Integrative Metabolomic and Transcriptomic Analysis Reveals the Mechanism of Specific Color Formation in Phoebe zhennan Heartwood.

Nanmu (Phoebe zhennan) is an extremely valuable tree plant that is the main source of famous "golden-thread nanmu" wood. The potential metabolites and gene regulation mechanisms involved in golden thread formation are poorly understood, even though the color change from sapwood to heartwood has been investigated in several tree plants. Here, five radial tissues from sapwood to heartwood were compared via integrative metabolomic and transcriptomic analysis to reveal the secondary metabolites and molecular mechanisms involved in golden thread formation. During heartwood formation, gradual starch grain loss is accompanied by the cell lumen deposition of lipids and color-related extractives. Extractives of 20 phenylpropanoids accumulated in heartwood, including cinnamic acids and derivatives, coumarin acid derivatives, and flavonoids, which were identified as being closely related to the golden thread. Phenylpropanoids co-occurring with abundant accumulated metabolites of prenol lipids, fatty acyls, steroids, and steroid derivatives may greatly contribute to the characteristics of golden thread formation. Additionally, the expression of nine genes whose products catalyze phenylpropanoid and flavonoids biosynthesis was upregulated in the transition zone, then accumulated and used to color the heartwood. The expression levels of transcription factors (e.g., MYB, bHLH, and WRKY) that act as the major regulatory factors in the synthesis and deposition of phenylpropanoid and flavonoids responsible for golden thread formation were also higher than in sapwood. Our results not only explain golden thread formation in nanmu, but also broaden current knowledge of special wood color formation mechanisms. This work provides a framework for future research focused on improving wood color.

Response of Soil Fauna to the Shift in a Riparian Landscape along an Urban-Rural Habitat Gradient.

Urbanization is accelerating worldwide, resulting in drastic alterations of natural riverbanks, which seriously affects the ecological functions and services of riparian landscapes. Our understanding of how anthropogenic activities influence soil animal communities within riparian zones is scarce. The soil fauna represents an important biotic component of the soil ecosystem and greatly contributes to soil structure and fertility formation. We investigated the richness, abundance, diversity, and distribution of soil animal groups, including macro- and mesofauna, in different riparian landscapes along an urban-rural habitat gradient. In natural riparian zones with permeable revetments, the soil fauna was richest and most abundant, mainly because of the low levels of human disturbance and the more suitable habitat conditions. Different soil animal groups responded differently to revetment type and distance from the water flow. The hygrophilous soil mesofauna, requiring a more humid environment, was more sensitive to shifts in revetment types, the location on the riverbank, and the seasons. In summer, when precipitation in the study area was highest, the abundance of the hygrophilous soil mesofauna was significantly higher than in autumn. Distance from the water flow significantly affected the abundance of the hygrophilous soil mesofauna. Our results demonstrated that hygrophilous soil mesofauna can serve as a good indicator in riparian zones, reflecting the hydrological conditions. We also observed interactions between revetment type and distance from the water flow; the distance effect was stronger in the natural riparian zone with a permeable revetment type. Our results highlight the importance of anthropogenic effects on soil ecosystem processes and functions in riparian landscapes, and the necessity of protecting and retaining the natural riverbank and native vegetation patches in riparian landscape planning and construction.

Temporal dynamics of mixed litter humification in an alpine treeline ecotone.

Loss of plant diversity affects mountain ecosystem properties and processes, yet few studies have focused on the impact of plant function type deficiency on mixed litter humification. To fill this knowledge gap, we conducted a 1279-day litterbag decomposition experiment with six plant functional types of foliar litter to determine the temporal dynamic characteristics of mixed litter humification in a coniferous forest (CF) and an alpine shrubland (AS). The results indicated that the humus concentrations, the net accumulations and their relative mixed effects (RME) of most types were higher in CF than those in AS at 146 days, and humus net accumulations fell to approximately -80% of the initial level within 1279 days. The RME of the total humus and humic acid concentrations exhibited a general change from synergistic to antagonistic effects over time, but the mixing of single plant functional type impeded the formation of fulvic acid due to consistently exhibited antagonistic effects. Ultimately, correlation analysis indicated that environmental factors (temperature, snow depth and freeze-thaw cycles) significantly hindered litter humification in the early stage, while some initial quality factors drove this process at a longer scale. Among these aspects, the concentrations of zinc, copper and iron, as well as acid-unhydrolyzable residue (AUR):nitrogen and AUR:phosphorous, stimulated humus accumulation, while water-soluble extractables, potassium, magnesium and aluminium hampered it. Deficiencies in a single plant functional type and vegetation type variations affected litter humification at the alpine treeline, which will further affect soil carbon sequestration, which is of great significance for understanding the material circulation of alpine ecosystems.

Sex-specific responses of Populus deltoides to interaction of cadmium and salinity in root systems.

More research about branch order-specific accumulation of toxic ions in root systems is needed to know root branch-related responses in growth and physiology. In this study, we used Populus deltoides females and males as a model to detect sex-specific differences in physiology, biochemistry, ultrastructure of absorbing roots and distribution of toxic ions in heterogeneous root systems under Cd, salinity and combined stress. Healthy annual male and female plants of P. deltoides were cultivated in soils including 5 mg kg-1 of Cd, 0.2% (w/w) of NaCl and their combination for a growth season. Our results are mainly as follows: (1) females suffered more growth inhibition, root biomass decline, root viability depression, and damage to distal root cells, but lower ability to scavenge reactive oxygen species (ROS) than the males under all stresses; (2) In both sexes, salinity adopted in the present study caused more significant negative effects on growth and organelles integrity than Cd stress, while interaction treatment did not induced a further depression in growth or more impairments in root cells of both sexes in comparison to salinity, indicating influence of combined stress was not equal simply to a superposition of the effects caused by single factors; (3) Cd and Na accumulation in root systems is highly heterogeneous and branch order-specific, with lower-order roots containing more Cd2+ but less Na+, and higher-order roots accumulating more Na+ but less Cd2+. Besides, it is noteworthy that females accumulated more Cd2+ in 1-2 order roots and more Na+ in 1-3 order roots than males under the interaction treatment. These results indicated that strategies in toxic ions accumulation in heterogeneous root systems of P. deltoides was highly branch order-specific, and may closely correlate with sex-specific root growth and physiological responses to the interaction of Cd and salinity.

Ecoenzymatic stoichiometry and microbial nutrient limitations in rhizosphere soil along the Hailuogou Glacier forefield chronosequence.

Mountain glaciers retreat at an increased rate under global warming, resulting in exposed barren surfaces for primary succession. Soil microbes are an important driver of ecosystem processes. Although variations in soil microbes after deglaciation have been studied extensively, the roles of rhizosphere soil microbes in the biogeochemistry cycle during primary succession are less understood. In this study, Populus purdomii was present throughout the 123-year chronosequence as a representative tree species. We therefore investigated variations in the rhizosphere enzyme activity, microbial community structure, and ecoenzymatic stoichiometry of P. purdomii along Hailuogou Glacier chronosequences. The objective was to determinechanges in rhizosphere enzyme activities and microbial communities, as well as the effects of nutrient limitation on rhizosphere microbes. According to the results, the enzyme activities and microbial group biomass in rhizosphere soil all showed a bimodal trend and were highest at the 43rd or 123rd year, and enzyme activity varied with succession time but not microbial community structure. The rhizosphere soil bacterial community was the dominant community during the 123-year chronosequence. Ecoenzymatic stoichiometry indicated nitrogen restrictions on microbial activity throughout primary succession, with early succession stages (5-15 years) showing greater carbon restriction than late succession stages. Moreover, redundancy and correlation analyses demonstrated that soil microbial phospholipid fatty acid biomass was an important factor for increases in enzyme activities and that enzyme activities in turn played important roles in carbon, nitrogen and phosphorus cycling in rhizosphere soil. Additionally, rhizosphere soil microbial development significantly affected soil organic carbon, total nitrogen and dissolved organic carbon accumulation. Overall, our study links the rhizosphere microbial community and activity to successional chronosequences, providing a deeper understanding of the dynamics of ecosystem succession.

Higher soil fauna abundance accelerates litter carbon release across an alpine forest-tundra ecotone.

Upward shifts of alpine treelines and shrub expansion are occurring under climate change, and Abies faxoniana (AF) and Rhododendron lapponicum (RL) may become distributed at higher altitudes. How do abiotic factors and litter quality modulate the effects of soil fauna on carbon release in this context? A field decomposition experiment involving the foliar litter of AF and RL was conducted along an elevation gradient encompassing coniferous forest, alpine shrubland and alpine meadow by using litterbags with different mesh sizes (3 and 0.04 mm). The objective was to determine the influences of soil fauna, litter quality and abiotic factors on species-specific carbon release and their contributions during litter decomposition. Our findings demonstrated that higher soil fauna abundance and diversity facilitated litter carbon release. The contribution rates of soil fauna to carbon release (Cfau) decreased with elevation increasing and decomposition time. Cfau are influenced by soil faunal diversity, dominant fauna groups (Collembola, Oribatida, Mesostigmata), and abiotic factors (temperature). Soil fauna significantly and directly regulated carbon release, abiotic factors indirectly regulated carbon release via altering soil fauna community composition and litter quality. This study improve our understanding in the mechanisms of decomposer contributions to carbon cycling in the context of global climate change.

CHARACTERIZATION OF VIRULENCE GENES AND ANTIMICROBIAL RESISTANCE OF LUNG PATHOGENIC ESCHERICHIA COLI ISOLATES IN FOREST MUSK DEER (MOSCHUS BEREZOVSKII).

This study investigated genotypic diversity, 26 virulence genes, and antimicrobial susceptibility of lung pathogenic Escherichia coli (LPEC) isolated from forest musk deer. Associations between virulence factors (VFs) and phylogenetic group, between antimicrobial resistance (AMR) and phylogenetic group, and between AMR and VFs were subsequently assessed. The results showed 30 LPEC isolated were grouped into seven different clusters (A, B, C, D, E, F, and G). The detection rates of crl (90%), kpsMT II (76.67%), mat (76.67%), and ompA (80%) were over 75%. The most frequent types of resistance were to amoxicillin (100%), sulfafurazole (100%), ampicillin (96.67%), and tetracycline (96.67%), with 93.33% (n = 28) of isolates resistant to more than eight types of drugs. There were significant relationships between resistance to cefalotin and the presence of iucD(a) (P < 0.001), papC (P = 0.032), and kpsMT II (P = 0.028); between resistance to chloromycetin and the presence of irp2 (P = 0.004) and vat (P = 0.047); between resistance to nalidixic acid and the presence of crl (P = 0.002) and iucD(a) (P = 0.004); and between resistance to ampicillin/sulbactam and the presence of vat (P = 0.013). These results indicated there could be some association between resistance and VFs, and there is a great need for the prudent use of antimicrobial agents in LPEC.

Electrophysiological and behavioral responses of the whitestriped longhorned beetle, Batocera lineolata, to the diurnal rhythm of host plant volatiles of holly, Viburnum awabuki.

The adsorption method of Tenax-TA absorbent with GC-MS was used to analyze diurnal rhythms of volatiles from undamaged holly plants, Viburnum awabuki Kock (Dipsacales: Adoxaceae) holly infested by the white-striped longhorned beetle, Batocera lineolata Chevrolat (Coleoptera: Cerambycidae). Electroantennography and a Y-tube olfactometer were used to compare and analyze electroantennogram and behavioral responses of unmated male and female adults to the volatiles from V. awabuki (both undamaged and infested plants). The results of the GC-MS analysis showed that phytosterol and alkane are major volatiles for V. awabuki. The relative content of V. awabuki volatiles changed during the day. Electroantennogram and behavioral responses of unmated male and female adults to the volatiles from both undamaged and infested plants of V. awabuki were stronger between 08:00 and 10:00 and 16:00 and 18:00, which is consistent with early morning and evening feeding behaviors of adults in the field.