CC Sites Research Articles

Conversion of the CG specific M.MpeI DNA methyltransferase into an enzyme predominantly methylating CCA and CCC sites.

We used structure guided mutagenesis and directed enzyme evolution to alter the specificity of the CG specific bacterial DNA (cytosine-5) methyltransferase M.MpeI. Methylation specificity of the M.MpeI variants was characterized by digestions with methylation sensitive restriction enzymes and by measuring incorporation of tritiated methyl groups into double-stranded oligonucleotides containing single CC, CG, CA or CT sites. Site specific mutagenesis steps designed to disrupt the specific contacts between the enzyme and the non-substrate base pair of the target sequence (5'-CG/5'-CG) yielded M.MpeI variants with varying levels of CG specific and increasing levels of CA and CC specific MTase activity. Subsequent random mutagenesis of the target recognizing domain coupled with selection for non-CG specific methylation yielded a variant, which predominantly methylates CC dinucleotides, has very low activity on CG and CA sites, and no activity on CT sites. This M.MpeI variant contains a one amino acid deletion (ΔA323) and three substitutions (N324G, R326G and E305N) in the target recognition domain. The mutant enzyme has very strong preference for A and C in the 3' flanking position making it a CCA and CCC specific DNA methyltransferase.

Tailoring chemoselectivity of Fe/Ni catalyst for hydrogenation of carbonyl compound

Selective hydrogenation of carbonyl moiety in the presence of olefinic group and other reducible functionality is an industrially important transformation. However, the protocol of green chemistry cannot be sacrificed for its formidable challenging transformation. Therefore, iron nickel bimetallic recyclable catalyst (Fe/Ni) was used for base free hydrogenation of carbonyl compound with high activity and chemoselectivity in microwave environment. The microwave irradiation and pre-treatment of bimetallic catalyst (Fe/Ni) divert conversion/selectivity towards CO group as compared to CC or another reducible moiety. This is further confirmed by DFT calculations which shows that the CO site is strongly interacted with the surface compared to the CC site. The pyridine adsorption studies revealed that pre-treated (Fe/Ni) possess more acidic sites as compared to untreated catalyst. Furthermore, the selectivity of bimetallic catalysts towards hydrogenation of carbonyl function group was correlated with Fe content present in the matrix of catalyst.

Efficient capture and detoxification of mercury dichloride from wastewater by a PVDF/PEI adsorption membrane

Poly(vinylidene fluoride) (PVDF), as one of the halogenated alkanes, has excellent membrane performance. Polyethyleneimine (PEI), with excellent chelating performance and strong alkalinity, could enable halogenated alkanes to produce active CC bonds, and subsequently, PEI can be grafted onto the CC sites in-situ. In this paper, a novel adsorption membrane (PVDF/PEI) was fabricated via a one-step bulk grafting reaction of branched PEI to PVDF networks by non-solvent-induced phase inversion. This membrane showed highly efficient removal of Hg(II) ions, where 97% of Hg(II) from 20 mL of simulated wastewater solution containing 400 mg/L Hg(II) was removed in just 30 min using 20 mg of the adsorbent. The Langmuir isotherm model fitted the adsorption process well and gave a maximum adsorption capacity of 1036 mg/g at 30 °C, which agreed with the experimental saturation adsorption capacity of 1023 mg/g, suggesting that all binding sites on the membrane were involved in adsorption. After adsorption, Hg(II) was reduced to Hg2Cl2 with low toxicity to generate the crystals with a regular shape. Mechanisms studies implied that the adsorption of Hg(II) onto PVDF/PEI was an integrated chemical process that involved chemical chelation and a redox reaction due to the strong interactions between the mercury atoms and the active sites on the membrane. This novel PVDF/PEI adsorption membrane was resistant to acid and alkali, and can be separated and recovered directly from aqueous by fishing out. To the best of our knowledge, this is the first time to report on a PEI-functionalized PVDF adsorption membrane for the efficient removal of Hg(II).

Osteoclast density is not increased in bone adjacent to radiolucencies (cysts) in juvenile equine medial femoral condyles.

There is a knowledge gap about how equine MFC subchondral radiolucencies (SR) arise and evolve. Osteoclasts are believed to have a role but have not been studied in situ. To measure and compare osteoclast density and the percentage of chondroclasts in healthy and MFC SR specimens from juvenile Thoroughbreds. Cadaveric study. Medial femoral condyles (MFC) from a tissue bank of equine stifles were studied. Inclusion criteria were MFCs (≤8months old) with a computed tomography SR lesion and histological focal failure of endochondral ossification (L group). Contralateral, lesion-free, MFCs were a control group (CC). Osteochondral slabs were cut through the lesion (L), a healthy site immediately caudal to the lesion, (internal control; IC) and the contralateral, site-matched controls (CC). Histological sections were immunostained with Cathepsin K for osteoclast counting. Osteoclasts in contact with the growth cartilage (chondroclasts) were also counted. The sections were segmented into regions of interest (ROI) at different depths in the subchondral bone: ROI1 (0-1mm), ROI2 (1-3mm) and ROI3 (3-6mm). Osteoclasts were counted and the bone area was measured in each ROI to calculate their density. Chondroclasts were counted in ROI1 . Sections were studied from L and IC (n=6) and CC sites (n=5). Osteoclast density was significantly higher in ROI1 when compared with ROI3 in all groups. Although higher osteoclast density was measured in ROI1 in the L group, no significant differences were detected when compared with control ROIs. The proportion of chondroclasts in ROI1 was lower in the L sections when compared with controls but no significant differences were detected. Limited sample size. Osteoclasts are important actors in MFC subchondral bone development, digesting both growth cartilage (chondroclasts) and bone, but the pathophysiology of early MFC SRs cannot be explained solely by an increased osteoclast presence in the subchondral bone.

Synthesis and characterization of walnut husk extract-silver nanocomposites for removal of heavy metals from petroleum wastewater and its consequences on pipework steel corrosion

A new nano-scale bio-based nanocomposite for treating petroleum wastewater has been synthesized using walnut husk (an agro industrial by-product). The walnut husk extract-silver nanoparticles (WHE-AgNPs) were round-shaped, monodispersed, none-aggregated and crystalline with nearly 46.2 nm size and zeta potential of –41.2 eV. On introduction into petroleum wastewater (PWW), WHE-AgNPs reduced the magnitude of some key water pollution indicators, which were initially very high, to values within World Health Organization (WHO) prescribed safe limits. Also, 0.75 g WHE-AgNPs removed Pb, Cr and Cd ions from PWW at efficiency of 72.6%, 81.3% and 88.1%, respectively, at 25 oCwithin 5 h, facilitated by physisorption of CN, NH, CO, CC, CO and OH sites on WHE-AgNPs surfaces with the metal ions. The extent of metal ions removal varies with temperature, concentration of WHE-AgNPs, dose of metal ions, contact time and pH. Unlike the crude extract feedstock, WHE-AgNPs remains efficient, stable and resistant to thermal and biochemical degradation even after 120 days of storage. Discharged untreated PWW produces higher corrosive effect on pipework steel than treated PWW. The extent and mechanism of anticorrosion effect of WHE-AgNPs on pipework steel is investigated using electrochemical, weight loss, FTIR and SEM/EDS analyses.

Effect of Long-Acting Injectable Antipsychotics vs Usual Care on Time to First Hospitalization in Early-Phase Schizophrenia

Long-acting injectable antipsychotics (LAIs) can potentially reduce hospitalization risk by enhancing medication adherence but are rarely considered for early-phase schizophrenia treatment. To determine whether encouraging use of a LAI compared with usual care delays the time to first hospitalization with patients with early-phase illness. The Prevention of Relapse in Schizophrenia (PRELAPSE) trial was cluster randomized with a follow-up duration of 2 years. The study began in December 2014, was completed in March 2019, and was conducted in 39 mental health centers in 19 US states. Site randomization assigned 19 clinics to encourage treatment with long-acting aripiprazole monohydrate (aripiprazole once monthly [AOM] condition) and 20 to provide treatment as usual (clinician's choice [CC] condition). Participant eligibility criteria included (1) schizophrenia diagnosis confirmed by a structured clinical interview, (2) fewer than 5 years of lifetime antipsychotic use, and (3) age 18 to 35 years. The AOM sites identified 576 potentially eligible participants, of whom 234 (40.6%) enrolled; CC sites identified 685 potentially eligible participants, of whom 255 (37.2%) enrolled. There were no restrictions on treatment at CC sites (including using LAIs) or at AOM sites with the exception that aripiprazole monohydrate had to be prescribed within US Food and Drug Administration-approved guidelines. The primary outcome was time to first psychiatric hospitalization based on participant interviews every 2 months, the service use resource form administered every 4 months, and other sources (eg, health records) as available. Potential events were adjudicated by an independent committee masked to treatment assignment. The 489 participants (368 men [75.3%]) had a mean (SD) age of 25.2 (4.2) years and 225 (46.0%) had 1 year or less lifetime antipsychotic use. Fifty-two AOM (22%) and 91 CC participants (36%) had at least 1 hospitalization. The mean survival time until first hospitalization was 613.7 days (95% CI, 582.3-645.1 days) for AOM participants and 530.6 days (95% CI, 497.3-563.9 days) for CC participants. For time to first hospitalization, the hazard ratio was 0.56 (95% CI, 0.34- 0.92; P = .02), favoring AOM. Survival probabilities were 0.73 (95% CI, 0.65-0.83) for AOM participants and 0.58 (95% CI, 0.50-0.67) for CC participants. The number needed to treat to prevent 1 additional hospitalization was 7 participants treated with AOM compared with CC. Long-acting injectable antipsychotic use by patients with early-phase schizophrenia can significantly delay time to hospitalization, a personally and economically important outcome. Clinicians should more broadly consider LAI treatment for patients with early-phase illness. ClinicalTrials.gov Identifier: NCT02360319.

First-principles calculations of stability of graphene-like BC3 monolayer and its high-performance potassium storage

With increasing demand for renewable energy, graphene-like BC3 monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently. However, its structural stability, potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet. In this work, phonon spectra, AIMD simulations and elastic constants of graphene-like BC3 monolayer are investigated. Our results show that graphene-like BC3 monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653mAh/g with the corresponding open circuit voltages 0.66V. Due to potassium atom can be effectively adsorbed at the most energetically favorable h−CC site with obvious charge transfer, making adsorbed graphene-like BC3 monolayer change from semiconductor to metal which is really good for electrode utilization. Moreover, the migrations potassium atom on the graphene-like BC3 monolayer is rather fast with the diffusion barriers as low as 0.12eV, comparing lithium atom with a relatively large diffusion barrier of 0.46eV. Additionally, the tensile strains applied on the graphene-like BC3 monolayer have marginal effect on the adsorption and diffusion performances of lithium, sodium and potassium atoms.

Synthesis and evaluation of anticorrosion properties of onion mesocarp-nickel nanocomposites on X80 steel in acidic cleaning solution

New Ni-nanocomposites were synthesized from waste onion mesocarp extracts and characterized by UV-Vis, FTIR, XRD, SEM/EDS, DLS and TEM techniques. Monodispersed non-agglomerating colloidal nanoparticles with spherical shape and particle sizes of 30–50 nm were obtained. The nanocomposites (Ni-OMNPs) exhibit O, N and CC sites which facilitated their physisorption on X80 steel surface from aqueous 1 M HCl and efficient protection of the steel surface against corrosion in the acid solution. Ni-OMNPs inhibits X80 steel corrosion in 1 M HCl with 93.99 ± 2.10 % efficiency at 30 °C and reduces surface pitting and roughness by 51.2 % and 52.3 % respectively. AFM, SEM, EDAX and FTIR techniques were used to check extent of surface protection and inhibitor-steel interaction mechanism. Compared to crude extract feedstock, Ni-OMNPs show higher corrosion inhibition and resistance to thermal and biochemical degradation. Unlike the crude extract, inhibition efficiency of Ni-OMNPs did not change considerably throughout 150 days of storage at different temperatures.

Inhibition of erosion corrosion of pipework steel in descaling solution using 5-hydroxytryptamine-based additives: Empirical and computational studies

Mildly HCl (5%) used in formulating acid wash and descaling solution in the oilfield corrodes steel pipework especially at elevated temperatures. 5-Hydroxytryptamine (5-HTM) was tested as alternative non-toxic and eco-friendly anticorrosion additive for protection of steel in 5% HCl at different temperatures. Experimental corrosion monitoring techniques, quantum chemical calculations and molecular dynamics simulations were employed to probe corrosion inhibition, adsorption phenomenon and binding characteristics of 5-HTM to steel surface. It was observed that 5-HTM acts as mixed type inhibitor with domino effect on anodic half reaction. Addition of 5-HTM decreases corrosion current and double layer capacitance but increases charge transfer and polarization resistances. Kinetic, thermodynamic and adsorption parameters were determined and used to further explain the interaction of 5-HTM species with X80 steel surface species. Frontier molecular orbitals energies, ELUMO and EHOMO values reveal high and low electron density sites. At the atomic and molecular levels, interaction and binding energies and mechanism are predicted based on results of geometry optimization, quantum chemical calculations and molecular dynamics (MD) simulations. Some N, O and CC sites in 5-HTM are predicted as active adsorption sites from FTIR, EDS analyses and MD simulations while surface morphology is screened by SEM.

Unexpected Pd/C-catalyzed room temperature and atmospheric pressure hydrogenation of 2-methylenecyclobutanones

Pd/C-catalyzed hydrogenation reaction of 2-methylenecyclobutanones (2-MCBones) occurs at their exocyclic CC sites regio-specifically to produce 2-substituted cyclobutanones, which are useful building blocks for the synthesis of drug and pesticide intermediates and are key intermediates in the total synthesis of many natural products. Surprisingly, atmospheric pressure H2 in balloon can be used as the cheap, clean and safe reductant and the reaction occurs smoothly at room temperature (25 °C). Quantitative calculation demonstrates that the release of the intramolecular ring strain caused by the combined effect of the four-membered ring and exocyclic CC bond in 2-MCBones provides additional dynamic driving forces for the reaction. The higher hydrogenation energy releasing of the exocyclic CC than CO was also found to be the causation for good regio-selectivity of the reaction. These new findings may broaden the understandings on the catalytic hydrogenation reactions of strained organic molecules.

RNA Exclusion Mechanism of the Cytidine Deaminase APOBEC3G

APOBEC3G (A3G) is a potent antiretroviral protein that specifically targets and deaminates cytidine nucleotides to uracil in single stranded DNA (ssDNA) intermediates produced during HIV replication. A3G displays high selectivity for specific polynucleotide contexts targeting 5′‐CC sites for deamination. A3G binds strongly to RNA via the N‐terminal non‐catalytic domain, which is crucial for recruitment of A3G to the virion, yet A3G displays no deamination activity on the cytidines in single stranded RNA. Our recent structure of A3G bound to ssDNA shows the preferred substrate conformation but does not reveal the mechanisms of substrate selection and non‐substrate exclusion. Here, we report NMR and molecular dynamics (MD) simulation based analysis of the interactions between the C‐terminal catalytic domain of A3G (A3Gctd) and multiple substrate and non‐substrate ssDNAs, which are coupled with deamination assays. The extent of interaction with residues located in helix1 and loop1 (T201‐L220) distinguishes substrate ssDNAs from non‐substrate ssDNAs, revealing the difference between catalytic and non‐catalytic ssDNA‐binding modes of A3Gctd. Using fluorine substituted ribonucleotides we show that 2′‐endo sugar pucker of the target cytidine is an essential factor for effective deamination. Furthermore, MD simulations show that ribose cytidine does not stay at catalytic position during 100ns of simulation time whereas deoxy‐ribose cytidine does. Trajectories of the MD simulation suggest that 2′‐hydroxyl group of RNA forms a hydrogen bond with His257 that chelates Zn2+, which results in loss of two hydrogen bonds between the target cytidine and A3Gctd, dislocating cytosine base from the catalytic position. This study provides mechanistic models of the catalytic selectivity of A3G against RNA.Support or Funding InformationInstitute for Molecular Virology Training Program (NIH grant T32 AI83196) University of MinnesotaThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Synthesis of nanostructured amorphous carbon-copper composite films by plasma-enhanced chemical vapour deposition

Nanostructured amorphous carbon-copper composite films were formed by plasma-enhanced chemical vapour deposition. The formation was done on copper-silicon substrates at 25°C, 300°C, 520°C, and 700°C temperatures using an acetylene gas at 40–70Pa pressure. The heating of the CuSi substrate induced formation of Cu nanospheres with 50–500nm size depending on the substrate temperature. The microstructure and composition of nanostructured carbon-copper composite films were investigated. The SEM views showed formation of amorphous carbon films with the randomly distributed nanostructures. The oxygen concentration in the composite films decreased with the increased heating temperature. The surface roughness measurements indicated that the surface roughness values increased with the increase of the temperature. The increase of the substrate temperature stimulated to the graphitization, enhanced the fraction of sp2 CC sites and lead to the formation of the nanocrystaline graphite clusters in composite films. The nanohardness values of the formed nanostructured amorphous carbon-Cu films varied in the range of 0.2–3GPa.

Prescribed burning of harvested boreal black spruce forests in eastern Canada: effect on understory vegetation

Ecosystem-based management advocates that forestry disturbances should aim to emulate natural disturbances to mitigate the landscape-level impact of forest management. This study compares the impact of clear-cuts followed by a prescribed burn (CCPB) with clear-cuts alone (CC) and current careful logging practices (CLAAG: “careful logging around advanced growth”) on understory composition within black spruce (Picea mariana Miller (BSP)) paludified forest stands at the plot, site, and treatment levels using a functional-type approach. Vascular and nonvascular taxa showed significant differences in composition at the plot level among treatments. We found that pioneer taxa occurred mainly in CCPB sites, while late-successional taxa characterized CC sites. CLAAG sites had higher taxa richness than CCPB and CC sites, and we found that CCPB treatments were most likely to promote vascular taxa compositions that are more similar to those observed after natural disturbances. Additionally, the relative abundance of Sphagnum spp., responsible for paludification, was significantly reduced in sites treated by prescribed burning. This study therefore presents results suggesting that prescribed burning might represent a sustainable alternative to current harvesting techniques in the Clay Belt of eastern Canada that could help in preserving biodiversity (in terms of understory species assemblage) while maintaining or even enhancing forest productivity.

The sharing economy: Why people participate in collaborative consumption

Information and communications technologies (ICTs) have enabled the rise of so‐called “Collaborative Consumption” (CC):the peer‐to‐peer‐based activity of obtaining, giving, or sharing the access to goods and services, coordinated through community‐based online services.CChas been expected to alleviate societal problems such as hyper‐consumption, pollution, and poverty by lowering the cost of economic coordination within communities. However, beyond anecdotal evidence, there is a dearth of understanding why people participate inCC. Therefore, in this article we investigate people's motivations to participate inCC. The study employs survey data (N = 168) gathered from people registered onto aCCsite. The results show that participation inCCis motivated by many factors such as its sustainability, enjoyment of the activity as well as economic gains. An interesting detail in the result is that sustainability is not directly associated with participation unless it is at the same time also associated with positive attitudes towardsCC. This suggests that sustainability might only be an important factor for those people for whom ecological consumption is important. Furthermore, the results suggest that inCCan attitude‐behavior gap might exist; people perceive the activity positively and say good things about it, but this good attitude does not necessary translate into action.

Analysis of Promoter Non-CG Methylation in Prostate Cancer

In vertebrates, DNA methylation occurs primarily at CG dinucleotides but recently, non-CG methylation has been found at appreciable levels in embryonic stem cells. To assess non-CG methylation in cancer, we compared the extent of non-CG methylation at several biologically important CG islands in prostate cancer and normal cell lines. An assessment of the promoter CG islands EVX1 and FILIP1L demonstrates a fourfold higher rate of non-CG methylation at EVX1 compared with FILIP1L across all cell lines. These loci are densely methylated at CG sites in cancer. No significant difference in non-CG methylation was demonstrated between cancer and normal. Treatment of cancer cell lines with 5-azacytidine significantly reduced methylation within EVX1 at CG and CC sites, preferentially. Non-CG methylation does not correlate with CG methylation at hypermethylated promoter regions in cancer. Furthermore, global inhibition of DNA methyltransferases does not affect all methylated cytosines uniformly.

The Sharing Economy: Why People Participate in Collaborative Consumption

Information and communications technologies (ICTs) have enabled the rise of so-called “Collaborative Consumption” (CC): the peer-to-peer-based activity of obtaining, giving, or sharing the access to goods and services, coordinated through community-based online services. CC has been expected to alleviate societal problems such as hyper-consumption, pollution, and poverty by lowering the cost of economic coordination within communities. However, beyond anecdotal evidence, there is a dearth of understanding why people participate in CC. Therefore, in this article we investigate people’s motivations to participate in CC. The study employs survey data (N = 168) gathered from people registered onto a CC site. The results show that participation in CC is motivated by many factors such as its sustainability, enjoyment of the activity as well as economic gains. An interesting detail in the result is that sustainability is not directly associated with participation unless it is at the same time also associated with positive attitudes towards CC. This suggests that sustainability might only be an important factor for those people for whom ecological consumption is important. Furthermore, the results suggest that in CC an attitudebehavior gap might exist; people perceive the activity positively and say good things about it, but this good attitude does not necessary translate into action.

Effect of vegetation switch on soil chemical properties

Soil chemical properties were investigated under four types of forest to evaluate the effect of replacement of tree species on soil chemical properties in the north of Japan. Two sites had undergone a vegetation switch around 1960 from broadleaved to coniferous trees (BC) and coniferous to broadleaved trees (CB), while the other two sites had had no vegetation change and carried broadleaved trees (BB) and coniferous trees (CC). Soil samples from the four sites were analyzed for pH (water, H2O), electrical conductivity (EC), total carbon (C) and nitrogen (N) content, exchangeable cations [Ex. calcium (Ca), magnesium (Mg), potassium (K) and sodium (Na)], inorganic nitrogen (Inorg-N), nitrogen mineralization potential, total phosphorus (P), and available phosphate. Most of the soil chemical properties in both the upper (0–5 cm) and lower (5–10 cm) layers at the BC site had lower values than those at the BB site. Values of soil chemical properties in the upper and lower soil layers were similar at the BC and CC sites. pH, Inorg-N, EC, Ex.Ca and Ex.Mg in the upper layer at the CB site were significantly higher than those at CC site, whereas all soil properties at the CB site except for Inorg-N were similar to those at the BB site. In the lower layer at the CB site, values of soil chemical properties except for the C/N ratio were almost the same as those at the CC site, but lower than those at the BB site. The upper soil layer at sites where a vegetation switch had occurred was affected by the current tree species, whereas in the lower soil layer, the effects differed between the different vegetation switch patterns. At the CB site, where the vegetation switch was from coniferous to broadleaved trees, the soil chemical properties in the lower layer remained similar to those at the coniferous site (CC) 50 years after the vegetation switch, while changes in soil properties have occurred following the switch from broadleaved to coniferous trees. The change in soil nutrient content by vegetation switch was considerably affected by change in not only litter quality but also composition of earthworm community. In particular, a combination of epigeic and endogeic earthworms exhibited important roles for nutrient dynamics to the deeper soil layer.

Highly error-free role of DNA polymerase η in the replicative bypass of UV-induced pyrimidine dimers in mouse and human cells

Cyclobutane pyrimidine dimers (CPDs) constitute the most frequent UV-induced DNA photoproduct. However, it has remained unclear how human and other mammalian cells mitigate the mutagenic and carcinogenic potential of CPDs emanating from their replicative bypass. Here, we examine in human cells the roles of translesion synthesis (TLS) DNA polymerases (Pols) in the replicative bypass of a cis-syn TT dimer carried on the leading or the lagging strand DNA template in a plasmid system we have designed, and we determine in mouse cells the frequencies and mutational spectra generated from TLS occurring specifically opposite CPDs formed at TT, TC, and CC dipyrimidine sites. From these studies we draw the following conclusions: (i) TLS makes a very prominent contribution to CPD bypass on both the DNA strands during replication; (ii) Pols eta, kappa, and zeta provide alternate pathways for TLS opposite CPDs wherein Pols kappa and zeta promote mutagenic TLS opposite CPDs; and (iii) the absence of mutagenic TLS events opposite a cis-syn TT dimer in human cells and opposite CPDs formed at TT, TC, and CC sites in mouse cells that we observe upon the simultaneous knockdown of Pols kappa and zeta implicates a highly error-free role of Poleta in TLS opposite CPDs in mammalian cells. Such a remarkably high in vivo fidelity of Poleta could not have been anticipated in view of its low intrinsic fidelity. These observations have important bearing on how mammalian cells have adapted to avoid the mutagenic and carcinogenic consequences of exposure to sunlight.

Energy and water balance of two contrasting loblolly pine plantations on the lower coastal plain of North Carolina, USA

During 2005–2007, we used the eddy covariance and associated hydrometric methods to construct energy and water budgets along a chronosequence of loblolly pine ( Pinus taeda) plantations that included a mid-rotation stand (LP) (i.e., 13–15 years old) and a recently established stand on a clearcut site (CC) (i.e., 4–6 years old) in Eastern North Carolina. Our central objective was to quantify the differences in both energy and water balances between the two contrasting stands and understand the underlining mechanisms of environmental controls. We found that the LP site received about 20% more net radiation ( R n ) due to its lower averaged albedo ( α) of 0.25, compared with that at the CC ( α = 0.34). The mean monthly averaged Bowen ratios ( β) at the LP site were 0.89 ± 0.7, significantly ( p = 0.02) lower than at the CC site (1.45 ± 1.2). Higher net radiation resulted in a 28% higher ( p = 0.02) latent heat flux (LE) for ecosystem evapotranspiration at the LP site, but there was no difference in sensible heat flux ( H) between the two contrasting sites. The annual total evapotranspiration (ET) at the LP site and CC site was estimated as 1011–1226 and 755–855 mm year −1, respectively. The differences in ET rates between the two contrasting sites occurred mostly during the non-growing seasons and/or dry periods, and they were small during peak growing seasons or wet periods. Higher net radiation and biomass in LP were believed to be responsible to the higher ET. The monthly ET/Grass Reference ET ratios differed significantly across site and season. The annual ET/ P ratio for the LP and CC were estimated as 0.70–1.13 and 0.60–0.88, respectively, indicating higher runoff production from the CC site than the LP site. This study implied that reforestation practices reduced surface albedos and thus increased available energy, but they did not necessarily increase energy for warming the atmosphere in the coastal plain region where soil water was generally not limited. This study showed the highly variable response of energy and water balances to forest management due to climatic variability.

Phenology of five tree species of a tropical dry forest in Yucatan, Mexico: effects of environmental and physiological factors

In order to relate phenological responses of trees to environmental variables we recorded the phenological patterns and select morphological and physiological traits (wood density and water potentials) of five tree species (Acacia gaumeri, Apoplanesia paniculata, Bursera simaruba, Gymnopodium floribundum, and Diospyros cuneata) in the tropical dry deciduous forest of the National Park of Dzibilchaltun, Yucatan, Mexico, over a period of 2 years (2004 and 2005). We chose two sites: one close to a permanent water source, locally known as ‘cenote’ (the CC site, ground water table was found at 2 m) and the other far from the cenote (FC site ground water table was at a depth of 10 m). Sites mainly differed in soil depth (FC site having greater soil depth) and soil nutrient characteristics (FC site more potassium, CC site more phosphorous). Our results indicated significant differences in phenology within species between sites and years, with leaf, flower and fruit production tending to be higher at the CC site and in the year 2004. Wood density and xylem water potentials were negatively related to each other, and midday water potentials were higher at the CC site. Differences in phenology found among years suggest that the timing of rainfall as well as the duration of periods without rain may play a more important role in phenology than total annual precipitation. Also differences inter-sites suggest a strong effect of site on tree phenology. Proximity to superficial bodies of water, such as cenotes, coupled with a greater concentration of available phosphorus in the soil may modify the effect of drought in this tropical dry deciduous forest.