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Extraction of nanocellulose is challenging, especially from hardwoods due to its complex chemical structure as well as structural hierarchy. In this study, nanocellulose was isolated from wood pulp of two hardwood species, namely Eucalyptus tereticornis Sm. and Casuarina equisetifolia L. by steam explosion process. Pure cellulose wood pulp was obtained through Kraft pulping process followed by alkaline and bleaching pre-treatments. Isolated nanocellulose was characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Fourier Transformed Infrared (FTIR) Spectra, Thermogravimetric Analysis (TGA), and X-ray diffraction (XRD) studies. Nanocellulose obtained from both species showed non-significant difference with average diameter of 27.801 nm for eucalyptus and 28.690 nm for casuarina, which was confirmed from TEM and AFM images. FTIR spectra of nanocellulose showed prominent peaks corresponding to cellulose and absence of peaks corresponding to lignin. The elemental purity of nanocellulose was confirmed with EDAX detector. XRD analysis showed the enrichment of crystalline cellulose in nanocellulose, and also confirmed the significant conversion of cellulose I to cellulose II. During TG analysis the untreated fibres started to degrade earlier than the nanocellulose which indicated the higher thermal stability of nanocellulose. Highly entangled network like structure along with high aspect ratio make the nanofibres a versatile material for reinforcing the composites. This successful method can be replicated for industrial level production of cellulose nanofibres.

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.

Understanding physiological acclimation of photosynthesis and respiration is important in elucidating the metabolic performance of trees in a changing climate. Does physiological acclimation to climate warming mirror acclimation to seasonal temperature changes? We grew Eucalyptus tereticornis trees in the field for 14 months inside 9-m tall whole-tree chambers tracking ambient air temperature (T air) or ambient T air + 3°C (i.e. ‘warmed’). We measured light- and CO2-saturated net photosynthesis (A max) and night-time dark respiration (R) each month at 25°C to quantify acclimation. Tree growth was measured, and leaf nitrogen (N) and total nonstructural carbohydrate (TNC) concentrations were determined to investigate mechanisms of acclimation. Warming reduced A max and R measured at 25°C compared to ambient-grown trees. Both traits also declined as mean daily T air increased, and did so in a similar way across temperature treatments. A max and R (at 25°C) both increased as TNC concentrations increased seasonally; these relationships appeared to arise from source–sink imbalances, suggesting potential substrate regulation of thermal acclimation. We found that photosynthesis and respiration each acclimated equivalently to experimental warming and seasonal temperature change of a similar magnitude, reflecting a common, nearly homeostatic constraint on leaf carbon exchange that will be important in governing tree responses to climate warming.

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.

Background and aimsTropical soils often present two issues that can hinder plant growth: low phosphorus (P) and high manganese (Mn) availability. Eucalyptus tereticornis is frequently cultivated in such soils. We investigated the effects of Mn in E. tereticornis under contrasting soil P availability and hypothesized that arbuscular mycorrhizal (AM) symbiosis could alleviate Mn toxicity by improving P nutrition and altering the expression of Mn transporter genes.MethodsInoculated (AM) and non-inoculated (NM) seedlings grew for seven months in a soil with low or sufficient P availability, under three Mn doses: control, 75 and 150 mg kg−1 Mn. We assessed growth, AM colonization, nutrient concentrations, and the expression of eight genes related to Mn transport and homeostasis in roots. Mn distribution at one-leaf level was determined by μ-XRF.ResultsLow P exacerbated Mn toxicity and hindered plant growth. Mycorrhizal symbiosis did not influence Mn accumulation, but improved growth and Mn tolerance at low P, partly by improving P nutrition. At sufficient P, foliar Mn reached 3500 mg kg−1, and μ-XRF patterns suggest preferential accumulation in the leaf lamina compared to margins or midribs. In NM plants, the vacuolar transporters EtVIT1 and EtMTP8 and the Mn-nicotianamine influx transporter EtYSL6 were the most responsive genes to Mn, while in AM roots most were downregulated.ConclusionVacuolar sequestration and transport of complexed Mn are important mechanisms behind Mn tolerance in E. tereticornis. We propose that Mn is transported via the mycorrhizal pathway, explaining why it does not elicit the same molecular response observed in NM roots.

The allocation of carbon (C) is an important component of tree physiology that influences growth and ecosystem C storage. Allocation is challenging to measure, and its sensitivity to environmental changes such as warming and altered water availability is uncertain. We exposed young Eucalyptus tereticornis trees to +3°C warming and elimination of summer precipitation in the field using whole-tree chambers. We calculated C allocation terms using detailed measurements of growth and continuous whole-crown CO₂ and water exchange measurements. Warming increased growth respiration, but maintenance respiration acclimated homeostatically. The increasing growth in the warmed treatment resulted in higher rates of respiration, even with complete acclimation of maintenance respiration. Warming-induced stimulations of tree growth likely involve increased C allocation above ground, particularly to leaf area development, whereas reduced water availability may not stimulate allocation to roots. Trees grew from small saplings to nearly 9 m height during this 15-month experiment. Warming accelerated growth and leaf area development, and it increased the partitioning of gross primary production (GPP) to aboveground respiration and growth while decreasing partitioning below ground. Eliminating summer precipitation reduced C gain and growth but did not impact GPP partitioning. Trees utilized deep soil water and avoided strongly negative water potentials.

Reference genes are generally used as endogenous normalization factor for relative quantification of target genes in quantitative real-time PCR (qRT-PCR). The present work aimed at identifying suitable reference genes for normalization of qRT-PCR data in tissues of Eucalyptus tereticornis. The expression levels of housekeeping genes like Actin (EtAct2), Isocitrate dehydrogenase (EtIDH), ribosomal RNA (Etl8s rRNA), SAND family protein (EtSAND), Histone protein (EtH2B), alpha -Tubulin (EtTUB), and eukaryotic initiation factor (EteIF4B) were studied to characterize their normalization stability in different tissues including young leaves, internodes, developing and mature xylem. The expression level of these genes was analyzed using different algorithms like geNorm, NormFinder and Best-Keeper. Among the seven reference genes analyzed, EtAct2 was expressed with less variance and was found to be the most stable reference gene across different tissues using all the three programs, while the least stable gene identified was EtH2B. Further, the normalization efficiency of the reference genes were assessed to predict the expression levels of three primary cell wall specific cellulose synthase transcripts (EtCesAs) in E. tereticornis tissues. The relative expression of EtCesA4, EtCesA5 and EtCesA6 was determined to be 3-19 fold higher in leaf and internode tissues when compared to developing and mature xylem tissues. This study will allow accurate normalization of qRT-PCR experiments across different tissues in E. tereticornis for future genomic research in this tropical eucalypt species.

Background and aims Twenty-four species of eucalypts were studied regarding their ability to grow under low P and their responsiveness to P inputs. Methods Growth and photosynthesis-related parameters were evaluated. Results Growth of all species was influenced by low P availability. No significant correlation was found between leaf P concentration and biomass, indicating that P concentrations in leaves cannot be solely considered an indication of the responsiveness to P in eucalypts. Species responsive to P-input (high agronomic P efficiency values, APE) were those with low P use efficiency - PUE (here assessed as relative efficiency of P-use, REP) and low P uptake efficiency (PUpE). But, non-responsive species were related to higher P-efficiency under low soil P-availability. Eucalyptus tereticornis , E. cladocalyx , E. globulus and E. camaldulensis were efficient under low-P availability. Whereas, E. crebra and E acmenoides were the most responsive species, with high APE, suggesting that for these species P-inputs are needed to guarantee plant growth. The root:shoot ratio remained constant at different P availabilities, suggesting that biomass allocation towards the root in response to P and greater investment in roots were not correlated with greater PUE. Under limited P, E. robusta and E. botryoides exhibited low foliar P contents and higher root:shoot ratios than those of other species with higher P contents, indicating that greater root investment does not necessarily result in greater PUE. Conclusion The results suggest that the divergence among species is probably related to different mechanisms, which may improve P-use efficiency.

Given the contrasting short-term temperature dependences of gross primary production (GPP) and autotrophic respiration, the fraction of GPP respired by trees is predicted to increase with warming, providing a positive feedback to climate change. However, physiological acclimation may dampen or eliminate this response. We measured the fluxes of aboveground respiration (R a), GPP and their ratio (R a/GPP) in large, field-grown Eucalyptus tereticornis trees exposed to ambient or warmed air temperatures (+3°C). We report continuous measurements of whole-canopy CO2 exchange, direct temperature response curves of leaf and canopy respiration, leaf and branch wood respiration, and diurnal photosynthetic measurements. Warming reduced photosynthesis, whereas physiological acclimation prevented a coincident increase in R a. Ambient and warmed trees had a common nonlinear relationship between the fraction of GPP that was respired above ground (R a/GPP) and the mean daily temperature. Thus, warming significantly increased R a/GPP by moving plants to higher positions on the shared R a/GPP vs daily temperature relationship, but this effect was modest and only notable during hot conditions. Despite the physiological acclimation of autotrophic respiration to warming, increases in temperature and the frequency of heat waves may modestly increase tree R a/GPP, contributing to a positive feedback between climate warming and atmospheric CO2 accumulation.

• Photosynthetic water-use efficiency (WUE) describes the link between terrestrial carbon (C) and water cycles. Estimates of intrinsic WUE (iWUE) from gas exchange and C isotopic composition (δ13C) differ due to an internal conductance in the leaf mesophyll (g m) that is variable and seldom computed. • We present the first direct estimates of whole-tree g m, together with iWUE from whole-tree gas exchange and δ13C of the phloem (δ13Cph). We measured gas exchange, online 13C-discrimination, and δ13Cph monthly throughout spring, summer, and autumn in Eucalyptus tereticornis grown in large whole-tree chambers. Six trees were grown at ambient temperatures and six at a 3°C warmer air temperature; a late-summer drought was also imposed. • Drought reduced whole-tree g m. Warming had few direct effects, but amplified drought-induced reductions in whole-tree g m. Whole-tree g m was similar to leaf g m for these same trees. iWUE estimates from δ13Cph agreed with iWUE from gas exchange, but only after incorporating g m. δ13Cph was also correlated with whole-tree 13C-discrimination, but offset by −2.5 ± 0.7‰, presumably due to post-photosynthetic fractionations. • We conclude that δ13Cph is a good proxy for whole-tree iWUE, with the caveats that post-photosynthetic fractionations and intrinsic variability of g m should be incorporated to provide reliable estimates of this trait in response to abiotic stress.