Intermediate Situation Research Articles

Optical response of threaded chain plasmons: from capacitive chains to continuous nanorods.

We present a detailed theoretical analysis of the optical response of threaded plasmonic nanoparticle strings, chains of metallic nanoparticles connected by cylindrical metallic bridges (threads), based on full-electrodynamic calculations. The extinction spectra of these complex metallic nanostructures are dominated by large resonances in the near infrared, which are associated with charge transfer along the entire string. By analysing contour plots of the electric field amplitude and phase we show that such strings can be interpreted as an intermediate situation between metallic nanoparticle chains and metallic nanorods, exhibiting characteristics of both. Modifying the dielectric environment, the number of nanoparticles within the strings, and the dimensions of the threads, allows for tuning the optical response of the strings within a very broad region in the visible and near infrared.

Generalized Hund's rule for two-atom systems

Hund's rule is one of the fundamentals of the correlation physics at the atomic level, determining the ground state multiplet of the electrons. It consists of three laws: (i) maximum $S$ (total spin), (ii) maximum $L$ (total orbital angular momentum) under the constraint of (i), and (iii) the total angular momentum $J$ is $|L\ensuremath{-}S|$ for electron number less than half, while $J=L+S$ for more than half due to the relativistic spin-orbit interaction (SOI). In real systems, the electrons hop between the atoms and gain the itinerancy, which is usually described by the band theory. The whole content of theories on correlation is to provide a reliable way to describe the intermediate situation between the two limits. Here we propose an approach toward this goal, i.e., we study the two-atom systems of three ${t}_{2g}$ orbitals and see how the Hund's rule is modified by the transfer integral $t$ between them. It is found that the competition between $t$ and the Hund's coupling $J$ at each atom determines the crossover from the molecular orbital limit to the strong correlation limit. Especially, the focus is on the generalization of the third rule, i.e., the inter- and intra-atomic SOI's in the presence of the correlation. We have found that there are cases where the effective SOI's are appreciably enhanced by the Hund's coupling. The conditions for the enhancement are the intermediate Hund's coupling and the filling of four or five electrons.

Aspects of the Macroscopic Testicular and Epididymal Morphology in the Greater Rhea, Rhea Americana (Linneaus - 1758) Birds.

The purpose of this research was to study the macroscopic testicular and epididymal morphology of the greater rhea. The testicles of 54 greater rhea bred in captivity were utilized. The samples were collected November 2005 (n = 14), December 2006 (n = 20) and May 2007 (n = 20). During commercial slaughter, the testicles and epididymides were collected and their following morphometric parameters were immediately measured: length, width, thickness, circumference, volume, weight of the parenchyma and the tunica albuginea, also aspects such as shape, cavity implantation, relationship with other organs and vascularization. The testicles presented cylindrical shape, with a thin, dense and transparent tunica albuginea, and the vascularization was accomplished by the testicular artery that ramifies from the cranial rectal artery. In the samples from December 2006 and May 2007, the media from the macroscopic measures of the right testicles were volume 58.7 and 14.7 ml, length 9.87 and 3.5 cm, width 2.4 and 0.6 cm, thickness 2.4 and 0.5 cm, circumference 8.0 and 2.3 cm, parenchyma weight 27.6 and 6.1 g and tunica albuginea weight 1.0 and 0.3 g, P < 0.05, respectively. The epididymides, the media from macroscopic measures December 2006 and May 2007 were volume 7.7 and 3.0 ml, length 5.8 and 1.3 cm, width 0.7 and 0.3 cm, thickness 0.6 and 0.3 cm, circumference 2.5 and 1.2 cm, tissue weight 6.4 and 2.8 g and capsule weight 0.4 and 0.1 g, P < 0.05, respectively. Some measures from the right testicle and epididymis were superior to measures taken from the left ones (P < 0.05), but these were not characterizing asymmetry. The morphometric parameters observed during November 2005 remained on an intermediate situation (P < 0.05); however, they were quantitatively closer to the means of December 2006, which may characterize it as a potential transition period between repose and sexual activity. Morphologically, the testicles and epididymides of greater rhea have common points with other researched birds; however, differences were observed. The testicles and epididymides of the Rhea americana are influenced by the environment, presenting reproductive activity season (November-December) during late spring, early summer and sexual repose season (May) during autumn-winter. The morphometric testicular and epididymal measurements were introduced. The morphometric parameters of testicles and epididymides exhibited differences between winter and spring-summer that could be established like sexual activity season.

Elementary reactions of CO and H2 on C-terminated χ-Fe5C2(0 0 1) surfaces

CO and H2 (co-)adsorption, direct and H-assisted CO activation, and surface carbon hydrogenation were investigated on C-terminated χ-Fe5C2(001) surfaces. Periodic DFT simulations at different surface carbon contents on the carbide surface showed that CO adsorbs preferably linearly on Fe top sites; CO and H2 adsorptions being stable. The perfect carbide surface favors carbidic carbon hydrogenation (i.e. CH formation), whereas carbon-free surface favors direct CO dissociation and restoration of the carbide structure. In partially carbon-vacant intermediate situations, both direct and H-assisted CO activations are energetically feasible, the latter being the preferred path. Considering CHx and CHxO species as initiators for different product types can explain the catalytic behavior and selectivity patterns of iron carbide catalysts. The catalytically active surfaces are concluded to be dynamic, where carbon atoms of the carbide surface participate in the surface reactions, and CO dissociation on vacant sites leads to restoration of the carbide structure.

Quantum probes for fractional Gaussian processes

We address the characterization of classical fractional random noise via quantum probes. In particular, we focus on estimation and discrimination problems involving the fractal dimension of the trajectories of a system subject to fractional Brownian noise. We assume that the classical degree of freedom exposed to the environmental noise is coupled to a quantum degree of freedom of the same system, e.g. its spin, and exploit quantum limited measurements on the spin part to characterize the classical fractional noise. More generally, our approach may be applied to any two-level system subject to dephasing perturbations described by fractional Brownian noise, in order to assess the precision of quantum limited measurements in the characterization of the external noise. In order to assess the performances of quantum probes we evaluate the Bures metric, as well as the Helstrom and the Chernoff bound, and optimize their values over the interaction time. We find that quantum probes may be successfully employed to obtain a reliable characterization of fractional Gaussian process when the coupling with the environment is weak or strong. In the first case decoherence is not much detrimental and for long interaction times the probe acquires information about the environmental parameters without being too much mixed. Conversely, for strong coupling information is quickly impinged on the quantum probe and can be effectively retrieved by measurements performed in the early stage of the evolution. In the intermediate situation, none of the two above effects take place: information is flowing from the environment to the probe too slowly compared to decoherence, and no measurements can be effectively employed to extract it from the quantum probe. The two regimes of weak and strong coupling are defined in terms of a threshold value of the coupling, which itself increases with the fractional dimension.

Impact of indication-shift of primary and adjuvant chemo radiation in advanced laryngeal and hypopharyngeal squamous cell carcinoma.

Based on level I evidence, postoperative platinum-based radiochemotherapy (PORCT) is the recommended standard of care in defined risk situations after resection of squamous cell carcinomas of the larynx and hypopharynx (LHSCC). The value of the addition of chemotherapy to adjuvant radiation in intermediate and high risk situations other than extracapsular spread or R1-/R2 resection is still debated. From 1993 to 2009, 555 patients (median follow-up: 24.4 months) with advanced LHSCC (UICC stages III-IVB) were treated in a curative intent. Patient data were continuously documented in the county of Leipzig cancer registry and were retrospectively analyzed as mono institutional survey. PORCT was introduced into the standard procedures in 2004, but also applied before in selected cases. Based on this paradigm shift, the patient population was divided into two comparative groups treated before and after 2004. 361 patients were treated before 2004. 43.8 % received primary surgery (OP) + postoperative radiotherapy (PORT) and 20.2 % OP + PORCT. 194 patients were treated after 2004: 21.1 % received OP + PORT and 35.6 % OP + PORCT. Regarding the PORCT groups, 20.6 % received cisplatin plus 5FU before 2004 which shifted to 59.4 % after 2004. The 3-year tumor-specific-survival rate of the whole cohort was improved from 47 to 60 % (p = 0.006). The subgroup treated with OP + PORT or PORCT improved from 56.1 to 68.5 % (p = 0.028). Localization proved to be a significant and independent factor. Only patients with advanced laryngeal cancer had significant improved survival (p < 0.01), while the improvement for hypopharyngeal cancer patients was not significant (p < 0.2). After 2004, there was a slight increase (+10.2 %) of primary radiochemotherapy (pRCT) due to stronger selection if R0 > 5 mm-resectability is unlikely. Standardised use of PORCT and pRCT considering clear indications showed to be significantly involved in improved survival in advanced LHSCC.

Population characteristics and the impact of tourism on economic development

Currently, there are two opposing research lines regarding the capacity of tourism to influence the level of economic development. In this context, this research study, after analysing the validity of each one of these two lines, advocates for an intermediate situation based on the premise that there is no automatic relationship between these two dimensions, but instead, a country must meet certain characteristics in order for this link to occur. In this sense, once proven the importance of population characteristics in the level of socioeconomic progress by scientific literature, applying an econometric model, using a sample of 144 countries – divided between more developed countries and less developed countries –, it has showed that the reduction of the emigrant population – especially high-qualified people – and the existence of low unemployment rates have contributed to the transformation of tourism growth into economic development. In addition, it has also demonstrated that countries with regressive population pyramids have greater difficulties for tourism growth improve their socioeconomic conditions. Therefore, international agencies and institutions that seek to use tourism as an effective tool for alleviate poverty should consider these factors before making significant investments that ultimately do not produce the expected results

Emergence of macro-variables by evaluation and clustering of micro- activities

Recent finance and economic forecasting and risk calculation failures made obvious that macro-modelling without micro-foundation may be treacherous. Reliable macro-modelling requires the consistent bundling of individual actions into intermediate and macro-variables exploiting the individual actions’ coordination and its dynamics. The degree of coordination may range from chaos – absence of coordination – to determined situations caused by macro-level equilibrium dictating any agent's actions and inhibiting interactions. Coordination clusters individual actions into real decision units such as companies, political parties and unions. It structures the emergent intermediate and macro-level situations vitally.The paper presents first a centennial history of prominent scholars’ quotes questioning the equilibrium paradigm, a short survey of prevailing paradigm's deficiencies laid bare once again by the latest financial crises.It proposes second discrete choice (DC) – successfully applied in different fields – to model the individual agent's decision. DCs innovative integration into a Markov process provides a steady foundation to model interactions of individual agents consistently.The final section justifies the actions’ proposed interactive bundling by referring to recent advances in data processing and network topology. The dynamic modelling of the actions’ and interactions’ coordination breaks fresh grounds both with regards to mathematical, computational and economic modeling requirements. The combination of latest developments in data processing like Big Data and the recently (re)discovered network topology capabilities may cope with these challenges.

Effects of local negative feedbacks on the evolution of species within metacommunities

Local negative feedbacks occur when the occupation of a site by a species decreases the subsequent fitness of related individuals compared to potential competitors. Such negative feedbacks can enhance diversity by changing the spatial structure of the environment. The conditions, however, involve dispersive, environmental and evolutionary processes in complex interactive ways. We introduce a model that accounts for four mechanisms: colonisation-competition-extinction ecological dynamics, evolutionary dynamics, local negative feedbacks and environmental averaging. Three qualitatively distinct dynamics are possible, one dominated by specialists, another dominated by generalists and an intermediate situation exhibiting taxon cycles. We discuss how metacommunity diversity, macro-ecological patterns and environmental patterning are linked to the three qualitative dynamics. The model provides classical shapes for morph-abundance distributions, or diversity-area relationships. Diversity can be high when specialists dominate or when taxon cycles happen. Finally, local negative feedbacks often yield fine-grain environments for taxon cycle dynamics and coarse-grain environments when generalists dominate.

Different toxic mechanisms are activated by emission PM depending on combustion efficiency

Ambient air levels of fine particulate matter (PM ≤ 2.5 μm) are associated with mortality and morbidity. In addition to traffic, large quantities of fine and ultrafine particles (UFPs ≤ 100 nm) are emitted by residential wood combustion. Polycyclic aromatic hydrocarbon (PAH) and soot-rich emissions from small scale heating appliances have been linked with a plethora of toxicological effects. Recently, new technology appliances have been introduced into use although there are several uncertainties related to the toxicological properties of those emissions. In this study, PM1 (PM ≤ 1 μm) emissions from three different biomass combustion situations were compared. PM samples were produced in a novel adjustable biomass combustion reactor to avoid the problems encountered if one uses different appliances to generate the desired combustion conditions. The combustion conditions represented efficient, intermediate and smoldering situations. The concentration related effects of the particles (15, 50,150 and 300 μg ml−1) were investigated in a RAW264.7 macrophage cell line after 24 h' exposure. We analyzed cellular metabolic activity, cell cycle, and indicators of genotoxicty, oxidative stress and proinflammatory responses. Interestingly, the particles collected from smoldering and intermediate combustion conditions decreased cellular metabolic activity less than those from efficient combustion (10-fold difference). However, the samples from intermediate and smoldering combustion evoked greater DNA damage in the comet assay (2.5-fold difference). In contrast, only the particulate samples from efficient combustion triggered G2-cell cycle arrest and oxidative stress in the macrophages. These results indicate that ash rich PM emissions from appliances with almost complete combustion may still exert health impacts. However, particulate emissions from efficient combustion were small when compared to the two other situations. Thus, even with their faults and the obvious need for development, consumers should be encouraged to purchase efficient combustion devices in order to reduce exposure to PM induced adverse health effects.

The intermediate situation. On affection and time in Michel Henry

When we go back-by means of the epoché of the world, following Michel Henry-towards the originary “how” of all manifestation (videor), we stumble once and again upon the phenomenological situation of the body. The body is, then that originary hinge by means of which I manifest world in a continuous resistance. It will be, as well, within my own body where I am always aware of oneself, according to my own affection (self-affection, not previously constituted). Thus, the material condition of the body will be that of my internal body, or subjective body-as Henry initially read in Maine de Biran-or that of my flesh, as Henry himself would later say. Bearing all this in mind, the intermediate situation of one’s own affection, of this body of mine, with regard to the world and the videor, turns out to be an appropriate medium to attempt a preliminary study of the problematic situation of the internal time of affection. For this purpose, we shall revise the analysis offered by Michel Henry in Material Phenomenology and in Incarnation, indicating possible aporias, as well as alternatives to these last ones.Cuando, siguiendo a Michel Henry, retrocedemos en una epoché hacia el “cómo” originario de toda manifestación (videor), tropezamos una y otra vez con la situación fenomenológica del cuerpo. El cuerpo es, pues, esta bisagra originaria a través de la cual yo manifiesto el mundo en continua resistencia. También será dentro del propio cuerpo donde uno será siempre autoconsciente, de acuerdo con la propia afección (autoafección, no constituida previamente). Por eso, la condición material del cuerpo será la de mi cuerpo interior o cuerpo subjetivo, de acuerdo con la lectura inicial que Henry hace de Maine de Biran; o de mi carne, como dirá el mismo Henry más tarde. Teniendo en cuenta todo ello, la situación intermedia, situación de la afección propia y la de mi cuerpo en relación con el mundo y el videor, resulta ser un medio apropiado para emprender un estudio preliminar de la problemática situación del tiempo interno de la afección. Para ello, revisaremos el análisis que Michel Henry ofrece en Material Phenomenology y en Incarnation, indicando las posibles aporías, así como posibles alternativas.

Shear and thermal effects in boundary film formation during sliding

A prerequisite for understanding mechano- and tribochemical reaction pathways is that the interface be in thermodynamic equilibrium and that the temperature be well defined. It is suggested that this occurs in two regimes: when the surfaces are only slightly perturbed during sliding, leading to negligible frictional heating, and when the surface temperatures are very high (∼1000 K), in the so-called extreme pressure regime. The tribochemistry occurring in each regime is discussed in terms of the elementary steps leading to tribofilm formation, namely (i) a reaction of the additive or gas-phase lubricant on the surface to form an adsorbed precursor, (ii) decomposition of the molecular precursor, (iii) a process that causes the formation of a tribofilm that (iv) regenerates a clean surface that allows this tribochemical cycle to continue to form a thicker film. These steps are thermally driven in the extreme-pressure regime, while under milder conditions, they are induced by interfacial shear. In intermediate situations, the processes are likely to be a combination of those occurring at the extrema.

El derecho positivo o convencional, su naturaleza: el carácter creativo (constitutivo) y derivado de las leyes humanas

El siguiente trabajo intenta presentar algunos criterios para reconocer una norma de derecho positivo. Si bien es cierto que para el iusnaturalismo clásico una misma norma contiene elementos naturales y convencionales, es posible, creo, determinar si una disposición cualquier pertenece, stricto sensu, al derecho positivo o al derecho natural. En particular, se propone que una regla de justicia convencional mantiene una situación intermedia entre las llamadas normas ónticas y los principios terciarios de la ley natural. Aunque comparte elementos con esos tipos de reglas de justicia, no puede ser clasificada ni como derecho natural terciario ni como una norma de justicia que crea ex nihilo nuevos estados de cosas.

Influence of shift-work schedule on circadian disruption in nursing staff

Many shift work schedules (SWS) have been proposed to promote performance and to reduce circadian impairment, however, few studies have been devoted to demonstrate the benefits of such shifts under real work conditions. The aim of this study was to characterize the impact of different SWS, on circadian disruption assessed by ambulatory circadian monitoring (ACM), in nursing staff. To this, wrist temperature (T), motor activity (A), body position (P), light exposure (L) and environmental temperature (ET) were recorded. Two hundred eighty-six healthy nursing staff (45 males and 241 females) enrolled in eight different SWS (Permanent 8 h-day, PD; Permanent night, PN; morning with nights, MN; evening with nights, EN; permanent 12 h-day, 12D; anti-stress, AS and rotating three-shifts, R3), from 22 to 62 years old, participated in this study. Volunteers were monitored by ACM during 7–10 days using a multichannel device (KronowiseTM, Chronolab, Univ. of Murcia). Circadian robustness was assessed by the circadian function index (CFI) of composite TAP variable. The regularity of life style was measured by calculating Interdaily stability (IS). Restfulness (RS), a measure of sleep quality, was calculated from L5 of TAP and expressed as a score from 0 to 10 (10 = very restfully sleep). As phase marker was selected the midpoint of TL5 from TAP (the midpoint of five consecutive hours of minimum values). The circadian status evaluation on nurses staff by ACM showed that those subject engaged in both PD and 12D shifts presents higher stability (IS) and RS scores than those subjects on PN, MN, EN and R3 schedules. However, the more disruptive shift seems to be PN, since nurses under this schedule show the lowest stability, CFI and RS values, besides presenting the most delayed TL5. The remaining shifts present an intermediate situation between PD and PN. As expected, the two permanent day shifts (PD and 12D) are the less chonodisruptive, since nurses under this schedule present more robust and regular rhythms with deeper sleep during the night. On the contrary a PN shift produces higher rhythm instability and more superficial sleep. So according to our results when working during the night is a must rotating shifts (AS, R3) seems to be more recommendable than MN or EN. To RETICEF (RD12/0043/0011), MINECO (BFU2010–21945-C02–01), and INNPACTO (IPT-2011–0833-900000) with FEDER cofounding to JAM.

Morphology of adult and juvenile instars of Galumna obvia (Acari, Oribatida, Galumnidae), with discussion of its taxonomic status

The adult instar of the oribatid mite, Galumna obvia (Berlese, 1914), is redescribed in detail, on the basis of specimens from Finland. The morphology of juvenile instars of G. obvia is described and illustrated for the first time, and compared to that of other species of the family Galumnidae. The position of the insertion of the lamellar seta in adults proved variable in studied European populations, being either on or medial to the lamellar line. Since the genera Galumna and Pergalumna are currently distinguished only by the relative positions of the seta and line, specimens of G. obvia in some populations show an intermediate situation between other studied Galumna species – with lamellar seta on or lateral of lamellar line – and Pergalumna with lamellar seta at a distinct distance medially of lamellar line. A detailed reevaluation of the two genera is needed.

Tourism and economic development: analysis of geographic features and infrastructure provision

The idea of committing to tourism as a tool for economic development – a decision supported by a large number of countries and international organizations – is becoming widespread, since the potential of tourism has been advocated, without a doubt, to improve the socio-economic conditions of host countries. However, in recent years, a critical school of thought has emerged that questions the universal validity of tourism as a development tool, and therefore calls into question the solution implemented by these countries and institutions. In this context, this research study, after analysing the validity of each one of these two schools of thought, advocates for an intermediate situation based on the premise that there is no automatic relationship between the two dimensions, but instead a country must meet certain characteristics in order for this link to occur. In this sense, since the scientific literature has shown the importance of geography and infrastructure provision in improving the living conditions of the population, the aim of this work is to identify what are the determining factors that help or hinder the transformation of tourism growth into economic development.

Bindings of hMRP1 transmembrane peptides with dodecylphosphocholine and dodecyl-β-d-maltoside micelles: A molecular dynamics simulation study

In this paper, we describe molecular dynamics simulation results of the interactions between four peptides (mTM10, mTM16, TM17 and KTM17) with micelles of dodecylphosphocholine (DPC) and dodecyl-β-d-maltoside (DDM). These peptides represent three transmembrane fragments (TM10, 16 and 17) from the MSD1 and MSD2 membrane-spanning domains of an ABC membrane protein (hMRP1), which play roles in the protein functions. The peptide–micelle complex structures, including the tryptophan accessibility and dynamics were compared to circular dichroism and fluorescence studies obtained in water, trifluoroethanol and with micelles. Our work provides additional results not directly accessible by experiments that give further support to the fact that these peptides adopt an interfacial conformation within the micelles. We also show that the peptides are more buried in DDM than in DPC, and consequently, that they have a larger surface exposure to water in DPC than in DDM. As noted previously by simulations and experiments we have also observed formation of cation–π bonds between the phosphocholine DPC headgroup and Trp peptide residue. Concerning the peptide secondary structures (SS), we find that in TFE their initial helical conformations are maintained during the simulation, whereas in water their initial SS are lost after few nanoseconds of simulation. An intermediate situation is observed with micelles, where the peptides remain partially folded and more structured in DDM than in DPC. Finally, our results show no sign of β-strand structure formation as invoked by far-UV CD experiments even when three identical peptides are simulated either in water or with micelles.

Sustainability of grape-ethanol energy chain

The aim of this work is to evaluate the sustainability, in terms of greenhouse gases emission saving, of a new potential bio-ethanol production chain in comparison with the most common ones. The innovation consists of producing bio-ethanol from different types of no-food grapes, while usually bio-ethanol is obtained from matrices taken away from crop for food destination: sugar cane, corn, wheat, sugar beet. In the past, breeding programs were conducted with the aim of improving grapevine characteristics, a large number of hybrid vine varieties were produced and are nowadays present in the CRA-VIT (Viticulture Research Centre) Germplasm Collection. Some of them are potentially interesting for bio-energy production because of their high production of sugar, good resistance to diseases, and ability to grow in marginal lands. LCA (Life Cycle Assessment) of grape ethanol energy chain was performed following two different methods: (i) using the spreadsheet “BioGrace, developed within the “Intelligent Energy Europe” program to support and to ease the RED (Directive 2009/28/EC) implementation; (ii) using a dedicated LCA software. Emissions were expressed in CO2 equivalent (CO2eq). The results showed that the sustainability limits provided by the normative are respected to this day. On the contrary, from 2017 this production will be sustainable only if the transformation processes will be performed using renewable sources of energy. The comparison with other bioenergy chains points out that the production of ethanol using grapes represents an intermediate situation in terms of general emissions among the different production chains.

Implications of land-cover types for soil erosion on semiarid mountain slopes: Towards sustainable land use in problematic landscapes

The impact of land-cover types on soil erosion and runoff, as well as on physico-chemical soil properties, was monitored. The study area, an agroforestry landscape was located in Sierra Nevada Mountains in south-eastern Spain. Eight land-cover types were investigated: farmland planted with olive, almond, and cereals; forest with P. halepensis and P. sylvestris; shrubland; grassland; and abandoned farmland. The erosion plots replicated twice were located on hillslopes, where erosion and runoff were measured after 22 storm events. Forest dominated by Pinus stands exhibited significantly the lowest amounts of erosion and runoff, contrasting with abandoned farmland. Olive had higher erosion than did almond, cereals, or grasslands, but with the highest runoff rate under almond groves. The erosion and runoff response to shrubland showed an intermediate situation between forest and farmland–grassland uses. Under forest and shrubland, better soil properties were determined, especially higher organic C and total N, and lower soil-bulk density. Erosion was highly dependent on runoff, bulk density, soil organic C, and the degree of soil surface covered. Thus, the alteration in land cover is essential to an understanding of productivity of soil undergoing erosion, as sustainable planning can mitigate soil-degradation processes in the overall agroforestry landscape.

Pyrosequencing evidences the impact of cropping on soil bacterial and fungal diversity in Laos tropical grassland

It is widely assumed that agricultural practices have a major impact on soil living organisms. However, the impact of agricultural practices on soil microbes is poorly known, notably for species richness, evenness, and taxonomic composition. The taxonomic diversity and composition of soil indigenous microbial community can be assessed now using pyrosequencing, a high throughput sequencing technology applied directly to soil DNA. Here, we studied the effect of agriculture management on soil bacterial and fungal diversity in a tropical grassland ecosystem of northeastern Laos using 454 pyrosequencing of 16S and 18S rRNA genes. We studied soil microbial diversity of agricultural soils 3 years after conversion from native grasslands. We compared five systems: one tillage, two no-tillage rotational, one no-tillage improved pasture, and one natural grassland. Our results show first that compared to the natural grassland, tillage decreases fungal richness and diversity by −40 % and −19 %, respectively and increases bacterial richness and diversity by +46 % and +13 %, respectively. This finding evidences an early impact of agricultural management on soil microbial diversity. Such an impact fits with the ecological concept of "intermediate perturbation"—the hump-backed model—leading to classify agricultural practices according to the level of environmental stress they generate. We found also that land use modified soil microbial taxonomic composition. Compared to the natural pasture, tillage decreased notably the relative abundance of Actinobacteria (by −6 %), Acidobacteria (by −3 %) and Delta-proteobacteria (by −4 %) phyla, and by contrast increased the relative abundance of Firmicutes (by +6 %), Gamma-proteobacteria (by +11 %), and Chytridiomycota (+2 %) phyla. We conclude that soil microbial diversity can be modified and improved by selecting suitable agricultural practices. Moreover no-till systems represented intermediate situations between tillage and the natural pasture and appear therefore as a fair trade-off between the need for agriculture intensification and soil ecological integrity preservation.