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Herbivorous insects are important nutrient cyclers that produce nutrient-rich frass. The impact of elevated atmospheric [CO sub(2)] on insect-mediated nutrient cycling, and its potential interaction with precipitation and temperature, is poorly understood and rarely quantified. We tested these climatic effects on frass deposition in a nutrient-limited mature woodland. Frass deposition by leaf-chewing insects and its chemical composition was quantified monthly over the first 2 years at the Eucalyptus free-air CO sub(2) enrichment experiment and contrasted with leaf nitrogen concentration, rainfall and temperature. Leaf-chewing insects produced yearly between 160 and 270 kg ha super(-1) of frass depositing 2 to 4 kg ha super(-1) of nitrogen. Frass quantity and quality were influenced by rainfall and average maximum temperatures. In contrast, elevated CO sub(2) did not impact nitrogen concentrations in fully expanded leaves and frass deposition to the woodland floor. Two years of elevated CO sub(2) did not alter nutrient transfer by leaf-chewing insects. This may be due to the low nutrient status of this ecosystem, duration of CO sub(2) fumigation or climatic conditions. However, rainfall co-occurring with seasonally higher temperatures exerted strong effects on nutrient cycling, potentially through shifts in leaf phenology with consequences for insect population dynamics and insect-mediated nutrient transfer.

Background As an efficient and high-quality additive in agriculture and forestry production, silicon (Si) plays an important role in alleviating heavy metal stress and improving plant growth. However, the alleviating effect of aluminum (Al) toxicity by Si in Eucalyptus is still incomplete. Results Here, a study was conducted using two Al concentrations (0 and 4.5 mM) with four Si concentrations (0, 0.5, 1, and 1.5 mM) to investigate plant growth, tolerance and antioxidant defense system in four Eucalyptus species ( Eucalyptus tereticornis , Eucalyptus urophylla , Eucalyptus grandis , and  Eucalyptus urophylla  ×  Eucalyptus grandis ). The results showed that the stress induced by 4.5 mM Al increased oxidative damage, disturbed the balance of enzymatic and non-enzymatic antioxidant systems, and negatively affected plant growth and tolerance quality in the four Eucalyptus species. However, the addition of 0.5 mM and 1 mM Si alleviated the effects of Al toxicity on plant growth and improved plant growth quality by strengthening stress tolerance. Besides, adding Si significantly facilitated the synergistic action of enzymatic and non-enzymatic antioxidant defenses, increased the removal of reactive oxygen species, reduced lipid peroxidation, and oxidative stress, and promoted the phytoremediation rate of the four Eucalyptus species by 18.7 ~ 34.8% compared to that in the absence of Si. Conclusions Silicon can alleviate the effect of Al toxicity by enhancing the antioxidant capacity and improving plant growth and tolerance quality. Hence, the application of Si is an effective method for the phytoremediation of Eucalyptus plantations in southern China.

Eucalyptus urophylla X Eucalyptus grandis is an important afforestation hybrid clone that supports wood safety in China. To explore the mechanism of callus formation and differentiation of different types of E. urophylla × E. grandis , we cultivated four different types of E. urophylla × E. grandis calli, measured their enzyme activities and endogenous hormones, and sequenced them at the transcriptome level. Transcriptome analysis revealed that there were significant differences in the clustering of differentially expressed genes. Compared with the green calli, 2203, 2485, and 2078 differentially expressed genes were identified in the red, white, and yellow calli, respectively. Differentially expressed genes were involved in metabolic processes, biological regulation, signal transduction, stimulus response, catalytic activity, and binding, such as GRFs gene. Combined with the changes in physiological indices and transcription levels, we revealed the regulatory characteristics of substance storage and antioxidant capacity in the process of callus differentiation of E. urophylla × E. grandis , which contributes to the understanding of the mechanism of plant cell growth and differentiation.

Eucalyptus is well reputed for its use as medicinal plant around the globe. The present study was planned to evaluate chemical composition, antimicrobial and antioxidant activity of the essential oils (EOs) extracted from seven Eucalyptus species frequently found in South East Asia (Pakistan). EOs from Eucalyptus citriodora, Eucalyptus melanophloia, Eucalyptus crebra, Eucalyptus tereticornis, Eucalyptus globulus, Eucalyptus camaldulensis and Eucalyptus microtheca were extracted from leaves through hydrodistillation. The chemical composition of the EOs was determined through GC-MS-FID analysis. The study revealed presence of 31 compounds in E. citriodora and E. melanophloia, 27 compounds in E. crebra, 24 compounds in E. tereticornis, 10 compounds in E. globulus, 13 compounds in E. camaldulensis and 12 compounds in E. microtheca. 1,8-Cineole (56.5%), α-pinene (31.4%), citrinyl acetate (13.3%), eugenol (11.8%) and terpenene-4-ol (10.2%) were the highest principal components in these EOs. E. citriodora exhibited the highest antimicrobial activity against the five microbial species tested (Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Aspergillus niger and Rhizopus solani). Gram positive bacteria were found more sensitive than Gram negative bacteria to all EOs. The diphenyl-1-picrylhydazyl (DPPH) radical scavenging activity and percentage inhibition of linoleic acid oxidation were highest in E. citriodora (82.1% and 83.8%, respectively) followed by E. camaldulensis (81.9% and 83.3%, respectively). The great variation in chemical composition of EOs from Eucalyptus, highlight its potential for medicinal and nutraceutical applications.

Compound-specific isotopic analyses were used to assess the dynamics and origin of organic matter in soils across a 30 year chronosequence where native savanna (C sub(4)) had been replaced with eucalyptus (C sub(3)). Apolar lipid fractions were recovered from plants and soils planted with Eucalyptus 0, 7.5, 17 and 30 years ago. The molecular composition of lipids in plants and soils identified three major pentacyclic triterpene methyl esters (PTMEs) specific to savanna, and three odd n-alkanes common to both vegetation types. Savanna-derived PTMEs and delta super(13)C remained at similar levels in soils after 30 years of eucalyptus growth. super(14)C content of PTMEs under savanna was lower than that of bulk soil and displayed the presence of older (1,000s of years) PTMEs in soils. However, the super(14)C content of soil PTMEs under eucalyptus was higher than that of the soil PTMEs under savanna. This suggests both recent (10s of years) and \"pre-bomb\" mineralization of savanna-derived PTMEs. Compound-specific super(13)C analyses of soil n-alkanes showed a trend typical of a C sub(3)/C sub(4) vegetation shift, with more depleted delta super(13)C values with increasing time under Eucalyptus. super(14)C analyses of n-alkanes suggest that n-alkanes have high turnover rates in the first few years after land conversion, and n-alkane composition thereafter is dominated by eucalyptus inputs. Compound-specific analyses reveal that lipids from past vegetations remained in soils. Compound-specific analyses allow a more nuanced description of carbon turnover in soils, and may improve our mechanistic understanding of soil organic carbon dynamics.

Eucalyptus grandis × E. urophylla was a unique hybridization in China. However, the chemical and pharmacological properties were rarely reported. Therefore, in this work, we used a steam distillation method to obtain essential oils from leaves of E. grandis × E. urophylla, and further evaluated the antioxidant, antimicrobial, and phytotoxic potential of the essential oil. Gas chromatography mass spectrometry (GC-MS) was applied to investigate the chemical composition of E. grandis × E. urophylla essential oil (EEO) and the results showed that the main components of EEO were monoterpenes followed by sesquiterpenes. Among them, α-pinene accounted about 17.02%. EEO could also well scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2, 2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals showing a good free radical clearance ability. In addition, EEO efficiently inhibited the growth of six kinds of bacteria as well as seven kinds of plant pathogens, especially Salmonella typhimurium and Colletotrichum gloeosporioides. Moreover, the seedling germination of Raphanus sativus, Lactuca sativa, Lolium perenne, and Bidens pilosa was significantly suppressed by EEO, thus, indicating essential oils from eucalyptus possessed an excellent phytotoxic activity. This study may give a better understanding on EEO and provide a pharmacological activities analysis contributing to the further research of EEO as a functional drug in agronomic and cosmetic industries.

A basic understanding of nutrition effects on the mechanisms involved in tree response to drought is essential under a future drier climate. A large-scale throughfall exclusion experiment was set up in Brazil to gain an insight into the effects of potassium (K) and sodium (Na) nutrition on tree structural and physiological adjustments to water deficit. Regardless of the water supply, K and Na supply greatly increased growth and leaf area index (LAI) of Eucalyptus grandis trees over the first 3 yr after planting. Excluding 37% of throughfall reduced above-ground biomass accumulation in the third year after planting for K-supplied trees only. E. grandis trees were scarcely sensitive to drought as a result of the utilization of water stored in deep soil layers after clear-cutting the previous plantation. Trees coped with water restriction through stomatal closure (isohydrodynamic behavior), osmotic adjustment and decrease in LAI. Additionally, droughted trees showed higher phloem sap sugar concentrations. K and Na supply increased maximum stomatal conductance, and the high water requirements of fertilized trees increased water stress during dry periods. Fertilization regimes should be revisited in a future drier climate in order to find the right balance between improving tree growth and limiting water shortage.

Eucalyptus maideni F. v. Muell., a rare species cultivated for both oil and timber, yields high-quality wood and economically valuable eucalyptus oil (EO). Previous studies revealed substantial variation in leaf oil content among individual seedlings and families. However, the selection and breeding of superior germplasm for oil production have not yet been initiated. In this study, 15 superior trees were used as seed trees, while commercial seeds served as the controls. Seedlings were sown in family groups, and leaves from seed trees and 480 seedlings (sampled at 180 and 360 days post-sowing) were analyzed. EO was extracted from seed tree leaves by steam distillation and from seedling leaves by headspace solid-phase microextraction, with gas chromatography-mass spectrometry (GC–MS) used for component quantification. Among 249 compounds identified, 1,8-cineole (eucalyptol) consistently exhibited the highest relative content (40.61–71.27%). Significant differences in eucalyptol content were found among families and individuals at both seedling ages, with a coefficient of variation (CV) of approximately 25%. Eucalyptol content at both 180 and 360 days was primarily influenced by within-family variance (56.91% and 62.43%, respectively), exceeding between-family variance (42.13% and 36.73%). Additionally, moderate correlations between eucalyptol concentrations at 180 and 360 days suggest partial temporal stability in essential oil composition across developmental stages. Therefore, the relative eucalyptol content was identified as a key indicator for the preliminary selection of superior germplasm in oil-producing E. maideni . Using the mean + standard deviation ( C  + σ) as the selection threshold, two superior families (Families 2 and 3) and 56 elite seedlings were preliminarily identified across both growth stages. The selected superior families exhibited an average increase of 29.85% in leaf eucalyptol content, while the elite seedlings showed an average increase of 37.61%. These results demonstrate the feasibility and effectiveness of early selection for superior germplasm in oil-producing E. maideni . The selected superior germplasm provides foundational material for the subsequent propagation of improved varieties, thereby supporting the development of the oil-producing E. maideni industry in Yunnan Province.

Summary Eucalyptus trees are among the most important species for industrial forestry worldwide. However, as with most forest trees, flowering does not begin for one to several years after planting which can limit the rate of conventional and molecular breeding. To speed flowering, we transformed a Eucalyptus grandis × urophylla hybrid (SP7) with a variety of constructs that enable overexpression of FLOWERING LOCUS T (FT). We found that FT expression led to very early flowering, with events showing floral buds within 1–5 months of transplanting to the glasshouse. The most rapid flowering was observed when the cauliflower mosaic virus 35S promoter was used to drive the Arabidopsis thaliana FT gene (AtFT). Early flowering was also observed with AtFT overexpression from a 409S ubiquitin promoter and under heat induction conditions with Populus trichocarpa FT1 (PtFT1) under control of a heat‐shock promoter. Early flowering trees grew robustly, but exhibited a highly branched phenotype compared to the strong apical dominance of nonflowering transgenic and control trees. AtFT‐induced flowers were morphologically normal and produced viable pollen grains and viable self‐ and cross‐pollinated seeds. Many self‐seedlings inherited AtFT and flowered early. FT overexpression‐induced flowering in Eucalyptus may be a valuable means for accelerating breeding and genetic studies as the transgene can be easily segregated away in progeny, restoring normal growth and form.

Background Eucalyptus urophylla × Eucalyptus grandis ( E. urograndis ) is a globally significant forest tree species renowned for its rapid growth, high yield, and exceptional wood production efficiency. A comparative analysis of its parental genomes, coupled with an in-depth investigation of the expression patterns of wood-related genes, will provide critical genomic resources to enhance research and utilization of this superior eucalypt hybrid species. Results In this study, we present a draft genome assembly consisting of 592.09 Mb of data, with 99.91% anchored to 11 pseudochromosomes. The assembly achieved a contig N50 of up to 3.73 Mb and a scaffold N50 of up to 58.62 Mb. Gene annotation and evaluation revealed that the E. urograndis genome contains 32,151 genes, of which 93.50% were fully annotated using Benchmarking Universal Single-Copy Orthologs (BUSCOs). Based on evolutionary analysis, E. grandis and E. urograndis are estimated to have diverged approximately 2.90 million years ago (Mya). Additionally, 131 gene families were found to be significantly expanded, and 475 positively selected genes (PSGs) were identified in the E. urograndis genome. Furthermore, RNA sequencing (RNA-seq) technology was employed to analyze allele-specific expression patterns of key enzymes involved in cellulose, xylan, and lignin biosynthesis. Several allele-specific expression genes (ASEGs) were identified, potentially associated with heterosis in E. urograndis . Conclusions The chromosomal-level genome assembly of E. urograndis presented in this study serves as a valuable genomic resource for eucalyptus molecular breeding, provides novel insights into its evolution, wood formation improvement, and adaptability, and enhances our understanding of genetic and molecular mechanisms underlying heterosis in Eucalyptus hybrids.