Fine root turnover of Japanese white birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> var. <Emphasis Type="Italic">japonica</Emphasis>) grown under elevated CO<Subscript>2</Subscript> in northern Japan

Key message

Elevated CO ₂ reduced fine root dynamics (production and turnover) of white birch seedlings, especially grown in volcanic ash soil compared with brown forest soil.

Abstract

Increased atmospheric CO₂ usually enhances photosynthetic ability and growth of trees. To understand how increased CO₂ affects below-ground part of trees under varied soil condition, we investigated the responses of the fine root (diameter <2 mm) dynamics of Japanese white birch (Betula platyphylla var. japonica) which was planted in 2010. The three-year-old birch seedlings were grown in four experimental treatments comprising two levels of CO₂, i.e., ambient: 380–390 and elevated: 500 μmol mol^?1, in combination with two kinds of soil: brown forest (BF) soil and volcanic ash (VA) soil which has few nutrients. The growth and turnover of fine roots were measured for 3 years (2011–2013) using the Mini-rhizotron. In the first observation year, live fine root length (standing crop) in BF soil was not affected by CO₂ treatment, but it was reduced by the elevated CO₂ from the second observation year. In VA soil, live fine root length was reduced by elevated CO₂ for all 3 years. Fine root turnover tended to decrease under elevated CO₂ compared with ambient in both soil types during the first and second observation years. Turnover of fine root production and mortality was also affected by the two factors, elevated CO₂ and different soil types. Median longevity of fine root increased under elevated CO₂, especially in VA soil at the beginning, and a shorter fine root lifespan appeared after 2 years of observation (2011–2012). These results suggest that elevated CO₂ does not consistently stimulate fine root turnover, particularly during the plant seedlings stage, as it may depend on the costs and benefits of constructing and retaining roots. Therefore, despite the other uncontrollable environment factors, carbon sequestration to the root system may be varied by CO₂ treatment period, soil type and plant age.

     

Impact of elevated CO<Subscript>2</Subscript> on root traits of a sapling community of three birches and an oak: a free-air-CO<Subscript>2</Subscript> enrichment (FACE) in northern Japan

Key message

The CO ₂ effect on the root production of a broad-leaved community was insignificant when grown in brown forest soil, however, it was positively large when grown in volcanic ash soil.

Abstract

We evaluated the root response to elevated CO₂ fumigation of 3 birches (Betula sp.) and 1 deciduous oak (Quercus sp.) grown in immature volcanic ash soil (VA) or brown forest soil (BF). VA is a nutrient-poor, phosphorus-impoverished soil, broadly distributed in northern Japan. Each species had been exposed to either ambient (375–395 μmol mol^?1) (aCO₂) or elevated (500 μmol mol^?1) (eCO₂) CO₂ during the daytime (more than 70 μmol m^?2 s^?1) over 4 growing seasons. The results suggest that eCO₂ did not cause an increase in total root production when the community had grown in fertile BF soil, however, it did cause a large increase when the community was grown in infertile VA soil. Yet, carbon allocation to plant roots was not affected by eCO₂ in either the BF or VA soils. Rhizo-morphogenesis appeared to occur to a greater extent under eCO₂. It seems that the saplings developed a massive amount of fine roots under the VA and eCO₂ conditions. Unexpectedly, eCO₂ resulted in a larger total root mass when the community was grown in VA soil than when grown in BF soil (eCO₂ × VA vs. eCO₂ × BF). These results may hint to a site-specific potential of communities to sequester future atmospheric carbon. The growing substance of plants is an important factor which root response to eCO₂ depends on, however, further studies are needed for a better understanding.

     

The mechanisms for N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO<Subscript>2</Subscript> and propargylic alcohols

The mechanistic details of N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO₂ and propargylic alcohols were investigated by DFT calculations. Six mechanisms, four for the formation of five-membered cyclic carbonate (M-A, M-B, M-B’ and M-C), and two for six-membered cyclic carbonate (M-D and M-E), were fully investigated. The energy profiles in dichloromethane showed that M-B is the predominant reaction with the lowest barrier of 31.99 kcal mol^?1, while M-C and M-D may be kinetically competitive to M-B. The very high activation energy of 45.37 kcal mol^-1, 57.07 kcal mol^-1 and 59.61 kcal mol^?1 for M-A, M-B’ and M-E, respectively, suggest that they are of lesser importance in the overall mechanism.

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Graphical abstract Formations of five-membered ring product and six-membered ring product are kinetically competitive, but five-membered ring product is thermodynamically more preferable.

     

Bonding,aromaticity, and planar tetracoordinated carbon in Si<Subscript>2</Subscript>CH<Subscript>2</Subscript> and Ge<Subscript>2</Subscript>CH<Subscript>2</Subscript>

Natural bond orbital (NBO) analyses and dissected nucleus-independent chemical shifts (NICS _{π z z} ) were computed to evaluate the bonding (bond type, electron occupation, hybridization) and aromatic character of the three lowest-lying Si₂CH₂ (1-Si, 2-Si, 3-Si) and Ge₂CH₂ (1-Ge, 2-Ge, 3-Ge) isomers. While their carbon C₃H₂ analogs favor classical alkene, allene, and alkyne type bonding, these Si and Ge derivatives are more polarizable and can favor “highly electron delocalized”? and “non-classical”? structures. The lowest energy Si ₂CH₂ and Ge ₂CH₂ isomers, 1-Si and 1-Ge, exhibit two sets of 3–center 2–electron (3c-2e) bonding; a π-3c-2e bond involving the heavy atoms (C–Si–Si and C–Ge–Ge), and a σ-3c-2e bond (Si–H–Si, Ge–H–Ge). Both 3-Si and 3-Ge exhibit π and σ-3c-2e bonding involving a planar tetracoordinated carbon (ptC) center. Despite their highly electron delocalized nature, all of the Si₂CH₂ and Ge₂CH₂ isomers considered display only modest two π electron aromatic character (NICS(0) _{π z z} =--6.2 to –8.9 ppm, computed at the heavy atom ring center) compared to the cyclic-C ₃H₂ (–13.3 ppm).

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Graphical Abstract The three lowest Si2CH2 and Ge2CH2 isomers.

     

Fine root traits in <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> forest soils with different acid buffering capacities

Key message

The biomass, morphology, and respiration of the fine roots of Chamaecyparis obtusa did not change between different soil acid buffering capacities. Soil nitrate has noticeable effects on morphology and respiration.

Abstract

Low soil acid buffering capacity (ABC) accelerates soil acidification because of the lower concentrations of base cations (BC) and higher concentrations of aluminum (Al) present under such conditions. More information on fine root traits across soil ABC gradients is required to evaluate the effects of accelerated soil acidification in mature forests, especially in East Asia. We investigated the biomass, morphology (specific root length; SRL), and respiration rates of fine roots and analyzed the soil nitrogen status in seven Chamaecyparis obtusa stands with two highly contrasting ABC soils. There were no significant differences in the biomass, SRL, and respiration rates of fine roots between high- and low-ABC stands. However, fine roots in the low-ABC stands were concentrated in the uppermost soil layers and the biomass proportion of roots <0.5 mm in diameter was higher in low-ABC stands than in high-ABC stands. The fine root biomass increased with increasing soil Al, NH₄ ⁺-N, and C and with decreasing soil BC and bulk density. The SRL and respiration rates of fine roots were positively correlated with soil NO₃ ^?-N. We conclude that the fine root traits were affected not only by soil ABC but also by other soil properties in the forest.

     

Does tree species composition affect soil CO<Subscript>2</Subscript> emission and soil organic carbon storage in plantations?

Key message

Mixed tree plantations are potential silvicultural systems to increase soil carbon storage through altering litter and root inputs and soil physiochemical properties.

Abstract

Afforestation and reforestation are major strategies for global climate change mitigation. Different tree species composition can induce diverse changes in soil CO₂ emission and soil carbon sequestration in tree plantation. This study employed three plantations of monoculture and mixed Pinus yunnanensis and Eucalyptus globulus to estimate the effect of tree species composition on soil CO₂ emission and soil organic carbon storage in subtropical China. We found that tree species composition had a significant effect on the soil CO₂ emission and soil organic carbon storage. Soil CO₂ emission was lower in the mixed plantation than in the P. yunnanensis plantation, whereas it was higher than in the E. globulus plantation. Differences in soil CO₂ emission among the three plantations were determined by leaf litterfall mass, fine root biomass, soil available nitrogen, pH, soil bulk density, and soil C:N ratio. Soil organic carbon storage was 34.5 and 23.2 % higher in the mixed plantation than in the P. yunnanensis and E. globulus plantations, respectively. Higher soil organic carbon stock in the mixed plantation was attributed to lower C/N ratio of leaf litter and soil, greater fine root biomass and soil organic carbon content, and lower soil CO₂ emission. We conclude that mixed tree plantation can enhance soil carbon sequestration, but can decrease or increase soil CO₂ emission through altering litter and root inputs and soil physiochemical properties.

     

Root proteomics reveals cucumber 24-epibrassinolide responses under Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> stress

Key message

The application of exogenous 24-epibrassinolide promotes Brassinosteroids intracellular signalling in cucumber, which leads to differentially expressed proteins that participate in different life process to relieve Ca(NO ₃ ) ₂ damage.

Abstract

NO₃ ^? and Ca²⁺ are the main anion and cation of soil secondary salinization during greenhouse cultivation. Brassinosteroids (BRs), steroidal phytohormones, regulate various important physiological and developmental processes and are used against abiotic stress. A two-dimensional electrophoresis gel coupled with MALDI-TOF/TOF MS was performed to investigate the effects of exogenous 24-epibrassinolide (EBL) on proteomic changes in cucumber seedling roots under Ca(NO₃)₂ stress. A total of 80 differentially accumulated protein spots in response to stress and/or exogenous EBL were identified and grouped into different categories of biological processes according to Gene Ontology. Under Ca(NO₃)₂ stress, proteins related to nitrogen metabolism and lignin biosynthesis were induced, while those related to cytoskeleton organization and cell-wall neutral sugar metabolism were inhibited. However, the accumulation of abundant proteins involved in protein modification and degradation, defence mechanisms against antioxidation and detoxification and lignin biosynthesis by exogenous EBL might play important roles in salt tolerance. Real-time quantitative PCR was performed to investigate BR signalling. BR signalling was induced intracellularly under Ca(NO₃)₂ stress. Exogenous EBL can alleviate the root indices, effectively reduce the Ca²⁺ content and increase the K⁺ content in cucumber roots under Ca(NO₃)₂ stress. This study revealed the differentially expressed proteins and BR signalling-associated mRNAs induced by EBL in cucumber seedling roots under Ca(NO₃)₂ stress, providing a better understanding of EBL-induced salt resistance in cucumber seedlings. The mechanism for alleviation provides valuable insight into improving Ca(NO₃)₂ stress tolerance of other horticultural plants.

     

DFT study of isomers of the ruthenium dihydride complex RuH<Subscript>2</Subscript>(CO)<Subscript>2</Subscript>(AsMe<Subscript>2</Subscript>Ph)<Subscript>2</Subscript>

A density functional theory (DFT) study of cct-As, ccc, and cct-CO isomers of the ruthenium dihydride complex RuH₂(CO)₂(AsMe₂Ph)₂ is reported (see Scheme for the labeling isomer 34 structures of RuH₂(CO)₂(AsMe₂Ph)₂). Complex geometries and relative energies of different isomers have been calculated with both B3LYP and M06-2X functionals. The results show that the B3LYP calculated Boltzmann populations of cct-As, ccc, and cct-CO isomers are 65.5, 34.2, and 0.3%, respectively. These are in better agreement with the experimental data than those calculated at the M06-2X level. However, the calculations of ¹H NMR chemical shifts were found to be better described with M06-2X than with B3LYP or with HF level of theories. In addition, a transition state between the two most stable isomers was determined through DFT/(B3LYP or M06-2X) calculations.

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Graphical Abstract Scheme: Labeling structure of RuH₂(CO)₂(AsMe₂Ph)₂

     

Putrescine protects hulless barley from damage due to UV-B stress via H<Subscript>2</Subscript>S- and H<Subscript>2</Subscript>O<Subscript>2</Subscript>-mediated signaling pathways

Key message

In hulless barley, H ₂ S mediated increases in H ₂ O ₂ induced by putrescine, and their interaction enhanced tolerance to UV-B by maintaining redox homeostasis and promoting the accumulation of UV-absorbing compounds.

Abstract

This study investigated the possible relationship between putrescence (Put), hydrogen sulfide (H₂S) and hydrogen peroxide (H₂O₂) as well as the underlying mechanism of their interaction in reducing UV-B induced damage. UV-B radiation increased electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and UV-absorbing compounds but reduced antioxidant enzyme activities and glutathione (GSH) and ascorbic acid (AsA) contents. Exogenous application of Put, H₂S or H₂O₂ reduced some of the above-mentioned negative effects, but were enhanced by the addition of Put, H₂S and H₂O₂ inhibitors. Moreover, the protective effect of Put against UV-B radiation-induced damage to hulless barley was diminished by dl-propargylglycine (PAG, a H₂S biosynthesis inhibitor), hydroxylamine (HT, a H₂S scavenger), diphenylene iodonium (DPI, a PM-NADPH oxidase inhibitor) and dimethylthiourea (DMTU, a ROS scavenger), and the effect of Put on H₂O₂ accumulation was abolished by HT. Taken together, as the downstream component of the Put signaling pathway, H₂S mediated H₂O₂ accumulation, and H₂O₂ induced the accumulation of UV-absorbing compounds and maintained redox homeostasis under UV-B stress, thereby increasing the tolerance of hulless barley seedlings to UV-B stress.

     

Dwarf pine invasion in an alpine tundra of discontinuous permafrost area: effects on fine root and soil carbon dynamics

Key message

Recent invasion of Pinus pumila , a highly productive shrub-like tree species, into alpine tundra does not significantly modify the dynamics of fine root and soil carbon in the tundra.

Abstract

Climate warming may directly and indirectly affect the large carbon stock in discontinuous permafrost soil at high latitudes. In recent decades, Siberian dwarf pine [Pinus pumila (Pall.) Regel] has been invading dry heath alpine tundra in the northern Amur region of Far East Russia. Siberian dwarf pine is known to have high aboveground productivity, comparable to that of tall coniferous trees. We hypothesised that the invasion of Siberian dwarf pine into alpine tundra could increase soil carbon stocks via an increase in fine roots. Contrary to our expectations, the invasion of dwarf pine did not significantly increase the fine root biomass and productivity of the tundra, probably due to the belowground competitive exclusion between the dwarf pine and alpine tundra plants. Furthermore, the invasion of the dwarf pine did not affect soil carbon in the alpine tundra ecosystem. These results show that the recent invasion of Siberian dwarf pine into tundra did not influence the fine root dynamics or the soil carbon stock in the study site. Together, these results implied that (1) it takes a long time for pine invasion to change the belowground ecosystem properties of tundra vegetation to that of pine thickets and therefore (2) the lack of an increase in soil carbon from recent tree invasion should be taken into account when modelling future carbon dynamics in alpine tundra.

     

Sap flow of the southern conifer, <Emphasis Type="Italic">Agathis australis</Emphasis> during wet and dry summers

Key message

Analysis of sap flux density during drought suggests that the large sapwood and rooting volumes of larger trees provide a buffer against drying soil.

Abstract

The southern conifer Agathis australis is amongst the largest and longest-lived trees in the world. We measured sap flux densities (F _d) in kauri trees with a DBH range of 20–176 cm to explore differences in responses of trees of different sizes to seasonal conditions and summer drought. F _d was consistently higher in larger trees than smaller trees. Peak F _d was 20 and 8 g m^?2 s^?1 for trees of diameters of 176 and 20 cm, respectively, during the wet summer. Multiple regression analysis revealed photosynthetically active radiation (PAR) and vapour pressure deficit (D) were the main drivers of F _d. During drought, larger trees were more responsive to D whilst smaller trees were more responsive to soil drying. Our largest tree had a sapwood area of 3,600 cm². Preliminary analysis suggests stem water storage provides a buffer against drying soil in larger trees. Furthermore, F _d of smaller trees had higher R ² values for soil moisture at 30 and 60 cm depth than soil moisture at 10 cm depth (R ² = 0.68–0.97 and 0.55–0.67, respectively) suggesting that deeper soil moisture is more important for these trees. Larger trees did not show a relationship between F _d and soil moisture, suggesting they were accessing soil water deeper than 60 cm. These results suggest that larger trees may be better prepared for increasing frequency and intensity of summer droughts due to deeper roots and/or larger stem water storage capacity.

     

Mode of competition for light and water amongst juvenile beech and spruce trees under ambient and elevated levels of O3 and CO2

Key message

Our study provides evidence that neither elevated CO ₂ nor elevated O ₃ alters the positive asymmetric competition for light and the symmetric competition for water among beech and spruce individuals grown in monoculture. We conclude that the mechanism of competition (i.e. symmetric/asymmetric) above (e.g shading or overtopping effect) and belowground (e.g. non-preemption or foraging) rather than abiotic treatments such as elevated CO ₂ , O ₃ and CO ₂ /O ₃ regimes, plays a dominant role for ensuring competitive success among tree saplings.

Abstract

Despite numerous studies conducted on plant responses to increasing CO₂ and O₃ concentrations, there is still a gap in understanding on how these gasses would affect the mode of competition (e.g., the ability by which larger and smaller plants capture resources) at the individual level of intra-specific beech and spruce saplings. Using empirical data and simulations from the plant-growth model PLATHO, we analyzed underlying mechanisms of competition and extrapolated effects beyond the time span of the experiment. We hypothesized that among juvenile beech and spruce trees planted in monoculture, +CO₂ would diminish the positive asymmetric competition for light. Conversely, +O₃ would enhance this outcome. In addition, we hypothesized that the symmetric mode of competition belowground for water would remain unchanged, irrespective of +CO₂ and/or +O₃ treatments. Our results showed that +CO₂ and/or +O₃ treatments did not alter the mode of competition aboveground for light. Conversely, we accepted our hypothesis that the mode of competition for water would remain unchanged under both treatments. Overall, we conclude that neither +CO₂ nor +O₃ alters the positive asymmetric competition for light and the symmetric competition for water among beech and spruce individuals grown in monoculture. We further conclude that competitive mechanism above (e.g., shading or overtopping effect) and belowground (e.g., non-preemption or foraging) rather than abiotic treatments, such as elevated CO₂, O₃ and CO₂/O₃ regimes, plays a dominant role for ensuring competitive success among tree saplings.     

Estimating the absorptive root area in Norway spruce by using the common direct and indirect earth impedance methods

Aims

Estimates of root absorption magnitude are needed for the balanced management of forest ecosystems, but no methods able to work on the whole tree and stand level were available. Modified earth impedance method was developed recently and here it was tested, by comparing the results with those obtained by combination of several classical methods.

Methods

We used direct (soil cores, scanning and microscopy) and indirect (sap flow patterns and modified earth impedance) methods in an attempt to estimate the absorptive root area indexes (RAI) at two sites of about 25 and 40-years-old Norway spruce. We considered the geometric surfaces of all scanned fine roots to be equal to the fine root absorptive area (RAI _scan ). To estimate the potentially physically permeable area of fine roots, we microscopically evaluated the point of secondary xylem appearance and calculated the geometric area of root portions with primary structure (RAI _micro ). We termed the area of electrically conductive root surface as the active (ion) absorptive area (RAI _mei ) and measured its extent by the modified earth impedance (MEI) method.

Results

The highest values for absorptive root areas at the two experimental sites we obtained with the scanning method (RAI _scan was considered to be 100%), followed by the RAI _micro (51%) and RAI _mei (32%). RAImei reached about 2/3 of RAImicro. The surface area of the ectomycorrhizal hyphae was an order of magnitude larger than that of all fine roots, but the MEI did not measure such increase.

Conclusions

We showed that the absorptive root area, indirectly estimated by the MEI, provides consistent results that approach the values obtained for fine roots with a primary structure estimated by traditional direct methods. The similar range of the values for the absorptive root surface area obtained by microscopy and by the MEI method indicates that this method is feasible and that it could be used to determine the extent of active absorptive root surface areas in forests.     

Impacts of nitrogen-fixing and non-nitrogen-fixing tree species on soil respiration and microbial community composition during forest management in subtropical China

Forest management with N-fixing trees can improve soil fertility and tree productivity, but have little information regarding belowground carbon processes and microbial properties. We aimed to evaluate the effects of three forest management regimes, which were Erythrophleum fordii (N-fixing tree), Pinus massoniana (non-N-fixing tree), and their mixed forest, on soil respiration and microbial community composition in subtropical China, using Barometric Process Separation and phospholipid fatty acid profiles, respectively. We found that the inclusions of N-fixing species in forests significantly increased the soil respiration, but have no effects on SOC and ecosystem total C stock. In addition, soil microbial communities were obviously different among the three forest management regimes. For instance, total and bacterial PLFAs were higher in the E. fordii and mixed forest than in the P. massoniana forest. Conversely, fungal PLFAs in the P. massoniana forest were elevated versus the other two forests. Soil total N, nitrate-N and pH were the key determinants shaping the microbial community composition. Our study suggests that variations in soil respiration in the studied forests could be primarily explained by the differences of root biomass and soil microbial biomass, but not soil organic carbon. Although soil fertility and microbial biomass were promoted, N-fixing plantings also brought on increased CO₂ emissions in laboratory assays. The future decision of tree species selection for forest management in subtropical China therefore needs to consider the potential influences of tree species on CO₂ emissions.     

Mangrove root: adaptations and ecological importance

Key message

This review gives a comprehensive overview of adaptations of mangrove root system to the adverse environmental conditions and summarizes the ecological importance of mangrove root to the ecosystem.

Abstract

In plants, the first line of defense against abiotic stress is in their roots. If the soil surrounding the plant root is healthy and biologically diverse, the plant will have a higher chance to survive in stressful conditions. Different plant species have unique adaptations when exposed to a variety of abiotic stress conditions. None of the responses are identical, even though plants have become adapted to the exact same environment. Mangrove plants have developed complex morphological, anatomical, physiological, and molecular adaptations allowing survival and success in their high-stress habitat. This review briefly depicts adaptive strategies of mangrove roots with respect to anatomy, physiology, biochemistry and also the major advances recently made at the genetic and genomic levels. Results drawn from the different studies on mangrove roots have further indicated that specific patterns of gene expression might contribute to adaptive evolution of mangroves under high salinity. We also review crucial ecological contributions provided by mangrove root communities to the ecosystem including marine fauna.

     

Tyrosinase and catechol oxidase activity of copper(I) complexes supported by imidazole-based ligands: structure–reactivity correlations

Four new imidazole-based ligands, 4-((1H-imidazol-4-yl)methyl)-2-phenyl-4,5-dihydrooxyzole (L _OL 1), 4-((1H-imidazol-4-yl)methyl)-2-(tert-butyl)-4,5-dihydrooxyzole (L _OL 2), 4-((1H-imidazol-4-yl)methyl)-2-methyl-4,5-dihydrooxyzole (L _OL 3), and N-(2,2-dimethylpropylidene)-2-(1-trityl-1H-imidazol-4-yl-)ethyl amine (L _imz 1), have been synthesized. The corresponding copper(I) complexes [Cu(I)(L _OL 1)(CH₃CN)]PF₆ (CuL _OL 1), [Cu(I)(L _OL 2)(CH₃CN)]PF₆ (CuL _OL 2), [Cu(I)(L _OL 3)(CH₃CN)]PF₆ (CuL _OL 3), [Cu(I)(L _imz 1)(CH₃CN)₂]PF₆ (CuL _imz 1) as well as the Cu(I) complex derived from the known ligand bis(1-methylimidazol-2-yl)methane (BIMZ), [Cu(I)(BIMZ)(CH₃CN)]PF₆ (CuBIMZ), are screened as catalysts for the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC-H₂) to 3,5-di-tert-butylquinone (3,5-DTBQ). The primary reaction product of these oxidations is 3,5-di-tert-butylsemiquinone (3,5-DTBSQ) which slowly converts to 3,5-DTBQ. Saturation kinetic studies reveal a trend of catalytic activity in the order CuL _OL 3 ≈ CuL _OL 1 > CuBIMZ > CuL _OL 2 > CuL _imz 1. Additionally, the catalytic activity of the copper(I) complexes towards the oxygenation of monophenols is investigated. As substrates 2,4-di-tert-butylphenol (2,4-DTBP-H), 3-tert-butylphenol (3-TBP-H), 4-methoxyphenol (4-MeOP-H), N-acetyl-l-tyrosine ethyl ester monohydrate (NATEE) and 8-hydroxyquinoline are employed. The oxygenation products are identified and characterized with the help of UV/Vis and NMR spectroscopy, mass spectrometry, and fluorescence measurements. Whereas the copper complexes with ligands containing combinations of imidazole and imine functions or two imidazole units (CuL _imz 1 and CuBIMZ) are found to exhibit catalytic tyrosinase activity, the systems with ligands containing oxazoline just mediate a stoichiometric conversion. Correlations between the structures of the complexes and their reactivities are discussed.     

Differential alkaloid profile in <Emphasis Type="Italic">Uncaria tomentosa</Emphasis> micropropagated plantlets and root cultures

The alkaloids of Uncaria tomentosa micropropagated plantlets and root cultures were isolated and identified by NMR and mass spectrometry. Plantlets yielded pteropodine (1), isopteropodine (2), mitraphylline (3), isomitraphylline (4), uncarine F (5), speciophylline (6), rhynchophylline (7) and isorhynchophylline (8). In plantlets growing under continuous light, tetracyclic alkaloids 7 and 8 decreased from 20 ± 1.8 at 2 months to 2.2 ± 0.33 mg/g dry wt at 6 months, while the pentacyclic alkaloids 1–4 increased from 7.7 ± 1.4 to 15 ± 0.05 mg/g dry wt, supporting their biogenetic conversion. Micropropagated plantlets produced four times more alkaloids (27.6 ± 3.1 mg/g dry wt) than greenhouse plants. Plantlet roots yielded 3, 4, 8 and the glucoindole alkaloids 3α-dihydrocadambine (9) and dolichantoside (10), the last one not previously found in Uncaria.     

Root-derived CO<Subscript>2</Subscript> flux from a tropical peatland

Tropical peatlands release significant quantities of greenhouse gases to the atmosphere, yet the relative contributions of heterotrophic and autotrophic respiration to net CO₂ fluxes remains sparsely quantified. We used a combination of in situ trenching and vegetation removal in ex situ pots to quantify root-derived CO₂ under two plant functional types within a mixed species forest. Trenching significantly reduced surface CO₂ flux, indicating that approximately two-thirds of the released CO₂ was derived from roots. In contrast, ex situ vegetation removal in pots indicated that root-derived CO₂ accounted for 27% of the total CO₂ flux for Campnosperma panamensis, a broadleaved evergreen tree, and 49% for Raphia taedigera, a canopy palm. The results show that root-derived CO₂ is a major contribution to net CO₂ emissions in tropical peatlands, and that the magnitude of the emissions is affected by plant species composition. This is important in the context of land use change driving alterations in vegetation cover.     

Distorted tetrahedral nickel-nitrosyl complexes: spectroscopic characterization and electronic structure

The linear nickel-nitrosyl complex [Ni(NO)(L3)] supported by a highly hindered tridentate nitrogen-based ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3), was prepared by the reaction of the potassium salt of the ligand with the nickel-nitrosyl precursor [Ni(NO)(Br)(PPh ₃ ) ₂ ]. The obtained nitrosyl complexes as well as the corresponding chlorido complexes [Ni(NO)(Cl)(PPh ₃ ) ₂ ] and [Ni(Cl)(L3)] were characterized by X-ray crystallography and different spectroscopic methods including IR/far-IR, UV–Vis, NMR, and multi-edge X-ray absorption spectroscopy at the Ni K-, Ni L-, Cl K-, and P K-edges. For comparative electronic structure analysis we also performed DFT calculations to further elucidate the electronic structure of [Ni(NO)(L3)]. These results provide the nickel oxidation state and the character of the Ni-NO bond. The complex [Ni(NO)(L3)] is best described as [Ni ^II (NO ^– )(L3)], and the spectroscopic results indicate that the phosphane complexes have a similar [Ni ^II (NO ^– )(X)(PPh ₃ ) ₂ ] ground state.