlite, biochar and calcium-based bentonite) on the physicochemical properties, nitrogen leaching and total nitrogen content of coral sand under the same gradient using an indoor soil column simulation test. The results showed that the application of biochar significantly reduced the pH of coral sand by 1.4% compared to the control (CK), and calcium-based bentonite, biochar, and vermiculite were able to significantly increase the cation exchange capacity of coral sand to 24.21, 10.43, and 9.43 times that of CK. Meanwhile, during the leaching process, nitrogen was rapidly leached out mainly in the form of nitrate nitrogen, and the application of biochar, calcium-based bentonite and vermiculite could not reduce the nitrogen leaching loss, but it could achieve the effect of promoting nitrogen fixation in coral sands by promoting nitrogen fixation through other pathways, which resulted in the reduction of total soil nitrogen loss under the addition of the three amendments versus CK by 40.92%, 27.32% and 25.09%, respectively. The utilization of biochar, vermiculite and calcium-based bentonite can therefore effectively improve the quality of coral sand soil, which is of great significance for the improvement of coral sand and the restoration of tropical coral island vegetation, among which biochar has the most significant improvement effect and is the ideal material for the improvement of coral sand.

Abstract:Based on the known distribution and 20 environmental factors, the potential distribution pattern of genus Paphiopedilum was simulated by using MaxEnt model under two different sharing economy scenarios (SSP1-2.6, SSP5-8.5) in the present (1970—2000) and the future (2081—2100). The contribution rate of climate factors was analyzed to find out the dominant climate factors affecting species distribution and their variation range. The results showed that the most suitable distribution areas of the genus were located in southeast Yunnan, southwest Guizhou, western Guangxi, southern Guangdong and northern Hainan. The main environmental factors affecting the distribution of the genus were annual precipitation, annual temperature range and precipitation in the driest season. With global warming, the suitable area had a tendency to expand northward and northwestward, gradually extending to the northwest subtropical direction. Under the SSP5-8.5 scenario, the high suitability area showed a large shrinkage. In the future climate scenarios, the distribution patterns of different populations are not consistent, and their distribution patterns respond to climate change trends. Therefore, different conservation strategies are proposed for species with different distribution trends.

Abstract:Mixed-species plantations composed of Eucalyptus and native tree species have great potential in improving stand productivity and ecosystem functions. In this study, we investigated leaf physiological, structural and chemical traits of three dominant native tree species (Machilus chinensis, Cinnamomum burmannii and Manglietia glauca) and Eucalyptus urophylla in Eucalyptus monocultures (EM) and four mixtures of Eucalyptus (EU) and native trees species (NS) with different mixed proportions (EU:NS=5:5, 6:4, 7:3, 8:2, respectively) in south China. The results showed that there was substantial interspecific variation in leaf traits among four dominant tree species. On average, M. glauca had the highest SLA, PPUE, A_mass, T_mass, N_mass and P_mass, indicating that M. glauca adopts resource acquisition strategies. E. urophylla had the lowest SLA, PPUE, A_mass, T_mass, N_mass, P_mass but the highest PNUE, indicating that E. urophylla occupies characteristics typical of fast-growing and nutrient-conserving in order to adapt nutrient-poor environments. There was nearly no overlap between M. glauca and E. urophylla in leaf traits, such as SLA, N:P, A_mass, T_mass, PPUE and N_mass, indicating that M. glauca and E. urophylla were highly complementary in the leaf resource use. Manglietia glauca may be an ideal candidate tree species for establishing mixed plantations of Eucalyptus and native tree species. At the species level, N_mass of M. glauca, P_mass of M. chinensis, A_mass and PPUE of C. burmannii in dry season increased with the mixed proportion of native species, but leaf traits of four dominant tree species were generally not affected by the mixed proportion as a whole. At the stand level, SLA, PPUE, A_mass, T_mass and N:P in mixtures of Eucalyptus and native species were significantly higher than those in Eucalyptus monocultures. Thus, plantations established with Eucalyptus and high diversity native tree species can improve the light capture and photosynthetic capability from the stand level, but also aggravate the phosphorus limitation of plant growth. Overall, it was suggested that native species with complementary resource use to Eucalyptus and capability of optimizing phosphorus biogeochemical cycle of mixed plantations should be prioritized in designing and improving the Eucalyptus plantations in south China.

Abstract:Mangrove species are a group of trees, shrubs or herbs that grow in intertidal zones of tropical and subtropical coasts. They are generally categorized into true mangrove and semi-mangrove species according to their distribution. Understanding the eco-physiological strategies of light adaptation of mangrove species is of important theoretical significance to revealing the community assembly mechanisms of mangrove forests, and can provide scientific guidance for the reconstruction and transformation of mangrove forests. In order to reveal the physiological and ecological strategies to light conditions of mangrove plant species and provide theoretical guidance for optimal assembly of mangrove community structure, the light response characteristics in leaves of eight mangrove seedlings, such as Sonneratia apetala, Kandelia candel, Bruguiera gymnorrhiza, Aegiceras corniculatum, Acanthus ilicifolius, Acrostichum aureum, Heritiera littoralis and Hibiscus tiliaceus, grown under different light intensities, including 100%, 45%, 30%, and 10% of natural sunlight, were studied using shading control experiment. The results showed that the effects of growth light intensities on the photosynthetic light response characteristics were different among mangrove species. Shading significantly increased the maximum net photosynthetic rate (P_max) of K. candel and B. gymnorrhiza, but had no significant effects on P_max of other mangrove species. Kandelia candel had a higher P_max under 45% light intensity treatment, while B. gymnorrhiza had higher P_max under 45% and 30% light intensities. With the decrease of growth light intensity, the light saturation point of leaves of K. candel seedlings significantly increased, the light compensation points of B. gymnorrhiza, Acanthus ilicifolius and Acrostichum aureum appeared a decreasing trend, the apparent quantum yield of B. gymnorrhiza and Acrostichum aureum showed an increasing pattern, and the dark respiration rate of B. gymnorrhiza and Acrostichum aureum decreased. Therefore, it was suggested that B. gymnorrhiza, Acanthus ilicifolius and Acrostichum aureum are suitable for planting under forest with high canopy density, while S. apetala, K. candel, Aegiceras corniculatum, Heritiera littoralis and Hibiscus tiliaceus are suitable to be planted as upper layer species in mangrove forests or planted under forest with low canopy density.

Abstract:Rhododendron pudingense is a new species in genus Rhododendron. The population structure and spatial distribution pattern of R. pudingense were analyzed by means of smoothing technique and mean ratio in four distribution regions first discovered in Guizhou Province. The results showed that there were 1113 indivduals, including 611 in Qinglong, 308 in Wangmo, 83 in Puding and 111 in Zhenning. The population of R. pudingense was mainly concentrated in the first and second age classes. The survival curves of population in Qinglong, Wangmo and Puding showed Deevey-Ⅱ type, while that in Zhenning showed Deevey-Ⅲ type. The distribution patterns of all populations were aggregated. The population of R. pudingense in the four distribution areas belonged to the growth type. However, due to the small number of R. pudingense in the distributed forest community, it was in a subordinate position in species composition of community, the vulnerability of its habitat caused by a large amount of bare bedrock in the growth area, the new species of R. pudingense might be eliminated by other species in the forest community if human disturbance measures are not strengthened to protect R. pudingense.

Abstract:Ottelia cordata, a wild plant under State second-class protection, likes to be grown in clean water, and is extremely sensitive to environmental changes. It is one of the key indicator species for testing wetland environment and climate change. In China, it is only distributed sporadically in volcanic lava wetland in northern Hainan, the survival condition is not optimistic. The study of potential habitat selection and spatial pattern evolution of O. cordata population will help strengthen the conservation of endangered species and the restoration as well as the management of wetland ecosystem. Based on GIS platform and MaxEnt model, combining with climate, topography and soil factors, the environmental limiting factors of O. cordata population and the evolution pattern of potential suitable habitat in the context of climate change were studied. The results showed that O. cordata population was sensitive to temperature difference and precipitation change. Besides, isothermality, precipitation in the coldest quarter, type of soil and annual precipitation were key environmental factors affecting the distribution of O. cordata population. Under the background of climate change from the middle Holocene to current to 2070s, the area of suitable habitat of O. cordata decreased first and then increased, and the distribution center showed a transfer pattern from southwest to northeast to southwest. Under the future climate scenarios, the highly and moderately suitable habitats were decrease, while the low suitable habitats will increase. The new habitats will appear in the southern region, and the suitable habitats will decrease in the northeast, northwest and southwest. Therefore, the potential habitat selection and spatial distribution characteristics of O. cordata population were discussed from the perspective of climate environment, which could provide reference and theoretical basis for endangered species conservation, wetland management and biodiversity maintenance.

Abstract:To further understand the growth development characteristics and survival strategies of semi-parasitic plants, the biomass allocation pattern and allometric growth characteristics of Taxillus nigrans, a typical southwestern semi-parasitic plant, were studied, and regression models of individual biomass (TB) with length (L) or base diameter (BD) as independent variables were established: TB=0.0027L^2.3077, TB=134.99BD^3.334, and TB= 4.35L+8.34BD–183.85. The results showed that the biomass allocation ratio of T. nigrans at juvenile stage and the nonjuvenile stage was leaf > stem > haumator and stem > leaf > haumator, respectively. At juvenile stage, there was an isometric relationship between haustoria and shoots (leaf, stem, and fruit). At nonjuvenile stage, the allometric growth relationships among the organs of T. nigrans were not consistent with the allometric biomass partitioning theory (APT), the allometric exponent (1.01) between leaves and haustoria was significantly higher than the predicted value from APT (0.75) (P<0.001), and there was a significant allometric relationship between stems and haustoria (P=0.001). The unique biomass allocation patterns and allometric growth characteristics of T. nigrans were beneficial to its adaptation to parasitic life.

Abstract:In order to understand the characteristics of soil seed bank in Eucalyptus plantations, the storage, vertical distribution and similarity of seed bank in E. urophylla×E. grandis plantations with different age were analyzed. The results showed that the active soil seed storage of 1-2-year-old E. urophylla×E. grandis plantations were the highest, which was significantly higher than other plantations, followed by 3-4-year-old E. urophylla×E. grandis and Pinus massoniana plantation, and that of Cunninghamia lanceolata plantation was the lowest, which was significantly lower than other plantations. The soil seed bank storage of E. urophylla×E. grandis plantations decreased rapidly along the stand age. The most abundant plant species in soil seed bank were mixed forest and P. massoniana plantation, which were significantly larger than other plantations. In E. urophylla×E. grandis plantations, the number of plant species in soil seed bank increased at first and then decreased with the increase of stand age. Among all forest types, the seed bank density of 0-5 cm soil layer was significantly higher than that of 5-10 cm soil layer. The co-existed specie number of seed banks and understory in the mixed forest was the largest, followed by P. massoniana plantation and the least was C. lanceolata plantation. With the increase of stand age, the number of coexisting plant species in E. urophylla×E. grandis plantation also increased at first and then decreased. The soil seed bank similarity coefficients of Jaccard (CJ) and Sorensen (CS) of E. urophylla×E. grandis plantations were increased at first and then decreased along stand age. Therefore, appropriate interplanting (retention) of native tree species in the management of fast-growing Eucalyptus plantations could increase the biodiversity and stability of ecological functions of forest ecosystems.

Abstract:The aim was to screen the superior germplasm resources of Hemerocallis citrina. The yield formation and quality of 20 H. citrina germplasms were evaluated by using correlation analysis, stepwise regression, path analysis and TOPSIS analysis. The results showed that variations in agronomic, yield and quality traits among different H. citrina germplasms were rich with coefficient of variation (CV) from 1.9% to 75.6%. The CV of bud chroma a^* (redness) was the highest (75.6%), followed by total flavone content (67.9%) and bud weight (41.0%), and water content of bud was the lowest (1.9%). Bud weight, bud diameter and flower moss number were significantly correlated with yield with CV of 0.737, 0.583 and 0.517, respectively. The correlation among nutrient quality traits was weak, while the correlation between appearance color index and some nutritional quality was extremely significant. The results of stepwise regression and path analysis suggested that floral bud weight and scape number were the main determinant of yield formation across all investigated germplasms, with decision coefficients of 0.534 and 0.239, respectively. The combination weights of nutritional quality and color parameters, calculated by using the method of coefficient of variation-entropy weight, were 0.523 and 0.477, respectively, and the results could effectively distinguish the best quality rank of different germplasm resources with application of combined the TOPSIS analysis method. Two-dimensional scatter distribution diagrams, a visualized overall assessment result simultaneously considering yield and quality, could be derived for use in the high yield and bud quality quickly screening of H. citrina.

Abstract:Casein kinase (CK), a ubiquitous Ser/Thr protein kinase, plays an important role in the whole physiological process and signal transduction pathway of plants through regulating activity and stability of target protein. The CK gene family in Jatropha curcas was identified from J. curcas genome based on the BLAST method. The results showed that a total of seven CK1s, five PS-CK1s, three CK2-αs, and two CK2-βs were identified from J. curcas genome, and the four subfamily members owned family-specificity in amino acid length, isoelectrical point, and exon number. Domain and motif analysis revealed that all of CK1 contain N-terminal conserved kinase domain, and the kinase activation loop (A-loop), ATP-binding core motif, and nuclear localization signal peptide (NLS) were identified in its interior. A plant-specific casein kinse 1-5 gene, named JcPS-CK1-5, was cloned. qRT-PCR analysis showed that JcPS-CK1-5 gene was a low temperature-induced gene in both leaves and roots, and might be involved in cold resistance of J. curcas. A prokaryotic expression vector pET-32a-JcPS-CK1-5 was constructed and transformed into Escherichia coli BL21(DE3). A band of 81.6 kD was obtained, which was consistent with the expected weight. Therefore, these would provide a reference for studying the functional identification of CK gene and the stress signal transduction mechanism in J. curcas.

Abstract:Flavonoids play an important role in plant resistance to low temperature stress. To reveal the effects of low temperature on flavonoid synthesis in leaves of Phyllostachys edulis, the content of flavonoid in leaves of bamboo seedlings at different growth stages and under low temperature stress was determined by spectrophoto- metric method, the key enzyme genes of early biosynthesis of flavonoid in bamboo were identified by bioinfor- matics methods and their expression patterns were analyzed using qPCR. The results showed that the flavonoid content increased at first and then decreased, while that in the functional leaves increased under low temperature and reached significant level at 8 hours. There were a total of 29 members, belonging to three gene families, involved in early biosynthesis of flavonoid in P. edulis, including 20 chalcone synthase genes (PeCHSs), eight chalcone isomerase genes (PeCHIs) and one flavanone-3-hydroxylase gene (PeF3H1), the promoters of these genes all contained regulatory elements in response to low temperature and other abiotic stress responses. The PeCHSs tended to be expressed in roots and leaves, while PeCHIs expressed constitutively. Only the expression trend of PeCHS1 was consistent with the content of flavonoid in P. edulis leaves at different growth stages, while six key enzyme genes (3 PeCHSs, 2 PeCHIs and PeF3H1) were upregulated continuously in functional leaves under low temperature, which was consistent with the change trend of flavonoid content. Therefore, Phyllostachys edulis might respond to low temperature stress by increasing the expression of genes involved in early biosynthesis of flavonoid.

Abstract:In order to understand the effect of light on ash accumulation of Ardisia giantifolia, four light intensities (100%, 60%, 40% and 20% natural light intensity) and four light qualities (green, white, blue and red light) were set by using sunshade net and film, the response characteristics of height, basal diameter and biomass of A. giantifolia under different treatment conditions was analyzed, and the relationship between ash content and growth indexes was studied. The results showed that with the weakening of light intensity, the ash content of A. giantifolia decreased under green light with the decrease of light intensity, showing a “low-high-low-high” change trend under white light. Moreover, there was no significant change under blue light or red light. The ash content of A. giantifolia was the lowest under white light and 100% light intensity, showing significantly differences with that of the rest light intensity. At 60%, 40% and 20% natural light intensity, light quality had no significant effect on ash content of A. giantifolia. The ash content had no significant correlation with plant height, basal diameter and biomass of A. giantifolia. With the decrease of light intensity, the plant height, basal diameter and biomass of A. giantifolia increase, and reach maximum under white light. Therefore, it was suggested that light had effect on ash accumulation and growth index of A. giantifolia, and it was necessary to choose the forest type with proper shade intensity or canopy density when planting.

Abstract:Hevea brasiliensis seeds generally cultivated in sand bed. Sand is a non-renewable resource. In order to choose a suitable seed cultivation method to replace the dependence on sand, the growth vigor, physiological indexes and nutrient contents of H. brasiliensis seedlings were compared, when the first leaf was stable through hydroponic, airborne and sand cultures. The results showed that the above-ground height, stem diameter and leaf area of hydroponic seedlings had the best growth, and the strong seedling index and biomass were the highest, but the roots were too long and relatively thin. The contents of soluble sugar, malondialdehyde, free proline and superoxide dismutase activity were low in the leaves, stems and roots of hydroponic culture. There was no significant difference in the contents of chlorophyll, carotenoid in leaf and stem and root activity between hydroponic culture and airborne culture, which were all higher than sand culture. The contents of nitrogen and phosphorus in leaf, stem and root of hydroponic culture were the lowest, while those of sand culture were the highest. The content of potassium in roots and stems of hydroponic seedlings was higher, and the content of potassium in leaves was not significantly different from that in airborne culture and sand cultivation. The content of potassium in leaves, stems and roots of airborne culture was the lowest. Hydroponic culture can promote the growth of seedlings, reduce drought stress and improve nutrient utilization, but it is necessary to regulate the root system and build a good root mass. The seedling growth in airborne culture is weak, so the method needs to be further perfected.

Abstract:Handroanthus impetiginosus, introduced from South America and Central America, had widely used as ornamental tree in southern China, which had rich germplasm resources. However, the resources of introduction is complex while the work of improved variety breeding is lagging. In order to reveal genetic variation of H. impetiginosus populations, the genetic diversity and population genetic structure of 72 samples from 12 populations collected from 6 cities in Guangdong Province were analyzed. The results showed that a total of 123 alleles were amplified by 9 pairs of SSR primers with average PIC of 0.754, indicating that the H. impetiginosus germplasm had high genetic diversity. All 12 populations of H. impetiginosus also had high genetic diversity, the average effective alleles between populations was 3.272, and the average Shannon information index was 1.159. AMOVA analysis showed that genetic differentiation among populations was relatively low, while that within populations was high. The overall genetic differentiation coefficient of populations was 0.077, which was in the medium degree. Based on the Structure analysis, PCoA analysis and NJ clustering analysis, 12 populations of H. impetiginosus could be divided into 2 groups, and the grouping results had certain similarity, indicating that the genetic structure of tested populations was not complex. These would provide a theoretical basis for the utilization of germplasm resources, genetic variation and scientific breeding for H. impetiginosus.

Abstract:In order to understand the causes of fruit quality differences in Momordica charantia, the contents of cell wall components and related enzyme activities in thick flesh-type ‘LX1-3’ and thin flesh-type ‘ZK54’ were studied during fruit development. The results showed that diameter (FD), lumen diameter (FLD)，pulp thickness (PT), fresh weight (FFW) and fresh weight (FDW) of fruit in ‘LX1-3’ were all higher than those in ‘ZK54’ at 17 days after flowering (DAF). The contents of cell wall components and related enzyme activities were different among cultivars. the content of water-soluble pectin in ‘LX1-3’ was higher than that of ‘ZK54’, and it was significantly positively correlated with PT, FFW, FDW. The contents of hemicellulose (HCE) and cellulose (CE) in ‘LX1-3’ were higher than those in ‘ZK54’ at 17-23 DAF. The activities of β-Gal and β-Xyl of both cultivars at 3 DAF were higher than those at the other three stages. The variation trend of PG, β-Gal and pectinase activities was consistent with that of ionic pectin and covalent pectin. The activities of β-Gal, β-Xyl and cellulase had (extremely) significantly negatively correlated with 5 growth traits, as well as PG with FD, FLD and PT. Therefore, cell wall components and enzyme activities were closely related to fruit development. β-Xyl and β-Gal played major roles in early fruit development, while HCE and CE had great influence on middle and later fruit developments.

Abstract:Light is one of the most important critical factors that regulate plant growth and development. Photoreceptors perceive the changes in light intensity, direction and photoperiod to regulate the entire lifecycle of plants further. Phytochrome A (PHYA) is the unique far-red light receptor in plants. PHYA is synthesized in the cytosol in the dark; upon light illumination, PHYA is translocated into the nucleus and degraded rapidly. PHYA precisely regulates the transcription network via multiple pathways. Furthermore, post-translational modifications have been shown to play an essential role in modulating the stability and activity of PHYA. The research progress on PHYA-mediated transcription and post-translational modifications of PHYA were summarized, and the application prospects of PHYA in molecular design breeding in crops were also discuss.