Evaluating the character and preservation of DNA within allophane clusters in buried soils on Holocene tephras, northern New Zealand

Clay minerals possess sorptive capacities for organic and inorganic matter, including DNA (Lorenz and Wackernagel, 1994), and hence reduce the utilization and degradation of organic matter or DNA by microorganisms. Buried allophane-rich soils on tephras (volcanic-ash beds) on the North Island, dated using tephrochronology, provide a valuable paleobiological ‘laboratory’ for studying the preservation of ancient DNA (aDNA) (Haile et al., 2007). Allophane comprises Al-rich nanocrystalline spherules ~3.5-5 nm in diameter (Fig. 1) with extremely large surface areas (up to 1000 m2 g-1). Moreover, allophanic soils are strongly associated with organic matter (Parfitt, 2009), and so we hypothesize that allophane also plays an important role for DNA protection within such soils

Understanding soil nitrogen supply: organic matter quality and quantity

The soil organic matter (SOM) contents of organic and conventionally farmed soils were compared. Whilst the quantity of SOM was found to be similar with both systems, the quality of SOM differed in respect of higher amounts of N released by the organic soils under anaerobic incubation. This indicated a greater potential rate of mineralization and suggested that the inherent fertility of the organic soils had been improve

Ús i gestió del territori a la mediterrània: implicacions en la matèria orgànica del sòl

Land use and management in Mediterranean ecosystems: implications for soil organic matter. - In the Mediterranean basin, soils have been intensively used to supply food, raw materials and energy. Here we aim to interpret the current status of Mediterranean soils by considering their long history of human use. Mediterranean soils are characterized by their poverty of organic matter and frequent carbonate content. Classical studies indicate that carbonates may favor the retention of soil organic matter. As historic soil data is lacking, we have focused on studying the distribution of organic matter across contrasting land uses. We have seen that soil organic matter poverty mainly affects agricultural soils and pastures (mostly shrublands and grassy swards). In contrast, soil organic matter content in forest soils is very rich, especially in the case of carbonatic soils. However, high levels of organic matter in carbonatic soils are not found in arable or pasture soils. Moreover, pastures contain soil organic matter levels very similar to those of arable soils, particularly in carbonatic soils. In Mediterranean lands the lack of soil structure and the presence of carbonates may jeopardize soil aggradation after the cessation of agricultural practices. In this context soil protection strategies should be adapted to Mediterranean ecosystems in order to better withstand climate change

Organic and conservation agriculture, the best of both worlds?

In millions of years huge amounts of organic matter were stored in the soil as organic matter or fossil energy carriers as oil, gas and coal. We make use of these stocks to supply us with energy and to be able to grow plants for our needs. However what has been stored in our soils for millions of years we now are depleting in a few hundred years. The amount of organic matter we return back to the soil is in general too low to maintain its capacity for plant production on the long term. Various studies show there is a decrease of organic matter in arable soils all over the world

Soil Air-Water Properties in Catena of Sepopol Lowland

In the sequence of soil composed of black earths, deluvial soils, organic soils covered with a thin layer of mineral-organic deposit and moorsh soils, soil texture, bulk density, content of organic carbon and organic matter, total porosity, total and readily available water as well as resources of organic matter and water in 0-25 cm and 0-100 cm layers of the soil profile were studied. A catenal variabilities of organic matter content and physical-water properties were found. Physical properties and the contents of total and readily available water depended on soil texture, organic matter content and location in a relief. Total porosity, field water capacity and volume of macropores were positively correlated with organic matter content, and negatively with bulk density. Differences in studied properties between the pedons of black earths and deluvial soils were small, whereas these differences between deluvial and moorsh soils were distinct. In the development of water resources in the profiles of these soils, presence of organic subsoil with high retention capacity played the important role. The studied soils had unfavorable distribution of soil pores, resulting from a small volume of air pores

Organic farming effects on clay dispersion in carbon-exhausted soils

Many Danish soils are depleted in organic matter (OM) after decades of intensive cereal cultivation (Schjønning et al., 2009). In this paper we show that clay particles (colloids) in soils that are low in OM content are easily dispersed in the soil water, which in turn has important effects on soil ecosystem functions and services. Organic farming systems generally tend to increase soil OM contents and may thus mitigate the negative effects

Predicting nitrogen mineralization from soil organic matter - a chimera?

Predicting nitrogen (N) mineralization from soil organic matter is difficult because N mineralization is affected by several environmental factors, while being the net outcome of concurrent N processes that produce and consume mineral N. One aim of the present thesis was to study the effects of freezing and thawing on carbon (C) and N mineralization. A second aim was to elucidate if, and how, the quantity and quality of organic matter inputs affect N mineralization from the pool of soil organic matter. C and net N mineralization were determined in soils from the Ultuna Long-Term Soil Organic Matter Experiment exposed to repeated freezing and thawing (temperatures ranging from –5 °C to +5 °C). C, gross and net N mineralization in relation to quantity and quality of organic matter inputs were determined during long-term laboratory incubations at 20 °C. Gross N mineralization rates were estimated using the 15N isotope dilution technique, which is based on several assumptions. The assumption of ‘equilibrium between added and native N’ was tested by using a published data set in a dynamic compartmental model. Freezing and thawing of soils resulted in a flush in C and N mineralization, but the effect was only short-lived. It was concluded that freezing and thawing of soils during late winter and early spring is unlikely to be of importance to crop N availability in spring. Both quantity and quality of organic matter were major determinants of C and gross N mineralization, and these were proportional suggesting that C mineralization may be used as a predictor for gross N mineralization. Preferential use of added N may be a more common occurrence in 15N isotope dilution studies than hitherto thought and the assumption of ‘equilibrium between added and native N’ needs therefore critical evaluation. The data analysis presented in this thesis offers a way to estimate the potential effects of preferential use on gross N mineralization rate estimates. This thesis indicates that studies based on the mechanisms underlying N processes may improve our understanding of the relation between soil organic matter and N mineralization. Further mechanistic studies should therefore be considered in future N research

Long-term Effects of Tillage on the Retention and Transport of Soil Water

Quantitative measurements were made of the physical and chemical properties of two virgin prairie soils, Crowley and Jay, that remain in their native Arkansas environments and of similar soils that had been tilled extensively. Comparisons were made of soil properties at several depths. When compared with the tilled soils the virgin soils had higher organic matter contents, saturated hydraulic conductivities and water retained at several applied pressures. Bulk densities and hydraulic resistances were lower in the virgin soils. For the Crowley silt loam, values of pH and elemental contents of the virgin soil were higher than those of the tilled soil. Determinations also were made of the effects of a 14-year addition of winter cover crops on a Dubbs-Dundee soil in continuous cotton production. In general, the winter cover crops tended to increase hydraulic conductivity~. ·porosity and organic matter content. These results indicated that the detrimental effects of long-term tillage on soil hydraulic properties could partially be overcome with the planting of these crops during the winter. However, the rate of improvement in the hydraulic properties was not dramatic

Potential energetic return on investment positively correlated with overall soil microbial activity

Microbial communities are a critical component of the soil carbon (C) cycle as they are responsible for the decomposition of both organic inputs from plants and of soil organic C. However, there is still no consensus about how to explicitly represent their role in terrestrial C cycling. The objective of the study was to determine how the molecular and energetic properties of readily available organic matter affect the metabolic activity of the resident microbial communities in soils. This was achieved by cross-amending six soils, taken from woodland and grassland sites along an urban pressure gradient, with organic matter extracted from the same six soils and measuring heat dissipated due to the increase in microbial metabolic activity. The energetic properties of the organic matter were used to estimate a potential energetic return on investment (ROI) that microbial communities could obtain from the transformation of the organic matter. Specifically, the ROI was calculated as the ratio between the total net energy available (ΔE) and the weighted average standard state Gibbs energies of oxidation half reactions of organic C (ΔG°Cox). ΔE was measured as the heat of combustion using bomb calorimetry. ΔG°Cox was estimated using the average nominal oxidation state of C (NOSC) of the molecular species in the organic matter. The overall metabolic activity of microbial communities was positively related to the potential energetic return on investment but no significant relationship was found with the molecular diversity of organic matter. The temporal differences in metabolism across soils indicate that bacterial communities do not exploit the potential energetic return on investment in the same way: the suburban grassland communities responded more rapidly and the suburban woodland communities more slowly to the organic matter additions than the other communities. The urban gradient did not affect the properties of the molecular or energetic properties of the organic matter nor the response of the microbial communities to the organic matter additions. However, the organic matter from the grassland soils caused soils to dissipate 36.4% more heat than organic matter from the woodland soils. The metabolic response was also more rapid after the addition of grassland organic matter: the time taken for half the heat to be dissipated was 6.4 h after the addition of grassland organic matter and 6.1 h after the addition of woodland organic matter. Overall, our results suggest that microbial communities preferentially use organic matter with a high potential energetic return on investment, i.e. organic molecules that do not require high cost associated with catalysis whilst yielding a high net energetic benefit