Carmen Trasar-Cepeda

Towards a biochemical quality index for soils : An expression relating several biological and biochemical properties

Abstract Soil biological and biochemical properties are highly sensitive to environmental stress and thus can be used to assess quality. Any soil quality index should include several biological and biochemical variables so as to reflect better the complex processes affecting soil quality and to compensate for the wide variations occurring in individual properties. Many authors recommend the use of a native soil supporting climax vegetation that has undergone minimal anthropogenic disturbance as a high quality reference soil. In this study which examined three such native soils of Galicia (N.W. Spain) bearing Atlantic oakwood as the climax vegetation, biological and biochemical properties were found to vary widely seasonally and with sampling site and depth. These variations were closely correlated with the total carbon (C) and/or total nitrogen (N) contents of the soils. The following equation:Total N= (0.38×10–3) microbial biomass C +(1.4×10–3) mineralized N +(13.6×10–3) phosphomonoesterase +(8.9×10–3) β-glucosidase+(1.6×10–3) ureaseexplained 97% of the variance in total N for the soils studied, suggesting that a balance exists between the organic matter content of a soil and its biological and biochemical properties. A simplified expression of the above equation may be useful as a biochemical quality index for soils.

Dependence of mineralization of soil organic matter on temperature and moisture

Abstract It is widely believed that increases in ambient temperature due to global climatic change will decrease the organic matter content of soils and increase the emission of greenhouse gases from them. These effects, which are due to stimulation of the decomposition of fresh and humified organic matter, are predicted to be most pronounced in temperate regions between the 40th and 70th parallels. To investigate the possible implications of this for organic matter mineralization in soils of Galicia (northwest Spain, north of the 40th parallel), in this work samples of O and Ah layers taken at various times of the year (to account for seasonal effects) were subjected to incubation experiments. The results indicate that the effects of soil temperature and moisture content on C- and N-mineralization can be modelled by simple equations, the equation for CO2 evolved being more reliable than that for N-mineralized. The effects of interactions between soil moisture and temperature on the mineralization of organic matter were also modelled, using multiple regression to fit an equation including a term for their product to the results. The equation for N-mineralized explained 30–40% of the variance in this parameter, while that for CO2 evolved explained almost 80% of its variance. The latter equation allowed prediction of the effects of climatic change on respiration processes.

Limitations of soil enzymes as indicators of soil pollution

Abstract Soil enzyme activities are considered to be sensitive to pollution and have been proposed as indicators for measuring the degree of soil degradation. In this work we found that in three galician soils exposed to various degrees of pollution by tanning effluent, hydrocarbons or landfill effluent, the changes in the activities of individual enzyme did not allow precise quantification of soil degradation. Thus, the enzymatic activities in polluted soils with respect to that in control soils was between 37 and 260% for phosphomonoesterase, between 16 and 250% for β-glucosidase, between 28 and 194% for urease and between 24 and 251% for dehydrogenase. The degree of degradation was, however, clearly shown in all cases by the ratio Nc/Nk, where Nk is Kjeldahl nitrogen and Nc is a function of microbial biomass C and nitrogen mineralization capacity combined with three enzyme activities (phosphomonoesterase, β-glucosidase and urease). This ratio, Nc/Nk, exhibited all the attributes of a good pollution indicator and, in particular, was able to discriminate between the effect of the pollutant and any prior degradation of the sites. It is concluded that quantification of soil degradation can require that information on enzyme activities be supplemented with information on other biochemical soil properties.

Biochemical properties of acid soils under climax vegetation (Atlantic oakwood) in an area of the European temperate–humid zone (Galicia, NW Spain): general parameters

The general and specific biochemical parameters of soils are highly sensitive to disturbance of the environment, but their use for diagnosis of soil degradation is limited by lack of comparable published data and lack of accepted methodological standards. With a view to establishing an appropriate data base for the soils of Galicia (NW Spain), we investigated the biochemical properties of the O and Ah horizons of 40 native Umbrisols under climax Atlantic oakwood in this region. We report here our results on specific biochemical parameters (i.e. extracellular hydrolytic enzyme activities) characterizing the phosphorus, nitrogen, carbon and sulphur cycles. The enzymes studied were phosphomonoesterase (23.51210.37 and 6.6223.29 mmol p-nitrophenol g ˇ1 h ˇ1 , values for O and Ah horizons, respectively), phosphodiesterase (3.60 21.95 and 0.96 20.51 mmol p-nitrophenol g ˇ1 h ˇ1 ), casein-protease (2.97 20.83 and 0.9420.32 mmol tyrosine g ˇ1 h ˇ1 ), BAA-protease (23.74 211.35 and 15.26 28.91 mmol NH3 g ˇ1 h ˇ1 ), urease (24.90 213.60 and 16.59 210.61 mmol NH3 g ˇ1 h ˇ1 ), CM-cellulase (0.59 20.17 and 0.23 20.10 mmol glucose g ˇ1 h ˇ1 ), invertase (12.6622.75 and 6.9322.14 mmol glucose g ˇ1 h ˇ1 ), b-glucosidase (8.4325.14 and 1.5520.89 mmol p-nitrophenol g ˇ1 h ˇ1 ), and arylsulfatase (0.6720.30 and 0.4620.20 mmol p-nitrophenol g ˇ1 h ˇ1 ). For the variables for which comparable data are available, the values observed are generally within previously published ranges. Principal components analysis of the combined biochemical, physical and chemical data for these soils shows five factors, of which the three most important concern microbial activity and its logical dependence on nutrient content, the accumulation of soil organic matter and the mineralization of soil organic matter. 7 2000 Elsevier Science Ltd. All rights reserved.

Measurement of dehydrogenase activity in acid soils rich in organic matter

Abstract Dehydrogenase activity can be considered to be a good measure of microbial oxidative activity in soils. It is usually determined by measuring the amount of an artificial electron acceptor reduced by microbial activity, such as a soluble tetrazolium salt with a red colored reduced form (a formazan) that can be determined colorimetrically following extraction with a suitable solvent. In an earlier study of acid organic-matter rich forest soils of Galicia (N.W. Spain), measured dehydrogenase activities were low, at variance with respiratory activity data indicating high biological activity. To investigate the possibility that these low dehydrogenase activities were underestimated due to adsorption of the formazan, we have studied the interaction of six soils with iodonitotetrazolium formazan (INTF). At the same time, the capacities of two extractants, methanol and 1:1 dimethylformamide–ethanol (DMF-ethanol), to extract INTF were compared. The results show that INTF is adsorbed by the soils studied with an intensity that closely correlates with soil carbon content, and that dehydrogenase activity is thus underestimated to a different degree for each soil. A mixture of 1:1 DMF-ethanol was more effective than methanol in extracting INTF, thereby improving estimates of dehydrogenase activity. Correction for the effects of INTF adsorption could be achieved by using reference standards containing soil to construct a separate calibration curve for each soil. These standards were prepared by incorporating different concentrations of INTF with the soil under the same conditions used for determination of the dehydrogenase activity. The use of DMF-ethanol and reference standards containing soil is thus recommended for determination of dehydrogenase activity, at least in soils with similar properties to those studied here.

Biochemical properties in managed grassland soils in a temperate humid zone: modifications of soil quality as a consequence of intensive grassland use.

Although soil biochemical properties are considered to be good indicators of changes in soil quality, few studies have been made of the changes in biochemical properties brought about by anthropogenic disturbance of grassland ecosystems. In the present study, several biochemical properties were analysed in 31 grassland soils subjected to a high level of management, and the values obtained were compared with known values corresponding to native grasslands from the same region (Galicia, NW Spain). The 31 managed grasslands were divided into two groups (re-sown grasslands and improved grasslands) according to their management and past land use. The biochemical properties studied were: labile carbon, microbial biomass carbon, microbial respiration, metabolic quotient, net nitrogen mineralisation and the activities of dehydrogenase, catalase, phosphodiesterase, phosphomonoesterase, casein hydrolysing proteases, benzoyl arginamide (BAA)-hydrolysing proteases, urease, cellulase, ß-glucosidase, invertase and arylsulphatase. Managed grasslands exhibited lower values of soil biochemical properties than native grasslands. Three biochemical equilibrium equations were used to compare soil quality in managed and native grasslands. One of the equations did not show any significant difference between the groups of grassland soils considered. In contrast, two of the equations showed similar soil quality for improved and native grasslands, while re-sown grasslands exhibited a loss of soil quality when compared to native grassland soils.

Sensitivity of soil respiration to moisture and temperature

The sensitivity of soil respiration to moisture and temperature was evaluated in three soils from the Atlantic temperate humid zone (Galicia, NW Spain) dedicated to different types of land use (forest, grassland and cropland). Samples of the soils were incubated in the laboratory for 42 days under different temperature (10, 15, 20, 25, 30, 35 °C) and moisture (40, 60, 80, 100% of field capacity) conditions. Emission of CO 2 from Grassland soil was higher than from the other soils. However, despite the different organic matter contents and biochemical activities in the three soils, temperature and moisture were the main factors affecting respiration. It was not possible to demonstrate the effect of soil use on the temperature sensitivity of organic matter mineralization. Sensitivity to temperature was accurately determined by Q 10 expressions, but some results indicate that for correct estimation of Q 10 in the incubation experiments, the CO 2 emission data obtained during the first few days of incubation should be disregarded. Furthermore, the sensitivity of the soil organic matter to temperature was higher at low soil moisture contents. This finding was surprising as it is generally considered that temperature has a greater effect on respiration in nearly saturated soils than in drier soils.

Biochemical properties of acid soils under native grassland in a temperate humid zone

Abstract The biochemical properties of 29 soils under native grassland in a temperate humid zone (Galicia, north‐west Spain) and subject to low intensity management (at least during the last 100 years) were determined with the aim of establishing a reference database to allow future comparative studies of the effect of grassland management on soil quality. Several biochemical properties were quantitatively and qualitatively studied. These properties were: labile carbon, microbial biomass carbon, microbial respiration, metabolic quotient, net nitrogen mineralisation and the potential activities of dehydrogenase, catalase, phosphodiesterase, phosphomonoesterase, case in‐protease, BAA‐protease, urease, cellulase, β‐glucosidase, invertase and arylsulphatase. The values of these properties were generally within the ranges of those reported for grassland soils from other parts of the world, but some properties differed both quantitatively and qualitatively from those of forest climax soils in the same area. An equation showing a balance between soil organic matter content and soil biochemical properties was obtained, indicating the existence of a biochemical equilibrium similar to that previously obtained for Galician (north‐west Spain) forest climax soils.

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

Soil response 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 between 0 and 5000 mg kg(-1) of 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 ED(50) 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 ED(50) values, which better reflect the alteration of a soil due to the presence of a xenobiotic substance.

Relationships among bulk soil physicochemical, biochemical, and microbiological parameters in an organic alfalfa-rice rotation system

The microbial communities of bulk soil of rice paddy fields under an ancient organic agriculture regimen, consisting on an alfalfa-rice rotation system, were characterized. The drained soil of two adjacent paddies at different stages of the rotation was compared before rice seeding and after harvesting. The relationships among the soil microbial, physicochemical, and biochemical parameters were investigated using multivariate analyses. In the first year of rice cropping, aerobic cultivable heterotrophic populations correlated with lineages of presumably aerobic bacteria (e.g., Sphingobacteriales, Sphingomonadales). In the second year of rice cropping, the total C content correlated with presumable anaerobic bacteria (e.g., Anaerolineae). Independently of the year of rice cropping, before rice seeding, proteolytic activity correlated positively with the cultivable aerobic heterotrophic and ammonifier populations, the soil catabolic profile and with presumable aerobes (e.g., Sphingobacteriales, Rhizobiales) and anaerobes (e.g., Bacteroidales, Anaerolineae). After harvesting, strongest correlations were observed between cultivable diazotrophic populations and bacterial groups described as comprising N2 fixing members (e.g., Chloroflexi-Ellin6529, Betaproteobacteria, Alphaproteobacteria). It was demonstrated that chemical parameters and microbial functions were correlated with variations on the total bacterial community composition and structure occurring during rice cropping. A better understanding of these correlations and of their implications on soil productivity may be valid contributors for sustainable agriculture practices, based on ancient processes.