Sex-specific responses of Populus cathayana to drought and elevated temperatures

Drought stress-mediated differences in phyllosphere microbiome and associated pathogen resistance between male and female poplars

Phyllosphere-associated microbes play a crucial role in plant-pathogen interactions while their composition and diversity are strongly influenced by drought stress. As dioecious plant species exhibited secondary dimorphism between the two sexes in response to drought stress, whether such difference will lead to sex-specific differences in phyllosphere microbiome and associated pathogen resistance between male and female conspecifics is still unknown. In this study, we subjected female and male full siblings of a dioecious poplar species to a short period of drought treatment followed by artificial infection of a leaf pathogenic fungus. Our results showed that male plants grew better than females with or without drought stress. Female control plants had more leaf lesion area than males after pathogen infection, whereas drought stress reversed such a difference. Further correlation and in vitro toxicity tests suggested that drought-mediated sexual differences in pathogen resistance between the two plant sexes could be attributed to the shifts in structure and function of phyllosphere-associated microbiome rather than the amount of leaf main defensive chemicals contained in plant leaves. Supportively, the microbiome analysis through high-throughput sequencing indicated that female phyllosphere enriched a higher abundance of ecologically beneficial microbes that serve as biological plant protectants, while males harbored abundant phytopathogens under drought-stressed conditions. The results could provide potential implications for the selection of suitable poplar sex to plants in drought or semi-drought habitats.

Nutrient resorption responses of female and male Populus cathayana to drought and shade stress

Nutrient resorption can increase nutrient use and play important roles in terrestrial plant nutrient cycles. Although several studies have reported individual responses of plant nutrient resorption to drought or shade stress, the interaction of drought and shade remains unclear, especially for dioecious plants. This study explored whether nutrient resorption is correlated to growth characteristics (such as biomass and root/shoot ratio [R/S ratio]) and leaf economics (such as leaf thickness, leaf mass per area [LMA] and leaf vein density [LVD]) in female and male Populus cathayana across different conditions. We found that drought stress significantly increased nitrogen (N) resorption efficiency (NRE) in both sexes, but shade and interactive stress decreased NRE in P. cathayana females. Under drought stress, nutrient resorption was sexually dimorphic such that P. cathayana males have higher NRE than females. Furthermore, NRE and phosphorous (P) resorption efficiency (PRE) were positively related to R/S ratio, leaf thickness, LMA, and LVD in both sexes across different treatments. Our study is the first to present how nutrient resorption is related to biomass accumulation and allocation, and leaf economics, suggesting that nutrient uptake may be modulated by R/S ratio and leaf economics, which is important for understanding the conservation mechanism of plant nutrients.

Effects of α-Fe2O3 nanoparticles and biochar on plant growth and fruit quality of muskmelon under cadmium stress

Cadmium pollution in farmland has become a global environmental problem, threatening ecological security and human health. Biochar is effective in remediation of soil pollution. However, high concentrations of biochar can inhibit plant growth, and low concentrations of biochar have limited mitigation effect on cadmium toxicity. Therefore, the combination of low-concentration biochar and other amendments is a promising approach to alleviate cadmium toxicity in plants and improve the safety of edible parts. In this study, muskmelon was selected as the research object, and different concentrations of α-Fe₂O₃ nanoparticles were used alone or combined with biochar to explore the effects of different treatments on muskmelon plants in cadmium-contaminated soil. The results showed that the combined application of 250 mg/kg α-Fe₂O₃ nanoparticles and biochar had a good effect on the repair of cadmium toxicity in muskmelon plants. Compared with cadmium treatment, its application increased plant height by 32.53%, cadmium transport factor from root to stem decreased by 32.95%, chlorophyll content of muskmelon plants increased by 14.27%, and cadmium content in muskmelon flesh decreased by 18.83%. Moreover, after plant harvest, soil available cadmium content in 250 mg/kg α-Fe₂O₃ nanoparticles and biochar combined treatment decreased by 31.18% compared with cadmium treatment. The results of this study provide an effective reference for the composite application of different exogenous amendments and a feasible idea for soil heavy metal remediation and mitigation of cadmium pollution in farmland.

Differences in ecophysiological responses of Populus euphratica females and males exposed to salinity and alkali stress

Soil salinity is usually accompanied by alkalization in northwest China, and they both negatively impact plant growth and result in severe ecological problems. Some studies have reported tree responses to salinity or alkali stress alone, however, the interactive salinity and alkali effects are still unclear, especially in dioecious trees. In this study, we measured growth, morphology, leaf stomata, gas exchange, carbon isotope composition (δ¹³C), total soluble sugar and starch contents, Na⁺ accumulation and allocation, oxidative stress, and antioxidants of female and male Populus euphratica seedlings in response to salinity, alkali and their interaction. Our study showed no significant sexual differences in studied traits under control conditions. In addition, P. euphratica females showed greater inhibitory and negative effects, such as bigger decreases in growth and gas exchange, lower stomatal density and water use efficiency (as described by δ¹³C), and lower levels of soluble sugars and antioxidant enzyme activities compared with males under salinity, alkali and interactive stress conditions. Furthermore, P. euphratica males had a greater ability of ion exclusion and Na ⁺ transport restriction. For example, males allocated more Na⁺ to stems and roots than females, whereas females had higher Na⁺ contents in leaves under stress conditions. In conclusion, our results indicated that P. euphratica males have superior resistance and they perform better than females under salinity, alkali and their interactive stress conditions.

Biochar and nano-ferric oxide synergistically alleviate cadmium toxicity of muskmelon

Cadmium is toxic to plants. The accumulation of cadmium in edible plants such as muskmelon may affect the safe production of crops and result in human health problem. Thus effective measures are urgently needed for soil remediation. This work aims to investigate the effects of nano-ferric oxide and biochar alone or mixture on muskmelon under cadmium stress. The results of growth and physiological indexes showed that compared with the application of cadmium alone, the composite treatment (biochar and nano-ferric oxide) decreased malondialdehyde content by 59.12% and ascorbate peroxidase activity increased by 276.6%. Their addition can increase the stress resistance of plants. The results of soil analysis and cadmium content determination in plants showed that the composite treatment was beneficial to reduce the cadmium content in various parts of muskmelon. In the presence of high concentration of cadmium, the Target Hazard Quotient value of peel and flesh of muskmelon in the composite treatment was less than 1, which means the edible risk was greatly reduced. Furthermore, the addition of composite treatment increased the content of effective components; the contents of polyphenols, flavonoids, and saponins in the flesh of the compound treatment were increased by 99.73%, 143.07%, and 18.78% compared with the cadmium treatment. The results provide a technical reference for the further application of biochar combined with nano-ferric oxide in the field of soil heavy metal remediation, and provide a theoretical basis for further research on reducing the toxicity of cadmium to plants and improving the edible quality of crops.

DNA methylation-mediated phenylpropane and starch metabolism causes male poplars to be more tolerant to nitrogen deficiency than females

Nitrogen (N) is an essential nutrient for plant growth and development. Dioecious plants, especially perennial plants, are often faced with a shortage of N supply in nature. Poplar is one of the most important dioecious and perennials species. Due to the different ecological functions, female and male poplars adopt different adaptation strategies to N limitation. However, the regulation in epigenetic mechanism is poorly understood on sexes. Here, the integrative analysis of whole-genome bisulfite sequencing (WGBS), RNA sequencing, and plant physiological analysis on female and male Populus cathayana were performed. We found that N deficiency reprograms methylation in both sexes, and the CG and CHH methylation types played critical roles in female and male poplars, respectively. Induced by DNA methylation, N-deficient males had a stronger phenylpropanoid synthesis pathway and less anthocyanin accumulation than females, which not only strengthened the N cycle but also reduced the defense cost of males. In addition, compared with male poplars, females accumulated more starch to expend excess energy under N limited condition. Additionally, DNA methylation also mediated hormone signalling involved in anthocyanin synthesis and starch metabolism. Therefore, our study reveals new molecular evidences that male poplars are more tolerant to N deficiency than females, which provides a reference for ecological adaptability of forest trees.

Chromosome-scale assemblies of the male and female Populus euphratica genomes reveal the molecular basis of sex determination and sexual dimorphism

Reference-quality genomes of both sexes are essential for studying sex determination and sex-chromosome evolution, as their gene contents and expression profiles differ. Here, we present independent chromosome-level genome assemblies for the female (XX) and male (XY) genomes of desert poplar (Populus euphratica), resolving a 22.7-Mb X and 24.8-Mb Y chromosome. We also identified a relatively complete 761-kb sex-linked region (SLR) in the peritelomeric region on chromosome 14 (Y). Within the SLR, recombination around the partial repeats for the feminizing factor ARR17 (ARABIDOPSIS RESPONSE REGULATOR 17) was potentially suppressed by flanking palindromic arms and the dense accumulation of retrotransposons. The inverted small segments S1 and S2 of ARR17 exhibited relaxed selective pressure and triggered sex determination by generating 24-nt small interfering RNAs that induce male-specific hyper-methylation at the promoter of the autosomal targeted ARR17. We also detected two male-specific fusion genes encoding proteins with NB-ARC domains at the breakpoint region of an inversion in the SLR that may be responsible for the observed sexual dimorphism in immune responses. Our results show that the SLR appears to follow proposed evolutionary dynamics for sex chromosomes and advance our understanding of sex determination and the evolution of sex chromosomes in Populus.

Reference-quality genomes of both sexes of the dioecious tree species, Populus euphratica, provide further insight into the evolution of Populus sex chromosomes and highlight male-specific fusion genes that may contribute to sexual dimorphism.

Drought stress drives sex-specific differences in plant resistance against herbivores between male and female poplars through changes in transcriptional and metabolic profiles

Drought stress poses adverse influence on plant growth and further alters plant-herbivore interactions. Such effect is enhanced as drought occurrence is reported to increase due to global warming. Although dioecious plant species have shown sex-specific response to drought stress through the changes in growth performance and stress tolerance, whether such changes will drive sex-specific differences in defense against herbivores between male and female plant conspecifics is barely studied. In the current study, female and male poplar full-siblings were submitted to moderate (75 % field water capacity) and severe drought (50 % field water capacity) stresses, followed by herbivore growth and feeding bioassays to test the effect of plant gender on herbivore growth and feeding performance of two specialist and two generalist leaf herbivores. The results showed that although the growth of both plant sexes was inhibited by the two drought levels, male plants performed better than female conspecifics. In the paired-choice bioassays, the specialist herbivores preferred female plants while the generalist herbivores fed more on the male plants without drought stress. Both the moderate and severe drought stresses reversed such preferences. In the triple-choice bioassays, the specialist herbivores preferred female control plants while the generalist herbivores fed more on female plants under severe drought. In addition, the specialist herbivores fed on female plants from severe drought stress grew the worst while the generalist herbivores gained the highest fresh weight. The transcriptomic and metabolomic profiling revealed that female plant leaves contained higher levels of flavonoids than males under control condition while severe drought stress remarkably reduced the levels of defensive metabolites such as flavonoids, isoflavonoids, neoflavonoids and alkaloids in female but not in male plant leaves.

Arbuscular Mycorrhizal Fungi Enhanced Drought Resistance of Populus cathayana by Regulating the 14-3-3 Family Protein Genes

Plants can improve their resistance to a variety of stresses by forming mutualistic relationships with arbuscular mycorrhizal fungi (AMF). The 14-3-3 protein is a major regulator of the plant stress response. However, the regulation mechanism of 14-3-3 family protein genes (14-3-3s) of mycorrhizal plants coping with stress during AMF symbiosis remains unclear. Here, we analyzed the physiological changes and 14-3-3 expression profiles of Populus cathayana inoculated with AMF under different water conditions. The results showed that good colonization and symbiotic relationships with plants were formed under all water conditions (63.00% to 83.67%). Photosynthesis, peroxidase (POD) activity, and Mg and Ca content were significantly affected by drought and AMF. In addition, thirteen 14-3-3 protein genes (PcGRF1-PcGRF13) were identified by quantitative real-time PCR (qRT-PCR), of which the expression levels of PcGRF10 and PcGRF11 induced by AMF were significantly positively correlated with superoxide dismutase (SOD), POD, and sugar content, indicating that the 14-3-3s of mycorrhizal symbiotic plants may respond to drought through antioxidant and osmotic regulation. This is the first study on 14-3-3s in the symbiosis system of forest arbor plants and AMF, and it may help to further study the effects of 14-3-3s during AMF symbiosis on stresses and provide new ideas for improving mycorrhizal seedling cultivation under stress.

IMPORTANCE The 14-3-3 protein may regulate many biochemical and physiological processes under abiotic stress. Studies have shown that the 14-3-3 protein gene of AMF is not only upregulated under drought stress, but also enhances the regulation of AMF on plant drought tolerance by regulating plant signal pathways and drought response genes; however, knowledge about the biological relevance of these interactions remains limited and controversial. The precise functions of Populus cathayana 14-3-3s under drought stress remain poorly resolved and the mechanisms of action of these genes in mycorrhizae-induced drought stress are still unknown. Thus, studying the drought-resistance mechanism of the AMF symbiotic plant 14-3-3 gene is of special significance to improving the drought tolerance of the plant. Further systematic study is needed to probe the mechanism by which AMF regulates different 14-3-3 genes and their subsequent physiological effects on drought.

Physiological Responses and Metabonomics Analysis of Male and Female Sargassum thunbergii Macroalgae Exposed to Ultraviolet-B Stress

Ultraviolet-B (UV-B) radiation is a major environmental stress that suppresses or activates defense responses in organisms. UV-B radiation affecting growth and development in intertidal species have been researched for a long time, but a series of unknown knowledge remain in the male and female macroalgae comparison. To compare the different responses of male and female Sargassum thunbergii macroalgae under UV-B radiation, PSII photochemical efficiency determination, metabolomic analysis, and main carbon-based metabolites (including soluble sugar, total amino acid, and lipid) content measuring have been performed in our experiments. Results showed that males have significantly superiority performance in the chlorophyll fluorescence parameters of F _v/F _m, Y(II), and Y(NO) either low or high UV-B radiation treatments. Metabolomics analysis revealed that carbon and nitrogen metabolism pathways in male and female S. thunbergii were significant components responding to enhanced UV-B radiation. Based on measuring, female S. thunbergii lipid content expressed higher than males without any stimulation. Additionally, under low UV-B radiation stimulation, females total amino acid content shown significantly higher than control group and their lipid content also significantly higher than males. Under high UV-B radiation, males soluble sugar, total amino acid, and lipid content significantly varied from females, which meant that enhancing UV-B stress might altered mainly carbon-based metabolites flowing directions. The present study elucidated the potential role of enhanced UV-B radiation in regulating macroalgae physiological responses, metabolites changing, and reflecting differences between male and female S. thunbergii, contributing to understanding of brown-macroalgae diecious adopting mechanisms in defending intertidal UV-B stresses.

Sexual differences in above- and belowground herbivore resistance between male and female poplars as affected by soil cadmium stress

Dioecious plant species presented sexual differences in metal accumulation and allocation between male and female conspecifics that grown on metal contaminated soil. As the Elemental defense hypothesis postulates that metals accumulated in plant tissues could protect plants from herbivory, whether such sexual dimorphism in response to metal stress of a dioecious plant will lead to differences in herbivore resistance between male and female conspecifics is still unknown. In this study, we used female and male siblings of Populus deltoides to investigate the effect of plant sex on the growth and feeding preferences of four leaf herbivores and a root herbivore under soil cadmium (Cd) stress. The results showed that the male plants accumulated significantly higher Cd in the leaves while the females allocated more Cd in the roots. Leaf herbivores fed on male leaves grew worse than those fed on female leaves under Cd exposure, while the root herbivore showed the opposite results. In addition, all leaf herbivores strongly preferred the leaves from Cd-stressed female plants than male ones. The quantification of gene expression further showed that Cd stress could significantly upregulate more genes involved in Cd uptake, transport and detoxification pathways in male leaves and female roots. In combination with the correlation tests, we postulated that such sexual differences in herbivore resistance between the two plant sexes was most likely due to the different Cd allocation patterns in plant leaves and roots.

Rich but not poor conditions determine sex-specific differences in growth rate of juvenile dioecious plants

Causes of secondary sexual dimorphism (SSD) in dioecious plants are very poorly understood, especially in woody plants. SSD is shown mainly in mature plants, but little is known about whether secondary sexual dimorphism can occur in juveniles. It is also assumed that stress conditions intensify differences between the sexes due to the uneven reproductive effort. Therefore, the following research hypotheses were tested: (1) secondary sexual dimorphism will be visible in juveniles; (2) unfavourable soil conditions are the cause of more pronounced differences between the sexes. Rooted shoots of the common yew (Taxus baccata L.) and common juniper (Juniperus communis L.), previously harvested from parental individuals of known sex were used in the study. During two growing seasons vegetation periods and four times a year, comprehensive morphological features of whole plants were measured. Some SSD traits were visible in the analysed juveniles. Contrary to expectations, differences were more pronounced in the fertilized treatment. Both species reacted to fertilization in different ways. Female yew had a clearly higher total plant mass, root mass, and mean root area when fertilized, whereas male juniper had a higher root mass when fertilized. Differences between the sexes independent of the fertilization treatment were seen, which can be interpreted as sexual adaptations to a continued reproduction. Female yews and male junipers made better use of fertile habitats. Our study showed that SSD may be innate, and sexual compensatory mechanisms could generate uneven growth and development of both sexes. Because the SSD pattern was rather different in both species, it was confirmed that SSD is connected with the specific life histories of specific species rather than a universal strategy of dioecious species.

Drought and Nitrogen Application Modulate the Morphological and Physiological Responses of Dalbergia odorifera to Different Niche Neighbors

Mixed stands can be more productive if growth facilitation via niche segregation occurs. Dalbergia odorifera T. Chen, a tropical tree species endemic to Hainan Island with great economic values, belongs to the family Leguminosae. However, selecting mixed species with suitable ecological niches to efficiently construct mixed forests of D. odorifera in the context of abiotic stress [drought, nitrogen (N) deposition] remained obscure. In the present study, the target plant D. odorifera was planted with the same species D. odorifera, heterogeneous but the same family Delonix regia and non-Leguminous Family Swietenia mahagoni in the root interaction and isolated models under two watering regimes [100% and 30% field capacity (FC)] and two N applications (application, non-application), respectively. Principle component analysis based on the performances of growth, phenotype, and physiology was performed to identify the main factors affected by the treatments and the most discriminatory effects of water, N level, and species interaction models. Both comprehensive evaluation values and comprehensive index values were calculated to evaluate the influences of different niche neighbors on D. odorifera. Results showed that D. odorifera was benefited from S. mahagoni but inhibited from D. odorifera in all treatments under root system interaction. Drought stress aggravated the inhibitory effects on D. odorifera from D. odorifera. N application stimulated the promoted effects on D. odorifera from S. mahagoni but enhanced competition intensity of D. odorifera from D. regia under the 100% FC condition. N application alleviated the inhibitory effect of drought stress on D. odorifera from D. odorifera and S. mahagoni. Furthermore, the responses of D. odorifera to different niche neighbors were dominated by belowground interaction rather than the negligible aboveground one. Therefore, the feasibility of niche segregation as the criterion for selecting neighbors to construct D. odorifera mixed stands was confirmed. In addition, water level and N application could alter responses of D. odorifera to different niche neighbors under the root system interaction. Appropriate N application could alleviate the inhibitory effect of drought stress on D. odorifera in its mixed forests. A mixture with S. mahagoni under appropriate N application could be the optimal planting model.

Sexual differences in root growth and antioxidant characteristics in Salix viminalis exposed to cadmium stress

Salix viminalis, a dioecious shrub willow, has been widely used in phytoremediation, yet sexually differences in tolerance to cadmium of which remained unclear. This study focused on different responses to cadmium stress between roots of male and female S. viminalis. Results show that male plants of S. viminalis have stronger cadmium tolerance than female plants, which indicates male S. viminalis should be more considered to be applied for phytoremediation and ecological restoration of cadmium-accumulated soil considering cadmium tolerance characteristics. The findings can provide valuable evidence and insights for researches focused on phytoremediation with dioecious woody plants and sexual dimorphism under abiotic stress.

Combined effects of water stress and salinity on growth, physiological, and biochemical traits in two walnut genotypes

Due to its great economic value, walnut (Juglans regia L.) has received increasing attention during recent years. However, water stress and salinity limit walnut growth, production, and quality. We employed two walnut genotypes, precocious walnut, and late-bearing walnut, to investigate their growth, photosynthetic capacity, non-structural carbohydrate contents, Cl^- allocation, reactive oxygen species (ROS) accumulation, and osmotic regulation under water stress, salinity, and their combination. We found that late-bearing walnut showed higher total biomass and net photosynthetic rate, higher activities of antioxidant enzymes, higher osmoregulation, and lower ROS accumulation than precocious walnut under stressful conditions. In addition, late-bearing walnut restricted salt transport and allocated more Cl^- into roots, whereas precocious walnut allocated more Cl^- into leaves when exposed to salinity stress. These data collectively demonstrated that late-bearing walnut possesses better stress tolerance under water stress, salinity, and especially under their combination. Such knowledge of genotype-specific responses and tolerances to water stress and salinity is important for walnut plantation management under increasing drought and aggravated soil salinization occurring with climate change.

Divergence of Phyllosphere Microbial Communities Between Females and Males of the Dioecious Populus cathayana

Females and males of dioecious plants have evolved sex-specific characteristics in terms of their morphological and physiological properties. However, the differentiation of phyllosphere microbiota in dioecious plants remains largely unexplored. Here, the diversity and composition of female and male Populus cathayana phyllosphere bacterial and fungal communities were investigated using 16S rRNA/ITS1 gene-based MiSeq sequencing. The divergences of bacterial and fungal community compositions occurred between females and males. Both females and males had their unique phyllosphere bacterial and fungal microbiota, such as bacterial Gemmata spp. (5.41%) and fungal Pringsheimia spp. (0.03%) in females and bacterial Chitinophaga spp. (0.009%) and fungal Phaeococcomyces spp. (0.02%) in males. Significant differences in the relative abundance of phyla Proteobacteria and Planctomycetes bacteria and phyla Ascomycota and Basidiomycota fungi (P < 0.05) were also found between females and males. Some bacterial species of genera Spirosoma and Amnibacterium and fungal genera Venturia, Suillus, and Elmerina spp. were significantly enriched in males (P < 0.05). In contrast, levels of fungal genera Phoma and Aureobasidium spp. were significantly higher in females than in males (P < 0.05). The mineral, inorganic, and organic nutrients content contributed differently to the divergence of female and male phyllosphere microbial communities, with 87.08 and 45.17% of the variations being explained for bacterial and fungal communities, respectively. These results highlight the sexual discrimination of phyllosphere microbes on the dioecious plants and provide hints on the potential host-associated species in phyllosphere environments.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Effect of summer warming on growth, photosynthesis and water status in female and male Populus cathayana: implications for sex-specific drought and heat tolerances

Effects of climate warming on tree growth and physiology may be driven by direct thermal effects and/or by changes in soil moisture. Dioecious tree species usually show sexual spatial segregation along abiotic gradients; however, few studies have assessed the sex-specific responses to warming in dioecious trees. We investigated the sex-specific responses in growth, photosynthesis, nonstructural carbohydrate (NSC), water-use efficiency and whole-plant hydraulic conductance (KP) of the dioecious tree species Populus cathayana Rehd. under +4 °C elevated temperature with and without supplemental water. For both sexes, high-temperature treatments significantly decreased growth (height and biomass), photosynthetic rate (A), the ratio of A to dark respiration rate, stomatal conductance (gs), transpiration rate, NSC, leaf water potential and KP, but increased water-use efficiency (estimated from carbon isotope composition). Under warming with supplemental water, most traits of females did not change relative to ambient conditions, but traits of males decreased, resulting in greater sexual differences. Females showed a lower KP, and their gs and A responded more steeply with water-related traits than males. These results show that the effect of summer warming on growth and photosynthesis was driven mainly by soil moisture in female P. cathayana, while male performance was mainly related to temperature. Females may experience less thermal stress than males due to flexible water balance strategy via stomata regulation and water use.

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.

Grouping, Spectrum-Effect Relationship and Antioxidant Compounds of Chinese Propolis from Different Regions Using Multivariate Analyses and Off-Line Anti-DPPH Assay

49 samples of propolis from different regions in China were collected and analyzed for their chemical compositions, contents of total flavonoids (TFC), total phenolic acid (TPC) and antioxidant activity. High-performance liquid chromatography (HPLC) analysis identified 15 common components, including key marker compounds pinocembrin, 3-O-acetylpinobanksin, galangin, chrysin, benzyl p-coumarate, pinobanksin and caffeic acid phenethyl ester (CAPE). Cluster analysis (CA) and correlation coefficients (CC) analysis showed that these propolis could be divided into three distinct groups. Principal component analysis (PCA) and multiple linear regression analysis (MLRA) revealed that the contents of isoferulic acid, caffeic acid, CAPE, 3,4-dimethoxycinnamic acid, chrysin and apigenin are closely related to the antioxidant properties of propolis. In addition, eight peak areas decreased after reacting with 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radicals, indicating that these compounds have antioxidant activity. The results indicate that the grouping and spectrum–effect relationship of Chinese propolis are related to their chemical compositions, and several compounds may serve as a better marker for the antioxidant activity of Chinese propolis than TFC and TPC. The findings may help to develop better methods to evaluate the quality of propolis from different geographic origins.

Are males and females of Populus cathayana differentially sensitive to Cd stress?

This study clarifies the mechanisms of Cd uptake, translocation and detoxification in Populus cathayana Rehder females and males, and reveals a novel strategy for dioecious plants to cope with Cd contamination. Females exhibited a high degree of Cd uptake and root-to-shoot translocation, while males showed extensive Cd accumulation in roots, elevated antioxidative capacity, and effective cellular and bark Cd sequestration. Our study also found that Cd is largely located in epidermal and cortical tissues of male roots and leaves, while in females, more Cd was present in vascular tissues of roots and leaves, as well as in leaf mesophyll. In addition, the distributions of sulphur (S) and phosphorus (P) were very similar as that of Cd in males, but the associations were weak in females. Scanning electron microscopy and energy spectroscopy analyses suggested that the amounts of tissue Cd were positively correlated with P and S amounts in males, but not in females (a weak correlation between S and Cd). Transcriptional data suggested that Cd stress promoted the upregulation of genes related to Cd uptake and translocation in females, and that of genes related to cell wall biosynthesis, metal tolerance and secondary metabolism in males. Our results indicated that coordinated physiological, microstructural and transcriptional responses to Cd stress endowed superior Cd tolerance in males compared with females, and provided new insights into mechanisms underlying sexually differential responses to Cd stress.

Morphological and physiological responses of Dalbergia odorifera T. Chen seedlings to different culture substances

Dalbergia odorifera T. Chen seedlings do not grow well in the typical red soils of tropical regions. Eighteen culture substances filled with different substrate combinations and proportions of red soil, coconut coir powder, deciduous leaf powder, and sand were used as to determine their effects on the growth, root system development, dry matter accumulation and allocation, leaf relative electrolyte leakage, chlorophyll content, root superoxide dismutase activity, root malondialdehyde content, and total soluble sugar content of D. odorifera. Results demonstrated that different substrate combinations and proportions had different effects on the performance of D. odorifera. All mixed substrates were better than any single substrate. The suitable substrate combinations and proportions of sand, coconut coir powder, and deciduous leaf powder mixed with red soil improved the growth, root architecture, and physiological characteristics of D. odorifera seedling. For example, groups C1-2 (coconut coir/red soil = 2/2, v/v, the same below) and C3-2 (red soil/sand = 2/2) exerted the best effects on plant growth and biomass accumulation. Groups C1-2, C2-2 (deciduous leaf powder/red soil = 2/2), and C3-2 remarkably enhanced root system development. Group C6 (coconut coir/red soil/sand = 1/1/1) substantially promoted root nodule development. Group C3-1 (red soil/sand = 3/1) exhibited the best effects on physiological characteristics. On the basis of the comprehensive evaluation of Euclid's multidimensional space mathematical model, we found that the suitable substrate combinations followed the order of C1-2 > C3-1 > C2-2. This research provides scientific guidance for the proper seedling culture of D. odorifera and the rational utilization of solid wastes such as coconut coir and deciduous leaves of Ficus elastica.

Poplar males and willow females exhibit superior adaptation to nocturnal warming than the opposite sex

The Salicaceae family consists of dioecious woody plants. Morphological and physiological species-related, sex-specific responses to nocturnal warming in these plants are seldom-reported. In order to explore the different responses of sex-biased species to nighttime warming, males and females of Populus cathayana and Salix paraplesia were used in this study. After 60 days of nighttime warming (+4 °C ambient nighttime conditions) in growth chambers, nighttime warming significantly (p ≤ 0.05) increased height growth rate, leaf proline content, leaf soluble protein content, and root soluble sugar content, while decreased biomass accumulation, photosynthesis, specific leaf area, and ATP levels in both species. Also, nighttime warming resulted in distorted chloroplasts and a greater starch accumulation in P. cathayana and S. paraplesia leaves. Moreover, sex-specific, nighttime warming responses were different, where P. cathayana males and S. paraplesia females exhibited lower aboveground to root mass ratios and higher root dry mass, net photosynthetic rates, stomatal conductance, total chlorophyll contents, specific leaf area, and lower foliar ATP, and less damage to mesophyll cells compared to the opposite sex. Therefore, P. cathayana males and S. paraplesia females exhibit superior adaptability to nighttime temperatures by enlarging their root systems, accumulating more carbohydrates, and adjusting osmotic substances to support their growth processes. Based on these results, it is predicted that P. cathayana males and S. paraplesia females will outperform the opposite sex under ongoing, rising nighttime temperatures in the future.

Morphological, structural and physiological differences in heteromorphic leaves of Euphrates poplar during development stages and at crown scales

Euphrates poplar (Populus euphratica Oliv.) has heteromorphic leaves including strip, lanceolate, ovate, and broad-ovate leaves from base to top in the mature canopy. To clarify how diameter at breast height (DBH) and tree height affect the functional characteristics of all kinds of heteromorphic leaves, we measured the morphological anatomical structure and physiological indices of five crown heteromorphic leaves of P. euphratica at 2, 4, 6, 8, 10, and 12 m from the same site. We also analysed the relationships between morphological structures and physiological characteristics of heteromorphic leaves and DBH and the height of heteromorphic leaves. The results showed that the number of abnormalities regarding blade width, leaf area, leaf thickness, leaf mass per area, cuticle layer thickness, palisade tissue thickness, and palisade tissue/sponge tissue ratio increased with size order and sampling height gradient. Net photosynthetic rate, transpiration rate, stomatal conductance, instantaneous water use efficiency, stable delta carbon isotope ratio, proline and malondialdehyde (MDA) content increased with DBH and sampling height. By contrast, blade length, leaf shape index, and intercellular CO2 concentration decreased with the increase in path order and sampling height gradient. Although MDA content and leaf sponge thickness were not correlated with DBH or sampling height, other morphological structure and physiological parameters were significantly correlated with these variables. In addition, correlations were found among leaf morphology, anatomical structure, and physiological index parameters indicating that they changed with path order and tree height gradient. The differences in the morphology, anatomic structure and physiological characteristics of the heteromorphic leaves ofP. euphratica are related to ontogenesis stage and coronal position.

Sex-specific strategies of phosphorus (P) acquisition in Populus cathayana as affected by soil P availability and distribution

Soil phosphorus (P) availability and its distribution influence plant growth and productivity, but how they affect the growth dynamics and sex-specific P acquisition strategies of dioecious plant species is poorly understood. In this study, the impact of soil P availability and its distribution on dioecious Populus cathayana was characterized. P. cathayana males and females were grown under three levels of P supply, and with homogeneous or heterogeneous P distribution. Females had a greater total root length, specific root length (SRL), biomass and foliar P concentration under high P supply. Under P deficiency, males had a smaller root system than females but a greater exudation of soil acid phosphatase, and a higher colonization rate and arbuscular mycorrhizal hyphal biomass, suggesting a better capacity to mine P and a stronger association with arbuscular mycorrhizal fungi to forage P. Heterogeneous P distribution enhanced growth and root length density (RLD) in females. Female root proliferation in P-rich patches was related to increased foliar P assimilation. Localized P application for increasing P availability did not enhance the biomass accumulation and the morphological plasticity of roots in males, but it raised hyphal biomass. The findings herein indicate that sex-specific strategies in P acquisition relate to root morphology, root exudation and mycorrhizal symbioses, and they may contribute to sex-specific resource utilization patterns and niche segregation.

Microstructural and physiological responses to cadmium stress under different nitrogen levels in Populus cathayana females and males

Although increasing attention has been paid to the relationships between heavy metal and nitrogen (N) availability, the mechanism underlying adaptation to cadmium (Cd) stress in dioecious plants has been largely overlooked. This study examined Cd accumulation, translocation and allocation among tissues and cellular compartments in Populus cathayana Rehder females and males. Both leaf Cd accumulation and root-to-shoot Cd translocation were significantly greater in females than in males under a normal N supply, but they were reduced in females and enhanced in males under N deficiency. The genes related to Cd uptake and translocation, HMA2, YSL2 and ZIP2, were strongly induced by Cd stress in female roots and in males under a normal N supply. Cadmium largely accumulated in the leaf blades of females and in the leaf veins of males under a normal N supply, while the contrary was true under N deficiency. Furthermore, Cd was mainly distributed in the leaf epidermis and spongy tissues of males, and in the leaf palisade tissues of females. Nitrogen deficiency increased Cd allocation to the spongy tissues of female leaves and to the palisade tissues of males. In roots, Cd was preferentially distributed to the epidermis and cortices in both sexes, and also to the vascular tissues of females under a normal N supply but not under N deficiency. These results suggested that males possess better Cd tolerance compared with females, even under N deficiency, which is associated with their reduced root-to-shoot Cd translocation, specific Cd distribution in organic and/or cellular compartments, and enhanced antioxidation and ion homeostasis. Our study also provides new insights into engineering woody plants for phytoremediation.

Response of juveniles of seven forest tree species and their populations to different combinations of simulated climate change-related stressors: spring-frost, heat, drought, increased UV radiation and ozone concentration under elevated CO2 level

The study aimed to assess response of juvenile progeny of seven forest tree species, Pinus sylvestris, Picea abies, Betula pendula, Alnus glutinosa, Populus tremula, Quercus robur and Fraxinus excelsior, and their populations to different combinations of climate change-related multiple stressors, simulated in a phytotron under elevated CO₂ concentration: (1) heat + elevated humidity (HW); (2) heat + frost + drought (HFD); (3) heat + elevated humidity + increased UV-B radiation doses + elevated ozone concentration (HWUO); and (4) heat + frost + drought + increased UV-B radiation doses + elevated ozone concentration (HFDUO). Effects of the complex treatments, species and species-by-treatment interaction were highly significant in most of the growth, physiological and biochemical traits studied, indicating general and species-specific responses to the applied treatments. For deciduous trees, height increment was much higher under HW treatment than in ambient conditions (control) indicating a positive effect of elevated temperature and better water and CO₂ availability. HFD treatment caused reduction of height increment in comparison to HW treatment in most species except for Q. robur and F. excelsior which benefited from lower humidity. Treatments HWUO and HFDUO have caused substantial damages to leaves in fast growing deciduous P. tremula, A. glutinosa and B. pendula, and resulted in their lower height increment than in HW treatment, although it was the same or even higher than that in the control. Rates of photosynthesis in most of the tree species were greatest in HFD treatment. A lower photosynthetic rate (compared to control) was observed in B. pendula, P. tremula and F. excelsior in HW treatment, and in most species-in HWUO treatment. Compared to control, intrinsic water use efficiency in all treatments was significantly lower in P. tremula, A. glutinosa and F. excelsior and higher in conifers P. sylvestris and P. abies. Significant population-by-treatment interactions found for most traits showed variation in response of populations, implying that this reflects adaptive potential of each tree species. The observed responses may not always be considered as adaptive as deteriorating growth of some populations or species may lead to loss of their competitiveness thus compromising regeneration and natural successions.

Warming Treatment Methodology Affected the Response of Plant Ecophysiological Traits to Temperature Increases: A Quantitive Meta-Analysis

Global mean temperature is expected to significantly increase by the end of the twenty-first century and could have dramatic impacts on a plant's growth, physiology, and ecosystem processes. Temperature manipulative experiments have been conducted to understand the responsive pattern of plant ecophysiology to climate warming. However, it remains unknown how different methodology used in these experiments will affect plants ecophysiological responses to warming. We conducted a comprehensive meta-analysis of the warming manipulative studies to synthesize the ecophysiological traits responses to warming treatment of different intensities, durations, and conducted for different species and under different experimental settings. The results indicated that warming enhanced leaf dark respiration (Rd) and specific leaf area (SLA) but decreased net photosynthetic rate (Anet) and leaf nitrogen content (LN). The positive and negative effects of warming on Rd and Anet were greater for C4 species than C3 species, respectively. The negative effect of warming treatment on Anet and LN and the positive effect on Rd were more evident under >1 year warming treatment. Negative effects of warming were more evident for plants grown at <10 L pots when experiment duration was longer than 1 year. The magnitude of warming treatment had a significant impact on most of the parameters that were investigated in the study. Overall, the results showed that warming effects on plant ecophysiological traits varied among different response variables and PFTs and affected by the magnitude of temperature change and experimental methodology. The results highlight the need for cautiously selecting the values of plant ecophysiological parameters in forecasting ecosystem function changes in future climate regimes and designing controlled experiments to realistically reflecting ecosystems responses to future global warming.

Sexually differential tolerance to water deficiency of Salix paraplesia-A female-biased alpine willow

Salicaceae plants are dioecious woody plants. Previous studies have shown that male individuals are more tolerant to water deficiency than females for male-biased poplars. However, Salix paraplesia is a female-biased species in nature. It is still unknown whether female willows are more tolerant to drought stress than males. To better understand the sexually different tolerance to water deficiency in willows, a greenhouse experiment combined with a field investigation was conducted, and physiological traits were tested in male and female S. paraplesia under a drought-stressed condition (50% of soil water capacity). Our field investigation showed that S. paraplesia was a species with female-biased sex ratio along altitude gradients (2,400 m, 2,600 m and 2,800 m) in their natural habitats. Our results showed that the height growth, biomass accumulation, total chlorophyll pigment content (TChl), and the net photosynthetic rate were higher in female willows than in males at the low and middle altitudes (2,400 m and 2,600 m) rather than at a high altitude (2,800 m) under well-watered conditions. Under drought-stressed conditions, the growth, biomass, and photosynthesis were greatly inhibited in both sexes, while females showed higher biomass and TChl content and suffered less negative effects than did males. Particularly, females that originated from a high altitude showed lower leaf relative electrolyte leakage, malondialdehyde content, and less disorder of chloroplast ultrastructures but a higher peroxidase activity (POD) than that of males. Therefore, S. paraplesia females exhibited a better drought tolerance and self-protective ability than males from high altitude. There is a reason to speculate that the population structure of S. paraplesia at a high altitude would be likely to further female biases with the increased drought intensity in the alpine regions.

Elevated temperature differently affects growth, photosynthetic capacity, nutrient absorption and leaf ultrastructure of Abies faxoniana and Picea purpurea under intra- and interspecific competition

There is a limited understanding of the impacts of global warming on intra- and interspecific plant competition. Resolving this knowledge gap is important for predicting the potential influence of global warming on forests, particularly on high-altitude trees, which are more sensitive to warming. In the present study, effects of intra- and interspecific competition on plant growth and associated physiological, structural and chemical traits were investigated in Abies faxoniana and Picea purpurea seedlings under control (ambient temperature) and elevated temperature (ET, 2 °C above ambient temperature) conditions for 2 years. We found that A. faxoniana and P. purpurea grown under intra- and interspecific competition showed significant differences in dry matter accumulation (DMA), photosynthetic capacity, nutrient absorption, non-structural carbohydrate (NSC) contents and leaf ultrastructure under ET conditions. ET increased leaf, stem and root DMA of both conifers under both competition patterns. Moreover, under ET and interspecific competition, P. purpurea had overall superior competitive capacity characterized by higher organ (leaf, stem and root) and total DMA, height growth rate, net photosynthetic rate, specific leaf area, water use efficiency (δ13C), leaf and root N and NSC concentrations and greater plasticity for absorption of different soil N forms. Thus, the growth of P. purpurea benefitted from the presence of A. faxoniana under ET. Our results demonstrated that ET significantly affects the asymmetric competition patterns in subalpine conifer species. Potential alteration of plant competitive interactions by global warming can influence the composition, structure and functioning of subalpine coniferous forests.

Sex-specific structural and functional leaf traits and sun-shade acclimation in the dioecious tree Pistacia vera (Anacardiaceae)

In dioecious species, sex-related adaptive strategies, influenced by natural and sexual selection, allow each sex to meet the specific demands of reproduction. Differences in ecophysiological traits between males and females may rely on innate differences in secondary sex traits such as structural and functional leaf traits. We tested structural sexual leaf dimorphism in Pistacia vera L. and the intersexual differences in sun-shade acclimation processes expected from the different adaptive strategies of males and females. Fifteen structural and functional leaf traits were compared in 50-year-old trees between females with low fruit load and males under sun and shade conditions. Despite the low additional energy investment in reproduction in females, remarkable sex effects in leaf structure and function were observed. Male trees had smaller leaves with significantly lower total conducting petiole area (TCA) and higher stomatal density, water use efficiency and concentration of phenolic compounds; females had larger leaves with greater thickness, leaf mass per area, TCA and maximum photosynthetic capacity per area (Amax,a). The higher Amax,a and stomatal conductance of female leaves were associated with their ~20-fold higher TCA compared with male trees. Females seem to invest more in high xylem efficiency and rates of C gain; males invest more in defence-protection. Sun-shade plastic responses were sex- and trait-specific, but the plasticity assessment indicated that both sexes have evolved an almost equal degree of phenotypic plasticity that allows them to perform optimally under varying environmental conditions. However, the trait-specific differences indicate that each sex displays a different strategy of optimisation.

Asymmetric pruning reveals how organ connectivity alters the functional balance between leaves and roots of Chinese fir

The functional balance between leaves and roots is believed to be mediated by the specific location of shoots and roots, i.e. differences in transport distances and degrees of organ connectivity. However, it remains unknown whether the adaptive responses of trees to biomass removal depend on the relative orientation of leaf and root pruning. Here, we applied five pruning treatments to saplings of Cunninghamia lanceolata (Chinese fir) under field and glasshouse conditions, namely no pruning (control), half of lateral branches pruned, half of lateral roots pruned, half of the branches and roots pruned on the same side of the plant, and half of the branches and roots pruned on opposite sides of the plant. The effects of pruning on the growth, carbon storage and allocation, and physiology of leaves and fine roots on the same and opposite sides of the plant were investigated. Compared with the effect of root-pruning on leaves, fine roots were more limited by carbon availability and their physiological activity was more strongly reduced by shoot pruning, especially when branches on the same side of the plant were removed. Pruning of branches and roots on the opposite side of the plant resulted in the lowest carbon assimilation rates and growth among all treatments. The results of a stable-isotope labeling indicated that less C was distributed to fine roots from the leaves on the opposite side of the plant compared to those on the same side, but N allocation from roots to leaves depended less on the relative root and leaf orientation. The results collectively indicate that the functional responses of C. lanceolata to pruning are not only determined by the source-sink balance model but are also related to interactions between leaves and fine roots. We argue that the connectivity among lateral branches and roots depends on their relative orientation, which is therefore critical for the functional balance between leaves and fine roots.

Comparative Physiological and Metabolic Analysis Reveals a Complex Mechanism Involved in Drought Tolerance in Chickpea (Cicer arietinum L.) Induced by PGPR and PGRs

The plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can be applied to improve the growth and productivity of plants, with potential to be used for genetic improvement of drought tolerance. However, for genetic improvement to be achieved, a solid understanding of the physiological and biochemical changes in plants induced by PGPR and PGR is required. The present study was carried out to investigate the role of PGPR and PGRs on the physiology and biochemical changes in chickpea grown under drought stress conditions and their association with drought tolerance. The PGPR, isolated from the rhizosphere of chickpea, were characterized on the basis of colony morphology and biochemical characters. They were also screened for the production of indole-3-acetic acid (IAA), hydrogen cyanide (HCN), ammonia (NH₃), and exopolysaccharides (EPS) production. The isolated PGPR strains, named P1, P2, and P3, were identified by 16S-rRNA gene sequencing as Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium, respectively. The seeds of two chickpea varieties, Punjab Noor-2009 (drought sensitive) and 93127 (drought tolerant) were soaked for 2-3 h prior to sowing in 24 h old cultures of isolates. The salicylic acid (SA) and putrescine (Put) were sprayed (150 mg/L) on 25 day old chickpea seedlings. The results showed that chickpea plants treated with a consortium of PGPR and PGRs significantly enhanced the chlorophyll, protein, and sugar contents compared to irrigated and drought conditions. Leaf proline content, lipid peroxidation, and activities of antioxidant enzymes (CAT, APOX, POD, and SOD) all increased in response to drought stress but decreased due to the PGPR and PGRs treatment. An ultrahigh performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) analysis was carried out for metabolic profiling of chickpea leaves planted under controlled (well-irrigated), drought, and consortium (drought plus PGPR and PGRs) conditions. Proline, L-arginine, L-histidine, L-isoleucine, and tryptophan were accumulated in the leaves of chickpea exposed to drought stress. Consortium of PGPR and PGRs induced significant accumulation of riboflavin, L-asparagine, aspartate, glycerol, nicotinamide, and 3-hydroxy-3-methyglutarate in the leaves of chickpea. The drought sensitive chickpea variety showed significant accumulation of nicotinamide and 4-hydroxy-methylglycine in PGPR and PGR treated plants at both time points (44 and 60 days) as compared to non-inoculated drought plants. Additionally, arginine accumulation was also enhanced in the leaves of the sensitive variety under drought conditions. Metabolic changes as a result of drought and consortium conditions highlighted pools of metabolites that affect the metabolic and physiological adjustments in chickpea that reduce drought impacts.

Elevated temperature and CO2 affect responses of European aspen (Populus tremula) to soil pyrene contamination

High northern latitudes are climatic sensitive areas, and are also regions to which polycyclic aromatic hydrocarbons (PAHs) easily transport and accumulate with potential risk to natural ecosystems. However, the effect of PAHs on northern woody plant growth and defense under climate change is very little studied. Here, we conducted a unique experiment in greenhouses to investigate sex-related responses of the dioecious Populus tremula to pyrene (50mgkg^-1) and residue of pyrene in soils under ambient and elevated temperature (+1.8°C on average) and CO₂ (740ppm). Pyrene decreased stem biomass and leaf area by 9% and 6%, respectively under ambient conditions, and the reduction of leaf area was more severe under elevated temperature (38%), elevated CO₂ (37%), and combined T+CO₂ (42%). Other growth parameters were unchanged by pyrene. Pyrene did not affect the concentration of leaf total phenolics under ambient conditions, but increased it by 16%, 1%, and 20% compared to controls under elevated temperature, elevated CO₂, and T+CO₂, respectively. Pyrene had only minor sex-specific effects on plant growth and phenolics. The concentration of residual pyrene in pyrene-spiked soils was higher under elevated CO₂ than under ambient, elevated temperature, and combined T+CO₂. The results suggest that both sexes of P. tremula have the capacity to regulate growth and metabolism to adjust to the stress of the tested pyrene contamination under elevated temperature and CO₂, but potential risk of pyrene to plants still exists in the future changing climate.

Does sexual dimorphism predispose dioecious riparian trees to sex ratio imbalances under climate change?

Environmental changes have resulted in significant declines in native riparian forests that are comprised largely of dioecious tree taxa, including boxelder and iconic cottonwood/willow gallery forests. Dioecious species may be especially vulnerable to the effects of climate change given that they often exhibit skewed sex ratios that are reinforced by physiological and morphological specialization of each sex to specific microhabitats. A comprehensive data synthesis suggests that male individuals of boxelder and cottonwood taxa have a higher representation on dry microhabitats than females and are less physiologically sensitive to increased aridity than co-occurring females. Consequently, extreme male-biased sex ratios are possible under future climate conditions that could reduce population fitness below a sustainable threshold. Riparian willows, on the other hand, generally do not express obvious sexual dimorphism in habitat preference or physiological sensitivity to aridity. Thus, it is unclear whether climate change will impact population structure of willows in ways that parallel other dioecious riparian tree taxa. Future riparian tree restoration programs should aim to maintain future sex ratio balance that maximizes population fitness under projected hydro-climatological conditions. Recent advances in genomics will likely provide the critical tools for early sex determination in pre-reproductive trees across riparian tree species such that sex ratio balance could be targeted during initial stages of restoration, along with adaptations for drought tolerance and other key traits that are essential for survival under future conditions.

Sex-related responses of European aspen (Populus tremula L.) to combined stress: TiO2 nanoparticles, elevated temperature and CO2 concentration

The combined effects of climate change and chemical contaminants on plant performance are still not well understood. Especially, whether different sexes of dioecious plants respond differently to combined stresses is unknown. In order to study the sex-related responses of European aspen to soil nTiO₂ contamination (0, 50, 300 mg kg^-1) under elevated temperature (+1.6 °C) and CO₂ (730 ppm), we conducted a study in greenhouses. Ti accumulated in roots exposed to nTiO₂ (1.1-3.3 and 2.7-21.1 mg kg^-1 in 50 and 300 mg kg^-1 treatments, respectively). Elevated CO₂ had no effects on Ti uptake, while elevated temperature increased it in the 300 mg kg^-1 treatment. Males grew taller than females under ambient conditions, but females had greater height and biomass increment under elevated temperature. In all climate treatments, nTiO₂ increased leaf phenolics in females by 12-19% and 15-26% at 50 and 300 mg kg^-1, respectively. Leaf phenolics decreased under elevated temperature, but increased under elevated CO₂ in both sexes. Results suggest that females have better chemical defense against nTiO₂ than males under future climate conditions. In the longer run, this may cause changes in the competitive abilities of both sexes, which again may affect sex ratios and genetic variation in nature.

Additional AM Fungi Inoculation Increase Populus cathayana Intersexual Competition

Sex-specific responses to mycorrhiza have been reported in dioecious plant species, but little attention has been paid to the influence of arbuscular mycorrhizal (AM) fungi on competitive ability under intersexual competition. To further address whether this competition is affected by an additional AM fungi supply, Populus cathayana saplings were chosen and subjected to two mycorrhizal treatments [inoculated and non-inoculated (control) with an additional AM fungi Funneliformis mosseae] while growing with the opposite sex for 3 months. Compared with the control, the additional AM fungi inoculation induced P. cathayana saplings to exhibit significant sexual differences in root structure and nutrient uptake (e.g., cortical layer, cross-section area, radius of root tips, and N, K, and Mg content), and enlarged sexual differences in morphology and biomass accumulation (e.g., leaf number increment, shoot height increment, total leaf area, total specific root length, stem dry mass, leaf dry mass, and total dry mass). Meanwhile, inoculated females presented higher values in most of these traits mentioned above than males under intersexual competition. Therefore, we conclude that the intersexual competition can be increased by an additional AM fungi supply, with females gaining more symbiosis-mediated benefits than males.

Transcriptional profiling reveals mechanisms of sexually dimorphic responses of Populus cathayana to potassium deficiency

Potassium (K) deficiency causes a series of physiological and metabolic disorders in plants, and dioecious species exhibit different responses based on sex. Our previous morphological and physiological observations indicated that Populus cathayana males were more tolerant to K⁺ deficiency than females. To continue this work, comparative transcriptome analyses were carried out to investigate sexually differentially expressed genes (DEGs) in this study. The results indicate that 10 weeks of K⁺ deficiency result in 111 and 181 DEGs in males and females, respectively. These DEGs are mainly involved in photosynthesis, cell wall biosynthesis, secondary metabolism, transport, stress responses, gene expression regulation and protein synthesis and degradation. Comparing between sexes, P. cathayana females showed more changes in response to K⁺ deficiency than males with regard to photosynthesis, gene expression regulation and posttranslational modification but fewer changes in secondary metabolism, stress responses and redox homeostasis. These results provide evidence that P. cathayana females are more susceptible to K⁺ deficiency than males. Therefore, there are sex-related molecular strategies in response to K⁺ deficiency between sexes.

Sex determines xylem anatomy in a dioecious conifer: hydraulic consequences in a drier world

Increased drought frequency and severity may reshape tree species distribution in arid environments. Dioecious tree species may be more sensitive to climate warming if sex-related vulnerability to drought occurs, since lower performance of one sex may drive differential stress tolerance, sex-related mortality rates and biased sex ratios. We explored the effect of sex and environment on branch hydraulic (hydraulic conductivity and vulnerability to embolism) and trunk anatomical traits in both sexes of the dioecious conifer Juniperus thurifera L. at two sites with contrasting water availability. Additionally, we tested for a trade-off between hydraulic safety (vulnerability to embolism) and efficiency (hydraulic conductivity). Vulnerability to embolism and hydraulic conductivity were unaffected by sex or site at branch level. In contrast, sex played a significant role in xylem anatomy. We found a trade-off between hydraulic safety and efficiency, with larger conductivities related to higher vulnerabilities to embolism. At the anatomical level, females' trunk showed xylem anatomical traits related to greater hydraulic efficiency (higher theoretical hydraulic conductivity) over safety (thinner tracheid walls, lower Mork's Index), whereas males' trunk anatomy followed a more conservative strategy, especially in the drier site. Reconciling the discrepancy between branch hydraulic function and trunk xylem anatomy would require a thorough and integrated understanding of the tree structure-function relationship at the whole-plant level. Nevertheless, lower construction costs and higher efficiency in females' xylem anatomy at trunk level might explain the previously observed higher growth rates in mesic habitats. However, prioritizing efficiency over safety in trunk construction might make females more sensitive to drought, endangering the species' persistence in a drier world.

Reproductive investments driven by sex and altitude in sympatric Populus and Salix trees

The sex ratios of co-existing Populus and Salix vary depending on altitude and species: 1:1 equlibrium sex ratios are observed at mid-altitude but skewed ones at high altitudes, where Populus shows male-biased and Salix female-biased sex ratios. However, the underlying ecological mechanisms are poorly known. Reproductive investments of Populus purdomii Rehd. and Salix magnifica Hemsl. were assessed at altitudes of 2000 and 2600 m in the Gongga Mountain by different metrics, including biomass, carbon (C), nitrogen (N) and phosphorus (P) concentrations and construction cost, and by estimating the payback time that combines energy gain and associated costs. Reproductive investment measured as C, N and P concentrations, and construction cost was higher in P. purdomii females at 2600 m. However, in S. magnifica, no difference was observed for biomass, C and N at 2600 m, but the investments for P and construction cost were even greater in males. The payback time showed no significant differences for the sexes at 2000 m, but it was shorter for P. purdomii males and S. magnifica females at 2600 m. We concluded that nutrient- and construction cost-based estimates of reproductive allocation can provide more informative insight into the cost of reproduction than does biomass, and together with the payback time they can supply an explanation for divergent sex ratios in Populus and Salix. Consequently, our results improve our understanding of the causes and consequences of sexual dimorphism in dioecious species.

Sex-Specific Response to Stress in Populus

Populus is an effective model for genetic studies in trees. The genus Populus includes dioecious species, and the differences exhibited in males and females have been intensively studied. This review focused on the distinctions between male and female poplar and aspen plants under stress conditions, such as drought, salinity, heavy metals, and nutrient deficiency on morphological, physiological, proteome, and gene expression levels. In most studies, males of Populus species were more adaptive to the majority of the stress conditions and showed less damage, better growth, and higher photosynthetic capacity and antioxidant activity than that of the females. However, in two recent studies, no differences in non-reproductive traits were revealed for male and female trees. This discrepancy of the results could be associated with experimental design: different species and genotypes, stress conditions, types of plant materials, sampling sizes. Knowledge of sex-specific differences is crucial for basic and applied research in Populus species.

Winter Night-Warming Improves Post-anthesis Physiological Activities and Sink Strength in Relation to Grain Filling in Winter Wheat (Triticum aestivum L.)

The diurnal and seasonal temperature rising patterns "asymmetric warming," plays an important role in crop distribution and productivity. Asymmetric warming during the early growth periods of winter wheat (Triticum aestivum L.) profoundly affects vegetative growth and post-anthesis grain productivity, but the underlying physiological mechanism is still unclear. We conducted field experiments from 2012 to 2014 using two wheat cultivars, namely, Yangmai-13 (vernal type) and Yannong-19 (semi-winter type), to investigate the influences of night-warming during the winter (warming by 1.56-1.67°C from tillering to jointing) or during the spring (warming by 1.78-1.92°C from jointing to booting) on post-anthesis physiological activities and grain-filling processes. Both night-warming treatments enhanced the source activity by increasing flag leaf area, chlorophyll content, and photosynthetic capability in both cultivars compared with those of the control. The night-warming treatments caused an increase in the antioxidant activities of superoxide dismutase (SOD), peroxidase, and catalase (CAT) in the flag leaves of both cultivars, while ROS contents such as superoxide anion radical ([Formula: see text]) and hydrogen peroxide (H2O2) decreased. Moreover, the expression levels of Rubisco activase B (RcaB), major chlorophyll a/b-binding protein (Cab), chloroplast Cu/Zn superoxide dismutase (Cu/Zn-SOD), mitochondrial manganese superoxide dismutase (Mn-SOD), and CAT genes were upregulated at anthesis and were associated with higher photosynthetic capacity and antioxidant activities. Furthermore, night-warming improved sink activities by increasing the concentrations of grain indole-3-acetic acid and cytokinins as well as the sucrose synthase activity for both cultivars. Winter night-warming showed greater potential for improving source strength and grain filling, with consistent performance in both cultivars compared with that of spring night-warming. We concluded form these results that night-warming can improve source and sink capacities in winter wheat, and winter night-warming has greater advantages in this respect than does spring warming.

Sex-specific floral morphology, biomass, and phytohormones associated with altitude in dioecious Populus cathayana populations

Relationships between sex-specific floral traits and endogenous phytohormones associated with altitude are unknown particularly in dioecious trees. We thus examined the relationships between floral morphology or biomass and phytohormones in male and female flowers of dioecious Populus cathayana populations along an altitudinal gradient (1,500, 1,600, and 1,700 m above sea level) in the Xiaowutai Nature Reserve in northern China. The female and male flowers had the most stigma and pollen at 1,700 m, the largest ovaries and least pollen at 1,500 m, and the smallest ovaries and greater numbers of anthers at 1,600 m altitude. The single-flower biomass was significantly greater in males than in females at 1,600 or 1,700 m, but the opposite was true at 1,500 m altitude. The biomass percentages were significantly higher in anthers than in stigmas at each altitude, while significantly greater gibberellin A3 (GA 3), zeatin riboside (ZR), indoleacetic acid (IAA), and abscisic acid (ABA) concentrations were found in female than in male flowers. Moreover, most flower morphological traits positively correlated with IAA in females but not in males. The biomass of a single flower was significantly positively correlated with ABA or IAA in males but negatively with ZR in females and was not correlated with GA 3 in both females and males. Our results demonstrate a distinct sexual adaptation between male and female flowers and that phytohormones are closely related to the size, shape, and biomass allocation in the pollination or fertilization organs of dioecious plants, although with variations in altitude.

Root-mediated sex recognition in a dioecious tree

Recent studies have demonstrated that plants can determine the identity of neighbouring roots (e.g., self and non-self, kin and non-kin), but whether they can discriminate by sex remains an open question. Here, we predict that dioecious plants can modulate their root performance in response to local root conditions related to sex. Female and male Populus cathayana cuttings were planted in a greenhouse in root-owner (one individual without a root neighbour) or root-sharer pairs (two individuals with roots neighbouring each other) with equal amounts of nutrients and space per plant in three combinations (females-females, males-males or females-males); root morphology, biomass and allocation were investigated. P. cathayana root-sharers altered their root growth in same-sex but not in different-sex combinations. Females enhanced root growth and allocation but decreased root proliferation (greater diameter with reduced branching and specific root length) in the presence of a female root neighbour, while males reduced root growth but increased root morphological proliferation in contact with another male. Therefore, the effect of a neighbour of the same sex differed from that of a neighbour of the opposite sex, which suggests that these plants can recognize the sexual identity of their neighbours.

Contrasting responses in the growth and energy utilization properties of sympatric Populus and Salix to different altitudes: implications for sexual dimorphism in Salicaceae

An interesting ecological and evolutionary puzzle arises from the observations of male-biased sex ratios in genus Populus, whereas in the taxonomically related Salix, females are generally more dominant. In the present study, we combined results from a field investigation into the sex ratios of the Salicaceous species along an altitudinal gradient on Gongga Mountain, and a pot experiment by monitoring growth and energy utilization properties to elucidate the mechanisms governing sexual dimorphism. At middle altitudes 2000 and 2300 m, the sex ratios were consistent with a 1:1 equilibrium in sympatric Populus purdomii and Salix magnifica. However, at the lower and higher ends of the altitudinal gradient, skewed sex ratios were observed. For example, the male:female ratios were 1.33 and 2.36 in P. purdomii at 1700 and 2600 m respectively; for S. magnifica the ratio was 0.62 at 2600 m. At 2300 m, the pot-grown seedlings of both species exhibited the highest biomass accumulation and total leaf area, simultaneously with the balanced sex ratios in the field. At 3300 m, the specific leaf area in male P. purdomii was 23.9% higher than that of females, which may be the morphological cause for the observed 19.3% higher nitrogen allocation to Rubisco, and 20.6% lower allocation to cell walls. As such, male P. purdomii showed a 32.9% higher foliar photosynthetic capacity, concomitant with a 12.0% lower construction cost. These properties resulted in higher photosynthetic nitrogen- and energy-use efficiencies, and shorter payback time (24.4 vs 40.1 days), the time span that a leaf must photosynthesize to amortize the carbon investment. Our results thus suggested that male P. purdomii evolved a quicker energy-return strategy. Consequently, these superior energy gain-cost related traits and the higher total leaf area contributed to the higher growth rate and tolerance in stress-prone environments, which might, in part, shed new light on the male-biased sex ratios in Populus. However, no significant sexual difference was observed in S. magnifica for all the above parameters, thereby implying that the female-biased sex ratios in Salix cannot be explained in terms of the energy-use properties studied here.

Comparative photochemistry activity and antioxidant responses in male and female Populus cathayana cuttings inoculated with arbuscular mycorrhizal fungi under salt

We investigated the impact of arbuscular mycorrhizal fungi (AMF) on the morphology and physiology of two genders of the typical dioecious plant Populus cathayana under salt stress. We conducted a pot experiment containing seedlings of the two genders that were subjected to salt or non-salt and filled with soil that was either inoculated with Rhizophagus intraradices or not. The results showed that males had higher mycorrhizal dependency than females. Salt stress decreased growth, the relative water content and chlorophyll fluorescence. Meanwhile, salt increased the superoxide radical (O₂⁻), and hydrogen peroxide (H₂O₂) contents and antioxidant enzyme activities. Mycorrhizal male seedlings performed better than females in shoot morphological growth under both conditions and in chlorophyll fluorescence parameters, O₂⁻ and H₂O₂ contents, MDA concentration, proline content and antioxidant enzymes activities under salt stress. In females, under saline conditions, a lower MDA concentration and H₂O₂, O₂⁻ and proline contents were observed in the leaves and roots. In addition, inoculated female plants performed better in chlorophyll fluorescence parameters than non-inoculated plants. AMF inoculation had either slight or no effects on the performance of females. These findings suggested that when subjected to stress and AMF, differences in the genders existed, followed by the alleviation of the damage to P. cathayana by AMF via improving growth and photosynthesis and antioxidant systems under salt stress.

Sexual competition affects biomass partitioning, carbon-nutrient balance, Cd allocation and ultrastructure of Populus cathayana females and males exposed to Cd stress

Although increasing attention has been paid to plant adaptation to soil heavy metal contamination, competition and neighbor effects have been largely overlooked, especially in dioecious plants. In this study, we investigated growth as well as biochemical and ultrastructural responses of Populus cathayana Rehder females and males to cadmium (Cd) stress under different sexual competition patterns. The results showed that competition significantly affects biomass partitioning, photosynthetic capacity, leaf and root ultrastructure, Cd accumulation, the contents of polyphenols, and structural and nonstructural carbohydrates. Compared with single-sex cultivation, plants of opposite sexes exposed to sexual competition accumulated more Cd in tissues and their growth was more strongly inhibited, indicating enhanced Cd toxicity under sexual competition. Under intrasexual competition, females showed greater Cd accumulation, more serious damage at the ultrastructural level and greater reduction in physiological activity than under intersexual competition, while males performed better under intrasexual competition than under intersexual competition. Males improved the female microenvironment by greater Cd uptake and lower resource consumption under intersexual competition. These results demonstrate that the sex of neighbor plants and competition affect sexual differences in growth and in key physiological processes under Cd stress. The asymmetry of sexual competition highlighted here might regulate population structure, and spatial segregation and phytoremediation potential of both sexes in P. cathayana growing in heavy metal-contaminated soils.

Climate change perils for dioecious plant species

Climate change, particularly increased aridity, poses a significant threat to plants and the biotic communities they support. Dioecious species may be especially vulnerable to climate change given that they often exhibit spatial segregation of the sexes, reinforced by physiological and morphological specialization of each sex to different microhabitats. In dimorphic species, the overexpression of a trait by one gender versus the other may become suppressed in future climates. Data suggest that males will generally be less sensitive to increased aridity than co-occurring females and, consequently, extreme male-biased sex ratios are possible in a significant number of populations. The effects of male-biased sex ratios are likely to cascade to dependent community members, especially those that are specialized on one sex.