Top PDF Carbon and nitrogen dynamics in forest soils

Carbon and nitrogen dynamics in forest soils

Carbon and nitrogen dynamics in forest soils

The present simple models were the first attempt to include in soil model some formulations of substrate preference and co-limitation of decomposition by both substrate and decomposers with regards to degradation of soil organic matter within the contest of soil C-cycle. The qualitative observed pattern would make in discussion the condition of equilibrium in forest ecosystems but would support again how climate change and N deposition may alter the microbial activity and the process of soil C sequestration based on mechanisms of ecological nature. The complete mathematical formulation is similar to a population model studying the behaviour of a consumer- resources system. Markedly it has been referred to the input matching law and the achievement of an ecological goal considering the microbial community as a single individual working for the optimization of the total microbial performances (i.e. growth). Among optimization procedures used for plant C-allocation in some recent studies in literature, the same ecological concept applied to soil biological behaviour in the second model, constitutes a promising tool in order to deal with the complexity of mechanism that are present in the soil and to better understand the interactions of soil biology with abiotic factors. Although the simplicity of the second model and the several critical points that can be moved toward the choice of optimality criterion and microbial working condition, it is suggested how the consideration of the maximization of a specific ecological goal may be useful to explain some experimental evidences in literature at macroscopic level. Namely the positive and negative priming, and the potential for C accumulation in the presence of mineral N. Moreover it was an attempt to use external variables such as litter production, pools size and substrate quality to mimic the population behaviour without entering in the complexity of several populations existing and interacting for substrates (i.e. competition, co-metabolism etc). Experimentally, the model suggests how the enzymatic fingerprint of microbial community could be assessed as the link between the microbial community, considered as a whole feeding on the mixed substrates, and the ecological function expressed, thus the organic matter degradation.
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Climate change mitigation by forests: a case study on the role of management on carbon dynamics of a pine forest in South Italy

Climate change mitigation by forests: a case study on the role of management on carbon dynamics of a pine forest in South Italy

of the planet. In this context forests and their rational/optimal management is very important to contribute to the mitigation of the effects of climate change. Studying in deep how forest management modifies the processes that control carbon dynamics during stand development and in response to climate change, is therefore key to improve our understanding of land-based climate mitigation. For these reasons, modelling tools are increasingly used by both forest ecologists, who face the challenge of transferring knowledge to stakeholders and the general community, and forest managers, who benefit from the development of scenario-based supports for decision-making. In particular, the objective of this study is to analyse the impact of the current and alternative forestry practices on carbon fluxes in a pine forest in South Italy under scenarios of climate change. This was done by simulating three different forest planning scenarios using the 3D-CMCC-CNR-FEM model, and evaluated over time with respect to carbon fluxes variables. The first part of thesis has focused its attention on analysis of dendrometric characteristics of the forest, sensitivity analysis and Bayesian calibration of the model. This has allowed to estimate the uncertainty of the model output in comparison with the measured data and its analysis, in response of the model outputs. The second part is focused, firstly, on analysing the different behaviour of the forest under management (reference management: rotation: 90 yrs; interval: 15 yrs; intensity: 25%), in comparison with the “not managed” forest in terms of temporal variation of Gross Primary Production (GPP), Autotrophic Respiration (RA), woody C-stock and Net Primary Production (NPP) under different climate scenarios. In this respect, results show that a progressive reduction in forest cover
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Soil indicators set up to assess sustainable management in various agricultural and forest ecosystems

Soil indicators set up to assess sustainable management in various agricultural and forest ecosystems

Soil chemical and biochemical properties were statistically analysed in order to find the significant difference among various management types (cover crops C, tillage levels T and their interaction TxC). In particular, through ANOVA, significant differences were analysed between: 1. reduced and conventional tillage, 2. Leguminous and brassica spp. and living mulch LM (table 4.1.2). by comparing various climatic zones, the minor effects of management were observed in the very humid site (ART) where annual precipitation was abundant (1086 mm). The effects of treatments were significant, especially for the extractable C and N pool and for soil biochemical properties, such as microbial biomass and enzyme activities. Moreover, no significant differences were found in terms of soil total organic C (Corg), total nitrogen (TN) and C/N ratio. In general three of the four European experimental sites (SLU, UNI and ORC) showed more significant effects. The tillage effect was less evident than cover effect in all countries at both MEE‘s. The significant effect due to the interaction between cover crop (C) and tillage (T) was registered in terms of microbial biomass carbon (Cmic) and nitrogen (Nmic), both expressed per gram of soil and per unit of organic carbon (Cmic:Corg) or total nitrogen (Nmic:TN). Regarding soil enzyme, specific activity was chosen in order to compare various sites with very different soil organic matter content as background value. In this study, the enzyme activities involved in C and N cycles showed significant interactions between T and C at ORC, SLU and UNI sites at both MEEs. Conversely, at ART site the effect of management on soil specific enzyme activity (per unit of organic carbon) was not significant. The functional diversity calculated using the Shannon‘s index (H‘) showed significant differences only at ORC and UNI sites (Table 4.1.2).
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Nitrogen cycle dynamics in a Mediterranean agroforestry system under different management regimes

Nitrogen cycle dynamics in a Mediterranean agroforestry system under different management regimes

As expected, total bacteria population was higher where cattle effluent was applied, as it cointains its own microbial population, but no massive differences were found between treatments in qPCR. On the contrary, rapid changes in gene expression occurred in DMPP + effluent treatment: after 24h bacteria and archaea amoA mRNA were lower with respect to the effluent treatment, due to a high efficacy in the inhibition of the ammonia-oxidizing populations, but even bacteria 16S gene expression was reduced, suggesting a possible effect on non-targeted populations by DMPP. These results were confirmed by profiling analysis on active microbial community being separated in different ways on PCA, although application of cattle effluent combined with DMPP did not cause a massive change in the structure of the active general archaeal community. It’s important to identify the parameters influencing AOA and AOB populations in soils and to quantify and compare their specific activities under varying environmental conditions. Given that archaea contribute significantly to nitrification, as their abundance now suggests, estimates of the ecological impact of ammonia oxidation, including greenhouse gas emissions, based on bacterial ammonia-oxidizing activity should be re-assessed.
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Land use change and carbon stock dynamics in Sub-Saharan Africa - Case study of Western Africa – Ghana

Land use change and carbon stock dynamics in Sub-Saharan Africa - Case study of Western Africa – Ghana

The condition of Ghana‘s forests has been in decline for many years, particularly since the 1970s. Many forest reserves are heavily encroached and degraded, and the off-reserve stocks are being rapidly depleted. By and large, the problem is one of gradual ‗degradation‘ rather than ‗deforestation‘, and is incremental rather than dramatic, with no single dominant driver. The underlying causes involve a complex of demographic, economic and policy influences. According to Forestry Commission (2010), the immediate drivers include: forest industry over-capacity; policy/market failures in the timber sector; burgeoning population in both rural and urban areas; increasing local demand for agricultural and wood products; high demand for wood and forest products on the international market; heavy dependence on charcoal and fuelwood for rural and urban energy; limited technology development in farming systems and continued reliance on cyclical ‗slash and burn‘ methods to maintain soil fertility and fire as a tool in land management. Arresting deforestation and forest degradation is an important priority for the country, and Ghana has already embarked on a series of forest and natural resource governance initiatives to address these challenges (FC, 2010) although the provision in the Concessions Act to ―vest of all timber resources in the Office of the President‖ has institutionalized the myth that farmers had no rights over naturally occurring timber trees growing on their own land building up in this way, challenges to the process of REDD- plus readiness in Ghana. To support the process of preparation to the mechanism of the REDD+, the Government of Ghana, through Ghana‘s Forestry Commission 12 , has sought and received support from the World Bank‘s Forest Carbon Partnership Facility (FCPF). This support follows a three phase process (shown below in Figure 6) through which Ghana aims to build its capacity while developing its own strategy for engaging with future international and domestic mechanisms that will reward REDD+ actions (FCG, 2010; Mayers et al., 2010 ). The REDD Readiness Process beginning in 2007 when Ghana submitted the Readiness Plan Idea Note (R-PIN) 13 to the World Bank and
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Bi-directional exchange of greenhouse gases and pollutants between a Mediterranean holm oak forest and the atmosphere

Bi-directional exchange of greenhouse gases and pollutants between a Mediterranean holm oak forest and the atmosphere

Forest ecosystems net absorption of CO 2 is called Net Ecosystem Exchange (NEE) and is generally measured on annual scale. NEE represents the amount of carbon subtracted from the atmosphere and stored in live biomass, litter and soils. Although NEE is commonly positive, that is ecosystems subtract carbon from the atmosphere, in some cases is observed a net release of CO 2 from forests, imputable to many factors that enhance respiration, between them, climate variations end disturbance regimes (Rice et al., 2004; Williams et al., 2014). Mediterranean evergreen forests ensure CO 2 sequestration and storage all year long, although the CO 2 absorption rate changes among seasons depending on temperature and water availability, which represent the main environmental stress in this region. High temperature and drought re-occur cyclically every year in Summer and natural selection processes made Mediterranean vegetation adapted to these environmental conditions. Although, when natural stress factors are coupled with anthropogenic pollution, forest carbon sequestration potential can decrease.
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Greenhouse gases exchange over and within a tropical forest in Africa

Greenhouse gases exchange over and within a tropical forest in Africa

tropical forest soils are generally well drained but it depends on the surface horizons type, the sloping of the terrain and the plant species composition. This highlight the big variability that can occur in methane uptake/emissions, frequently scattered in hot spots. Most of the studies are still conducted through soil chambers [e.g. Castaldi et al., 2010] strictly linking the estimate to the selected sampling points or area. Eddy covariance below canopy measurements can help override such difficult by sampling over a relatively wide area. While the EC method is routinely used to measure carbon and energy fluxes above vegetation canopies, it has also been adopted for trunk-space measurements [Baldocchi et al., 1986; Subke and Tenhunen, 2004; Philatie et al., 2005; Mammarella et al., 2010]. The feasibility of sub-canopy EC measurements is anyway related to some assumptions [Baldocchi and Meyers 1991] and mainly depends on the develop of the turbulence. As stated in the previous chapters, below canopy turbulence can be intense but intermittent and no universal theory on it do exists [Launianen et al., 2005]. Turbulent transport is regulated by sporadic gusts that penetrate the canopy layer reaching the forest floor, hence is dependent also on the forest structure.
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Soil carbon cycle and sustainability of organic fertilization in a Mediterranean short rotation woody crops

Soil carbon cycle and sustainability of organic fertilization in a Mediterranean short rotation woody crops

When the soils are added with fresh and decomposable tissues (often containing water soluble compounds like sugars, amino acids) an immediate increase in metabolic activity among the soil microbes is stimulated. In this case, carbon compounds are enzymatically oxidized to produce carbon dioxide, water, energy and decomposer biomass, moreover the essential nutrients such nitrogen and phosphorous are released and/or immobilized by specific reactions. In temporal terms there are two kinds of inputs of organics into soil: (i) one-time or occasional or (ii) permanent (continuous) (Kuzyakov, 2010; Fontaine et al., 2003). The pulse inputs are typical for the breakdown of microbial, root and animal cells, decomposition of above-ground litter with subsequent leaching of dissolved organic matter (DOM), and root exudation. Because of the ready availability of soluble organics, such inputs produce hotspots of microbial activity in which the turnover rates are much higher than they are outside of these zones. The continuous inputs is typical for the slow decomposition of dead roots, leaf and shoot residues, and for some rhizo- deposits. In all these cases, the substrates are less immediately metabolisable and, therefore, utilized slowly and over longer periods. Because of the low availability, it is likely that the array of extracellular enzymes generated to degrade these organics may be more efficient at decomposing SOM in comparison with the largely intracellular enzymes that breakdown the easily available substrates (Fontaine et al., 2003).
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Lo studio degli isotopi del carbonio e dell'azoto per ricostruire cronologia, clima e agricoltura nell'Olocene medio ad Arslantepe (Anatolia) - Carbon and nitrogen  isotope analysis reveals chronology, palaeoclimate and agricultural practices at Arslantep

Lo studio degli isotopi del carbonio e dell'azoto per ricostruire cronologia, clima e agricoltura nell'Olocene medio ad Arslantepe (Anatolia) - Carbon and nitrogen isotope analysis reveals chronology, palaeoclimate and agricultural practices at Arslantepe (Turkey) during the mid-Holocene

The charcoal assemblage of Arslantepe revealed important changes in plant use, responding only partly to past climate and environment evolution. In fact the different distribution of tree taxa along the investigated sequence mainly addressed to the overexploitation and/or timber selection related to different technological and cultural needs. Wood resources were exploited from the forest-steppe and riverine gallery forest in the plain, with minor contribution from the surrounding mountain. On the contrary the area, where the site is settled, experienced times of enhanced/reduced precipitation in concert with regional trends. Anomalies in the Mediterranean atmospheric circulation probably influenced local climate oscillations. As carbon isotopes on charcoals have shown, stormtracks from North Atlantic regions seemed to occur during the wettest phases, whilst the high-pressure system from eastern regions was implicated especially in low rainfall patterns. From 4700 to 3400 BC, when social complexity increased at the site, wet conditions were recorded and followed by a slight reduce of moisture. Agriculture in the plain was characterised by irrigation and fertilisation practices at different levels since 4300 BC and was mainly wheat based. Interestingly both botanical and faunal data in the domestic contexts of 4700-3900 BC referred to a mixed primary economy, managed by single families with no evident interference of growing social elites.
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Carbon stocks and dynamics in Sub-Saharian Africa

Carbon stocks and dynamics in Sub-Saharian Africa

It is  impressive that some  of the  lowest fertility soils  support  rain  forests  of  massive structure  and  productivity (Proctor, et al., 1983). According to Baillie et al.(Baillie, et al., 1987) and Ashton (Ashton,  1992),  within  lowland  mixed  forests  in  Borneo,  the  floristic  composition  is  mainly  depend  to  soil  nutrients  and  topography  because  they  determine  water  relations.  According  to  van  Schaik  et  al.  (1985), variation in the trees growth strategies depends on soil fertility which results in higher tree  longevity on poor soilsand hence in forest with fewer gaps and with more large trees, than on rich  soils.  Hall  et  al.  (1981)  reported  the  influence  of  soil  fertility  on  tree  seedlings  for  different  plant  functional types. Escudero et al. (1992) mentioned that pioneers tree would be more demander in  soil  nutrients  because  of  their  higher  growth  rate  and  turnover.  However,  the  influence  of  soil  properties  on  tree  species  and  forest  dynamics  is  not  obvious.  Aragão  et  al.  (2009)  reported  no  relationship between above and below‐ground NPP and soil fertility in ten Amazonian forests.   According  to  Sollins  (1998),  important  spatial  and  temporal  noise  would  not  allow  identification  of  main  drivers.  This  could  be  due  to  methodological  problems,  because  some  quantities  such  as  the  nutrient  availability  to  the  plants  cannot  be  measured  directly.  An  additional  problem  would  be  related  to  the  difficulty  to  capture  the  spatial  and  temporal  variability  because  experiments  are  costly and time consuming and are limited in term of time period and size of measurements. While  Gourley‐Fleury  et  al  (submitted)  and  Maniatis  et  al  (submitted)  analyzed  large  areas  using  forest  inventories, their studies cannot consider the forest dynamics and the size of the unit plot (often less  than  0.3  ha)  limits  understanding  of  spatial  variability  (Chave,  et  al.,  2003).  Few  researches  considered  long  time  period  permanent  sample  plots  but  see  (Paracou  in  French  Guiana  (Gourlet  Fleury, et al., 2004), Bobiri forest reserve in Ghana (Alder, 1993), M’Baiki in Central African Republic  (Bedel, et al., 1998) and Barro Colorado Island in Panama (Condit, 1998)). Several permanent sample  plot experiments were also implemented in Nigeria (Lowe, 1996), Ghana (Alder, 1995) and Uganda  (Sheil, et al., 2000). They however fail to provide data that are adapted to fit the current needs such  as NPP, C and biodiversity. Most of the researches on the dynamic of forest focused on biomass and  nutrients  (Floret,  et  al.,  1993),  carbon  stocks  (Kotto‐Same,  et  al.,  1997,  Glenday,  2006)  or  floristic  composition  and  structure  (Kahn,  1982)  in  post  agricultural  forest  regeneration  systems  following  chronosequences.  
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Assessment of microbial functional and genetic diversity of forest soils in Central Italy

Assessment of microbial functional and genetic diversity of forest soils in Central Italy

48 In this study trees coppice significantly decreased soil total organic carbon content as a likely consequence of both the intense microbial decomposition activity observed (enhanced enzyme activities and respiration) and, at the same time, a strongly reduced input of plant litter in the years following trees cutting. In soils of natural forests a general condition of homeostasis leads to a long-term substrate constraint which controls microbial functioning. Conversely new inputs of fresh C due to coppicing as root exudates, plant residues and low molecular organic substances can activate microbial groups that were dormant or inactive, with synthesis of a broad variety of enzymes and possible SOM decomposition leading to a “priming effect” (Kuzyakov, 2010). Giai and Boerner (2007) found no significant differences in soil organic C content among different kind of forest management (prescribed fire, thinning, the combination of fire and thinning, and an untreated control), though they observed a significant increase in C/N ratio in the thin- only treatment. They supposed this increase in C/N ratio to be related to accumulations on the forest floor of woody remains from the trees cut during the thinning treatment. Several authors (Brais et al., 2003; Lundgren 1982; Pietikainen et al. 1995) observed that the greater part of changes in nutrient cycling occurred during the first years after management and included an increase in forest floor organic C, total N, base cations availability and a decrease in microbial C/N ratio. These changes may have occurred in response to reduced vegetation uptake and woody debris abundance.
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The anthropogenic impacts on tropical forest ecology and dynamics

The anthropogenic impacts on tropical forest ecology and dynamics

An important aspect in evaluating forest damage is the assessing of the extension of canopy gaps by selective timber harvests. In tropical forests, canopy gaps have immediate impacts on light interception, heat fluxes, water stress and plant productivity (43). In computer simulations the rate of forest regeneration strongly depends on the size, the number and the spatial arrangement of canopy gaps following harvest (44). Recent studies also suggest that canopy openings decrease in size with distance from each felled tree crown, but in recently logged forest the area initially affected by harvesting of each tree is at least 50-100 m in radius (45). One of the main effects of canopy gaps discontinuities appears to be the creation of spaces readily invaded by weeds, vines and climbers at the expense of the late-successional state cenosis (46). Typically, fragmentation and selective logging opens up gaps of light in which weeds displace or suppress native species. Conversely, natural gaps (e.g. due to big broken branches or naturally died trees) are usually smaller than logging gaps, and tree saplings seems to be prepared to grow fast enough to fill the canopy opening (47, 48, 49, 50, 51). This reduces the likelihood of vines, weeds and climbers invasion (52). Here we argue that changes in native cenosis caused by the selective removal of the tallest trees induce a local variation of forest structure with relative consequences on biodiversity and carbon stocks.
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Ecosystem respiration in a Mediterranean Turkey oak forest: eddy covariance and chamber-based models comparison

Ecosystem respiration in a Mediterranean Turkey oak forest: eddy covariance and chamber-based models comparison

7 described empirically via absolute or relative measures of volumetric water content and soil water potential as reviewed by Rodrigo et al. (1997). The relationship between soil water status and soil-respiratory processes is complex, since may individual processes vary with soil water content, in particular gas and solute diffusion, enzyme activities, and growth and mortality of microorganisms (Killham, 1994; Marshal et al., 1996). Also rewetting events often increase soil respiration, which can be explained by remineralization of dead biomass or by desorption processes, which make labile substrate available to microbes (Orchard & Cook, 1983). After a long soil drying and subsequent rewetting, soil respiration rates can exceed rates under well watered conditions before the drying (Birch, 1958). This effect has been found being of importance also for ecosystem carbon dynamics (Borken et al., 2003; Jarvis et al., 2007; Xu & Baldocchi, 2004). Thus, despite the obvious importance of biological control of soil respiration, empirical models have often focused mainly on the abiotic controls. Even for global and interannual variation, models are developed that predict soil respiration solely from climate variables (Raich et al., 2002; Raich & Potter, 1995).
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Carbon Nanotubes: from synthesis to characterization

Carbon Nanotubes: from synthesis to characterization

The name of the technique arises from the quantum mechanical tunneling-type mechanism by which the electrons can move between the tip and substrate. Quantum mechanical tunneling permits particles to tunnel through a potential barrier which they could not surmount according to the classical laws of physics - in this case electrons are able to traverse the classically-forbidden region between the two solids. In this model, the probability of tunnelling is exponentially-dependent upon the distance of separation between the tip and surface: the tunneling current is therefore a very sensitive probe of this separation. STM is able to measure the local density of states of a material at it surface as a function of lateral (x-y) position on the sample surface and energy. Within the sample, each individual electron has a specific energy level. Only a certain number of electrons may occupy any given energy level at any one time. The distribution that gives the number of electrons allowed per energy level as a function of which energy level you consider is called density of states which can be abbreviate as DOS. The DOS is a very useful quantity to be able to measure since it can be used to derive a wealth of information about the crystal's properties. The DOS can vary as a function of position in the crystal which means that one can define a local density of states (LDOS). LDOS is then a quantity which depends on both energy and on position, LDOS(x, y, E). A physically intuitive way to think about local density of states is that it gives the density of electrons of a certain energy at that particular spatial location [3].
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Contribute of Airborne Laser Scanning Data in assessing forest and their characteristics

Contribute of Airborne Laser Scanning Data in assessing forest and their characteristics

Nevertheless, optical images are not sensitive to below-canopy forest attribute, while ALS allow a reliable characterization of both horizontal and vertical forest structure. Tree species composition and stand structure strongly affect the specie richness (flora and fauna) within the forest. For this reason, mapping forest structure would facilitate habitat and diversity assessments for large, remote and steep areas that cannot be safely reached by field crews (Mura et al., 2015b), and thus supporting SFM. The increased availability of data from ALS is encouraging the use of remote sensing data to predict various forest parameters (e.g. tree height, tree diameter, stand structure variability, above ground biomass, carbon stock, etc.). Furthermore, the combined use of ALS data with multispectral satellite images and field measurements strongly support the development of new models for improving the precision of estimates of forest variables.
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Essays on financial stability, credit dynamics and policy challenges

Essays on financial stability, credit dynamics and policy challenges

in Duprey et al. [ 2017 ], which identify systemic financial stress dates using a Markov- switching model selection. One reason to use it is that the model captures on average 100% of the banking crises identified by Laeven and Valencia [ 2013 ] that is generally accepted as benchmark for crises identification. More specifically, the model selects financial stress episodes that are associated with prolonged declines in real economic activities. These are defined as at least six consecutive months of negative annual in- dustrial production growth concomitant to a decline in real GDP during at least two quarters. Moreover, the model allows to construct an EU crisis simultaneity index that preserves cross-country comparability. Crises dates are reported in Table 1.3. The fre- quency analysis reveals that 70% of credit booms are associated with crisis states, of which 80% relates to banking crises, while the rest to equity crashes in the private sec- tor. Almost 70% of credit booms start prior to the crisis, ranging from 2 to 9 quarters before. However, 30% of these do not end up in crises and they have a maximum dura- tion of four quarters. Finally, on average, countries have more than 50% of probability of experiencing a credit boom (that in MT definition includes also credit downswings after a peak) once the starting threshold is crossed.
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Coupled lithosphere-mantle dynamics and surface responses: insights from modeling

Coupled lithosphere-mantle dynamics and surface responses: insights from modeling

setup and proposed a delamination model in which a local instability induced a localized small-scale convection that thermally eroded the lithospheric mantle, enhancing the connection between the asthenosphere and lower crust by means of a low viscosity zone. Whatever the triggering mechanism, our setup reproduces similar scale situation. We performed experiments with a scaled lithospheric root of 42 to 83 km, present over a width of 83 to 250 km, coherent with the supposed delaminated root estimated to 40 to 70 km thick [Ducea and Saleeby, 1998] that probably underlain most of the ca. 100 km-wide Sierra Nevada range [Jones et al., 2004]. The density contrast with the asthenosphere is estimated to 10 kg m -3 (from three-dimensional shear-wave velocity structure [Fay et al., 2008a]) to 200 kg m -3 (from xenoliths studies [Ducea and Saleeby, 1998]), in the same order of magnitude as our scaled values of 23 to 100 kg m -3 . The presence of an adjacent weak area is generally attributed to the previous early Cenozoic subduction and could represent a fluid-weakened lithosphere by dehydration processes [Schott and Schmeling, 1998; Zandt et al., 2004; Valera et al., 2008]. Alternatively, an “asthenospheric conduit” would be more consistent with strong thermal thinning in the upper plate above the hydrated zone [Arcay et al., 2007]. For simplicity, the experiments performed in this study are always characterized by free boundaries while in nature plates are laterally confined. In particular, it would imply that the plate motion recorded during the last stage of our experimental delamination is not realistic since a laterally constrained natural plate would exhibit a strong active shortening retroward of the delamination’s direction, as recorded in models characterized by free-slip boundary conditions [e.g. Schott and Schmeling 1998]. Hence, in nature the topographic signal could also be affected by an extra uplift due to thickening of the crust.
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Transcriptional regulation and dynamics of Arabidopsis nuclear proteome in response to auxin and oligogalacturonides

Transcriptional regulation and dynamics of Arabidopsis nuclear proteome in response to auxin and oligogalacturonides

elongation factor EF-Tu (Kunze et al., 2004). However, there are exceptions; the elicitor effect of NPP1 (necrosis-inducing Phytophthora protein 1) requires an intact protein and overlapping peptide fragments were inactive (Fellbrich et al., 2002), perhaps indicating that it is the activity of this protein that is detected by the plant rather than a specific amino acid sequence. Presumably, there would be a huge selective advantage for mutations within these epitopes that rendered them inactive as elicitors of plant defense systems. However, it would seem that, in many cases, such mutations also have a deleterious effect on the function of these proteins in the pathogen. For example, in Pep-13, a 13 amino acid internal peptide of a 42 kDa transglutaminase enzyme from the cell wall of Phytophthora sojae, substitution of Trp231 to Ala abolished elicitor activity in parsley but with a concurrent 98% reduction in transglutaminase activity (Brunner and et al., 2002). Thus, it appears that plants have evolved receptors that recognize short highly conserved amino acid stretches of certain microbial proteins that cannot easily be altered without loss of the protein function. That said, certain microbes may have evolved the capacity to avoid detection by specific PRRs. For example, Agrobacterium tumefaciens and Ralstonia solanacearum (pathogens) as well as Rhizobium meliloti (symbiont) possess functional flagellins that do not elicit a defence response in Arabidopsis and the N-terminal peptide from Pseudomonas syringae pv. tomato DC3000 (Pst) EF-Tu is not as potent an elicitor in Arabidopsis as those from other bacteria (Kunze et al., 2004; Sun et al., 2006). The evolution of non-eliciting PAMPs is one way in which pathogens can overcome non-host resistance in plants; however, the lack of a single eliciting PAMP has not yet been directly shown to affect the virulence of the pathogen. Some experiments have shown that deletion of a specific PRR in the host affects susceptibility; however, in other studies wild-type plants and plants lacking a PRR were equally susceptible (Sun et al., 2006) (Zipfel et al., 2004). This could be explained by the evolution in plants of recognition systems for multiple PAMPs from the same micro-organism. For example, Arabidopsis recognizes both flagellin and EF-Tu and these PAMPs activate the same signalling and defence responses in a nonsynergistic manner (Zipfel et al., 2006). A recent gene expression profiling study has also demonstrated that the lack of flagellin perception does not dramatically alter PAMP-induced gene expression during infection of Arabidopsis by Pst (Thilmony et al., 2006).
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Carrier dynamics in semiconductor nanowires

Carrier dynamics in semiconductor nanowires

noise ratio, and the reflected half is directed to mirror M9 that reflects it to a collimating mirror M10, which focuses the probe on the sample. The reference beam reflects through flat mirror M8 and is collimated using L3 into an optical fiber that takes it to spectrograph 2 for detection. The intensity that enters the fiber is controlled by neutral density filter F4. An IR supercontinuum probe (800-1600 nm), obtained using a YAG crystal, is also available for TA experiments. After passing through the sample, the pump beam is blocked from entering the spectrograph by a beam blocker shown in Figure 2.2 as B, while the probe beam can be recorded either in transmission or reflection. Probe reflection from the sample is focused by concave mirror M11, while probe transmitted through the sample is reflected by mirror M12. Mirror M13 is a flip mirror to be used while measuring in reflection. F6 is a neutral density filter that helps to control the intensity of reflected/transmitted probe entering the fiber after being focused by L4 and taken to spectrograph 1 for detection.
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Air pollution mitigation and carbon uptake of some evergreen plant species

Air pollution mitigation and carbon uptake of some evergreen plant species

known to be efficient accumulators of pollutants on their needles (Freer-Smith et al., 2005). Paper III represents a further contribution to the knowledge of coniferous species for their pollution mitigation capacity. In addition, the results on the distribution of the different pollutants from the road to the neighboring area can represent a contribution to the knowledge of the local pollution dynamics. Modelling studies quantified the beneficial effects of trees in pollution removal and in improvement of the air quality (Nowak et al., 2006; Bealey et al., 2007; McDonald et al., 2007). These studies provided important knowledge on the quantity and the economic value of the pollution removal by trees. On the other hand, the real local improvement of air quality has not been very well examined. Due to the nature of the modelling analysis, still quite large uncertainties remain on the real capacity of plants in significantly improving air quality. While confirming the fundamental role of modeling and hope for an increasing reliability of the results, future attention should be paid on the study of local improvement of the air quality. The deposition of pollutants increases when the concentration of pollutants is higher (Freer-Smith et al., 2005). The potential of pollution accumulation is probably better used when plants are closely placed to the local source of emissions. New design of plantation, conceived as a barrier against the local polluting sources, could be a new interesting step in this field. The results reported in this thesis may represent a contribution in this direction.
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