M.C. Leirós

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.

Biochemical characterization of biological activity in very young mine soils

SummaryA number of biochemical parameters reflecting biological activity (respiration, ATP, enzyme activities) were determined in 0- to 7-year-old lignite mine soils. C (as CO2) and ATP contents and hydrolytic enzyme activities all increased with soil age. The kinetics of CO2 release showed that both labile and recalcitrant C-bearing substrates were mineralized, the mineralization constant of C decreased with soil age, but were always greater than those of native soils. The percentage of N mineralization, which tended to decrease with soil age, resulted in all cases in a predominance of ammoniacal forms. These findings suggest that since organic C and N accumulated with age in these soils, the C and N cycle is established progressively.

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.

EARLY STAGES OF LIGNITE MINE SOIL GENESIS : CHANGES IN BIOCHEMICAL PROPERTIES

Abstract The evolution of N and P forms, C and phosphatase activity was studied in mine soils from a lignite mine in Galicia (N.W. Spain) from 1 to 3 yr after seeding. Total C and N contents, humus-associated N and humin N increased with soil age. Acid hydrolysis indicated an accumulation of amino acid N and unknown N fractions. All organic P fractions increased slightly. As the soil aged, the behaviour of phosphatase activity changed considerably as regards pH-dependence and kinetic and thermodynamic parameters. The data show that considerable humiliation took place in the 3 yr of pedogenesis, with some of the biochemical properties of the mine soils becoming similar to those found in the native soils of the area. Possible reasons for this rapid evolution are the characteristics of the parent material, intense rhizosphere activity and the climatic conditions of the area.

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.

Humification processes in reclaimed open-cast lignite mine soils

Abstract To identify the principal humification pathways which occur during the initial stages of pedogenesis, organic matter from mine soils of different ages from the Meirama lignite mine in NW Spain was subjected to a series of physicochemical and chemical fractionations. Although humic molecules of molecular weight lower than 10,000 Da were always predominant, the percentage of C associated with molecules of between 50,000 and 200,000 Da increased with soil age, as did the percentage of chemically stabilized humus and the percentage of C associated with immobile complexes. In general, our results suggest that the principal humification pathway in these soils involves abiotic condensation reactions, as in the case of natural soils of this region. The low complexed metal content of the mine soils in comparison with natural soils indicates the low degree of weathering of inorganic fraction which has occurred in the former.