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In light of the detrimental effects of global warming, exacerbated by the intense sunlight and high temperatures prevalent during summer in southern China, on the growth of Melaleuca alternifolia ( M. alternifolia ) seedlings, this study sets out to examine the impact of various shading treatments on the growth and physiological attributes of M. alternifolia seedlings, with the aim of determining the optimum shading level. The seedling phase is of paramount importance in the growth cycle and regeneration process of M. alternifolia , as both excessive and insufficient light exposure can negatively influence seedling development. Four shading regimes (CK: no shading; C1: 35–45% shading; C2: 45–50% shading; C3: 60–70% shading) were imposed on M. alternifolia seedlings, following which observations were conducted after a 35-day period. The results reveal that the different shading treatments had a significant effect on the growth and physiological indicators of the seedlings, with the moderate shading treatment (C2) proving to be the most advantageous for seedling growth. Under the C2 treatment, an increase in chlorophyll content was observed in the leaves of the seedlings, accompanied by a decrease in malondialdehyde (MDA) content. Concurrently, there was a reduction in the activities of antioxidant enzymes, namely superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Furthermore, the levels of abscisic acid (ABA) and gibberellic acid (GA3) declined, while the concentrations of auxin (IAA), salicylic acid (SA), and cytokinin (CTK) ascended. Leaf anatomical analysis disclosed that, in comparison to the control group, the thickness of the lower epidermis and palisade tissue in the leaves of the seedlings subjected to the C2 treatment exhibited a significant reduction. Additionally, an increase in the number of spongy tissue cells was noted, along with a marked increase in total leaf thickness. Consequently, cultivating M. alternifolia seedlings under shading conditions ranging from 45 to 50% is deemed more favorable. The findings of this study offer novel insights into the adaptive responses of M. alternifolia seedlings to varying light intensities and provide theoretical guidance for the cultivation and management of M. alternifolia seedlings in the southern regions of China.

Synthesis of silver nanoparticles using the leaf extract of Melaleuca alternifolia (M-AgNPs), as evidenced by various physicochemical characterizations, including UV-Visible spectroscopy (UV-Vis), Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HR-TEM), and zeta potential analysis. The UV-Vis spectrum exhibited a characteristic absorption peak at 402 nm, confirming the formation of M-AgNPs. FT-IR analysis identified the presence of various functional groups associated with the silver nanoparticles. DLS measurements indicated a hydrodynamic size of 45.79 nm with a polydispersity index (PDI) of 0.335. Zeta potential analysis revealed a value of -21 mV, suggesting good stability of the nanoparticles. XRD analysis showed a crystalline size of 25.47 nm and confirmed the face-centered cubic (FCC) structure. SEM images revealed well-defined and uniformly dispersed nanoparticles. EDAX confirmed the presence of silver at the elemental level. HR-TEM analysis demonstrated that the actual size of the nanoparticles was approximately 10 nm. Antimicrobial studies demonstrated the effectiveness of the synthesized nanoparticles against both bacterial and fungal strains. The antioxidant activity of the M-AgNPs was measured at 41.17 µL/mL. Furthermore, cytotoxicity studies showed that the nanoparticles exhibited an IC 50 value of 8.16 µg/mL against MCF-7 breast cancer cells. The synthesized M-AgNPs possess significant potential as therapeutic agents, particularly against MCF-7 cancer cells, and may serve as promising candidates for future medical applications.

Tree stems are an important and unconstrained source of methane, yet it is uncertain whether internal microbial controls (i.e. methanotrophy) within tree bark may reduce methane emissions. Here we demonstrate that unique microbial communities dominated by methane-oxidising bacteria (MOB) dwell within bark of Melaleuca quinquenervia , a common, invasive and globally distributed lowland species. In laboratory incubations, methane-inoculated M. quinquenervia bark mediated methane consumption (up to 96.3 µmol m −2 bark d −1 ) and reveal distinct isotopic δ 13 C-CH 4 enrichment characteristic of MOB. Molecular analysis indicates unique microbial communities reside within the bark, with MOB primarily from the genus Methylomonas comprising up to 25 % of the total microbial community. Methanotroph abundance was linearly correlated to methane uptake rates (R 2  = 0.76, p  = 0.006). Finally, field-based methane oxidation inhibition experiments demonstrate that bark-dwelling MOB reduce methane emissions by 36 ± 5 %. These multiple complementary lines of evidence indicate that bark-dwelling MOB represent a potentially significant methane sink, and an important frontier for further research. The photosynthesis performed by trees makes them an important sink for atmospheric carbon dioxide, but trees are also sources of the potent greenhouse gas methane. Here the authors find that tree bark in some common lowland species is colonized by methane oxidizing bacteria that can reduce tree methane emissions by ~ 36%.

Introduction: Leaves of the Australian tea tree plant Melaleuca alternifolia were used traditionally by First Nations Australians for treating wounds, burns, and insect bites. Tea tree oil, the essential oil steam-distilled from M. alternifolia , is well-known for its medicinal properties, the evidence for most applications however is limited. This review aimed to critically appraise evidence from clinical trials examining the therapeutic efficacy and safety of tea tree oil on outcomes. Methods: Randomized controlled trials with participants of any age, gender, or health status, comparing tea tree oil to any control were included, without limit on publication date. Electronic databases were searched on 12 August 2022 with additional records sourced from article reference sections, reviews, and industry white papers. Risk of bias was assessed by two authors independently using the Cochrane risk-of-bias 1.0 tool. Results were summarized and synthesized thematically. Results: Forty-six articles were eligible from the following medical fields ( Dentistry n = 18, Dermatology n = 9, Infectious disease n = 9, Ophthalmology n = 6, Podiatry n = 3; and Other n = 1). Results indicate that oral mouthwashes with 0.2%–0.5% tea tree oil may limit accumulation of dental plaque. Gels containing 5% tea tree oil applied directly to the periodontium may aid treatment of periodontitis as an adjunctive therapy to scaling and root planing. More evidence is needed to confirm the benefits of tea tree oil for reducing acne lesions and severity. Local anti-inflammatory effects on skin, if any, also require further elucidation. Topical tea tree oil regimens show similar efficacy to standard treatments for decolonizing the body from methicillin-resistant Staphylococcus aureus , although intra-nasal use of tea tree oil may cause irritation to mucous membranes. Tea tree oil with added iodine may provide an effective treatment for molluscum contagiosum lesions in young children. More evidence on efficacy of tea tree oil-based eyelid wipes for Demodex mite control are needed. Side effects were reported in 60% of included studies and were minor, except where tea tree oil was applied topically in concentrations ≥ 25%. Discussion: Overall, the quality of research was poor to modest and higher quality trials with larger samples and better reporting are required to substantiate potential therapeutic applications of tea tree oil. Systematic Review Registration: PROSPERO, identifier [CRD42021285168].

The chemical composition of the essential oils of Melaleuca armillaris Sm., Melaleuca styphelioides Sm. and Melaleuca acuminata F. Muell., collected in Tunisia, was studied by means of GC and GC-MS analysis. In all, 46 compounds were identified, 38 for M. armillaris, 20 for M. acuminata and eight for M. styphelioides, respectively. The presence of a sesquiterpenic fraction (52.2%) characterized the oil from M. armillaris; M. sthypheliodes oil was rich in methyl eugenol, a phenolic compound (91.1%), while M. acuminata oil is mainly constituted by oxygenated monoterpenoids (95.6%). The essential oils were evaluated for their in vitro potentially phytotoxic activity against germination and initial radicle growth of Raphanus sativus L., Lepidium sativum L., Sinapis arvensis L., Triticum durum L. and Phalaris canariensis L. seeds. The radicle elongation of five seeds was inhibited at the highest doses tested, while germination of all seeds was not affected. Moreover, the essential oils showed low antimicrobial activity against eight selected microorganisms.

• Knowledge regarding mechanisms moderating methane (CH₄) sink/source behaviour along the soil–tree stem–atmosphere continuum remains incomplete. Here, we applied stable isotope analysis (δ13C-CH₄) to gain insights into axial CH₄ transport and oxidation in two globally distributed subtropical lowland species (Melaleuca quinquenervia and Casuarina glauca). • We found consistent trends in CH₄ flux (decreasing with height) and δ13C-CH₄ enrichment (increasing with height) in relation to stem height from ground. The average lower tree stem δ13C-CH₄ (0–40 cm) of Melaleuca and Casuarina (−53.96‰ and −65.89‰) were similar to adjacent flooded soil CH₄ ebullition (−52.87‰ and −62.98‰), suggesting that stem CH₄ is derived mainly by soil sources. Upper stems (81–200 cm) displayed distinct δ13C-CH₄ enrichment (Melaleuca −44.6‰ and Casuarina −46.5‰, respectively). • Coupled 3D-photogrammetry with novel 3D-stem measurements revealed distinct hotspots of CH₄ flux and isotopic fractionation on Melaleuca, which were likely due to bark anomalies in which preferential pathways of gas efflux were enhanced. Diel experiments revealed greater δ13C-CH₄ enrichment and higher oxidation rates in the afternoon, compared with the morning. • Overall, we estimated that c. 33% of the methane was oxidised between lower and upper stems during axial transport, therefore potentially representing a globally significant, yet previously unaccounted for, methane sink.

Background Terpene rich leaves are a characteristic of Myrtaceae. There is significant qualitative variation in the terpene profile of plants within a single species, which is observable as “chemotypes”. Understanding the molecular basis of chemotypic variation will help explain how such variation is maintained in natural populations as well as allowing focussed breeding for those terpenes sought by industry. The leaves of the medicinal tea tree, Melaleuca alternifolia , are used to produce terpinen-4-ol rich tea tree oil, but there are six naturally occurring chemotypes; three cardinal chemotypes (dominated by terpinen-4-ol, terpinolene and 1,8-cineole, respectively) and three intermediates. It has been predicted that three distinct terpene synthases could be responsible for the maintenance of chemotypic variation in this species. Results We isolated and characterised the most abundant terpene synthases (TPSs) from the three cardinal chemotypes of M. alternifolia . Functional characterisation of these enzymes shows that they produce the dominant compounds in the foliar terpene profile of all six chemotypes. Using RNA-Seq, we investigated the expression of these and 24 additional putative terpene synthases in young leaves of all six chemotypes of M. alternifolia . Conclusions Despite contributing to the variation patterns observed, variation in gene expression of the three TPS genes is not enough to explain all variation for the maintenance of chemotypes. Other candidate terpene synthases as well as other levels of regulation must also be involved. The results of this study provide novel insights into the complexity of terpene biosynthesis in natural populations of a non-model organism.

Tea tree oil (TTO) is a yellow liquid extracted from Melaleuca alternifolia . Although the antimicrobial activity of TTO has been known for a long time, its specific antimicrobial effects and mechanism underlying these remain poorly characterized. The present study investigated the chemical composition of TTO and the dynamics and mechanism of its antimicrobial activities in two bacterial and two fungal strains. Gas chromatography–mass spectrometry analysis identified alkenes and alcohols as the main constituents of TTO. Terpinen-4-ol was the most abundant individual component, accounting for approximately 23 % of the TTO. Poisoned food technique assessment showed that the minimum inhibitory concentrations of TTO for bacterial strains ( Escherichia coli and Staphylococcus aureus ) and fungal strains ( Candida albicans and Aspergillus niger ) were 1.08 and 2.17 mg/mL, respectively. Antimicrobial dynamic curves showed that with increasing concentrations of TTO, the rate of cell killing and the duration of growth lag phase increased correspondingly. These data indicated that TTO produced concentration and time-dependent antimicrobial effects. The minimum bactericidal and fungicidal concentrations of TTO were 2.17, 4.34, and 4.34 against E. coli , S. aureus , and C. albicans , respectively. However, A. niger conidia were not completely eradicated, even after 3 days in the presence of 17.34 mg/mL TTO. Transmission electron microscopy images indicated that TTO penetrated the cell wall and cytoplasmic membrane of all the tested bacterial and fungal strains. TTO may also penetrate fungal organelle membrane. These findings indicated that TTO maybe exerts its antimicrobial effects by compromising the cell membrane, resulting in loss of the cytoplasm and organelle damage, which ultimate leads to cell death.

The lemurs of Madagascar are among the most threatened mammalian taxa in the world, with habitat loss due to shifting cultivation and timber harvest heavily contributing to their precarious state. Deforestation often leads to fragmentation, resulting in mixed-habitat matrices throughout a landscape where disturbed areas are prone to invasion by exotic plants. Our study site, the Mandena littoral forest (southeast Madagascar), is a matrix of littoral forest, littoral swamp, and Melaleuca swamp habitats. Here, Melaleuca quinquenervia has invaded the wetland ecosystem, creating a mono-dominant habitat that currently provides the only potential habitat corridor between forest fragments. We sought to understand the role of this invasive Melaleuca swamp on the behavioral ecology of a threatened, small-bodied folivore, the southern bamboo lemur (Hapalemur meridionalis). We collected botanical and behavioral data on four groups of H. meridionalis between January and December 2013. Our results confirm Melaleuca swamp as an important part of their home range: while lemurs seasonally limited activities to certain habitats, all groups were capable of utilizing this invasive habitat for feeding and resting. Furthermore, the fact that Hapalemur use an invasive plant species as a dispersal corridor increases our knowledge of their ecological flexibility, and may be useful in the conservation management of remaining threatened populations.

The leaf oils of the 11 recorded Western Australian species of the broombush complex of the genus Melaleuca have been examined by a combination of GC and GC/MS. Melaleuca atroviridis produced a monoterpenic leaf oil with alpha-pinene (11.0%) and 1,8-cineole (73.2%) being the principal components. Melaleuca concreta showed the presence of three chemotypes, one of which was rich in terpinen-4-ol (35.4%), while a second was rich in 1,8-cineole (58-81%). A third chemotype contained significant amounts of alpha-pinene (16.7%), 1,8-cineole (28.4%) and globulol (11.3%). Melaleuca exuvia produced a monoterpenic oil, which appeared to exist in two chemotypes, which contained alpha-pinene (13-23%), 1,8-cineole (56-67%), terpinen-4-ol (0.1-2%) and alpha-terpineol (3-7%) in one form and alpha-pinene (5-7%), 1,8-cineole (28-38%), terpinen-4-ol (11-17%) and alpha-terpineol (3-4%) in the second form. Melaleuca hamata produced a leaf oil that was dominated by monoterpenes. There appeared to be two chemotypes present, one in which terpinen-4-ol (41.6%) was the major component and a second chemotype in which 1,8-cineole (40.0%) and linalool (33.9%) were the principal components. Melaleuca interioris (from one population) contained a mixture of mono- and sesquiterpenes, in which sesquiterpenes predominated. Melaleuca osullivanii gave a leaf oil in which sesquiterpenes predominated, the principal component being spathulenol (10-18%). Melaleuca scalena produced a leaf oil dominated by monoterpenes, with alpha-pinene (25-31%) and 1,8-cineole (43-55%) being the principal components. Melaleuca stereophloia was dominated by monoterpenes of which the principal component was 1,8-cineole (78-83%). Melaleuca uncinata sens. strict. existed in a variety of forms one of which had major amounts of 1,8-cineole (44-56%), while a second contained major amounts of terpinen-4-ol (21-31%), gamma-terpinene (10-14%) and alpha-terpinene (6-8%). Melaleuca vinnula appeared to exist in two chemotypes, one of which was rich in alpha-pinene (65.3%), while the second chemotype was rich in 1,8-cineole (60.6%). Melaleuca zeteticorum produced a leaf oil that was overwhelmingly monoterpene in character, the principal component being 1,8-cineole (63-68%).