The adaptive evolution of Quercus section Ilex using the chloroplast genomes of two threatened species.

Chloroplast (cp) genome sequences have been extensively used for phylogenetic and evolutionary analyses, as many have been sequenced in recent years. Identification of Quercus is challenging because many species overlap phenotypically owing to interspecific hybridization, introgression, and incomplete lineage sorting. Therefore, we wanted to gain a better understanding of this genus at the level of the maternally inherited chloroplast genome. Here, we sequenced, assembled, and annotated the cp genomes of the threatened Quercus marlipoensis (160,995 bp) and Q. kingiana (161,167 bp), and mined these genomes for repeat sequences and codon usage bias. Comparative genomic analyses, phylogenomics, and selection pressure analysis were also performed in these two threatened species along with other species of Quercus. We found that the guanine and cytosine content of the two cp genomes were similar. All 131 annotated genes, including 86 protein-coding genes, 37 transfer RNA genes, and 8 ribosomal RNA genes, had the same order in the two species. A strong A/T bias was detected in the base composition of simple sequence repeats. Among the 59 synonymous codons, the codon usage pattern of the cp genomes in these two species was more inclined toward the A/U ending. Comparative genomic analyses indicated that the cp genomes of Quercus section Ilex are highly conserved. We detected eight highly variable regions that could be used as molecular markers for species identification. The cp genome structure was consistent and different within and among the sections of Quercus. The phylogenetic analysis showed that section Ilex was not monophyletic and was divided into two groups, which were respectively nested with section Cerris and section Cyclobalanopsis. The two threatened species sequenced in this study were grouped into the section Cyclobalanopsis. In conclusion, the analyses of cp genomes of Q. marlipoensis and Q. kingiana promote further study of the taxonomy, phylogeny and evolution of these two threatened species and Quercus.

New insights on the phylogeny, evolutionary history, and ecological adaptation mechanism in cycle-cup oaks based on chloroplast genomes.

Cycle-cup oaks (Quercus section Cyclobalanopsis) are one of the principal components of forests in the tropical and subtropical climates of East and Southeast Asia. They have experienced relatively recent increases in the diversification rate, driven by changing climates and the Himalayan orogeny. However, the evolutionary history and adaptive mechanisms at the chloroplast genome level in cycle-cup oaks remain largely unknown. Therefore, we studied this problem by conducting chloroplast genomics on 50 of the ca. 90 species. Comparative genomics and other analyses showed that Quercus section Cyclobalanopsis had a highly conserved chloroplast genome structure. Highly divergent regions, such as the ndhF and ycf1 gene regions and the petN-psbM and rpoB-trnC-GCA intergenic spacer regions, provided potential molecular markers for subsequent analysis. The chloroplast phylogenomic tree indicated that Quercus section Cyclobalanopsis was not monophyletic, which mixed with the other two sections of subgenus Cerris. The reconstruction of ancestral aera inferred that Palaeotropics was the most likely ancestral range of Quercus section Cyclobalanopsis, and then dispersed to Sino-Japan and Sino-Himalaya. Positive selection analysis showed that the photosystem genes had the lowest ω values among the seven functional gene groups. And nine protein-coding genes containing sites for positive selection: ndhA, ndhD, ndhF, ndhH, rbcL, rpl32, accD, ycf1, and ycf2. This series of analyses together revealed the phylogeny, evolutionary history, and ecological adaptation mechanism of the chloroplast genome of Quercus section Cyclobalanopsis in the long river of earth history. These chloroplast genome data provide valuable information for deep insights into phylogenetic relationships and intraspecific diversity in Quercus.

Nitrogen addition affected the root competition in Cunninghamia lanceolata-Phoebe chekiangensis mixed plantation.

Little is known about below-ground competition in mixed-species plantations under increasing nitrogen (N) deposition. This study aims to determine the effects of N addition on root competition in coniferous and broad-leaved species mixed plantations. A pot experiment was conducted using the coniferous species Cunninghamia lanceolata and the broad-leaved species Phoebe chekiangensis planted in mixed plantations with different competition intensities under N addition (0 or 45 kg N ha-1 yr-1). Biomass allocation, root morphology, root growth level, and competitive ability were determined after five months of treatment. Our findings indicated that root interactions in mixed plantations did not influence biomass allocation in either C. lanceolata or P. chekiangensis but promoted growth in C. lanceolata when no N was added. However, N addition decreased biomass accumulation in both species in the mixed plantation and had a negative effect on the root growth of C. lanceolata due to intensified competition. Addition of N increased the relative importance of root predatory competition in P. chekiangensis, and increased the allelopathic competitive advantage in C. lanceolata. This suggests that N addition causes a shift in the root competitive strategy from tolerance to competition. Overall, these findings highlight the significant impact that the addition of N can have on plant interactions in mixed plantations. Our results provide implications for the mechanisms of root competition in response to increasing atmospheric N deposition in mixed plantations.

Enhanced cadmium phytoremediation capacity of poplar is associated with increased biomass and Cd accumulation under nitrogen deposition conditions.

Nitrogen (N) deposition plays a significant role in soil cadmium (Cd) phytoremediation, and poplar has been considered for the remediation of contaminated soil because of its enormous biomass and strong Cd resistance. To reveal the underlying physiological and root phenotypic mechanisms of N deposition affecting Cd phytoextraction in poplar, we assessed root phenotypic characteristics, Cd absorption and translocation, chlorophyll fluorescence performance, and antioxidant enzyme activities of a clone of Populus deltoides × P. nigra through combined greenhouse Cd and N experiments. Our results showed that Cd significantly changed the root phenotype by reducing root length, tip number, and diameter. Cd also caused the peroxidation of lipids, damaged the photosystem II (PSII) reaction centre, and reduced photosynthetic capacity, resulting in a decrease in biomass accumulation in poplar. The N60 (60 kg N·ha-1·yr-1) and N90 (90 kg N·ha-1·yr-1) treatments promoted the net photosynthetic rate of poplar by increasing the activity of antioxidant enzymes and proline content and repairing the PSII reaction centre, thus increasing the biomass accumulation of poplar exposed to Cd stress. Simultaneously, the N60 and N90 treatments might have increased Cd uptake from the soil by upregulating total root length, root tips, and fine root length. Cd mainly accumulated in roots and stems but not in leaves. The N30 (30 kg N·ha-1·yr-1) treatment had no obvious effects on these parameters compared with the single Cd treatment. Consequently, our study suggested that adequate N can improve biomass and Cd accumulation to enhance the phytoremediation capacity of poplar for Cd, which might be related to the improvement of leaf physiological defence and the change in root phenotypic characteristics.

Complete Chloroplast Genome of an Endangered Species Quercus litseoides, and Its Comparative, Evolutionary, and Phylogenetic Study with Other Quercus Section Cyclobalanopsis Species.

Quercus litseoides, an endangered montane cloud forest species, is endemic to southern China. To understand the genomic features, phylogenetic relationships, and molecular evolution of Q. litseoides, the complete chloroplast (cp) genome was analyzed and compared in Quercus section Cyclobalanopsis. The cp genome of Q. litseoides was 160,782 bp in length, with an overall guanine and cytosine (GC) content of 36.9%. It contained 131 genes, including 86 protein-coding genes, eight ribosomal RNA genes, and 37 transfer RNA genes. A total of 165 simple sequence repeats (SSRs) and 48 long sequence repeats with A/T bias were identified in the Q. litseoides cp genome, which were mainly distributed in the large single copy region (LSC) and intergenic spacer regions. The Q. litseoides cp genome was similar in size, gene composition, and linearity of the structural region to those of Quercus species. The non-coding regions were more divergent than the coding regions, and the LSC region and small single copy region (SSC) were more divergent than the inverted repeat regions (IRs). Among the 13 divergent regions, 11 were in the LSC region, and only two were in the SSC region. Moreover, the coding sequence (CDS) of the six protein-coding genes (rps12, matK, atpF, rpoC2, rpoC1, and ndhK) were subjected to positive selection pressure when pairwise comparison of 16 species of Quercus section Cyclobalanopsis. A close relationship between Q. litseoides and Quercus edithiae was found in the phylogenetic analysis of cp genomes. Our study provided highly effective molecular markers for subsequent phylogenetic analysis, species identification, and biogeographic analysis of Quercus.

Nitrogen addition alleviated sexual differences in responses to cadmium toxicity by regulating the antioxidant system and root characteristics, and inhibiting Cd translocation in mulberry seedlings.

Cadmium (Cd) toxicity and nitrogen (N) deposition are two major environmental stresses which can affect plant growth. It's less clear that how the combined Cd accumulation and N deposition affect the male and female plants of dioecious species. The aim of the present study was to detect sex-specific responses to Cd stress and simulated N deposition in one-year-old male, female and hermaphrodite seedlings of Morus alba. Changes in morphology, physiology, root architecture and biomass of the three sex types of mulberry seedlings were determined. The results showed that Cd toxicity caused limited growth, impaired photosynthetic apparatus and decreased gas exchange rates with significant sex-specific differences. Mulberry was found to deploy detoxification mechanisms to avoid or tolerate toxic Cd effects through the activation of the antioxidant system, increasing proline and non-protein thiol contents, translocating Cd into different plant parts and decreasing biomass. Females displayed a low tolerance to high Cd and were more sensitive to Cd stress. Simulated N deposition alleviated the negative effects of Cd on leaves and decreased sex-specific differences in the three kinds of mulberry seedlings, but N fertilizer did not affect the total biomass. The N-stimulated increasing in proline and non-protein thiol contents might play a crucial role in resisting the damage caused by Cd stress, and the three kinds of mulberry seedlings had slightly different ways of improving Cd tolerance by N deposition. Sexual differences in Cd accumulation are correlated with root architecture. This study provides evidence for the utilization of mulberry to treat Cd-contaminated soils under N deposition.

Nitrogen addition affects eco-physiological interactions between two tree species dominating in subtropical forests.

Nitrogen (N) deposition affects plant growth and interspecific interaction. This study aimed to explore the effect of N deposition on the growth and eco-physiological interactions between two tree species dominating in subtropical forests. A greenhouse experiment was conducted for 6 months in which the conifer Cunninghamia lanceolata and the broadleaved Phoebe chekiangensis were grown in monocultures and in a mixture under two levels of N addition: 0 and 45 kg ha-1 yr-1. The plant growth, root architecture, biomass distribution, element contents in plants and soil, and photosynthetic physiology were determined. The height and crown width of both seedlings tended to be higher in the mixture than in the monoculture when grown without N addition. P. chekiangensis was superior to C. lanceolata in resource acquisition and showed a greater net photosynthetic rate, plant height, crown width, total biomass, and belowground biomass distribution. In the mixture, N addition increased the net photosynthetic rate and decreased the height, ground diameter, and crown width of both species. Belowground biomass distribution was decreased in C. lanceolata but increased in P. chekiangensis under N addition. The P contents in both seedlings were higher in the mixture than in monocultures. Results showed N addition aggravated the competition and weakened the growth of both species in the mixture, largely determined by the competition for resources through the changing root architecture and biomass allocation. Our results provide new insights into the mechanisms of interspecific interaction in response to increasing N deposition in silvicultural practice.

Roots play a key role in drought-tolerance of poplars as suggested by reciprocal grafting between male and female clones.

Drought stress influences the growth of plants and thus grafting has been widely used to improve tolerance to abiotic stresses. Poplars possess sex-specific responses to drought stress, but how male or female rootstock affect the grafted plant is little known. To explore the mechanisms underlying changes in drought tolerance caused by grafting, we investigated the changes in growth, leaf traits, gas exchange and antioxidant enzyme activities of reciprocally grafted seedlings between Populus euramericana cv. "Nanlin895" (NL-895) (female) and Populus deltiodes cv."3412" (NL-3412) (male) under water deficit stress with 30% field capacity for 30 d. Results showed that drought stress affected adversely growth, morphological, and physiological characteristics in all seedlings studied. Grafted seedlings with male roots can effectively alleviated the inhibition of growth induced by drought stress, as shown by higher WUE, activities of SOD, POD and CAT, and lower levels of lipid peroxidation. Male seedlings with female roots were found to be less tolerance to drought than non-grafted male clones and female scions with male roots, but more tolerance than non-grafted female clones. This results suggested that drought tolerance of grafted seedlings is primarily caused by the rootstock, although the scion also affects the grafted plant. Thus, paying attention on the root genotype can provide an important means of improving the drought tolerance of poplars.

Physiological responses of Elaeocarpus glabripetalus seedlings exposed to simulated acid rain and cadmium.

Combined effects of cadmium (Cd) and acid rain on physiological characteristics in Eleocarpus glabripetalus seedlings were investigated under controlled conditions. The single Cd treatment and the combined Cd and acid rain treatment increased growth at low Cd concentrations, while decreased growth and photosynthesis at high Cd2+ concentrations. A low Cd2+ concentration (50 mg kg-1) combined with different acid rain treatments increased the seedling biomass. A high Cd2+ concentration (100 mg kg-1) under different acid rain treatments significantly decreased the biomass, the Fe content, chlorophyll fluorescence and photosynthetic parameters. Relative electric conductivity, malondialdehyde (MDA) content and peroxidase (POD) activity were increased while the reduced glutathione (GSH) content and catalase (CAT) activity were significantly lower at high Cd2+ concentration under acid rain. The results indicated that the combination of a high concentration of Cd2+ and acid rain aggravated the toxic effect of Cd2+ or acid rain alone on the growth and physiological parameters of E. glabripetalus due to serious damage to the chloroplast structure. These results provide novel insights into the combined effects of Cd2+and acid rain on woody plants and might also serve as a guide to evaluate forest restoration and biological safety in areas with Cd2+and acid rain pollution.

[Effects of simulating acid rain on photosynthesis and chlorophyll fluorescence parameters of Quercus glauca Quercus glauca].

At three levels of simulated acid rainfall intensities with pH values of 2.5 (severe), 40 (medium) and 5.6 (light) respectively, the responses of chlorophyll fluorescence and photosynthetic parameters of Quercus glauca seedlings were studied in three acid rainfall treatments, i. e. only the aboveground of seedlings exposed to acid rain (T1), both of the seedlings and soil exposed to acid rain (T2), only the soil exposed to acid rain (T3) compared with blank control (CK). Under the severe acid rainfall, T1 significantly inhibited chlorophyll synthesis, and thus reduced the primary photochemical efficiency of PS II ( F(v)/F(m)), potential activity of PS II (F(v)/F(o)) , apparent quantum (Y), net photosynthetic rate (P(n)), and transpiration rate (T(r)), but increased the light compensation point (LCP) and dark respiration rate (R(d)) of Q. glauca seedlings. T2 inhibited, but T3 played a little enhancement on the aforementioned parameters of Q. glauca seedlings. Under the conditions of medium and light acid rainfall intensities, the above parameters in the three treatments were higher than that of CK, except with lower R(d). The chlorophyll fluorescence and photosynthetic parameters showed a similar tendency in the three treatments, i. e. T2>T3 >T1. It indicated that T1 had the strongest inhibition on seedlings in condition of the severe acid rainfall, while T2 had the most dramatic facilitating effect on seedlings under the medium and light acid rainfall. Intensity of acid rainfall had significant influences on SPAD, F(v)/F(m), F(v)/F(o), Y, P(n), T(r), and maximum photosynthetic rate (A(max)), whereas treatments of acid rainfall affected SPAD, F(v)/F(m), Y, P(n), T(r), A(max) and light saturation point (LSP). The interaction of acid rainfall intensities and treatments played significant effects on SPAD, F(v)/F(m), Y, P(n) and A(max).

A green emitting phosphorescent copper(I) complex with tetrazole derived ligand for electroluminescence application.

In this paper, a tetrazole derived diamine ligand of 2-(1H-tetrazol-5-yl)pyridine (TP) owing electron-donors and short conjugation chain was synthesized to increase the band gap of its corresponding phosphorescent Cu(I) complex. This Cu(I) complex was characterized in detail, including its single crystal structure, singlet electronic transitions, photophysical parameters, thermal stability and electrochemical property. Upon on photoexcitation, this Cu(I) complex emitted green emission peaking at 497 nm with biexponential decay pattern of τ1=5.5414 µs (A1=0.137) and τ2=1.0679 µs (A2=0.11503). Cyclic voltammerty experiment suggested that this Cu(I) complex owned HOMO and LUMO energy levels of -5.79 eV and -2.39 eV. The thermal decomposition temperature was 170°C as indicated by thermogravimetric analysis. The optimal electroluminescence device constructed by solution processed coating procedure showed green electroluminescence peaking at 525 nm, with maximum luminance of 2860 cd/m2 and maximum current efficiency of 5.9 cd/A.