Labile carbon in biological soil crusts in the Tabernas desert, SE Spain.

Decomposition processes are extremely important in biological soil crusts (BSCs). Although the effects of temperature and moisture on such processes have been widely studied, little is known about the influence of the readily metabolizable substrate (labile C) and how this substrate varies in different types of BSCs. In the present study, BSCs formed by cyanobacteria (CYANO) and by lichens (DIPLOS and LEPRA) were incubated at 25 °C (optimum temperature) and different moisture levels, for evaluation of the pool of labile C in the crust layers. Labile C was estimated as the sum of CO2-C emitted and the C extracted with hot water (80 °C) at the end of the incubation period. In all crusts, the relationship between emission and moisture fitted a quadratic model. For the different moisture contents, the sum of CO2-C emitted and C extracted with hot water converged to a constant value for each type of crust. This value, considered as the maximum content of labile C in the crust, was extremely high in DIPLOS, reaching up to 40% of the total organic C (TOC) initially present. In all crusts, and independently of the consumption of labile C, simple sugars (sucrose, glucose) remained at the end of the incubation period, which suggests that these sugars may play a protective role in BSCs. The presence of mannitol suggests that the fructose released during hydrolysis of sucrose was reduced to mannitol, thus enabling electron transport during moments of intense respiratory stress. The intense respiration in DIPLOS is partly due to the metabolism of polyphenols, which are possibly derived from the growth and death of free-living fungi that proliferate during incubation of the crusts. These results demonstrate that the metabolic processes in BSCs differ depending on the type of organisms that form the crusts and that there is a high risk of C loss from Diploschistes BSCs after heavy rainfall events.Peer reviewe

Evaluation of various tests for the diagnosis of soil contamination by 2,4,5 trichlorophenol (2,4,5-TCP).

The response of different types of soils to contamination with 2,4,5-triclorophenol was studied to test the validity of the concept of generic reference levels (GRL), the main criterion used to define soil contamination. Soil samples were artificially contaminated with doses of between 0 and 5000 mg kg-1of 2,4,5-triclorophenol, and analysed by various tests. Where possible, the response of soils to the contaminant was modelled by a sigmoidal dose-response curve in order to estimate the ED50 values. The tests provided different responses, but only microbial biomass-C and dehydrogenase and urease activities demonstrated soil deterioration in response to contamination. The results suggest that the diagnosis of soil contamination has been greatly simplified in the legislation by the provision of a single figure for each compound, and that the GRL concept could perhaps be substituted by measurement of ED50 values, which better reflect the alteration of a soil due to the presence of a xenobiotic substance.Peer reviewe

Modification of enzymatic activity in soils of contrasting pH contaminated with 2,4-dichlorophenol and 2,4,5-trichlorophenol.

According to previous studies, acidic soils may receive larger quantities of 2,4-dichlorophenol (2,4-DCP) and of 2,4,5-trichlorophenol (2,4,5-TCP) than the concentrations indicated in the prevailing legislation for defining a soil as contaminated, without any important changes in their biochemical properties. In this study, we investigated whether neutral or slightly alkaline soils behave in the same way as acidic soils in response to contamination by these compounds. For this purpose, a large number of acidic soils (pH between 4.2 and 5.9) and calcareous soils (pH between 6.5 and 8.0 ) were contaminated in the laboratory with different doses of 2,4-DCP (up to 10000 times the GRL) and of 2,4,5-TCP (up to 500 times the GRL). After an incubation period of three days, the activities of several enzymes (dehydrogenase, catalase, ß-glucosidase and phosphomonoesterase) were measured in the soils. The effects of 2,4,5-TCP were much greater than those of 2,4-DCP in both the acidic and calcareous soils, regardless of the dose applied. Phosphomonoesterase and ß-glucosidase activities were scarcely affected by either of the contaminants in any of the soils, whereas the catalase activity decreased slightly. The dehydrogenase and urease activities were strongly affected in all soils and in some cases even disappeared, particularly after the application of 2,4,5-TCP. Multiple regression analysis of the percentage reductions in dehydrogenase and urease activities in relation to contaminant dose and different soil properties indicated that the reduction in enzyme activity depended, in decreasing order, on the dose of contaminant applied, total carbon content and soil pH. We suggest that the processes that regulate the toxicity of these compounds in soils are their adsorption by soil organic matter and the dissociation of the non-adsorbed compound into phenolate ions (which are toxic to microorganisms). In fact, the chlorophenols scarcely affected the biochemical properties of the soils under study because of their high organic matter contents (A horizons with total carbon contents of up to 11%). Moreover, both chlorophenols had slightly stronger effects on the calcareous soils than on the acidic soils, probably because the dissociation process was favoured at higher pH. On the other hand, the 2,4,5-TCP had stronger effects on soil biochemical properties than 2,4-DCP, which may be explained by the lower pKa value of 2,4,5- 2 TCP (6.9) than that of 2,4-DCP (7.9). The results show that the GRL values established by the legislation are not appropriate for either of these chlorophenol compounds.Peer reviewe

PRELIMINARY RESULTS ON ENZYMATIC ACTIVITIES IN TWO SALT MARSH SOILS DIFFERING IN HYDROMORPHIC CHARACTERISTICS AND VEGETATION COVER

Salt marsh soils are characterized by temporary hydric saturation and by vegetation cover that is dominated by different salt-tolerant plant species depending on factors such as duration of submersion. The composition of microbial communities is an essential component of trophic dynamics and biogeochemical processes in salt marshes and determines the activities of enzymes that catalyze the conversion of complex molecules into simpler ones. However, enzymatic activities have not yet been investigated in salt marsh soils. The aim of this study was to analyze the activities of some oxidoreductase and hydrolase enzymes in two salt marsh soils affected by different levels of water saturation and covered by vegetation dominated by different plant species [Juncus maritimus Lam and Spartina maritima (Curtis) Fernald]. The enzyme activities were measured both in air-dried (only) and in air-dried, re-moistened soil samples. The activities in soils under both types of vegetation were much lower than usually found in terrestrial ecosystems. However, in the air-dried samples, the enzyme activities were higher in the soil under Juncus than in the soil under Spartina and tended to decrease with depth, particularly in the former. The activities of all enzymes considered tended to be higher, throughout the whole soil profile, in the re-moistened than in the air-dried soils, especially in the soil under Spartina. Hydrolase activity was strongly and positively related to organic matter content in both air-dried and re-moistened soil samples, particularly in the latter. By contrast, oxidoreductase activity was generally only related to organic matter content in the re-moistened soil samples. Further studies, preferably with freshly collected soil samples, are required to clarify the relationship between enzymatic activities and environmental conditions

Translocation of soils to simulate climate change: CO2 emissions and modifications to soil organic matter.

The effect of climate change on CO2 emissions was studied on undisturbed soil monoliths (40-cm diameter, 25-cm high), which were translocated to warmer zones than their place of origin. Thirty-two months after the translocation, a climatic factor deduced from the moisture content of the soil and from the effective mean temperature (temperatures in excess of 5 ºC) revealed that translocation increased the potential of the climate to enhance the biological processes by between 73% and 26% compared with what the soil would support in its place of origin. At the end of the study, the transported soils had lost a large proportion of both total carbon and nitrogen (between 20 and 45%). During the experiment, the CO2 emissions from the soils, measured under field conditions, were quite variable, but were usually greater than from soils in situ. The variation in labile C in the soil throughout the experiment was calculated from a first-order kinetic equation for organic matter decay. The relative CO2 emissions, expressed in terms of the labile carbon fraction in the soils, were clearly greater in those translocated soils that underwent the most intensive climate change, which indicates that the variations in emissions over time are basically a function of the size of the labile organic matter pool.Peer reviewe

Hydrolase enzyme activities in a successional gradient of biological soil crusts in arid and semi-arid zones.

In arid and semi-arid regions, pioneer organisms form complex communities that penetrate the upper millimetres of the bare substrate, creating biological soil crusts (BSC). These thin crusts play a vital role in whole ecosystem functioning because they enrich bare surfaces with organic matter, initiate biogeochemical cycling of elements, modify hydrological cycles, etc., thus enabling the ground to be colonized by vascular plants. Various hydrolase enzymes involved in the carbon (cellulase, ß-glucosidase and invertase activities), nitrogen (casein-protease and BAA- protease activities) and phosphorus (alkaline phosphomonoesterase activity) cycles were studied at three levels (crust, middle and deep layers) of three types of BSCs from the Tabernas Desert (SE Spain), representing an ecological gradient ranging from crusts predominated by cyanobacteria to crusts predominated by lichens (Diploschistes diacapsis, Lepraria crassissima). All enzyme activities were higher in all layers of all BSCs than in the bare substrate. The enzymes that hydrolyze low molecular weight substrates were more active than those that hydrolyze high molecular weight substrates (cellulase, casein-protease), highlighting the pioneering characteristics of the BSCs. The hydrolytic capacity developed in parallel to that of ecological succession, and the BSCs in which enzyme activity was highest were those under Lepraria crassissima. The enzyme activity per unit of total organic C was extremely high; the highest values occurred in the BSCs formed by cyanobacteria and the lowest in those formed by lichens, which 2 indicates the fundamental role that the primary colonizers (cyanobacteria) play in enriching the geological substrate with enzymes that enable degradation of organic remains and the establishment of more developed BSCs. The results of the study combine information on different enzyme activities and provide a clear vision of how biogeochemical cycles are established in BSCs, thus confirming the usefulness of enzyme assays as key tools for examining the relationship between biodiversity and ecosystem function in biological soil crusts.Peer reviewe

Biological and microbial activity in biological soil crusts from the Tabernas desert, a sub-arid zone in SE Spain.

The ecology and functional role of biological soil crusts (BSCs) in arid and semi-arid zones have been extremely well studied. However, little is known about the biochemical properties related to the number and activity of the microbiota that form the crusts, even though information about these properties is very important for understanding many of the processes that affect the formations. In this study, several properties related to the activity and number of microorganisms (biomass-C, basal respiration, dehydrogenase activity and nitrogen mineralization potential) were determined at different depths (crusts, 0-0.5 cm; middle, 0.5-3 cm and deep, 3-5 cm layers) in two types of crusts (predominated by cyanobacteria and by lichens) in the Tabernas desert (Almeria, SE Spain). The absolute values of the above-mentioned properties and the values expressed relative to the total organic carbon (TOC) content were both much higher in the crust layers than in the surface horizons of soils under Mediterranean or Atlantic climates. A large part of the TOC in the BSCs was contained in the microbiota and another large part was readily metabolized during incubation of the crusts for 10 days at 25 °C. The net nitrogen mineralization rate was also high, and ammonification predominated in the crust layers, whereas nitrification predominated in the middle and deep layers. In all types of BSCs, the microbiota colonized the deep layers, although with greater intensity in the lichen-dominated BSCs than in the cyanobacterial BSCs. The results also indicate that hydrolytic enzymes are not stabilized on soil colloids and their activity depends only on the active microbiota.Peer reviewe

Does Soil Organic Matter Affect the Impact of the Ionic Liquid Ethylammonium Nitrate in the Pure State and as Mixture with Lithium Salt on Basal Soil Respiration?

Although ionic liquids (ILs) do not contaminate the atmosphere (because of their low vapourpressure), they may have toxic effects in aquatic and terrestrial environments. Therefore, beforeILs can be widely used for different applications, their toxicity must be tested in different environments.The IL ethylammonium nitrate (EAN) is of interest in electrochemical applications, and research is currently underway to investigate the electrochemical activity of mixtures of this compound with inorganic salts. In this study, we investigated the impacts of different amounts of pure EAN and of mixtures of EAN and lithium salt on basal soil respiration in two soils differing in organic matter content.Fil: Sixto, Teresa. Consejo Superior de Investigaciones Científicas. Instituto de Investigaciones Agrobiológicas de Galicia; EspañaFil: Priano, Maria Eugenia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; ArgentinaFil: Reyes, Otilia. Universidad de Santiago de Compostela; EspañaFil: Parajó, Juan José. Universidad de Santiago de Compostela; EspañaFil: Salgado, Josefa. Universidad de Santiago de Compostela; EspañaFil: Trasar Cepeda, Carmen. Consejo Superior de Investigaciones Científicas. Instituto de Investigaciones Agrobiológicas de Galicia; Españ

Comparative study of the microbial diversity of bulk paddy soil of two rice fields subjected to organic and conventional farming

Two adjacent paddies of an experimental rice field, subjected to organic and conventional farming, were characterized aiming the comparative assessment of microbiological variations occurring in the bulk paddy soil over the rice cycle. This study comprehended the simultaneous characterization of general physicochemical soil properties [total carbon and nitrogen, pH (H2O and KCl), C:N ratio and water content], biochemical properties [enzymatic activities and Community Level Physiological Profiles (CLPP)], the estimation of cultivable organisms (enumeration of fast growing heterotrophic bacteria, actinomycetes and fungi) and the assessment of bacterial diversity using a culture-independent method (PCR-DGGE fingerprinting). The linkage of the parameters measured was analysed by canonical correspondence analysis (CCA). CCA ordination plots of the CLPP showed a similar pattern of microbial functional activity in both agronomic management systems, except in June. Enzymatic activity, water content and fungi counts were the main factors affecting the observed CLPP time variation. Such a variation was not expressed by the Shannon and evenness indices, which did not evidence significant differences in the bacterial and functional diversity between or within farming type over the analysed period. The cluster and CCA analyses of the DGGE profiles allowed the distinction of the bacterial communities of both paddies, with temporal variations being observed in the organically managed field but not in the conventional paddy. Enzymatic activity, pH and molinate content were the factors which most contributed to the observed variations. Altogether these results underline the functional redundancy of the rice paddy soil and evidence the temporal variations on the metabolic activity of soil, irrespective of farming type.info:eu-repo/semantics/acceptedVersio

Modification of the method to determine dehydrogenase activity in soils spiked with 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4)

The 20th International Electronic Conference on Synthetic Organic Chemistry session Ionic LiquidsThe ionic liquids (ILs) are often denominated as “green fluids”, because they are considered as innocuous due to their negligible volatility. Due to this apparent innocuousness, the ILs are attracted a great attention as an alternative to traditional organic solvents, highly contaminant. However, the problem of contamination is not limited to the atmosphere, since also aquatic and terrestrial environments can be affected. Therefore, and because the toxic effects of ILs on the environment are largely unknown, research studies are needed to deepen this aspect before to assign them the appellation of “green fluids”. Nevertheless, and despite the increased number in the last few years of studies on different aspects of ILs, the toxicity of these compounds to the environment in general, and to the soils in particular, only rarely is investigated. One of the most used ILs in different applications is 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4). Among all the soil properties, those determining the edaphic metabolism, and especially the enzymatic activities, are highly sensitive to ascertain the disturbance caused by any external agent. Given the lack of studies investigating the effect of ILs on the edaphic environment, before the use of enzymatic activities as indicators of the toxicity for soils of any given IL, it is necessary to test if classical methods to determine the soil enzymatic activities are adequate for their use in soils spiked with that given IL. In this study we investigated the suitability of dehydrogenase method to determine the activity of this enzyme in soils with spiked BMIMBF4, modifying the method according to the problems identifiedhis research was financed by the Spanish Ministerio de Economía y Competitividad (Project No. CGL2015-66857-C2-1-R