Cultivation of a Wild Strain of Wood Ear Auricularia cornea from Brazil.

Auricularia cornea has become one of the most important cultivated mushrooms worldwide. Although not remarkably flavorful, Auricularia species are very versatile and rehydrate easily after drying, adding a unique and pleasing texture to the dishes. In this study, we collected, identified, and domesticated a wild strain of A. cornea from the Brazilian Atlantic Rainforest. The wild strain was evaluated for mycelial growth at different temperatures and substrates, biological efficiency, and nutritional composition. The temperature that best favored the A. cornea mycelium growth was 30 °C, and the substrate was sterile Eucalyptus sawdust. The highest biological efficiency value obtained was 106.90 ± 13.28%. Nutritional analysis showed that the produced wood ears contained 71.02% carbohydrates, 19.63% crude fiber, 11.59% crude protein, 10.19% crude fat, and 4.24% ash on dry matter basis. For the mineral content profile, the elements K and P were the most abundant. This is the first report on cultivation of a wild strain of A. cornea from Brazil.

Age trends of genetic parameters and genotype-by-environment interactions for growth traits of Eucalyptus urophylla clones in South-China.

Eucalyptus urophylla S.T. Blake, an important economic tree species, is widely cultivated as a raw material source for pulpwood, veneer plywood, and sawlog timber in southern China. As a tree in multiple environments, tree-breeding programs can assess genotype by environment (G × E) interactions and identify the suitable genotype for a specific environment. G × E interactions related to growth traits and soil factors have not been adequately studied for clones of Eucalyptus urophylla and its hybrids. To examine this important question, trials containing 20 clones of E. urophylla and its hybrids were established at three sites in southern China: Shankou (SK), Tiantang (TT), and Xiniujiao (XNJ). These sites each have different soil conditions but similar geographical and climatic conditions. With the data across nearly eight years, average phenotypic trends and broad sense repeatability (H2) were modeled, G×E interactions between clones and diverse soil environments were estimated, genetic gains of clones were calculated, and the adaptabilities of E. urophylla clones in different soil environments were compared. Average survival trends for clones tended to show a moderate decrease while growth traits tended to show sharp increases with age. At the same age, sites were ordered for average survival and growth traits as TT>SK>XNJ while H2 values for growth traits by site followed the basic order TT>SK>XNJ. The H2 values for growth traits at SK tended to increase at first, platform, and then smooth with age. The H2 values for growth traits at TT were high and stable across ages, and those at XNJ tended to undulate largely at a relatively low level across ages. Genetic correlations for growth traits between any pair of sites tended to increase at first and then decrease. A genetic correlation was strong between SK and TT, intermediate between SK and XNJ, and weak between TT and XNJ. It was concluded that: (1) clones tended to be adapted better to an environment with acidic and loamy soil with a clay content of about 45.6%, the soil depth from the surface to parent material about 1.5 m, and the previous vegetation of Eucalypts. (2) The G×E interactions between clones and sites are weaker if the environmental conditions between the sites are similar, and which are stronger if the environmental conditions between the sites are different. (3) The optimum selection age for clones ranged from 1.5 to 3.5 years old, while the optimum selection growth trait is individual tree volume.

Exogenous silicon alleviates aluminum stress in Eucalyptus species by enhancing the antioxidant capacity and improving plant growth and tolerance quality.

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.

Easily overlooked petiole traits are key factors that affect soil carbon sequestration in plantations in karst areas.

Vegetation restoration in karst areas has shifted from expanding planting areas to the collective enhancement of various ecological functions, especially carbon sequestration. Identifying and regulating key plant functional traits involved in the carbon cycle is an effective approach to increase carbon sequestration. However, reports on the significant contribution of petiole traits to the carbon cycle are scarce. Eucalyptus globulus and Bauhinia purpurea plantations in Liujiang river basin were investigated in this study. Petiole traits, understory characteristics, and soil organic carbon have been measured. The aim is to explore key effect of petiole traits for increasing soil carbon sequestration and to provide scientific evidence for the high-quality development of plantations in karst areas. The results indicate that in Eucalyptus globulus plantations, when the understory vegetation coverage is below 50 %, petioles tend to elongate rather than thicken, leading to an increase in specific petiole length. In Bauhinia purpurea plantations, petioles consistently tend to increase diameter. However, when specific leaf area decreases, specific petiole length increases. In both plantations, an increase in specific petiole length accelerates leaf shedding. It leads to increased litter accumulation so that soil carbon content increases. In Eucalyptus globulus plantations, to enhance soil carbon sequestration as an ecological goal, it is recommended to keep the soil total nitrogen below 1.20 mg/g, to control understory vegetation coverage below 50 %, and to limit the extension of Bidens pilosa. In Bauhinia purpurea plantations, within 100 m of altitude, the soil total nitrogen can be controlled below 1.00 mg/g to increase soil organic carbon from large leaf shedding due to the increase of specific petiole length. At lower altitudes, increasing soil total nitrogen can enhance understory vegetation coverage, allowing soil organic carbon to originate from both leaf shedding and understory vegetation residues.

The use of Pisolithus albus found in saline areas to improve the growth of Eucalyptus seedlings under high salinity conditions.

Salinity is an abiotic factor limiting plant fitness and therefore forest crop productivity, and salt-affected areas have been expanding throughout the world. Ectomycorrhizal (ECM) fungi can improve the salt tolerance of woody plants, including Eucalyptus species To screen for salt-resistant Pisolithus albus (PA) isolates, 16 PA isolates were cultivated on modified Melin-Norkrans agar containing NaCl at concentrations of 0, 10, 20, and 30 dS m-1. The P. albus isolate PA33 had the greatest salt resistance under 10 and 20 dS m-1 NaCl, which are soil salinity levels in salt-affected areas of Thailand. We studied the effect of PA33 on Eucalyptus camaldulensis × E. pellita cuttings under salt stress (0 and 16 dS m-1) for 1 month. PA enhanced the growth of the Eucalyptus seedlings, as indicated by higher relative growth rates in height and root collar diameter of inoculated seedlings compared with non-inoculated seedlings. Moreover, the inoculated seedlings had less cell damage from NaCl, as indicated by significantly lesser leaf thickness and electrolyte leakage than the controls. These findings could lead to practices conferring socioeconomic and environmental benefits, as abandoned salt-affected areas could be reclaimed using such Eucalyptus seedlings inoculated with salt-tolerant ECM fungi.

Integration analysis of transcriptome and proteome profiles brings new insights of somatic embryogenesis of two eucalyptus species.

BACKGROUND: Somatic embryogenesis (SE) is recognized as a promising technology for plant vegetative propagation. Although previous studies have identified some key regulators involved in the SE process in plant, our knowledge about the molecular changes in the SE process and key regulators associated with high embryogenic potential is still poor, especially in the important fiber and energy source tree - eucalyptus. RESULTS: In this study, we analyzed the transcriptome and proteome profiles of E. camaldulensis (with high embryogenic potential) and E. grandis x urophylla (with low embryogenic potential) in SE process: callus induction and development. A total of 12,121 differentially expressed genes (DEGs) and 3,922 differentially expressed proteins (DEPs) were identified in the SE of the two eucalyptus species. Integration analysis identified 1,353 (131 to 546) DEGs/DEPs shared by the two eucalyptus species in the SE process, including 142, 13 and 186 DEGs/DEPs commonly upregulated in the callus induction, maturation and development, respectively. Further, we found that the trihelix transcription factor ASR3 isoform X2 was commonly upregulated in the callus induction of the two eucalyptus species. The SOX30 and WRKY40 TFs were specifically upregulated in the callus induction of E. camaldulensis. Three TFs (bHLH62, bHLH35 isoform X2, RAP2-1) were specifically downregulated in the callus induction of E. grandis x urophylla. WGCNA identified 125 and 26 genes/proteins with high correlation (Pearson correlation > 0.8 or < -0.8) with ASR3 TF in the SE of E. camaldulensis and E. grandis x urophylla, respectively. The potential target gene expression patterns of ASR3 TF were then validated using qRT-PCR in the material. CONCLUSIONS: This is the first time to integrate multiple omics technologies to study the SE of eucalyptus. The findings will enhance our understanding of molecular regulation mechanisms of SE in eucalyptus. The output will also benefit the eucalyptus breeding program.

Evolution of rarity and phylogeny determine above- and belowground biomass in plant-plant interactions.

Rare species are often considered inferior competitors due to occupancy of small ranges, specific habitats, and small local populations. However, the phylogenetic relatedness and rarity level (level 1-7 and common) of interacting species in plant-plant interactions are not often considered when predicting the response of rare plants in a biotic context. We used a common garden of 25 species of Tasmanian Eucalyptus, to differentiate non-additive patterns in the biomass of rare versus common species when grown in mixtures varying in phylogenetic relatedness and rarity. We demonstrate that rare species maintain progressively positive non-additive responses in biomass when interacting with phylogenetically intermediate, less rare and common species. This trend is not reflected in common species that out-performed in monocultures compared to mixtures. These results offer predictability as to how rare species' productivity will respond within various plant-plant interactions. However, species-specific interactions, such as those involving E. globulus, yielded a 97% increase in biomass compared to other species-specific interaction outcomes. These results are important because they suggest that plant rarity may also be shaped by biotic interactions, in addition to the known environmental and population factors normally used to describe rarity. Rare species may utilize potentially facilitative interactions with phylogenetically intermediate and common species to escape the effects of limiting similarity. Biotically mediated increases in rare plant biomass may have subsequent effects on the competitive ability and geographic occurrence of rare species, allowing rare species to persist at low abundance across plant communities. Through the consideration of species rarity and evolutionary history, we can more accurately predict plant-plant interaction dynamics to preserve unique ecosystem functions and fundamentally challenge what it means to be "rare".

Pushing the envelope: do narrowly and widely distributed Eucalyptus species differ in response to climate warming?

Contemporary climate change will push many tree species into conditions that are outside their current climate envelopes. Using the Eucalyptus genus as a model, we addressed whether species with narrower geographical distributions show constrained ability to cope with warming relative to species with wider distributions, and whether this ability differs among species from tropical and temperate climates. We grew seedlings of widely and narrowly distributed Eucalyptus species from temperate and tropical Australia in a glasshouse under two temperature regimes: the summer temperature at seed origin and +3.5°C. We measured physical traits and leaf-level gas exchange to assess warming influences on growth rates, allocation patterns, and physiological acclimation capacity. Warming generally stimulated growth, such that higher relative growth rates early in development placed seedlings on a trajectory of greater mass accumulation. The growth enhancement under warming was larger among widely than narrowly distributed species and among temperate rather than tropical provenances. The differential growth enhancement was primarily attributable to leaf area production and adjustments of specific leaf area. Our results suggest that tree species, including those with climate envelopes that will be exceeded by contemporary climate warming, possess capacity to physiologically acclimate but may have varying ability to adjust morphology.

Assessing assemblage-wide mammal responses to different types of habitat modification in Amazonian forests.

Tropical forests are being heavily modified by varying intensities of land use ranging from structural degradation to complete conversion. While ecological responses of vertebrate assemblages to habitat modification are variable, such understanding is critical to appropriate conservation planning of anthropogenic landscapes. We assessed the responses of medium/large-bodied mammal assemblages to the ecological impacts of reduced impact logging, secondary regrowth, and eucalyptus and oil palm plantations in Eastern Brazilian Amazonia. We used within-landscape paired baseline-treatment comparisons to examine the impact of different types of habitat modification in relation to adjacent primary forest. We examined assemblage-wide metrics including the total number of species, number of primary forest species retained in modified habitats, abundance, species composition, and community integrity. We ranked all types of habitat modification along a gradient of assemblage-wide impact intensity, with oil palm and eucalyptus plantations exerting the greatest impact, followed by secondary regrowth, and selectively logging. Selectively-logged and secondary forests did not experience discernible biodiversity loss, except for the total number of primary forest species retained. Secondary forests further experienced pronounced species turnover, with loss of community integrity. Considering the biodiversity retention capacity of anthropogenic habitats, this study reinforces the landscape-scale importance of setting aside large preserved areas.

Leaf 13C and 15N composition shedding light on easing drought stress through partial K substitution by Na in eucalyptus species.

This work aimed to investigate the partial K-replacement by Na supply to alleviate drought-induced stress in Eucalyptus species. Plant growth, leaf gas exchange parameters, water relations, oxidative stress (H2O2 and MDA content), chlorophyll concentration, carbon (C) and nitrogen (N) isotopic leaf composition (δ13C and δ15N) were analyzed. Drought tolerant E. urophylla and E. camaldulensis showed positive responses to the partial K substitution by Na, with similar dry mass yields, stomatal density and total stomatal pore area relative to the well K-supplied plants under both water conditions, suggesting that 50% of the K requirements is pressing for physiological functions that is poorly substituted by Na. Furthermore, E. urophylla and E. camaldulensis up-regulated leaf gas exchanges, leading to enhanced long-term water use efficiency (WUEL). Moreover, the partial K substitution by Na had no effects on plants H2O2, MDA, δ13C and δ15N, confirming that Na, to a certain extent, can effectively replace K in plants metabolism. Otherwise, the drought-sensitive E. saligna species was negatively affected by partial K replacement by Na, decreasing plants dry mass, even with up-regulated leaf gas exchange parameters. The exclusive Na-supplied plants showed K-deficient symptoms and lower growth, WUEL, and δ13C, besides higher Na accumulation, δ15N, H2O2 and MDA content.

Metagenomic analyses, isolation and characterization of endophytic bacteria associated with Eucalyptus urophylla BRS07-01 in vitro plants.

Eucalyptus is the main species for the forestry industry in Brazil. Biotechnology and, more recently, gene editing offer significant opportunities for rapid improvements in Eucalyptus breeding programs. However, the recalcitrance of Eucalyptus species to in vitro culture is also a major limitation for commercial deployment of biotechnology techniques in Eucalyptus improvement. We evaluated various clones of Eucalyptus urophylla for their in vitro regeneration potential identified a clone, BRS07-01, with considerably higher regeneration rate (85%) in organogenesis, and significantly higher than most works described in literature. Endophytic bacteria are widely reported to improve in vitro plant growth and development. Hence, we believe that inclusion of endophytic plant growth promoting bacteria enhanced was responsible for the improved plantlets growth and development of this clone under in vitro culture. Metagenomic analysis was performed to isolate and characterize the prominent endophytic bacteria on BRS07-01 leaf tissue in vitro micro-cultures, and evaluate their impact on plant growth promotion. The analysis revealed the presence of the phyla Firmicutes (35%), Proteobacteria (30%) and much smaller quantities of Actinobacteria, Bacteroidetes, Gemmatimonadetes, Crenarchaeota, Euryarchaeota and Acidobacteria. Of the thirty endophytic bacterial strains isolated, eleven produced indole-3-acetic acid. Two of the isolates were identified as Enterobacter sp. and Paenibacillus polymyxa, which are nitrogen-fixing and capable of phosphate and produce ammonium. These isolates also showed similar positive effects on the germination of common beans (Phaseolus spp.). The isolates will now be tested as a growth promoter in Eucalyptus in vitro cultures. Graphical abstract for the methodology using cultivation independent and dependent methodologies to investigate the endophytic bacteria community from in vitro Eucalyptus urophylla BRS07-01.

Transcriptome and metabolite analysis related to branch development in two genotypes of Eucalyptus urophylla.

Branching in long-lived plants can cause scarring at the base and affect wood density, which greatly inhibits wood yield and quality. Eucalyptus urophylla is one of the most important commercial forest tree species in South China, with diverse branch number and branch angles under different genetic backgrounds. However, the main elements and regulatory mechanisms associated with different branching traits in E. urophylla remain unclear. To identify the factors that may influence branching, the transcriptome and metabolome were performed on the shoot apex (SA), lateral shoot apex (LSA), and stem segment at the 5th axillary bud from the shoot apex (S1) in lines ZQUC14 (A) and LDUD26 (B), with A exhibiting a smaller Ba than B. A total of 307.3 million high-quality clean reads and nine hormones were identified from six libraries. Several differentially expressed regulatory factors were identified between the two genotypes of E. urophylla. The Kyoto Encyclopedia of Genes and Genomes pathways were enriched in plant hormone signal transduction, plant hormone biosynthesis and their transport pathways. Furthermore, gene expression pattern analysis identified genes that were significantly downregulated or upregulated in S1 relative to the SA and LSA segments, and the plant hormone signal transduction pathway was constructed to explain branching development. This study clarified the main plant hormones and genes underlying branch numbers and angles of E. urophylla, confirmed that ABA and SA could promote a larger branch angle and smaller branch number, while IAA has an opposite function. Numbers of key candidate genes involved in plant hormone signal transduction were found in the positive regulation of branch formation. These novel findings should aid molecular breeding of branching in Eucalyptus.

Hyperspectral band selection and modeling of soil organic matter content in a forest using the Ranger algorithm.

Effective soil spectral band selection and modeling methods can improve modeling accuracy. To establish a hyperspectral prediction model of soil organic matter (SOM) content, this study investigated a forested Eucalyptus plantation in Huangmian Forest Farm, Guangxi, China. The Ranger and Lasso algorithms were used to screen spectral bands. Subsequently, models were established using four algorithms: partial least squares regression, random forest (RF), a support vector machine, and an artificial neural network (ANN). The optimal model was then selected. The results showed that the modeling accuracy was higher when band selection was based on the Ranger algorithm than when it was based on the Lasso algorithm. ANN modeling had the best goodness of fit, and the model established by RF had the most stable modeling results. Based on the above results, a new method is proposed in this study for band selection in the early phase of soil hyperspectral modeling. The Ranger algorithm can be applied to screen the spectral bands, and ANN or RF can then be selected to construct the prediction model based on different datasets, which is applicable to establish the prediction model of SOM content in red soil plantations. This study provides a reference for the remote sensing of soil fertility in forests of different soil types and a theoretical basis for developing portable equipment for the hyperspectral measurement of SOM content in forest habitats.

Changes in taxonomic and functional diversity of plants in a chronosequence of Eucalyptus grandis plantations.

Tree plantations have become one of the fastest-growing land uses and their impact on biodiversity was evaluated mainly at the taxonomic level. The aim of this study was to analyze environmental changes after the Eucalyptus plantation in an area originally covered by natural grasslands, taking into account the alpha and beta (taxonomic and functional) diversity of plant communities. We selected nine plantation ages, along a 12 years chronosequence, with three replicates per age and three protected grasslands as the original situation. At each replicate, we established three plots to measure plant species cover, diversity and environmental variables. Results showed that species richness, and all diversity indices, significantly declined with increasing plantation age. Canopy cover, soil pH, and leaf litter were the environmental drivers that drove the decrease in taxonomic and functional diversity of plants through the forest chronosequence. Based on the path analyses results, canopy cover had an indirect effect on plant functional diversity, mediated by leaf litter depth, soil pH, and plant species richness. The high dispersal potential, annual, barochorous, and zoochorous plant species were the functional traits more affected by the eucalypt plantations. We recommend two management practices: reducing forest densities to allow higher light input to the understory and, due to the fact that leaf litter was negatively associated with all diversity facets, we recommend reducing their accumulation or generate heterogeneity in its distribution to enhance biodiversity.

Belowground interactions affect shoot growth in Eucalyptus urophylla under restrictive conditions.

Plant-plant interactions like competition or facilitation between seedlings can have profound implications on their establishment and posterior development. These interactions are variable and depend upon the presence of neighbouring plants and environmental factors. In this work, we studied the effects of the interaction by the roots of Eucalyptus urophylla seedlings from a population under various environmental stressful conditions: water deficit, nutrient deficit, low light, low temperature, and high temperature. To evaluate it, we measured some growth and morphological parameters. We demonstrated that shoot parameters such as the number of leaves, leaf area, and dry weight of the leaves were the most affected parameters due to the belowground plant-plant interaction under various environmental conditions. We did not find evidence for competition among the plants, especially under restrictive conditions. Therefore, the study corroborates the stress-gradient hypothesis, which states that plants' differences under stressful conditions lead to facilitative interactions. It has implications for plant ecology and forestry techniques.

Silicon fertigation and salicylic acid foliar spraying mitigate ammonium deficiency and toxicity in Eucalyptus spp. clonal seedlings.

Nitrogen deficiency and toxicity, primarily in its ammonium form (NH4+), can suppress plant growth and development. The use of silicon (Si) or salicylic acid (SA) may be an alternative to minimize the harmful effects of nutrient imbalances caused by NH4+, thereby improving the photosynthetic efficiency of plants. The aim of the present study was to assess the action of fertigation-applied Si and SA foliar spraying in mitigating NH4+ toxicity and deficiency in eucalyptus clonal seedlings. Two experiments were performed with eucalyptus clonal seedlings (Eucalyptus urophylla x Eucalyptus grandis), in a greenhouse. Both were carried out using a 4x2 factorial design and four concentrations of NH4+ (5, 15, 30 and 60 mmol L-1), in the absence and presence of Si (2 mmol L-1), in experiment I; or with and without SA foliar application (10-2 mmol L-1), in experiment II, with six repetitions. Nitrogen content rose as a result of increasing N-NH4+ concentration in the nutrient solution, and Si supplied via the nutrient solution was efficient in increasing the Si content in eucalyptus seedlings. The rise in N-NH4+ concentration favored the maintenance of the photosynthetic apparatus, but high N-NH4+ concentration increased energy loss through fluorescence and decreased the efficiency of photosystem II. The addition of Si to the nutrient solution proved to be beneficial to the photosynthetic apparatus by decreasing F0 at 15 and 30 mmol L-1 of NH4+; and Fm at all NH4+ concentrations studied. In addition, the beneficial element also increases Fv/Fm at all NH4+ concentrations studied. SA foliar application was also efficient in reducing photosynthetic energy losses by decreasing F0 and Fm at all NH4+ concentrations studied. However, SA only increased the Fv/Fm at the high concentrations studied (30 and 60 mmol L-1 of NH4+). Nitrogen disorder by deficiency or N-NH4+ toxicity reduced shoot dry mass production. The addition of Si to the nutrient solution and SA foliar application increased shoot dry mass production at all N-NH4+ concentrations studied, and benefitted the photosynthetic apparatus by decreasing fluorescence and improving the quantum efficiency of photosystem II as well as dry mass production.

Evaluation of potential impacts on biodiversity of the salt-tolerant transgenic Eucalyptus camaldulensis harboring an RNA chaperonic RNA-Binding-Protein gene derived from common ice plant.

We recently reported that a genetic transformation of the RNA-Binding-Protein (McRBP), an RNA chaperone gene derived from common ice plant (Mesembryanthemum crystallinum), alleviated injury and loss of biomass production by salt stress in Eucalyptus camaldulensis in a semi-confined screen house trial. In this study, we assessed the potential environmental impact of the transgenic Eucalyptus in a manner complying with Japanese biosafety regulatory framework required for getting permission for experimental confined field trials. Two kinds of bioassays for the effects of allelopathic activity on the growth of other plants, i.e., the sandwich assay and the succeeding crop assay, were performed for three transgenic lines and three non-transgenic lines. No significant differences were observed between transgenic and non-transgenic plants. No significant difference in the numbers of cultivable microorganisms analyzed by the spread plate method were observed among the six transgenic and non-transgenic lines. These results suggested that there is no significant difference in the potential impact on biodiversity between the transgenic McRBP-E. camaldulensis lines and their non-transgenic comparators.

Growth promotion and protection from drought in Eucalyptus grandis seedlings inoculated with beneficial bacteria embedded in a superabsorbent polymer.

Eucalyptus grandis is a globally important tree crop. Greenhouse-grown tree seedlings often face water deficit after outplanting to the field, which can affect their survival and establishment severely. This can be alleviated by the application of superabsorbent hydrophilic polymers (SAPs). Growth promoting bacteria can also improve crop abiotic stress tolerance; however, their use in trees is limited, partly due to difficulties in the application and viability loss. In this work, we evaluated the improvement of drought tolerance of E. grandis seedlings by inoculating with two Pseudomonas strains (named M25 and N33), carried by an acrylic-hydrocellulosic SAP. We observed significant bacterial survival in the seedling rhizosphere 50 days after inoculation. Under gradual water deficit conditions, we observed a considerable increase in the water content and wall elasticity of M25-inoculated plants and a trend towards growth promotion with both bacteria. Under rapid water deficit conditions, which caused partial defoliation, both strains significantly enhanced the formation of new leaves, while inoculation with M25 reduced the transpiration rate. Co-inoculation with M25 and N33 substantially increased growth and photosynthetic capacity. We conclude that the selected bacteria can benefit E. grandis early growth and can be easily inoculated at transplant by using an acrylic-hydrocellulosic SAP.

Multi-volume modeling of Eucalyptus trees using regression and artificial neural networks.

The stem volume of commercial trees is an important variable that assists in decision making and economic analysis in forest management. Wood from forest plantations can be used for several purposes, which makes estimating multi-volumes for the same tree a necessary task. Defining its exploitation and use potential, such as the total and merchantable volumes (up to a minimum diameter of interest), with or without bark, is a possible work. The goal of this study was to use different strategies to model multi-volumes of the stem of eucalyptus trees. The data came from rigorous scaling of 460 felled trees stems from four eucalyptus clones in high forest and coppice regimes. The diameters were measured at different heights, with the volume of the sections obtained by the Smalian method. Data were randomly separated into fit and validation data. The single multi-volume model, volume-specific models, and the training of artificial neural networks (ANNs) were fitted. The evaluation criteria of the models were: coefficient of determination, root mean square error, mean absolute error, mean bias error, as well as graphical analysis of observed and estimated values and distribution of residuals. Additionally, the t-test (α = 0.05) was performed between the volume obtained in the rigorous scaling and estimated by each strategy with the validation data. Results showed that the strategies used to model different tree stem volumes are efficient. The actual and estimated volumes showed no differences. The multi-volume model had the most considerable advantage in volume estimation practicality, while the volume-specific models were more efficient in the accuracy of estimates. Given the conditions of this study, the ANNs are more suitable than the regression models in the estimation of multi-volumes of eucalyptus trees, revealing greater accuracy and practicality.

EgPHI-1, a PHOSPHATE-INDUCED-1 gene from Eucalyptus globulus, is involved in shoot growth, xylem fiber length and secondary cell wall properties.

MAIN CONCLUSION: EgPHI-1 is a member of PHI-1/EXO/EXL protein family. Its overexpression in tobacco resulted in changes in biomass partitioning, xylem fiber length, secondary cell wall thickening and composition, and lignification. Here, we report the functional characterization of a PHOSPHATE-INDUCED PROTEIN 1 homologue showing differential expression in xylem cells from Eucalyptus species of contrasting phenotypes for wood quality and growth traits. Our results indicated that this gene is a member of the PHI-1/EXO/EXL family. Analysis of the promoter cis-acting regulatory elements and expression responses to different treatments revealed that the Eucalyptus globulus PHI-1 (EgPHI-1) is transcriptionally regulated by auxin, cytokinin, wounding and drought. EgPHI-1 overexpression in transgenic tobacco changed the partitioning of biomass, favoring its allocation to shoots in detriment of roots. The stem of the transgenic plants showed longer xylem fibers and reduced cellulose content, while the leaf xylem had enhanced secondary cell wall thickness. UV microspectrophotometry of individual cell wall layers of fibers and vessels has shown that the transgenic plants exhibit differences in the lignification of S2 layer in both cell types. Taken together, the results suggest that EgPHI-1 mediates the elongation of secondary xylem fibers, secondary cell wall thickening and composition, and lignification, making it an attractive target for biotechnological applications in forestry and biofuel crops.