The effect of drought and subsequent precipitation pulse on productivity, species composition, and carbon fluxes of the herbaceous understorey in a cork oak woodland

In the Iberian Peninsula, the cork oak woodlands are of great ecological and socio-economic importance. These savanna-type woodlands are characterized by an herbaceous understorey, dominated by C3 annual species. The productivity and related ecosystem processes of this understorey are highly dependent on timing and magnitude of precipitation events. 

Climate change scenarios for the Iberian Peninsula suggest not only increasing air temperatures, but also the possibility of decreasing spring precipitation, accompanied by an increase in the interval between precipitation events, which might cause drought conditions to occur, with more severe effects on productivity and ecosystem processes. 

An experiment was carried out in southern Portugal to assess the effect of a drought treatment, with a subsequent extreme precipitation event, on the herbaceous component of managed cork oak woodland. The facility consisted of five plots with rainout shelters (2.5 x 2.5 m), which exclude normal rainfall inputs (drought treatment), and five non-sheltered control plots (control treatment). In the drought treatment, 193 mm of precipitation was excluded in the period from mid March to mid May, with a subsequent precipitation pulse of 50 mm in the middle of May. Variables measured included productivity, plant community composition, soil respiration and soil microbial activity. 

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Comparison of two extraction methods for evaluation of volatile constituents patterns in commercial whiskeys: Elucidation of the main odour-active compounds

An analytical procedure based on manual dynamic headspace solid-phase microextraction (HS-SPME) method and the conventional extraction method by liquid–liquid extraction (LLE), were compared for their effectiveness in the extraction and quantification of volatile compounds from commercial whiskey samples. Seven extraction solvents covering a wide range of polarities and two SPME fibres coatings, has been evaluated. The highest amounts extracted, were achieved using dichloromethane (CH2Cl2) by LLE method (LLECH2Cl2)(LLECH2Cl2) and using a CAR/PDMS fibre (SPMECAR/PDMS) in HS-SPME. Each method was used to determine the responses of 25 analytes from whiskeys and calibration standards, in order to provide sensitivity comparisons between the two methods. Calibration curves were established in a synthetic whiskey and linear correlation coefficient (r ) were greater than 0.9929 for LLECH2Cl2LLECH2Cl2 and 0.9935 for SPMECAR/PDMS, for all target compounds. Recoveries greater than 80% were achieved. For most compounds, precision (expressed by relative standard deviation, R.S.D.) are very good, with R.S.D. values lower than 14.78% for HS-SPME method and than 19.42% for LLE method. The detection limits ranged from 0.13 to 19.03 μg L−1 for SPME procedure and from 0.50 to 12.48 μg L−1 for LLE. A tentative study to estimate the contribution of a specific compound to the aroma of a whiskey, on the basis of their odour activity values (OAV) was made. Ethyl octanoate followed by isoamyl acetate and isobutyl alcohol, were found the most potent odour-active compounds

Direct and indirect effects of tree canopy facilitation in the recruitment of M editerranean oaks

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106739/1/jpe12189.pd

Incorporation of either molybdenum or tungsten into formate dehydrogenase from Desulfovibrio alaskensis NCIMB 13491; EPR assignment of the proximal iron-sulfur cluster to the pterin cofactor in formate dehydrogenases from sulfate-reducing bacteria

J Biol Inorg Chem (2004) 9: 145–151 DOI 10.1007/s00775-003-0506-zWe report the characterization of the molecular properties and EPR studies of a new formate dehydrogenase (FDH) from the sulfate-reducing organism Desulfovibrio alaskensis NCIMB 13491. FDHs are enzymes that catalyze the two-electron oxidation of formate to carbon dioxide in several aerobic and anaerobic organisms. D. alaskensis FDH is a heterodimeric protein with a molecular weight of 126+/-2 kDa composed of two subunits, alpha=93+/-3 kDa and beta=32+/-2 kDa, which contains 6+/-1 Fe/molecule, 0.4+/-0.1 Mo/molecule, 0.3+/-0.1 W/molecule, and 1.3+/-0.1 guanine monophosphate nucleotides. The UV-vis absorption spectrum of D. alaskensis FDH is typical of an iron-sulfur protein with a broad band around 400 nm. Variable-temperature EPR studies performed on reduced samples of D. alaskensis FDH showed the presence of signals associated with the different paramagnetic centers of D. alaskensis FDH. Three rhombic signals having g-values and relaxation behavior characteristic of [4Fe-4S] clusters were observed in the 5-40 K temperature range. Two EPR signals with all the g-values less than two, which accounted for less than 0.1 spin/protein, typical of mononuclear Mo(V) and W(V), respectively, were observed. The signal associated with the W(V) ion has a larger deviation from the free electron g-value, as expected for tungsten in a d(1) configuration, albeit with an unusual relaxation behavior. The EPR parameters of the Mo(V) signal are within the range of values typically found for the slow-type signal observed in several Mo-containing proteins belonging to the xanthine oxidase family of enzymes. Mo(V) resonances are split at temperatures below 50 K by magnetic coupling with one of the Fe/S clusters. The analysis of the inter-center magnetic interaction allowed us to assign the EPR-distinguishable iron-sulfur clusters with those seen in the crystal structure of a homologous enzyme

Too Many Is Too Bad: Long-Term Net Negative Effects of High Density Ungulate Populations on a Dominant Mediterranean Shrub

Plant–animal interactions imply costs and benefits with net balance depending on interacting species and ecological context. Ungulates, in particular, confer costs (e.g., plant leaf consumption, flower bud predation) and benefits (e.g., plant overcompensation, seed dispersal) to plants. Magnitude of costs and benefits may be altered by habitat management or ecological conditions favoring high density ungulate populations. Little is known however on whether plant costs or benefits predominate over the years, or the long-term outcomes of plant-animal interactions in habitat types sustaining high density ungulate populations. We investigated how high density ungulate populations alter plant costs and benefits by quantifying ungulate long-term effects on the shrub Cistus ladanifer (Cistaceae) individual size, seed weight and number, seed bank, and population density, through a 12-year ungulate exclusion experiment in a Mediterranean scrubland. We monitored plant size and flower buds in plants exposed or protected from ungulates and number of developed capsules and seeds consumed (potential seed dispersal) by ungulates during three reproductive seasons. We found that ungulates negatively affected shrub size and led to a dramatically decline of shrub reproductive structures and seed production, affecting the plant reproductive cycle. Number of buds was 27 times higher and number of developed seed 5 times higher in ungulate-excluded as compared to ungulate-exposed plots. After 9 years of ungulate exclusion, the C. ladanifer seed bank was 2.6 times higher in ungulate-excluded plots. The population density of C. ladanifer was 4 times higher in ungulate-excluded plots. Our long-term experiment showed that high density ungulate populations can alter plant-animal interactions by reducing plant benefits and increasing plant costs.Peer reviewe

Comparative study of the whisky aroma profile based on headspace solid phase microextraction using different fibre coatings

A dynamic headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to ion trap mass spectrometry (GC–ITMS) method was developed and applied for the qualitative determination of the volatile compounds present in commercial whisky samples which alcoholic content was previously adjusted to 13% (v/v). Headspace SPME experimental conditions, such as fibre coating, extraction temperature and extraction time, were optimized in order to improve the extraction process. Five different SPME fibres were used in this study, namely, poly(dimethylsiloxane)(PDMS),poly(acrylate)(PA),Carboxen-poly(dimethylsiloxane)(CAR/PDMS),Carbowax-divinylbenzene(CW/DVB)and Carboxen-poly(dimethylsiloxane)-divinylbenzene (CAR/PDMS/DVB). The best results were obtained using a 75 m CAR/PDMS fibre during headspace extraction at 40◦C with stirring at 750rpm for 60min, after saturating the samples with salt. The optimised methodology was then appliedtoinvestigatethevolatilecompositionprofileofthreeScotchwhiskysamples—BlackLabel,BallantinesandHighlandClan.Approximately seventy volatile compounds were identified in the these samples, pertaining at several chemical groups, mainly fatty acids ethyl esters, higher alcohols, fatty acids, carbonyl compounds, monoterpenols, C13 norisoprenoids and some volatile phenols. The ethyl esters form an essential group of aroma components in whisky, to which they confer a pleasant aroma, with “fruity” odours. Qualitatively, the isoamyl acetate, with “banana” aroma,wasthemostinteresting.Quantitatively,significantcomponentsareethylestersofcaprilic,capricandlauricacids.Thehighestconcentration of fatty acids, were observed for caprilic and capric acids. From the higher alcohols the fusel oils (3-methylbutan-1-ol and 2.phenyletanol) are the most important ones

Non‐linear plant‐plant interactions modulate impact of extreme drought and recovery on a Mediterranean ecosystem

Interaction effects of different stressors, such as extreme drought and plant invasion, can have detrimental effects on ecosystem functioning and recovery after drought. With ongoing climate change and increasing plant invasion, there is an urgent need to predict the short- and long-term interaction impacts of these stressors on ecosystems. We established a combined precipitation exclusion and shrub invasion (Cistus ladanifer) experiment in a Mediterranean cork oak (Quercus suber) ecosystem with four treatments: (1) Q. suber control; (2) Q. suber with rain exclusion; (3) Q. suber invaded by shrubs; and (4) Q. suber with rain exclusion In an average precipitation year, the interaction effects of both stressors were neutral. However, the combination of imposed drought and shrub invasion led to amplifying interaction effects during an extreme drought by strongly reducing tree transpiration. Contrarily, the imposed drought reduced the competitiveness of the shrubs in the following recovery period, which buffered the negative effects of shrub invasion on Q. suber. Our results demonstrate the highly dynamic and nonlinear effects of interacting stressors on ecosystems and urges for further investigations on biotic interactions in a context of climate change pressures

The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention

Background and aims A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention. Methods We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition. Results Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation. Conclusions Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem

The synergistic response of primary production in grasslands to combined nitrogen and phosphorus addition is caused by increased nutrient uptake and retention

Background and aimsA synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention.MethodsWe studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition.ResultsCombined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil delta N-15) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation.ConclusionsOur results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem

Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer

Charge transfer along the base-pair stack in DNA is modeled in terms of thermally-assisted tunneling between adjacent base pairs. Central to our approach is the notion that tunneling between fluctuating pairs is rate-limited by the requirement of their optimal alignment. We focus on this aspect of the process by modeling two adjacent base pairs in terms of a classical damped oscillator subject to thermal fluctuations as described by a Fokker-Planck equation. We find that the process is characterized by two time scales, a result that is in accord with experimental findings.Comment: original file is revtex4, 10 pages, three eps figure