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

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

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

Modification of biochemical properties by soil use

The present study is a summary of a wider paper to be Publisher in Soil Biology and Biochemistry. This was presented as a Keynote to the 3 International Conference on Soil Enzymes (Viterbo, Italy), 15-19 July 2007 and, partly, as a invited Conference to the Segundo Simposio Internacional: Suelo, Ecologí a y Medioambiente (Temuco, Chile), 8-9 noviembre 2007.[EN] Human activity is one of the main causes of the physical, chemical and biological degradation of soils. This degradation implies a change in soil quality as it involves both a decrease in productivity and changes in the ecological functions of the soil. The objective of the present study was to investigate the effect of soil use on soil biochemical properties, with the aim of providing data that allow assessment of the usefulness of enzymatic activities as indicators of soil quality. In addition to physical and chemical properties, different hydrolase enzymes involved in the C, N, P and S cycles, and other biochemical properties, such as the microbial biomass C and soil basal respiration, were analysed. The results obtained allowed different conclusions to be reached regarding the main processes involving the biochemical properties in soils affected by human activity.[ES] La actividad humana es una de las principales causas de la degradación física, química y biológica de los suelos. Dicha degradación implica un cambio en la calidad del suelo, ya que supone tanto una disminución en la productividad como cambios en las funciones ecológicas del suelo. El objetivo del presente estudio fue investigar el efecto del uso del suelo sobre las propiedades bioquímicas, con el fin de proporcionar datos que permitan estimar la utilidad de las actividades enzimáticas como indicadores de la calidad del suelo. Además de las propiedades físicas y químicas de los suelos, se analizaron diferentes hidrolasas implicadas en los ciclos del C, N, P y S, así como otras propiedades bioquímicas tales como el carbono asociado a la biomasa microbiana o la respiración basal del suelo. Los resultados obtenidos permitieron obtener diversas conclusiones en relación a los principales procesos que afectan a las propiedades bioquímicas en los suelos afectados por la actividad humana.This study was financed by the Xunta de Galicia (Project No. XUGA 40003B94) and by the MCYT (ProjectNo. BTE 2001-0987). The authors thank Ana I. Iglesias-Tojo, Carolina López-Cotón, Támara Migué ns, Jorge Paz-Ferreiro and Diana Bello for their assistance in carrying out the analyses.Peer reviewe

Effect of sawdust amendment on mineralization of organic nitrogen in a 2,4,5-trichlorophenol contaminated soil.

Previous studies have demonstrated that the toxic effects of 2,4,5 trichlorophenol (2,4,5-TCP) are greater in agricultural soils than in forest soils; therefore these effects appear to be influenced by the total C content and soil pH. Agricultural soils (usually low in organic C) contaminated with 2,4,5-TCP may be able to be remediated by the addition of organic waste products. To test this hypothesis, an agricultural soil was artificially contaminated with 5000 mg kg-1, 500 times the Generic Reference Level (GRL) of 2,4,5-TCP, then pine sawdust was added to the contaminated soil at doses equivalent to 5% and 10% of the soil weight. The effect of the sawdust on the toxicity of the contaminant was studied by measuring the degree of mineralization of the organic nitrogen in the soil. The addition of 2,4,5-TCP produced a large increase in the amount of inorganic N present (basically ammoniacal forms), which suggests that the 2,4,5-trichlorophenol caused the death of a large part of the edaphic microbiota. The addition of sawdust buffered this effect, particularly at the highest dose (10%) as the degree of mineralization was similar to that observed in the control sample treated with the same amount of sawdust, this indicating that 10% dose of sawdust is capable of mitigating the toxic effects of 2,4,5-TCP.Peer reviewe

Effect of non-tillage on some biological activities in an Alfisol from Southern Chile

Due to the necessity to stabilize and protect the soil from degradation processes, the agronomic practices such non-tillage (NT) were applied. Microbial biomass (MB) and some enzyme activities were evaluated here because they are very sensitive to the changes taken place in the environment. The aim of this study was to measure some biological activities in an Alfisol of the Southern Chile under NT cropping. The biological activities evaluated were: carbon (BMC) and nitrogen (BMN) of microbial biomass, respectively), N- mineralization, dehydrogenase and catalase activities and some hydrolytic enzyme activities representative of different cycles of biological importance in soil (C, N, P, S). Soil organic C total N and S content also were evaluated. Soil samples were collected after harvest at three different depths (0-5, 5-10 and 10-20 cm), in soils cropped 4, 7 and 20 years under NT. The results showed an increment in organic C, N, S, N-mineralization and in the biological activities in the top soil 5 cm depth, with an increment of year under NT. In general, there was close relationships were found among almost all biological activities evaluated (r > 0.8; p< 0.05).Dada la necesidad de estabilizar y proteger los suelos, de los procesos de degradación, han surgido prácticas agronómicas conservacionistas, entre ellas, la cero labranza (CL). La medición de la biomasa microbiana (BM), junto a la determinación de algunas actividades enzimáticas en el suelo, fueron evaluadas ya que, son muy sensibles a los cambios producidos en el entorno. El objetivo de este estudio fue determinar algunas actividades biológicas en un Alfisol del sur de Chile sometido a un manejo de CL. Las actividades evaluadas fueron carbono (C) y nitrógeno (N) de la biomasa microbiana (CBM y NBM, respectivamente), mineralización del N, actividades dehidrogenasa y catalasa y algunas actividades enzimáticas hidrolíticas representativas de los diferentes ciclos de los elementos químicos de importancia biológica en suelos (C, N, P, S). Para ello se muestrearon suelos en postcosecha a diferentes profundidades (0-5, 5-10 y 10-20 cm), desde sitios cultivados con cuatro , siete y veinte años con manejo de CL. Los resultados mostraron un incremento en el C, N y azufre (S) orgánicos, en la mineralización de N y en las actividades enzimáticas evaluadas, en los primeros 5 cm de suelo, en la medida que aumentan los años de CL. Además, se encontró una alta correlación (r 0.8; p< 0.05) entre la mayoría de las actividades biológicas evaluadas.Este estudio fue financiado por la Dirección de Investigación de la Universidad de La Frontera, Proyecto DIDUFRO Nº 9810. Además, los autores agradecen al Convenio de Intercambio Universidad de La Frontera, Chile–Universidad Santiago de Compostela, España, que permitió que la Dra. M. Alvear hiciera una pasantía en los Laboratorios del Departamento de Edafología y Química Agrícola de la Universidad de Santiago de Compostela y en Laboratorios del Departamento de Bioquímica del Suelo, Instituto de Investigaciones Agrobiológicas de Galicia, CSIC, España.Peer reviewe

USE OF ENZYME ACTIVITIES TO MONITOR POLLUTION OF AGRICULTURAL LAND

Concern about environmental pollution has grown in the last few decades, amongst both specialists in the field and society at large. This concern is reflected in thenumerous studies that have been published on this topic in recent years. Soil pollution has been somewhat neglected as a topic of study, relative to air and waterpollution, which are considered harmful to human life. However, soil pollution is a particularly serious problem because of the impact on soil functioning and on theecosystem as a whole. Although natural processes such as volcanic activity and weathering of the parent material contribute to soil pollution, anthropogenicactivities represent the main cause of soil pollution. Apart from some accidental events, most pollution is generated by human activities such as industrialprocesses, transportation, construction, uncontrolled discharges, waste generation and agriculture. Agricultural land is particularly sensitive to pollution, partly because certain agricultural practices (soil preparation and tillage, soil fertilization, grazing, etc.) may affect basic soil properties, and partly because the soils usuallydisplay poor resilience. However, pollutants often reach already degraded agricultural soils and their impact will therefore be added to existing effects. Thepollutants most frequently encountered in the agricultural sector include heavy metals, petroleum derived products, persistent organic pollutants, pesticides and fertilizers. Soil enzymes such as oxidoreductases and hydrolases have been widelyused to investigate the impact of different pollutants on agricultural soils. However, the study findings are often inconclusive, because the impact of a given pollutanton the activity of different soil enzymes is influenced by various factors. In this report, we analyze the findings of different studies concerning pollution of agricultural soils