Thermodynamic parameters of enzymes in grassland soils from Galicia, NW Spain.

39: 311-319.The thermodynamic parameters of the enzymes catalase, dehydrogenase, casein-protease, a-N-benzoyl-L-argininamide (BAA)- protease, urease, Carboxymethyl (CM)-cellulase, invertase, b-glucosidase and arylsulphatase, were investigated in grassland soils from a European temperate-humid zone (Galicia, NW Spain). The effect of temperature on enzyme activity was determined at 5, 18, 27, 37, 57 and 70 1C. The temperature-dependence of the rate of substrate hydrolysis varied depending on the enzyme and soil. In general, the soil containing the least amount of organic matter (OM) showed the lowest enzyme activity for all temperatures and enzymes, whereas soils with similar OM contents showed similar levels of activity for the entire temperature range. Temperature had a noteworthy effect on the activity of oxidoreductases. Product formation in the reaction catalyzed by dehydrogenase increased with increasing temperature until 70 1C, which was attributed to chemical reduction of iodonitrotetrazolium violet (INT) at high temperatures. Catalase activity was not affected above 37 1C, which may be explained either by non-enzymatic decomposition of hydrogen peroxide or by the fact that catalase has reached kinetic perfection, and is therefore not saturated with substrate. The Arrhenius equation was used to determine the activation energy (Ea) and the temperature coefficient (Q10) for all enzymes. The values of Ea and Q10 for each enzyme differed among soils, although in general the differences were small, especially for those enzymes that act on substrates of low molecular weight. In terms of the values of Ea and Q10 and the differences established among soils, the results obtained for those enzymes that act on substrates of high molecular weight differed most from those corresponding to the other enzymes. Thus the lowest Ea and Q10 values corresponded to BAA-protease, and the highest values to CM-cellulase and casein-protease. Except for catalase in one of the soils, the values of Ea and Q10 for the oxidoreductases were similar to those of most of the hydrolases. In general, the effect of temperature appeared to be more dependent on the type of enzyme than on the characteristics of the soil. r 2006 Elsevier Ltd. All rights reserved.Peer reviewe

Hydrolitic enzyme activities in agricultural and forest soils. Some implications for their use as indicators of soil quality.

40: 2146-2155.Although a great deal of information exists about the effect of land use on soil enzyme activities, much of this is contradictory and brings into question the suitability of soil enzyme activities as indicators of how land use affects soil quality. The purpose of this study was to investigate the effect of land use on different soil biochemical properties, especially hydrolytic enzyme activities, with the aim of providing knowledge about the problems related to the use of enzymes as indicators of soil quality. The data presented derive from various studies in which a large number of soils under different types of forest or agricultural management were analysed by the same methods. All of the soil samples were characterized in terms of their main physical and chemical properties, the activity of several hydrolases, microbial biomass C and soil basal respiration. The results indicate that soil use causes a large reduction in organic matter content and that the effect on enzyme activity varies depending on the type of land use or management and the type of enzyme. Furthermore, the enzyme activities per carbon unit (specific activities) in soils affected by land use are almost always higher than in maximum quality soils (climax soils under oak vegetation or oak soils), and land use also generates greater increases in the specific activity as the C content decreases. The mechanism responsible for these increases probably involves loss of the most labile organic matter. Enzyme enrichment is not always produced to the same degree, as it varies as a function of the enzyme and the type of land use under consideration. It is concluded that the complexity of the behaviour of the soil enzymes raises doubts about the use of enzyme activities as indicators of soil degradation brought about by land use.Peer reviewe

Effect of soil use on the composition of circulating water: the Fonte Espiño river basin (Galicia, NW Spain).

En Difusse Phosphorus Loss (eds. Goswin Heckrath and Gitte H. Rubaek), págs. 397-399.Peer reviewe

Evaluation of C Stocks in Afforested High Quality Agricultural Land

18 páginas, 3 figuras, 7 tablasAfforestation of marginal land has been recommended by the Intergovernmental Panel on Climate Change (IPCC) as a means of enhancing the capacity of soil to act as a carbon (C) sink. However, the success of this practice is variable and depends on many factors, including the type of land management used. In this study, we quantified and compared the C stocks in two highly productive agricultural soils afforested with poplar 10 years before the study and in adjacent soils still used for agricultural purposes. One of the agricultural soils was sown with grass and maize in a crop rotation system and the other was alternately sown with maize (6 months) and left fallow (6 months). In all soils, we estimated the C pools associated with the live biomass (including the C extracted by harvesting in the cropped soils in the 10 years since afforestation), dead biomass, amount of fertiliser added (quantifying all inputs of C added as fertiliser in the cropped soils since the start of afforestation) and the soil organic matter (0–100 cm), to enable estimation of the total C stocks in the ecosystem. Afforestation had different effects on the various C pools. Thus, although afforestation enhanced the C sink capacity of the ecosystem when carried out on agricultural land, the degree to which this occurred varied according to previous land use. The increase in C stocks that occurred from afforestation was lower in the plots employing maize-grass rotation, compared to those with maize-fallow rotation. The ecosystem C balance was quite similar in both afforested plots (247.4 and 233.0 Mg C ha−1), while it was quite different in the cultivated plots (182.3 Mg C ha−1 in Laraño; 73.9 Mg C ha−1 in A Barca). Although at both sites the C balance was higher in the afforested plot than in the cultivated plot, the differences were much smaller in Laraño (65.1 Mg C ha−1 higher in the forested plot than in the cultivated plot) than in A Barca (159.1 Mg C ha−1 higher in the forested plot than in the cultivated plot). Our results from highly productive agricultural land are similar to previous findings on marginal land.This research was funded by the Spanish MICINN (Project No. CGL2008-01992/BTE) co-financed with ERDF funds from the EU and by the Xunta de Galicia through the RCG project IN607A 2021-06 and the Contrato-Programa CSIC-Xunta 2021–2022.Peer reviewe

Modifications of organic matter and enzymatic activities in response to change in soil use in semi-arid mountain ecosystems (southern Spain)

Soil organic matter composition and biochemical properties were determined in mountain calcimorphic Mediterranean soils under different vegetation (cultivated soils, secondary bush, high mountain bush, juniper, evergreen oak and pine) to assess the impact of soil use on the size and activity of microbial communities. Our results indicated that clearing forest leads to a general decline in the performance of soil organic carbon sequestration and associated enzymatic activities. However, when soil enzymatic activities (dehydrogenase, catalase, phosphodiesterase, β-glucosidase, urease and casein-protease) were expressed as ratios to total organic carbon (specific activities), a conspicuous increase in their activities was observed in cleared soils as compared with forest soils, suggesting enhanced hydrolytic potential in the former. In addition, the negative correlation observed between qCO 2 (metabolic quotient) and water retention at -1500 kPa, could be interpreted as an adaptive strategy against low soil moisture by microbial communities in cleared soils. This indicates the importance of describing soil quality in terms of long-term soil organic C sequestration and/or resistance of the organic matter to microbial transformation. These features were reflected in the visible and infrared spectra of humic acids, which suggested humification mechanisms involving mainly an alteration of plant macromolecules with poor incorporation of characteristic microbial metabolites in the forest soils whereas the opposite effect was observed in cleared soils. © 2012 The Authors. Journal compilation © 2012 British Society of Soil Science

Impacto do manejo de resíduos orgânicos durante a reforma de plantios de eucalipto sobre indicadores de qualidade do solo Impact of organic residue management on soil quality indicators during replanting of eucalypt stands

O uso agrícola do solo causa alterações em suas características físicas, químicas e microbiológicas. A conseqüência dessas alterações pode ser a perda da qualidade do solo, o que compromete a sustentabilidade do uso desse recurso. A análise de indicadores bioquímicos e microbiológicos de qualidade do solo é relevante para monitorar mudanças na qualidade do solo e no desempenho de suas funções-chave, como a capacidade de ciclar e armazenar nutrientes. Neste estudo, avaliaram-se indicadores químicos, físicos e microbiológicos do solo em plantios de eucalipto 5,5 anos após terem sido submetidos a diferentes métodos de manejo durante a fase de reforma do povoamento. A avaliação baseou-se na determinação de 18 atributos físicos e químicos, além de 12 outros de caráter bioquímico ou microbiológico, os quais foram adotados como indicadores da qualidade do solo. Os indicadores bioquímicos e microbiológicos mostraram-se mais sensíveis para avaliar mudanças qualitativas no solo devidas ao manejo, quando comparados com os químicos ou físicos. O maior distúrbio causado pelos tratamentos em que houve remoção ou queima do material orgânico da superfície do solo foi evidenciado pelos maiores valores de qCO2 e menores valores de qMIC na camada superior do solo (0 a 5 cm). A análise de componentes principais permitiu visualizar as semelhanças entre as áreas com base em todas as variáveis analisadas. A área de vegetação natural de mata secundária, usada como referência de qualidade do solo, foi a que apresentou a maior distância gráfica das demais áreas, demonstrando que a introdução da monocultura do eucalipto modifica a qualidade do solo estudado. A qualidade do solo da área de eucalipto onde não se efetuou o corte das árvores no primeiro ciclo (povoamento com 11 anos de idade) obteve a maior aproximação da área de vegetação natural, seguindo-se os solos sob eucalipto submetido a manejos que priorizaram a conservação dos resíduos orgânicos por ocasião da reforma do povoamento. Contrariamente, as áreas onde ocorreu a remoção ou a queima do material orgânico da superfície do solo foram as que mais se distanciaram da área de referência. Esses resultados demonstram que o sistema de manejo adotado na reforma dos povoamentos de eucalipto analisados influencia, em médio prazo, o potencial dos solos de estocar e ciclar nutrientes por meio da biomassa microbiana e das atividades bioquímicas ligadas a ela. A maior aproximação entre a área com vegetação nativa e a de eucalipto com 11 anos leva a supor que ciclos mais longos nas florestas de eucalipto, contrastando com o padrão atualmente em uso no Brasil (cerca de sete anos), pode ser relevante para se manter a sustentabilidade da atividade florestal em longo prazo, a despeito de uma menor produtividade média anual. Nesse caso, a opção pela produtividade de curto ou médio prazo, ou pela sustentabilidade do uso do solo, com a conseqüente manutenção da sua qualidade para as gerações futuras, poderá ser repensada a partir dos dados aqui apresentados.<br>Agricultural soil use induces changes in soil physical, chemical, and microbiological characteristics. These changes can eventually lead to a loss of soil quality and a consequent reduction in plant growth and productivity. The analysis of biochemical and microbiological soil quality indicators is relevant to monitor changes in soil quality and in the performance of key soil functions, such as the capacity of nutrient cycling and storage. This study reports on physical, chemical, and biochemical/microbiological quality indicators of soil under eucalyptus plantation, evaluated 5.5 years after the site had undergone different management practices during stand replanting. Evaluations were based on the determination of 18 physical or chemical besides 12 biochemical or microbiological attributes that are considered soil quality indicators. The microbiological and biochemical attributes proved more adequate than the chemical or physical indicators to detect soil quality changes due to management. The greatest disturbance caused by the removal or burning of organic material on the soil surface was evidenced by the higher qCO2 and lower qMIC in the upper soil layer (0 to 5 cm). The principal component analysis underlying the graphical representation demonstrated that soil under secondary forest, taken as reference for soil quality, was very distant from that under eucalyptus, demonstrating that the introduction of eucalyptus monoculture causes significant changes in soil quality. The soil quality of a eucalyptus stand left unharvested after the first normal seven years cycle (11 year-old stand) was the closest to the area with native forest, followed by the soils under eucalyptus subjected to management systems that prioritized organic residue conservation during stand replanting. Contrarily, areas from which the organic material at the soil surface was removed or burned appeared very distant from the reference area. Our results show that the management system adopted during eucalyptus stand replanting influenced, in the medium term, the potential of soils to store and cycle nutrients via microbial biomass and associated biochemical activities. The fact that the 11 years old eucalyptus stand was closest to the reference area may suggest that the adoption of longer cycles for eucalyptus plantations, contrasting with the actual model of short rotation eucalyptus forests in Brazil (about seven years), is relevant to maintain soil sustainability for eucalyptus production in the long run, in spite of the lower mean annual productivity. In this case, the option for a higher productivity in the short and medium term, or for the sustainability of soil use, with the consequent maintenance of its quality for the future generations, should be reevaluated from the data presented here