Eucalyptus Species Research Articles

Modelling individual tree maximum basal area growth rates of five tall eucalypt species growing in even-aged forests

Inventory plot data were available providing over 87,000 individual tree basal area growth rates from even-aged native forests of three ash eucalypts (Eucalyptus regnans, E. obliqua, and E. delegatensis), from temperate regions, and two other species from more sub-tropical climes (E. grandis and E. pilularis). Models were developed relating maximum observed growth rates for these species in relation to tree size when, presumably, trees were under ideal environmental conditions and without competition from neighbours for site growth resources. These maximum growth rates increased with increasing tree size to a maximum of their own and then declined as tree size (hence age) increased further. The tree sizes, at which these maximum growth rates reached their maxima, were much greater for the ash eucalypts than for the other two species. It is hypothesised that the ash eucalypts may have evolved physiological characteristics that make them more efficient in compensating for the well-known physiological constraints imposed on growth rates as trees grow to great heights and ages.

Insect repellent and insecticidal potential of two Eucalyptus species essential oils from subtropical desert climate

Insect repellent and insecticidal potential of two Eucalyptus species essential oils from subtropical desert climate

Eucalyptus Species Discrimination Using Hyperspectral Sensor Data and Machine Learning

The identification of tree species is very useful for the management and monitoring of forest resources. When paired with machine learning (ML) algorithms, species identification based on spectral bands from a hyperspectral sensor can contribute to developing technologies that enable accurate forest inventories to be completed efficiently, reducing labor and time. This is the first study to evaluate the effectiveness of classification of five eucalyptus species (E. camaldulensis, Corymbia citriodora, E. saligna, E. grandis, and E. urophyla) using hyperspectral images and machine learning. Spectral readings were taken from 200 leaves of each species and divided into three dataset sizes: one set containing 50 samples per species, a second with 100 samples per species, and a third set with 200 samples per species. The ML algorithms tested were multilayer perceptron artificial neural network (ANN), decision trees (J48 and REPTree algorithms), and random forest (RF). As a control, a conventional approach by logistic regression (LR) was used. Eucalyptus species were classified by ML algorithms using a randomized stratified cross-validation with 10 folds. After obtaining the percentage of correct classification (CC) and F-measure accuracy metrics, the means were grouped by the Scott–Knott test at 5% probability. Our findings revealed the existence of distinct spectral curves between the species, with the differences being more marked from the 700 nm range onwards. The most accurate ML algorithm for identifying eucalyptus species was ANN. There was no statistical difference for CC between the three dataset sizes. Therefore, it was determined that 50 leaves would be sufficient to accurately differentiate the eucalyptus species evaluated. Our study represents an important scientific advance for forest inventories and breeding programs with applications in both forest plantations and native forest areas as it proposes a fast, accurate, and large-scale species-level classification approach.

Cytokinin promotes anthocyanin biosynthesis via regulating sugar accumulation and MYB113 expression in Eucalyptus.

Anthocyanins are flavonoid-like substances that play important roles in plants' adaptation to various environmental stresses. In this research, we discovered that cytokinin (CK) alone could effectively induce the anthocyanin biosynthesis in Eucalyptus and many other perennial woody plant species, but not in tobacco and Arabidopsis, suggesting a diverse role of CK in regulating anthocyanin biosynthesis in different species. Transcriptomic and metabolomic strategies were used to further clarify the specific role of CK in regulating anthocyanin biosynthesis in Eucalyptus. The results showed that 801 and 2241 genes were differentially regulated at 6 and 24h, respectively, after CK treatment. Pathway analysis showed that most of the differentially expressed genes were categorized into pathways related to cellular metabolism or transport of metabolites, including amino acids and sugars. The metabolomic results well supported the transcriptome data, which showed that most of the differentially regulated metabolites were related to the metabolism of sugar, amino acids and flavonoids. Moreover, CK treatment significantly induced the accumulation of sucrose in the CK-treated leaves, while sugar starvation mimicked by either defoliation or shading treatment of the basal leaves significantly reduced the sugar increase of the CK-treated leaves and thus inhibited CK-induced anthocyanin biosynthesis. The results of in vitro experiment also suggested that CK-induced anthocyanin in Eucalyptus was sugar-dependent. Furthermore, we identified an early CK-responsive transcription factor MYB113 in Eucalyptus, the expression of which was significantly upregulated by CK treatment in Eucalyptus, but was inhibited in Arabidopsis. Importantly, the overexpression of EgrMYB113 in the Eucalyptus hairy roots was associated with significant anthocyanin accumulation and upregulation of most of the anthocyanin biosynthetic genes. In conclusion, our study demonstrates a key role of CK in the regulation of anthocyanin biosynthesis in Eucalyptus, providing a molecular basis for further understanding the regulatory mechanism and diversity of hormone-regulated anthocyanin biosynthesis in different plant species.

Traditional homegardens change to perennial monocropping of khat (Catha edulis) reduced woody species and enset conservation and climate change mitigation potentials of the Wondo Genet landscape of southern Ethiopia

Smallholder farmers in the Wondo Genet were forced to switch from long-standing, diverse traditional home gardens to monoculture khat production due to increasing population pressure-induced farmland constraints. The composition of woody species and the biomass carbon stock are thought to drop as homegardens transition from polyculture to monoculture; however there is little quantitative evidence to support this claim. This study was started to assess the effects on woody species, enset, and biomass carbon of converting traditional homegardens to a fast spreading perennial monocropping of khat (Catha edulis Forskal). In 10 m × 10 m (100m2) plots from 43 farms with neighboring land use patterns for each homegarden and khat, woody species and enset were inventoried, the total number of tree, shrub, and enset species counted, as well as the height and diameter of each species measured. To determine the biomass carbon stock of each land use type, both general and species-specific allometric equations are used. Simpson's diversity index, Shannon-Wiener, and Shannon equitability were used to evaluate the diversity of enset and woody species. There were 27 different types of woody species identified, with trees making up 67 % of the total and shrubs accounting for 33 %. Shannon, Simpson, and the richness of woody species all decreased by 46 %, 51 %, and 38 %, respectively, in comparison to residential gardens. For homegardens and khat, respectively, the mean Evenness values were 0.876 and 0.539. In homegardens, Coffea arabica was the most valuable woody species, followed by Cordia africana Lam, Persea americana, Eucalyptus camaldulensis, and Grevillea Robusta. In contrast, Catha edulis was the most valuable woody species in the Khat land use type, followed by Coffea arabica, Croton macrostachyus Del, and Cordia africana. In comparison to homegardens, the above-ground, below-ground, and total biomass carbon reported in khat land use types were reduced by 18 %, 63 %, and 42 %, respectively. Grevillea and Eucalyptus species made up 51 % of the total biomass carbon stock in the homegardens, which suggests that khat and quickly expanding fast-growing plants have displaced native woody species.Understanding the long-term effects of agro-biodiversity loss requires greater research on the implications of the decline in woody species diversity and biomass carbon stock on soil fertility and sustainable farming. This is due to the numerous functions that woody species and enset play.

Eucalyptus leaf spot disease caused by Coniella eucalyptorum in Sri Lanka

Coniella has a wide distribution as a plant pathogen in Eucalyptus species. Here we report a leaf spot disease caused by Coniella eucalyptorum on Eucalyptus camaldulensis in Sri Lanka. The pathogen was isolated from symptomatic leaf samples of E. camaldulensis plants from Polonnaruwa District in Sri Lanka. The isolated fungus was identified as C. eucalyptorum based on morphological characteristics and multi-gene phylogenetic analysis of combined sequences of the internal transcribed spacer region (ITS), the partial translation elongation factor 1-α gene (tef1-α), and large subunit of nuclear ribosomal RNA (LSU). The pathogenicity test was performed to confirm its pathogenicity to the host, which produced symptoms similar to those observed in the field. This is the first report of C. eucalyptorum associated with Eucalyptus plantations in Sri Lanka. This finding is important to expand the knowledge of plant pathogen diversity in Eucalyptus species and other economically important crops in Sri Lanka.

Detection of Genetic Relationship Between Eucalyptus Species in Iraq

Environmental factors that damage plant cells by dehydrating them, such cold, drought, and high salinity, are the most common environmental stresses that have an impact on plant growth, development, and productivity in cultivated regions around the world. Several types of plants have several drought, salinity, and cold inducible genes that make them tolerant to environmental challenges. The purpose of this study was to investigate several species in Eucalyptus plants and determined the evolutionary descent between different species of Eucalyptus. Samples from plants were used to extract genomic DNA. After sequence methods with phylogenetic analysis using MEGA6, program. According to our findings, demonstrate that the sequences of several spp. were submitted to Gene Bank: E. alba (OP696606.1), E. bortryoides (OP696601.1), E. camaldulensis (OP696607.1), E. curtisii (OP696596.1), E. delegatensis (OP696604.1), E. erythrocorys (OP696599.1), E. globoidea (OP696597.1), E. leucoxylon (OP696598.1), E. macarthurii (OP696610.1), E. nicholii (OP696602.1), E. pauciflora (OP696603.1), E. siderophloia (OP696605.1), E. tereticornis (OP696611.1), and E. vicina (OP696608.1). These genes can be used to create crop plants that are resistant to drought.

The anti-proliferative activity and cellular antioxidant activity of oenothein B and its content in different Eucalyptus species and region

The anti-proliferative activity and cellular antioxidant activity of oenothein B and its content in different Eucalyptus species and region

A simple method for Eucalyptus species discrimination: FTIR spectroscopy and machine learning

Wood sample classification is crucial in forestry, woodworking, and conservation efforts. It involves categorizing wood species based on physical characteristics like grain patterns, color, texture, and density. However, there are scientific gaps that hinder its effectiveness. One challenge is the difficulty in differentiating wood species with similar characteristics. To address this, we propose using FTIR spectroscopy and machine learning algorithms. In our study, we focused on the accurate classification of Corymbia citriodora (CIT), Eucalyptus grandis (GRA), and the hybrid species GG100 (GG). We evaluated bark and sapwood samples to determine the best for such a purpose. Using FTIR spectroscopy and Quadratic Discriminant Analysis with only seven PCs, we achieved 100% accuracy in bark sample classification. This approach offers advantages because FTIR spectroscopy captures unique chemical fingerprints, providing rapid and non-destructive analysis of wood samples. Machine learning algorithms learn from these spectral patterns for accurate species prediction. Notably, bark samples, easily obtained without tree damage, showed excellent classification results. By incorporating FTIR spectroscopy and machine learning, we can overcome the challenges of inter-species similarities and intra-species variations. This improves reliability and accuracy, supporting and ensuring high-quality wood products. Integrating FTIR spectroscopy and machine learning presents a promising solution for enhancing wood sample classification. Further research can expand species classification and improve wood identification processes.

Metabolite profiling of four Tunisian Eucalyptus essential oils and assessment of their insecticidal and antifungal activities

Aphids (Aphidoidea) and Fusarium spp. are widely recognized as destructive pests that cause significant damage to crops on a global scale. This study aimed to ascertain the chemical composition of essential oils (EOs) of four Tunisian Eucalyptus species and evaluate their toxicity against common aphids and phytopathogenic fungi.The EOs were obtained via hydrodistillation and subsequently analyzed using GC-MS. The chemical composition analysis revealed the presence of five distinct chemical classes in the EOs: monoterpene hydrocarbons (3.8–16.7 %), oxygenated monoterpenes (5.5–86.0 %), sesquiterpene hydrocarbons (0.2–2.2 %), oxygenated sesquiterpenes (4.2–86.7 %), and non-terpene derivatives (0.1–14.1 %).Hierarchical clustering analysis (HCA) and principal component analysis (PCA) of the Eucalyptus leaf EOs highlighted significant differences among them, leading to the generation of distinct HCA clades representing at least twelve major components.The statistical analysis clearly demonstrated a dose-response relationship, indicating the impact of the tested EOs on the growth of insects and fungal mycelium. The observed effects varied due to the variability in the chemical compositions of the EOs.Notably, among the EOs tested, Eucalyptus lesoufii Maiden exhibited particularly potent effects against the targeted insect and fungal species. This research contributes to the ongoing exploration of natural alternatives to chemical pesticides, providing further insights for potential industrial applications. It underscores the versatility of these EOs and their potential as valuable candidates in strategies for pest and disease management.

Eucalyptus-derived essential oils alleviate microbes and modulate inflammation by suppressing superoxide and elastase release

The Eucalyptus tree, belonging to the myrtle family, grows all over the world for its pharmaceutical and industrial benefits. In this article, we present a comparative analysis of the chemical composition of the hydrodistilled oils obtained from three different Eucalyptus species growing in Egypt viz. E. citriodora, E. camaldulensis, and E. ficifolia. Gas Chromatography-Mass Spectrometric guided analysis resulted in the identification of a total of 20 metabolites in E. citriodora oil with citronellal (54.9%) and citronellol (25.4%) being the most dominant components. β-cymene (12.7%) and 1,8-cineole (11.7%) were the major volatile constituents identified in E. camaldulensis oil, while trans-β-ocimene (22.4%), 1,8-cineole (13.5%), and L-trans-pinocarveol (12.5%) were the dominating components in the oil of E. ficifolia. The essential oils of the studied species were evaluated for their in vitro anti-inflammatory, antiviral including anti-SARS-CoV-2 (severe acute respiratory syndrome corona virus 2), antibacterial, and antifungal activities. E. citriodora oil displayed the highest inhibitory activity on the release of the superoxide radical (32%) and elastase enzyme (31%) in human neutrophils, while E. ficifolia oil had enhancing effects on elastase. The latter showed significant antiviral effects against hepatitis A, herpes simplex, and coxsackie viruses with IC50 values at 2.1, 2.5, and 5.6 μg/mL, respectively. Moderate antibacterial and antifungal activities were observed for Eucalyptus oils with Staphylococcus aureus being the most susceptible bacterial strain. E. ficifolia oil, similarly, displayed the best antibacterial activity with minimum inhibitory concentration (MIC) value at ca. 25 μg/mL (for S. aureus). On the contrary, E. camaldulensis oil was the most active against Candida albicans with an MIC value at 45 μg/mL. In silico studies were performed with a number of macromolecular drug targets for confirming the biological activities of the identified compounds and for interpreting their ADME (absorption-distribution-metabolism-elimination) parameters.

Heterosis from eucalypt single and multi-cross hybrids

Hybridizing is one of the most important ways to genetically improve eucalypts; especially to tropical species. Because of the high efficiency of asexual using hybrid heterosis, the current planting eucalypt varieties in most tropical areas in the world are hybrids. It’s well known that crossing different eucalypt species in different ways can create hybrids with different characters. But, it’s unclear what kind of species matings tend to create more heterosis. Here we systematically made and tested hybrids of: pure species by pure species (single cross), pure species by hybrids (three-way cross), hybrids by hybrids (double cross). The tropical eucalypt species we used as parents include: Eucalyptus urophylla, E. grandis, E. pellita, E. tereticornis and hybrids between them. The field testing results found: the overall performance of tree volume was: single cross > three way cross > intraspecies cross > double cross. Their 4-year advantages over intraspecies cross were: 29.9%, 8.0% and -12.5%. The coefficient of variation of the 4 types were: 55.3%, 61.2%, 64.0% and 67.1%. As for the survival rate, 4-year result was: double cross (72.6%) > three way cross (71.6%) > single cross (70.8%) > intraspecies cross (54.0%). This shows that the interspecies hybrids had similar environmental adaption, and they were all significantly higher than that of intraspecies cross. The single and multi-cross hybrids had similar coefficient of variation on survival rate. Combining with the results on family and individual tree level heterosis frequency and magnitude, we found that single-cross has more heterosis on volume growth while muti-cross has more heterosis on adaption. Genetic parameter analysis showed that single-cross hybrids have both high additive and high dominant heritability. But the heritability value on different species combinations can be very different. Three way-cross hybrids had the highest additive heritability, but very low dominant heritability. The double-cross hybrids had high dominant heritability, but very low additive heritability.

Strategies employed by Sappi Forests for improved seed production of temperate and sub-tropical pine and eucalypt species, and their hybrids, for long-term sustainability in a changing environment

The annual demand and supply of genetically improved planting stock suitable for sites across varying landscapes, with changing climatic conditions and increasing pest and disease threats are becoming more complex. The agility for effective responses to long-term sustainability of commercial plantations, aimed at different markets, requires a significant investment in genetic resource acquisitions, tree breeding, land management, gene conservation and plant production systems. Tree breeding is one of our most important adaptation strategies in response to climate change and related challenges. These include pests and diseases, drought, frost, and delivery of fit-for-purpose fibre. To supply an annual demand of over sixty million plants, consisting of both pure species seedlings and hybrid cuttings, Sappi requires a well-established pipeline. In addition, this pipeline allows for the sale of between 30 and 40 million viable seeds to both the domestic and international markets. Early acquisition of pine and eucalypt genetic resources suitable for sub-tropical to warm temperate, cool temperate and cold areas has allowed the development of pure species base populations containing genotypes improved for the traits of interest. Through recurrent selection, these populations have been advanced. Key traits include growth, pest and disease tolerance, and wood properties. Various strategies have been adopted to reduce breeding cycles, convert from pure species seedlings to hybrid clonal varieties to sustain productivity. Production of commercial quantities of seed is a key step in translating breeding and development into realised operational gains. A range of orchard types such as breeding seedling seed orchards (BSO), seedling seed orchards (SSO) and clonal seed orchards (CSO) have been developed to produce not only open pollinated seed but also to allow production of control pollinated hybrid seed. Each orchard type and combination of elite genotypes delivers a specific seed product with varying levels of improvement. In addition, associated technologies to produce control pollinated seed have been developed for the advancement of both clonal eucalypt and pine family cutting programmes.

Development and allocation of improved eucalyptus for biotic an abiotic tolerance

Since the 1960s, Altri Florestal is running a programme for selecting trees based on growth, wood density and cellulose content. Currently Eucalyptus globulus breeding programme is in third generation. Capturing the genetic gain is conducted through vegetative propagation to produce clones, as well as through seed production from a mass-controlled pollination programme for full-sib families. Ongoing climate change raises the importance of considering tolerance to abiotic stress in the Eucalyptus globulus breeding programme. Pursuing this objective has been done by carrying out a Best Linear Unbiased Prediction (BLUP) analysis considering macro climate regions with different exposure to cold and drought. Cold and drought maps were combined in one resulting in four regions of exposure: drought region (R1); cold region (R2); cold and drought region (R3); region with low exposure to cold and drought (R4). BLUP analysis included data from eighty-four field breeding trials with the following climatic distribution: 30 (R1); 19 (R2); 4 (R3), and 31 (R4). Data used comprises 160k genotypes and 210k measurements of height, diameter at breast height, and survival. It was possible to select around four genotypes with an overall superior performance in terms of growth and survival for the four regions considered. Furthermore, within each macro climate region groups of genotypes were selected with an increase of 50% volume per hectare above the original eucalyptus in the breeding programme. Altri is also involved in the development of new eucalyptus hybrids aiming to develop a new generation of eucalyptus hybrids more resilient to drought and cold, as well as pests such as Gonipterus platensis. This ongoing work is carried out via interspecific hybridization between E. globulus and other eucalyptus species. Eucalyptus hybrids are in several stages of development, namely: tested in several field trials, early field selection, being raised in the nursery, and being done through controlled crosses. Selection criteria will be based on performance from growth, survival, wood characteristics in field trials and in trials in controlled conditions. Finally, it is not enough to develop a portfolio of improved eucalyptus to ensure that realised genetic gain will be captured into operations. For this to happen it is necessary to ensure that allocation of improved eucalyptus is carefully planned. A prototype of decision tree for deploying improved eucalyptus has been already developed.

Rooting screening in Eucalyptus dunnii clones: inverting the order in a clonal selection process

One of the main goals of a tree breeding program is to increase forest productivity, adaptation and profitability of forest plantations. Eucalyptus dunnii is a main species used for pulp production in Uruguay. Montes del Plata (MdP) is one of the largest forest companies in Uruguay and has been focused on the development, testing and deployment of E. dunnii clones to establish commercial plantations in Uruguay. MdP clonal strategy starts with the generation, testing and selection of families (Open-pollination and|or Control-pollination) with a breeding population with a wide genetic diversity in order to have a sustainable clonal program. Seeds from the best families are used for clonal development in a two-phase strategy that takes place in the company research nursery. On the first phase, all potential clones are screened for rooting and only the ones that root more than 60% go to the next phase. An average of 4,000 E. dunnii clones is evaluated every year, and 200 clones overpass 60% rooting threshold. This represents 5% of screened clones. The second phase is to produce plants in the nursey for the establishment of clonal trials in field, and, based on the performance, to select the candidate clones for deployment and breeding. Although the strategy and the breeding program are relatively young, promising results are seen. In the last 6 years, 1,225 E. dunnii clones developed by this rooting strategy were successfully established in clonal field trials. For species of Eucalyptus that have an undesirable trait of difficulty-to-root (recalcitrance), the screening of genotypes by rooting allows to establish in field testing clones with efficient clonal propagation. This way, the measurement and wood sampling in field trials is funnelled to clones that, if selected, could be scaled to clonal plantations.

Identification of cold stress-responsive microRNAs and mRNA in Eucalyptus grandis

MicroRNAs (miRNAs) are a class of non-coding endogenous small RNAs that play a crucial role in plant growth, development, morphogenesis, signal transduction, and stress response. miRNAs negatively regulate gene expression at post-transcriptional level, causing translational repression or/and transcript degradation. The role of miRNAs in understanding gene expression reprogramming under different stress types has been pointed out. Low temperature is an important factor limiting the growth and distribution of plants. Under cold stress, plants attempt to maintain homeostasis and acquire cold acclimation, which involves extensive gene expression and metabolism reprogramming. Particularly, cold stress limits the distribution and productivity of Eucalyptus plantations, significantly affecting the survival and yield of seedlings. Despite the consensus on the relevance of miRNAs in regulating gene expression in plants and Eucalyptus's huge importance for the forest industry worldwide, information on miRNAs in Eucalyptus is still very scarce. In this work, we studied the miRNA and mRNA response to cold stress in E. grandis, one of Uruguay's most widely planted Eucalyptus species. Since seedlings are more susceptible to chilling injury, we subjected 3 different genotypes of seedlings to a cold shock followed by a 12-hour recovery phase at 25°C, analyzing a total of 4 treatments (G1: control, G2: 12 hours at 4°C, G3: 24 hours at 4°C, and G4: 24 hours at 4°C + 12 hours at 25°C). Cold treatment was evaluated measuring the electrolyte leakage. The membrane's damage was verified at 12 hours at 4°C, increasing the parameter at 24 hours. The membrane was partially recovered after 12 hours at 25°C, decreasing the electrolyte leakage. Transcriptome analysis showed an increase in the expression of genes belonging to the AP2|ERF family, including the DREB1|CBF genes —a group of genes that control the activation of protection mechanisms under cold stress. Within down-regulated genes, GO terms related to photosynthesis were enriched. Several conserved and new microRNAs were identified, but only a minority changed their expression with cold treatment, among them, the miR828. This microRNA was down-regulated after the cold treatment, which, according to several studies, induces the expression of anthocyanins. Anthocyanin levels are known to increase under different conditions, including cold stress. These results provided data on gene silencing mechanisms in E. grandis and allowed characterizing the response to cold mediated by small RNAs. This data could be potentially used by selection and improvement programs seeking to select clones more tolerant to cold stress.

Feasibility of using Uruguayan Eucalyptus for sustainable timber connections

Uruguayan fast-growing Eucalyptus grandis has emerged as a promising sustainable material for structural building components. However, traditional methods for joining timber components, such as beams and columns, typically rely on metallic fasteners, and mass timber products like glued laminated timber often use adhesives. In response to growing environmental concerns over the past five years, researchers have explored the substitution of petroleum-based adhesives and metallic fasteners with wooden pegs or dowels. To create effective connections, these dowels must be fashioned from denser wood than the lamellae. The embedment strength of both woods with varying densities is a critical factor in the design of timber connections using fasteners. This paper presents the results of a structural performance analysis of fully eucalyptus dowelled connections, constructed by combining Eucalyptus grandis (? = 473.2 kg|m3, COV = 13.2 %) for the lamellae and Eucalyptus tereticornis (? = 1042.4 kg|m^3, COV = 3.2 %) for the dowel. The bending strength of dowels was determined for specimens with 15- and 18-mm diameters, yielding 173.0 MPa (COV = 10.7 %) and 184.0 MPa (COV = 8.3 %), respectively. Four series of connections were tested, varying the fiber orientation of the lamellae (longitudinal L, transversal T) and dowel diameter (15, 18), following the half-hole method described in ASTM D 5764 standard. The embedment strength values obtained for the connections are as follows: L-15 = 31.3 MPa (COV = 9.3 %), T-15 = 11.2 MPa (COV = 28.7 %), L-18 = 29.6 MPa (COV = 10.1 %), T-18 = 16.7 MPa (COV = 25.7 %). These results reveal that the longitudinal application of the load, aligned with the fiber orientation, exhibits approximately twice the strength of the transversal orientation, with less variability in the outcomes. Furthermore, a strong correlation with the lamellae density was observed, while no significant dependency on the dowel diameter was found. These findings represent a crucial initial step in characterizing and designing glue-free wood-wood connections. The utilization of different eucalyptus species presents a promising path for the development of connections that promote more sustainable timber construction systems.

Drought effects on water status, plant hydraulics and growth in Eucalyptus grandis and clonal hybrids with red gums and E. urophylla

Afforestation with Eucalyptus species occupies over a million hectares in Uruguay, and E. grandis is one of the most cultivated species, mainly for the timber industry. However, the increasing frequency of drought and heat waves in the region raises the need to evaluate hybrids with red gums (E. camaldulensis and E. tereticornis), since they are known to sustain gas exchange and growth even under severe drought conditions. Hybrids with E. urophylla are also evaluated for plantations in subtropical regions. This study aimed to compare the effects of drought on plant water status, hydraulics, and growth of E. grandis (one clone; G), E. grandis × camaldulensis (one clone; GC), E. grandis × tereticornis (one clone; GT), and E. grandis × urophylla (two clones; GU1 and GU2). Two drought-stress cycles were applied to six-month rooted cuttings from mid-spring to early fall under greenhouse environmental conditions. Predawn leaf water potential (?pd), midday leaf water potential (?md), relative leaf water content (RWC), stomatal conductance (gs), and plant growth were measured across each cycle. Daily fluctuation of Ψ was calculated as ΔΨ = Ψpd - Ψmd. Specific (kS) and leaf-specific (kL) hydraulic conductivities and specific leaf area (SLA) were measured at the end of the experiment. Percentage loss of hydraulic conductivity (PLC) was calculated after removing the xylem embolism. Preliminary results suggest that both red-gum hybrids had higher PLC under moderate-to-severe drought, as a consequence of maintaining high water potential gradients to sustain transpiration and carbon fixation throughout the experiment. Under the well-watered condition, no clonal difference was observed. Also, GT showed a three-fold increase in cavitation and had 1.5 times stomatal opening (gs) than the most drought-sensitive clone (E. grandis, G), and exhibited the lowest reduction (17%) in diameter growth under drought. Also, GC attained the highest height at the end of the study, 40% higher than E. grandis, and increased by 25% the SLA under drought. GU clones reached the highest diameter at the end of the study. Correlations among functional variables are explored, and the water supply capacity to the foliage among clones is discussed for a better understanding of drought resistance strategies and growth performance of the different taxa.

Differential photosynthetic response to short- and long-term water deficit in Eucalyptus clones and hybrids with red gums

In Uruguay, there are more than a million hectares forested, and Eucalyptus species predominate. Drought events are becoming more frequent and affecting growth of the stands, especially during the early stages of the crop. Thus, the need arises to analyze the effects of such events on processes that determine growth, such as photosynthesis. The effect of water restriction on photosynthetic parameters was analyzed under greenhouse conditions in 6-months-old rooted cuttings of a clone of E. grandis (GG) and two hybrids with red gums: E. grandis × E. camaldulensis (GC) and E. grandis × E. tereticornis (GT). To define irrigation regimes water potential of substrate (MPa) was assessed using samples with increasing water content (%HR, w|w). Data was used to fit a water retention curve. Field’s capacity pot weight was determined on water drained pots. The control condition (WW) was established at Ψw = -0.15 MPa, while the water restricted (WR) was Ψw = -0.30 MPa. Treatments were maintained by manually water feeding for 16 weeks. Physiological parameters and photosynthetic pigments were recorded 6 and 16 weeks after water withholding to simulate short- and long-term water restriction scenarios, respectively. The following measurements were registered on current year fully expanded sun-exposed leaves: stomatal conductance (gs), maximum net assimilation rate (Amax), PSII quantum efficiency (FPSII), and proportion of chlorophyll and carotenoids in a HPLC elution (%Chl, %Carot). In the initial period, GG maintained Amax and gs between conditions. However, despite exhibiting lower gs in the restricted condition, GC maintained their Amax and GT increased in WR. There was no effect of treatment on photosynthetic pigments and energy partitioning varied little. At the end of the 16-week period, GG showed only decreased stomatal conductance values, and did not change photosynthetic pigment content nor Amax despite water restriction. Hybrids showed increasing values of FPSII, %Chl, and Amax. The PCA for long-term water restriction data showed that pigment content and FPSII may explain the increased assimilation rate of the hybrid clones under WR. Changes in water use efficiency due to higher % Chl in the restricted condition for both hybrids are discussed. There are few reports of increments in chlorophyll in Eucalyptus in drought. Recent information suggests that these types of strategies are adaptative responses that allow plants to cope with stress.

Macro- and Micronutrient Contents and Their Relationship with Growth in Six Eucalyptus Species

Knowing nutrient allocation dynamics in the tissues and the characteristics related to growth in different forest species is crucial to fertilization management and selecting better species for specific environments, ensuring greater fertilization efficiency and consequent sustainability in the forestry sector through the rational use of fertilizers. The objectives of this study were (i) to evaluate the content of macro- and micronutrients in different tissues of eucalyptus species and (ii) to relate them with their growth. The treatments were composed of six eucalyptus species (Eucalyptus camaldulensis Dehnh., Corymbia citriodora Hook., E. saligna Sm., E. grandis W. Hill ex Maiden, E. urograndis, and E. urophylla S. T. Blake). Macro- (nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur) and micronutrient (boron, copper, iron, manganese, and zinc) contents were determined in the leaves, bark, and sapwood. To study the functional patterns in macro- and micronutrient contents, Canonical Variable Analysis (CVA) was performed. The first two canonical variables in nutrient content of leaves, bark, and sapwood and the growth variables of eucalyptus species accumulated values greater than 80% of variance. The species E. grandis and E. urograndis showed the highest means for volume and total height but showed no differences regarding the concentration of major elements in the tissues, except the iron content in the bark, which was higher compared to other species. CVA proved to be an excellent tool for understanding, identifying, and classifying the strategies of Eucalyptus sp. regarding the content of nutrients in the shoot biomass tissues and may support genetic improvement programs aiming at identifying potential species. Future research involving the use of remotely piloted aircraft and remote sensors could be a strategy to monitor nutrient contents in different parts of trees throughout the cycle of different eucalyptus species.