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

Global dataset of soil organic carbon in tidal marshes.

Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organic carbon (MarSOC) from 99 studies that includes location, soil depth, site name, dry bulk density, SOC, and/or soil organic matter (SOM). The MarSOC dataset includes 17,454 data points from 2,329 unique locations, and 29 countries. We generated a general transfer function for the conversion of SOM to SOC. Using this data we estimated a median (± median absolute deviation) value of 79.2 ± 38.1 Mg SOC ha-1 in the top 30 cm and 231 ± 134 Mg SOC ha-1 in the top 1 m of tidal marsh soils globally. This data can serve as a basis for future work, and may contribute to incorporation of tidal marsh ecosystems into climate change mitigation and adaptation strategies and policies

Temperature sensitivity of soil enzymes along an elevation gradient in the Peruvian Andes

Soil enzymes are catalysts of organic matter depolymerisation, which is of critical importance for ecosystem carbon (C) cycling. Better understanding of the sensitivity of enzymes to temperature will enable improved predictions of climate change impacts on soil C stocks. These impacts may be especially large in tropical montane forests, which contain large amounts of soil C. We determined the temperature sensitivity (Q 10) of a range of hydrolytic and oxidative enzymes involved in organic matter cycling from soils along a 1900 m elevation gradient (a 10 °C mean annual temperature gradient) of tropical montane forest in the Peruvian Andes. We investigated whether the activity (V max) of selected enzymes: (i) exhibited a Q 10 that varied with elevation and/or soil properties; and (ii) varied among enzymes and according to the complexity of the target substrate for C-degrading enzymes. The Q 10 of V max for β-glucosidase and β-xylanase increased with increasing elevation and declining mean annual temperature. For all other enzymes, including cellobiohydrolase, N-acetyl β-glucosaminidase and phosphomonoesterase, the Q 10 of V max did not vary linearly with elevation. Hydrolytic enzymes that degrade more complex C compounds had a greater Q 10 of V max, but this pattern did not apply to oxidative enzymes because phenol oxidase had the lowest Q 10 value of all enzymes studied here. Our findings suggest that regional differences in the temperature sensitivities of different enzyme classes may influence the terrestrial C cycle under future climate warming

Global dataset of soil organic carbon in tidal marshes

Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organic carbon (MarSOC) from 99 studies that includes location, soil depth, site name, dry bulk density, SOC, and/or soil organic matter (SOM). The MarSOC dataset includes 17,454 data points from 2,329 unique locations, and 29 countries. We generated a general transfer function for the conversion of SOM to SOC. Using this data we estimated a median (± median absolute deviation) value of 79.2 ± 38.1 Mg SOC ha−1 in the top 30 cm and 231 ± 134 Mg SOC ha−1 in the top 1 m of tidal marsh soils globally. This data can serve as a basis for future work, and may contribute to incorporation of tidal marsh ecosystems into climate change mitigation and adaptation strategies and policies

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

The maintenance of soil quality is critical for ensuring the sustainability of the environment and the biosphere. Although soil biochemical properties are considered 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 in 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 mineralization, and the activities of the following enzymes: dehydrogenase, catalase, phosphodiesterase, phosphomonoesterase, casein-protease, BAA-protease, 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. On the contrary, 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.The present study was financed by the Spanish Ministry of Science and Technology, under Project No. BTE2001-0987. J. Paz-Ferreiro thanks the Spanish Ministry of Education for financial support (FPU programme).Peer reviewe

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

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.This research was financed by the Xunta de Galicia (Project No. XUGA 40003B94) and by the Spanish Ministerio de Ciencia y Tecnología (Project No. BTE 2001-0987).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

Variation throughout the year in different parameters associated with the risk of P loss in soils

En Difusse Phosphorus Loss (eds. Goswin Heckrath and Gitte H. Rubaek), págs. 353-355. The 5th International Phosphorus Workshop (IPW5). Department of Freshwater Ecology National Environmental Research Institute.Peer reviewe