Alpine Rhododendron population contractions lead to spatial distribution mismatch with their pollinators under climate change

The effect of global climate change on plant-pollinator interaction is not limited to changes in phenology and richness within communities but also includes the spatial mismatch caused by the inconsistency of geographical distribution changes. Subsequently, the pollinator interaction network may be remodeled or even disrupted. In this study, we simulated the suitable habitat niche of 15 Rhododendron species and their eight pollinator species as well as their overlapping versus geographical mismatch under the current and three future climate change scenarios in 2090s, using MaxEnt. Results showed that the suitable habitat of all Rhododendron species would decrease in 2090s. In particular, 10, 8, and 13 Rhododendron-pollinator assemblages would have a reduced spatial match region under the climate change scenarios, mainly due to the contraction of the suitable habitat of Rhododendron species. The results provide novel insights into the response of plant-pollinator interactions to global warming, useful to prioritize conservation actions of alpine plant ecosystems.

Synergistic effects of arbuscular mycorrhizal fungi and biochar are highly beneficial to Ligustrum lucidum seedlings in Cd-contaminated soil

Cadmium (Cd) contamination is a widespread environmental issue. There is a lack of knowledge about the impacts of applying arbuscular mycorrhizal fungi (AMF) and biochar, either alone or in their combination, on alleviating Cd phytotoxicity in Ligustrum lucidum. Therefore, a pot experiment was conducted in a greenhouse, where L. lucidum seedlings were randomly subjected to four regimes of AMF treatments (inoculation with sterilized AMF, with Rhizophagus irregularis, Diversispora versiformis, alone or a mixture of these two fungi), and two regimes of biochar treatments (with or without rice-husk biochar), as well as three regimes of Cd treatments (0, 15, and 150 mg kg-1), to examine the responses of growth, photosynthetic capabilities, soil enzymatic activities, nutritional concentrations, and Cd absorption of L. lucidum plants to the interactive effects of AMF, biochar, and Cd. The results demonstrated that under Cd contaminations, AMF alone significantly increased plant total dry weight, soil pH, and plant nitrogen (N) concentration by 84%, 3.2%, and 13.2%, respectively, and inhibited soil Cd transferring to plant shoot by 42.2%; biochar alone significantly enhanced net photosynthetic rate, soil pH, and soil catalase of non-mycorrhizal plants by 16.4%, 9%, and 11.9%, respectively, and reduced the soil Cd transferring to plant shoot by 44.7%; the additive effect between AMF and biochar greatly enhanced plant total dry weight by 101.9%, and reduced the soil Cd transferring to plant shoot by 51.6%. Furthermore, dual inoculation with D. versiformis and R. irregularis conferred more benefits on plants than the single fungal species did. Accordingly, amending Cd-contaminated soil with the combination of mixed-fungi inoculation and biochar application performed the best than either AMF or biochar alone. These responses may have been attributed to higher mycorrhizal colonization, soil pH, biomass accumulation, and biomass allocation to the roots, as well as photosynthetic capabilities. In conclusion, the combined use of mixed-fungi involving D. versiformis and R. irregularis and biochar addition had significant synergistic effects on enhancing plant performance and reducing Cd uptake of L. lucidum plants in Cd-contaminated soil.

Homogenization characteristics and regional effects in the diversity pattern of woody plants in 101 cities in China

Influenced by the interplay of global climate change and urbanization, urban plants have become increasingly homogenized in China. However, regional effects of biotic homogenization cannot be clearly explained due to the lack of continuous large-scale data. Thus, we explored the characteristics and regional effects of biotic homogenization, which not only contributes to the improvement of urban biodiversity, but also has important value for human well-being. Here, we analyzed the woody plants of 101 cities in 8 major urban agglomerations in China. The diversity patterns and influencing factors were explored using generalized additive, geographically weighted regression, and structural equation models. The main results were as follows: (1) The issue of woody plant homogenization is primarily manifested in urban greening species in China. (2) The characteristics of woody plant homogenization exhibit notable regional effects at a large scale. (3) Latitude, urban area, altitude and climatic factors all impact the woody plant homogenization. Thus, we found that the homogenization characteristics of urban greening species exhibit regional variations, influenced by both natural and anthropogenic factors. Finally, we suggested that urban biodiversity management should be considered specific regional environmental, both to meet the needs of residents.

Factors influencing the distribution of woody plants in tropical karst hills, south China

The seasonal rainforests distributed across the tropical karst hills of south China are of high biodiversity conservation value and serve many important ecosystem functions. However, knowledge surrounding distribution patterns of woody plants in tropical karst hills remains limited. In this study, we surveyed the distribution of families, genera and species of woody flora at four slope positions (depression, lower slope, middle slope, and upper slope), and analyzed the influence of topographic and soil variables on the distribution of woody plants in the tropical karst hills of south China. Forty forest plots (each 20 m × 20 m) contained 306 species of woody plants with a diameter at breast height (DBH) ≥1 cm, representing 187 genera and 66 families. As slope increased, the number of families increased slowly, and the number of genera and species followed a concave-shaped trend, with the lowest number of genera and species in the lower slope position. Differences in species composition were significantly stronger between slope positions than within slope positions. The topographic and soil variables explained 22.4% and 19.6%, respectively, of the distribution of woody plants, with slope position, slope degree, soil potassium and soil water content as the most significant variables. The results of generalized linear mixed model analysis showed that total R2 of fixed effects on variation of woody species richness was 0.498, and rock outcrop rate and soil total phosphorus were the best fitting effects. Our results help to explain the community assembly mechanism and to inform management and protection strategies for species-rich seasonal rainforests in the karst area.

Cellulase-lactic acid bacteria synergy action regulates silage fermentation of woody plant

BACKGROUND

Feed shortage is an important factor limiting livestock production in the world. To effectively utilize natural woody plant resources, we used wilting and microbial additives to prepare an anaerobic fermentation feed of mulberry, and used PacBio single-molecule real-time (SMRT) sequencing technology to analyse the "enzyme-bacteria synergy" and fermentation mechanism.

RESULTS

The fresh branches and leaves of mulberry have high levels of moisture and nutrients, and also contain a diverse range of epiphytic microorganisms. After ensiling, the microbial diversity decreased markedly, and the dominant bacteria rapidly shifted from Gram-negative Proteobacteria to Gram-positive Firmicutes. Lactic acid bacteria (LAB) emerged as the dominant microbial population, resulting in increased in the proportion of the carbohydrate metabolism and decreased in the proportion of the amino acid and "global and overview map" (GOM) metabolism categories. The combination of cellulase and LAB exhibited a synergistic effect, through which cellulases such as glycanase, pectinase, and carboxymethyl cellulase decomposed cellulose and hemicellulose into sugars. LAB converted these sugars into lactic acid through the glycolytic pathway, thereby improving the microbial community structure, metabolism and fermentation quality of mulberry silage. The GOM, carbohydrate metabolism, and amino acid metabolism were the main microbial metabolic categories during ensiling. The presence of LAB had an important effect on the microbial community and metabolic pathways during silage fermentation. A "co-occurrence microbial network" formed with LAB, effectively inhibiting the growth of harmful microorganisms, and dominating the anaerobic fermentation process.

CONCLUSIONS

In summary, PacBio SMRT was used to accurately analyse the microbial network information and regulatory mechanism of anaerobic fermentation, which provided a scientific basis for the study of woody silage fermentation theory. This study reveals for the first time the main principle of the enzyme-bacteria synergy in a woody silage fermentation system, which provides technical support for the development and utilization of woody feed resources, and achieves sustainable livestock production.

Evaluation of ammonia and nitrate distribution and reduction within stormwater green infrastructure with different woody plants under multiple influencing factors

The impact of stormwater green infrastructures (GIs) with different woody plants on nitrogen (N) distribution is still poorly understood. Laboratory experiments were conducted for GIs without or with Sophora japonica and Malus baccata to investigate the distribution of NH₃-N and NO₃-N. The test data was utilized to calibrate and validate the HYDRUS-2D. The validated model was subsequently used to analyze the distribution of NH₃-N and NO₃-N within the different GIs under three different rainfall conditions: inflow/runoff pollutant concentration, rainfall recurrence interval (runoff amount of a rainfall event), and number of dry days (during which no rainwater infiltrates into the soil). The average NH₃-N and NO₃-N concentrations in the upper soil (0-30 cm) of the GIs were about 4.8 and 2.4 times those of the lower layer (30-60 cm). Compared to the control (V_c), the average NH₃-N concentrations in soil with Sophora japonica (V_s) and Malus baccata (V_m) decreased by 15.8% and 35.1% while those of NO₃-N decreased by 15.5% and 27.2%, respectively. Degrees of influence by the three factors on the average soil NH₃-N and NO₃-N concentrations were inflow concentration > number of dry days > recurrence interval. The number of dry days was the smallest influence factor for the overflow N load while the inflow concentration was the most significant influence factor for the outflow, bio-utilization, and soil nitrogen loads. Compared to the control, outflow (groundwater recharge) loads of NO₃-N from the V_s and V_m increased by 14.0-16.6% and 3.7-6.8%, respectively under different conditions. The overflow (runoff) loads from V_s and V_m decreased by 16.8-36.3% and 6.6%-8.4%, respectively. A multiple regression equation was used to establish a quantitative coupling relationship between N pollutant load reduction rates and influence factors (R² ≥ 0.83). This relationship can be used to estimate the runoff treatment effectiveness of green infrastructure on target pollutants.

Metabolic engineering in woody plants: challenges, advances, and opportunities

Woody plant species represent an invaluable reserve of biochemical diversity to which metabolic engineering can be applied to satisfy the need for commodity and specialty chemicals, pharmaceuticals, and renewable energy. Woody plants are particularly promising for this application due to their low input needs, high biomass, and immeasurable ecosystem services. However, existing challenges have hindered their widespread adoption in metabolic engineering efforts, such as long generation times, large and highly heterozygous genomes, and difficulties in transformation and regeneration. Recent advances in omics approaches, systems biology modeling, and plant transformation and regeneration methods provide effective approaches in overcoming these outstanding challenges. Promises brought by developments in this space are steadily opening the door to widespread metabolic engineering of woody plants to meet the global need for a wide range of sustainably sourced chemicals and materials.

Tolerance capacities of Broussonetia papyrifera to heavy metal(loid)s and its phytoremediation potential of the contaminated soil

Broussonetia papyrifera, is a promising fast-growing woody plant for the phytoremediation of heavy metal(loid) (HM)-contaminated soil. In this study, a greenhouse experiment was conducted to explore the tolerance capacities of B. papyrifera and its phytoremediation potential in the HM-contaminated soil. The results indicated that B. papyrifera could effectively decrease malondialdehyde (MDA) content by enhancing the antioxidant enzyme activities along with the cultivation in the HM-contaminated soil. Significant (p < 0.05) negative relationships were found between MDA content and superoxide dismutase (r = -0.620) and catalase activities (r = -0.702) in B. papyrifera leaves. Fourier Transform Infrared Spectroscopy analysis indicated that the main functional groups in B. papyrifera roots were slightly influenced by HMs, and organic acids, carbohydrates, protein, and amino acids might bind with HMs in plant roots to alleviate the adverse effect of HMs on plants growth. Meanwhile, B. papyrifera had great potential used for the phytoextraction of Cd and Zn in HM-contaminated soil. The maximum total Cd and Zn accumulation amount in B. papyrifera shoots could attach to 2.26 and 66.8 mg·pot^-1, respectively. These observations suggested that B. papyrifera has large biomass and high tolerance to HMs, which can be regarded as a promising plant for the eco-remediation of HM-contaminated sites.Novelty statement In this study, a fast-growing woody plant, Broussonetia papyrifera, was used for heavy metal(loid) (HM)-contaminated soil remediation. We found that B. papyrifera can effectively alleviate the adverse effect of HMs on plant growth by enhancing the antioxidant enzyme activities in leaves and binding HMs with organic acids, carbohydrates, protein, and amino acids in roots. Furthermore, the maximum total Cd and Zn accumulation amount in B. papyrifera shoots could attach to 2.26 and 66.8 mg·pot^-1, which suggested that B. papyrifera might be regarded as a promising woody plant used for the phytoextraction of Cd and Zn in the contaminated soil.

Natural population re-sequencing detects the genetic basis of local adaptation to low temperature in a woody plant

Total of 14 SNPs associated with overwintering-related traits and 75 selective regions were detected. Important candidate genes were identified and a possible network of cold-stress responses in woody plants was proposed. Local adaptation to low temperature is essential for woody plants to against changeable climate and safely survive the winter. To uncover the specific molecular mechanism of low temperature adaptation in woody plants, we sequenced 134 core individuals selected from 494 paper mulberry (Broussonetia papyrifera), which naturally distributed in different climate zones and latitudes. The population structure analysis, PCA analysis and neighbor-joining tree analysis indicated that the individuals were classified into three clusters, which showed forceful geographic distribution patterns because of the adaptation to local climate. Using two overwintering phenotypic data collected at high latitudes of 40°N and one bioclimatic variable, genome-phenotype and genome-environment associations, and genome-wide scans were performed. We detected 75 selective regions which possibly undergone temperature selection and identified 14 trait-associated SNPs that corresponded to 16 candidate genes (including LRR-RLK, PP2A, BCS1, etc.). Meanwhile, low temperature adaptation was also supported by other three trait-associated SNPs which exhibiting significant differences in overwintering traits between alleles within three geographic groups. To sum up, a possible network of cold signal perception and responses in woody plants were proposed, including important genes that have been confirmed in previous studies while others could be key potential candidates of woody plants. Overall, our results highlighted the specific and complex molecular mechanism of low temperature adaptation and overwintering of woody plants.

Hydrolysis pattern analysis of xylem tissues of woody plants pretreated with hydrogen peroxide and acetic acid: rapid saccharification of softwood for economical bioconversion

BACKGROUND

Woody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals. Various pretreatment methods may be used to reduce the effects of retardation factors such as lignin interference and cellulose structural recalcitrance on the degradation of the lignocellulose material of woody plants.

RESULTS

A hydrogen peroxide-acetic acid (HPAC) pretreatment was used to reduce the lignin content of several types of woody plants, and the effect of the cellulose structural recalcitrance on the enzymatic hydrolysis was analyzed. The cellulose structural recalcitrance and the degradation patterns of the wood fibers in the xylem tissues of Quercus acutissima (hardwood) resulted in greater retardation in the enzymatic saccharification than those in the tracheids of Pinus densiflora (softwood). In addition to the HPAC pretreatment, the application of supplementary enzymes (7.5 FPU cellulase for 24 h) further increased the hydrolysis rate of P. densiflora from 61.42 to 91.94% whereas the same effect was not observed for Q. acutissima. It was also observed that endoxylanase synergism significantly affected the hydrolysis of P. densiflora. However, this synergistic effect was lower for other supplementary enzymes. The maximum concentration of the reducing sugars produced from 10% softwood was 89.17 g L^-1 after 36 h of hydrolysis with 15 FPU cellulase and other supplementary enzymes. Approximately 80 mg mL^-1 of reducing sugars was produced with the addition of 7.5 FPU cellulase and other supplementary enzymes after 36 h, achieving rapid saccharification.

CONCLUSION

HPAC pretreatment removed the interference of lignin, reduced structural recalcitrance of cellulose in the P. densiflora, and enabled rapid saccharification of the woody plants including a high concentration of insoluble substrates with only low amounts of cellulase. HPAC pretreatment may be a viable alternative for the cost-efficient production of biofuels or biochemicals from softwood plant tissues.

Plants and earthworms control soil carbon and water quality trade-offs in turfgrass mesocosms

Understanding how plants and earthworms regulate soil-based ecosystem services can guide design and management of built environments to improve environmental quality. We tested whether plant and earthworm activity results in trade-offs between soil carbon (C) retention and water quality. In a 2 × 2 factorial random block design, we introduced shrubs (Aronia melanocarpa) and earthworms (Lumbricus terrestris) to turfgrass (Lolium perenne) sandy loam mesocosms in a greenhouse. We measured soil respiration and soil microclimate every two weeks and leachate every two months. After 15 months, we assessed C and nitrogen (N) in bulk soil and aggregates (> 2000, 2000-250, 250-53 μm). Turfgrass mesocosms with earthworms retained less soil C (6.10 ± 0.20 kg/m²), especially when warmer. Soils planted with shrubs were drier and had 7% lower mean respiration rates than soils without shrubs. Turfgrass mesocosms with both shrubs and earthworms retained more soil C (6.66 ± 0.25 kg/m²), even when warmer, and held ~1.5 times more C in >2 mm aggregates than turfgrass-only mesocosms. Turfgrass mesocosms with shrubs and earthworms leached nitrate-N with increased respiration and retained phosphate-P and dissolved organic carbon (DOC) when wetter. In contrast, turfgrass mesocosms with only shrubs had the opposite response by leaching less nitrate-N with increased respiration, and more phosphate-P and DOC when wetter. Overall, shrub and earthworm activity in turfgrass mesocosms led to soil C-nutrient retention trade-offs. Our results reveal potential challenges in managing built environments to both retain soil C and improve water quality.

The effect of shrubland and grassland vegetation types on soil fauna and flora activities in a mountainous semi-arid landscape of Iran

The effect of vegetation types at mountainous sites on the relationships between soil biota and environmental variables applicable for the evaluation of soil quality and functions are barely studied and remain almost unknown. With the aim of studying the effect of shrubland and grassland plant coverings on soil fauna and flora activities, a mountainous semi-arid site in northern Iran (Diakooh) was selected for this research. Six vegetation types were selected with dominance in shrub and grassland coverage, i.e., (1) Crataegus microphylla CK. Koch., (2) Berberis integerrima Bunge, (3) Ribes uva-crispa L., (4) Prunus spinosa L., and with dominance in rangeland cover, i.e., (5) dominant Lecokia cretica (Lam.) DC., Orchis mascula L., Cardamine bulbifera (L.) Crantz, and (6) Fragaria vesca L. A total of 15 soil samples (30 × 30 × 10 cm) from each vegetation type were transferred to the laboratory. In addition, seasonal measurements (i.e. summer and autumn) were considered to achieve the temporal patterns of soil fauna and flora activities. Higher populations of soil earthworms (especially epigeic groups), acarina, collembola, nematode, and protozoa were found in the Crataegus site compared to other vegetation types with higher activities in the autumn season. Shrublands, especially with Crataegus cover, had increased activities of soil bacteria and fungi with higher abundances in the summer. Soils with higher fertility indicators and increased biota activities were attributed to the Crataegus and Berberis vegetation types by PCA. Overall, the findings of this study showed that shrubs can improve soil quality at high altitudes of mountainous, semi-arid sites that are often considered as especially fragile and sensitive ecosystems.

Overexpression of the MADS-box gene K-domain increases the yield potential of blueberry

MADS-box genes play a significant role for plant flowering. Keratin-like (K) domains are involved in protein-to-protein interactions in the formation of the MIKC-type MADS-box domain proteins. In this study, the potential of utilizing the K domain of a Vaccinium corymbosum SOC1-like gene (VcSOC1K) was investigated to modulate expression of other blueberry MADS-box genes for increasing blueberry productivity. Chilled transgenic blueberry plants overexpressing the VcSOC1K showed a significant increase in the number of canes, floral buds, and flower and fruit clusters compared to chilled non-transgenic plants. Additionally, nonchilled transgenic plants flowered whereas nonchilled non-transgenic plants did not. Transgenic plants showed an increase in tolerance to high soil pH. Comparative transcriptome analysis of transgenic and non-transgenic leaves showed differential expression of 17% of the MADS-box genes identified in blueberry. These differentially expressed (DE) MADS-box genes were associated with genes related to plant flowering, phytohormones, and response to various biotic and abiotic stimuli. The phenotypic changes and the DE MADS-box genes caused by the overexpression of VcSOC1K not only reveal that the MADS-box genes are involved in chilling/vernalization-mediated flowering in blueberry but also demonstrated that the overexpression of the K domain can effectively modulate plant reproductive processes.

Genome-wide analysis of long non-coding RNAs in Catalpa bungei and their potential function in floral transition using high-throughput sequencing

BACKGROUND

Long non-coding RNAs (lncRNAs) have crucial roles in various biological regulatory processes. However, the study of lncRNAs is limited in woody plants. Catalpa bungei is a valuable ornamental tree with a long cultivation history in China, and a deeper understanding of the floral transition mechanism in C. bungei would be interesting from both economic and scientific perspectives.

RESULTS

In this study, we categorized C. bungei buds from early flowering (EF) and normal flowering (NF) varieties into three consecutive developmental stages. These buds were used to systematically study lncRNAs during floral transition using high-throughput sequencing to identify molecular regulatory networks. Quantitative real-time PCR was performed to study RNA expression changes in different stages. In total, 12,532 lncRNAs and 26,936 messenger RNAs (mRNAs) were detected. Moreover, 680 differentially expressed genes and 817 differentially expressed lncRNAs were detected during the initiation of floral transition. The results highlight the mRNAs and lncRNAs that may be involved in floral transition, as well as the many lncRNAs serving as microRNA precursors. We predicted the functions of lncRNAs by analysing the relationships between lncRNAs and mRNAs. Seven lncRNA-mRNA interaction pairs may participate in floral transition.

CONCLUSIONS

This study is the first to identify lncRNAs and their potential functions in floral transition, providing a starting point for detailed determination of the functions of lncRNAs in C. bungei.

An Ultrahigh-Dimensional Mapping Model of High-order Epistatic Networks for Complex Traits

BACKGROUND

Genetic interactions involving more than two loci have been thought to affect quantitatively inherited traits and diseases more pervasively than previously appreciated. However, the detection of such high-order interactions to chart a complete portrait of genetic architecture has not been well explored.

METHODS

We present an ultrahigh-dimensional model to systematically characterize genetic main effects and interaction effects of various orders among all possible markers in a genetic mapping or association study. The model was built on the extension of a variable selection procedure, called iFORM, derived from forward selection. The model shows its unique power to estimate the magnitudes and signs of high-order epistatic effects, in addition to those of main effects and pairwise epistatic effects.

RESULTS

The statistical properties of the model were tested and validated through simulation studies. By analyzing a real data for shoot growth in a mapping population of woody plant, mei (Prunus mume), we demonstrated the usefulness and utility of the model in practical genetic studies. The model has identified important high-order interactions that contribute to shoot growth for mei.

CONCLUSION

The model provides a tool to precisely construct genotype-phenotype maps for quantitative traits by identifying any possible high-order epistasis which is often ignored in the current genetic literature.

Comparative transcriptome analysis of nonchilled, chilled, and late-pink bud reveals flowering pathway genes involved in chilling-mediated flowering in blueberry

BACKGROUND

Blueberry cultivars require a fixed quantity of chilling hours during winter endo-dormancy for vernalization. In this study, transcriptome analysis using RNA sequencing data from nonchilled, chilled, and late pink buds of southern highbush blueberry 'Legacy' was performed to reveal genes associated with chilling accumulation and bud break.

RESULTS

Fully chilled 'Legacy' plants flowered normally whereas nonchilled plants could not flower. Compared to nonchilled flower buds, chilled flower buds showed differential expression of 89% of flowering pathway genes, 86% of MADS-box genes, and 84% of cold-regulated genes. Blueberry orthologues of FLOWERING LOCUS T (FT) did not show a differential expression in chilled flower buds (compared to nonchilled flower bud) but were up-regulated in late-pink buds (compared to chilled flower bud). Orthologoues of major MADS-box genes were significantly up-regulated in chilled flower buds and down-regulated in late-pink buds. Functional orthologues of FLOWERING LOCUS C (FLC) were not found in blueberry. Orthologues of Protein FD (FD), TERMINAL FLOWER 1 (TFL1), and LEAFY (LFY) were down-regulated in chilled flower buds and in late-pink buds compared to nonchilled flower bud.

CONCLUSIONS

The changes from nonchilled to chilled and chilled to late-pink buds are associated with transcriptional changes in a large number of differentially expressed (DE) phytohormone-related genes and DE flowering pathway genes. The profile of DE genes suggests that orthologues of FT, FD, TFL1, LFY, and MADS-box genes are the major genes involved in chilling-mediated blueberry bud-break. The results contribute to the comprehensive investigation of the vernalization-mediated flowering mechanism in woody plants.

Non-linear direct effects of acid rain on leaf photosynthetic rate of terrestrial plants

Anthropogenic emissions of acid precursors have enhanced global occurrence of acid rain, especially in East Asia. Acid rain directly suppresses leaf function by eroding surface waxes and cuticle and leaching base cations from mesophyll cells, while the simultaneous foliar uptake of nitrates in rainwater may directly benefit leaf photosynthesis and plant growth, suggesting a non-linear direct effect of acid rain. By synthesizing data from literature on acid rain exposure experiments, we assessed the direct effects of acid rain on leaf photosynthesis across 49 terrestrial plants in China. Our results show a non-linear direct effect of acid rain on leaf photosynthetic rate, including a neutral to positive effect above pH 5.0 and a negative effect below that pH level. The acid rain sensitivity of leaf photosynthesis showed no significant difference between herbs and woody species below pH 5.0, but the impacts above that pH level were strongly different, resulting in a significant increase in leaf photosynthetic rate of woody species and an insignificant effect on herbs. Our analysis also indicates a positive effect of the molar ratio of nitric versus sulfuric acid in the acid solution on leaf photosynthetic rate. These findings imply that rainwater acidity and the composition of acids both affect the response of leaf photosynthesis and therefore result in a non-linear direct effect.

Transcriptomic changes reveal gene networks responding to the overexpression of a blueberry DWARF AND DELAYED FLOWERING 1 gene in transgenic blueberry plants

BACKGROUND

Constitutive expression of the CBF/DREB1 for increasing freezing tolerance in woody plants is often associated with other phenotypic changes including dwarf plant and delayed flowering. These phenotypic changes have been observed when Arabidopsis DWARF AND DELAYED FLOWERING 1 (DDF1) was overexpressed in A. thaliana plants. To date, the DDF1 orthologues have not been studied in woody plants. The aim of this study is to investigate transcriptomic responses to the overexpression of blueberry (Vaccinium corymbosum) DDF1 (herein, VcDDF1-OX).

RESULTS

The VcDDF1-OX resulted in enhanced freezing tolerance in tetraploid blueberry plants and did not result in significant changes in plant size, chilling requirement, and flowering time. Comparative transcriptome analysis of transgenic 'Legacy-VcDDF1-OX' plants containing an overexpressed VcDDF1 with non-transgenic highbush blueberry 'Legacy' plants revealed the VcDDF1-OX derived differentially expressed (DE) genes and transcripts in the pathways of cold-response, plant flowering, DELLA proteins, and plant phytohormones. The increase in freezing tolerance was associated to the expression of cold-regulated genes (CORs) and the ethylene pathway genes. The unchanged plant size, dormancy and flowering were due to the minimal effect of the VcDDF1-OX on the expression of DELLA proteins, flowering pathway genes, and the other phytohormone genes related to plant growth and development. The DE genes in auxin and cytokinin pathways suggest that the VcDDF1-OX has also altered plant tolerance to drought and high salinity.

CONCLUSION

A DDF1 orthologue in blueberry functioned differently from the DDF1 reported in Arabidopsis. The overexpression of VcDDF1 or its orthologues is a new approach to increase freezing tolerance of deciduous woody plant species with no obvious effect on plant size and plant flowering time.

Soil characterization and differential patterns of heavy metal accumulation in woody plants grown in coal gangue wastelands in Shaanxi, China

Soil contamination by heavy metals in coal mine wastelands is a significant environmental issue in most developing countries. The purpose of this study is to evaluate contamination characteristics in the coal mine wastelands of Sanlidong coal mine, Tongchuan, China. To achieve this goal, we conducted field sampling work, followed by further analysis of the properties of soil contamination and accumulation characteristics in woody plants. At this site, the pH value ranged from 4.41 to 7.88, and the nutrient content of the soil rose gradually with the time after deposition due to the weathering effect improving the soil quality. Meanwhile, the levels of Cd, Cr, Cu, Ni, and Zn gradually decreased with the passage time. Generally, heavy metal contamination was found to be more serious in the discharge refuse area, with Cd contamination at moderate or heavy levels; Ni, Zn, and Cu contamination at light levels; and with no Cr contamination. The geoaccumulation index (I geo) was highest for Cd (2.38-3.14), followed by Ni, Zn, Cu, and Cr. Heavy metals accumulated on the lower slopes and spread to the surrounding areas via hydrodynamic effects and wind. According to transfer and enrichment coefficient analyses, Robinia pseudoacacia, Ulmus pumila, and Hippophae rhamnoides with considerable biomass could be used as pollution-resistant tree species for vegetation restoration. This study provided a theoretical basis for the restoration of the ecological environment in the mining area. This report described a link between heavy metal contamination of soils and growth dynamics of woody plants in China.

Fire induced reproductive mechanisms of a Symphoricarpos (Caprifoliaceae) shrub after dormant season burning

BACKGROUND

Symphoricarpos, a genus of the Caprifoliaceae family, consists of about 15 species of clonal deciduous shrubs in North America and 1 species endemic to China. In North American tallgrass prairie, Symphoricarpos orbiculatus (buckbrush) is the dominant shrub often forming large colonies via sexual and asexual reproductive mechanisms. Symphoricarpos shrubs, in particular S. orbiculatus, use a unique sexual reproductive mechanism known as layering where vertical stems droop and the tips root upon contact with the soil. Because of conflicting societal values of S. orbiculatus for conservation and agriculture and the current attempt to restore historical fire regimes, there is a need for basic research on the biological response of S. orbiculatus to anthropogenic burning regimes.

RESULTS

From 2007 through 2013 we applied prescribed fires in the late dormant season on grazed pastures in the Grand River Grasslands of Iowa. From 2011 to 2013, we measured how S. orbiculatus basal resprouting and layering stems were affected by patchy fires on grazed pastures, complete pasture fires on grazed pastures or fire exclusion without grazing for more than three years. We measured ramet height, ramet canopy diameter, stems per ramet, ramets per 100 m2, and probability of new layering stems 120 days after fire. Height in burned plots was lower than unburned plots but S. orbiculatus reached ~ 84% of pre-burn height 120 days after fire. Stems per ramet were 2x greater in the most recently burned plots due to basal re-sprouting. Canopy diameter and density of ramets was not affected by time since fire, but burned pastures had marginally lower densities than plots excluded from fire (P = 0.07). Fire triggered new layering stems and no new layering stems were found in plots excluded from fire.

CONCLUSIONS

The mechanisms of both basal sprouting and aerial layering after fire suggest S. orbiculatus is tolerant to dormant season fires. Furthermore, dormant season fires, regardless if they were patchy fires or complete pasture fires, did not result in mortality of S. orbiculatus. Dormant season fires can reduce S. orbiculatus structural dominance and maintain lower ramet densities but also trigger basal resprouting and layering.

Functional analysis of BpDREB2 gene involved in salt and drought response from a woody plant Broussonetia papyrifera

The dehydration-responsive element binding proteins (DREBs) are important transcription factors in the regulation of plant responses to abiotic stresses. In this study, BpDREB2, an AP2/DREB-type transcription factor gene, was cloned from a woody plant, Broussonetia papyrifera by RACE-PCR. Sequence analyses revealed that BpDREB2 protein has three characteristic domains, including an AP2/EREBP, a nuclear localization signal and an acidic activation domain. Yeast one-hybrid assays showed that BpDREB2 protein specifically binds to the DRE sequence and activates the expression of reporter genes in yeast. These results suggested that BpDREB2 protein could function as a transcription factor of DREB family. The expression of BpDREB2 gene was remarkably induced by dehydration and high-salt treatments, but no significant change was observed under ABA or low-temperature conditions. Importantly, transgenic expression of BpDREB2 gene in Arabidopsis significantly enhanced its tolerance to salt and freezing without causing growth retardation. Taken together, these results suggested that BpDREB2 is a novel member of the AP2/EREBP trans-acting factor family which could enhance salt stress tolerance of plants and has the potential application in the improvement of crops and economical tree species.

Micropropagation of flowering dogwood (Cornus florida) from seedlings

A method for regenerating whole plants from nodal (axillary bud) cultures of seedlings was developed for flowering dogwood (Cornus florida L.). The seed source significantly influenced the rate of proliferation, although cultures initiated from each of the seven mother trees produced some shoots. Woody plant medium (WPM) was superior to either Murashige and Skoog or Schenk and Hildebrandt basal medium. 6-Benzyladenine (BA) at 2.2 or 4.4 μM stimulated the generation of significantly more useable shoots (≥1 cm) compared to all other concentrations (0.5-22.5 μM tested. Thidiazuron (TDZ) at 0.6 and 1.1 μM supported proliferation, but strongly inhibited shoot elongation. TDZ initiated cultures transferred to medium containing 4.4 μM BA produced usable shoots after five additional subcultures. Shoots generated adventitious roots when exposed to either a 12-h pulse of relatively high concentrations (246-1230 μM or continuous lower concentrations (0.5-49.0 μM of indolebutyric acid (IBA) for longer periods. Microshoots produced the significantly greatest number of roots when subjected to 4.9 μM IBA in WPM over a 4-week period. Whole plants were acclimatized to the laboratory conditions and subsequently to the greenhouse. The methodology described here should be useful in a breeding program by supplying multiple copies of unique, recombinant genotypes.