Seasonal variation in soluble soil carbon and nitrogen across a grassland productivity gradient

Understanding the fate and turnover of the pools that comprise dissolved organic nitrogen (DON) in soil is key to determining its role in ecosystem functioning. We investigated seasonal changes of dissolved organic carbon (DOC) and nitrogen (DON) concentrations within four molecular weight (MW) size fractions across an altitudinal gradient (from lowland to montane systems), and quantified individual amino acids and amino acid constituents of oligopeptidic-N, as well as nitrate and ammonium. We tested two ideas: first, that DON is more abundant than DIN in low-productivity relative to high-productivity grassland ecosystems; and second, that the abundance of peptides and amino acids is likewise greater in low- than high-productivity grassland. The most productive site had a history of inorganic fertiliser application, and hence in this site alone DIN was more abundant than DON. Plant productivity varied 3-fold between the other sites, and DON was generally at higher concentrations in the sites of lower productivity both in absolute terms as well as relative to DIN, with a large increase observed in spring. The fraction containing the highest concentration of the DON had a MW of >100 kDa, and in summer and autumn this fraction was more abundant at the lowest productivity site. We conclude that relationships between the abundance of DON relative to DIN and ecosystem productivity is dependent on season, and hence more complex than previously suggested, and that peptides are a dynamic and potentially nutritionally significant component of DON.     

Using neighbourhood statistics and GIS to quantify and visualize spatial variation in geochemical variables: An example using Ni concentrations in the topsoils of Northern Ireland

Spatial variation is a typical feature of geochemical variables, providing a challenge for sampling design and environmental monitoring. It is generally qualitatively but not quantitatively described using spatial distribution maps. In this study, the feasibility of quantifying spatial variation is investigated using neighbourhood statistics within a GIS environment, using, as an example, near-total Ni concentrations in the surface soils of Northern Ireland. A total of 6138 topsoil samples were collected at an average sampling density close to 1 sample per km². At this sampling density it was possible to calculate neighbourhood statistics directly from the raw data. Neighbourhood statistics of local mean, local standard deviation and local coefficient of variation were calculated using window sizes of 3 km × 3 km, 6 km × 6 km, 9 km × 9 km, 12 km × 12 km, 24 km × 24 km and 48 km × 48 km and visualized using GIS mapping techniques. The results showed that the highest soil Ni concentrations were located in the northern part of Northern Ireland where basalt is the main rock type. Lowest soil Ni concentrations were found in the western region of the Province on schist and limestone geologies. The granite area in the south-eastern region of Northern Ireland also displayed low soil Ni values. In terms of assessing the degree of spatial variation, high local standard deviation values were found to be associated with high local mean values thereby limiting the usefulness of local standard deviation as an indicator of spatial variation. This effect did not occur when local coefficient of variation values were used in place of local standard deviation so the coefficient of variation values are recommended as a more appropriate indicator to quantify spatial variation. The strongest spatial variations were observed on the western edge of the basalt area along the boundary of the basalt–sandstone areas and the schist area. Within each rock type, spatial variations were relatively weak and this was most clearly demonstrated in the basalt area. As the window size used for calculation of neighbourhood statistics was increased, so too was the resulting smoothing effect which led to clearer patterns but with loss of detail in the spatial variation observed. Neighbourhood statistics, coupled to a GIS, were found to be an effective way of quantifying and visualizing spatial variation in environmental geochemistry.     

Bioavailability of hydrophobic organic contaminants in soils: fundamental concepts and techniques for analysis

Soils represent a major sink for organic xenobiotic contaminants in the environment. The degree to which organic chemicals are retained within the soil is controlled by soil properties, such as organic matter, and the physico‐chemical properties of the contaminant. Chemicals which display hydrophobic and lipophilic characteristics, as well as a recalcitrant chemical structure, will be retained within the soil, and depending on the ‘strength’ of the association may persist for long periods of time. This review describes the behaviour of hydrophobic organic contaminants in soils, focusing on the mechanisms controlling interactions between soil and contaminants. The bioavailability of contaminants in soil is also discussed, particularly in relation to contact time with the soil. It considers the degradation of organic contaminants in soil and the mechanisms microbes use to access contaminants. Finally, the review discusses the ‘pros’ and ‘cons’ of chemical and biological techniques available for assessing bioavailability of hydrophobic organic chemicals in soils, highlighting the need to quantify bioavailability by chemical techniques. It concludes by highlighting the need for understanding the interactions between the soil, contaminants and biota which is crucial to understanding the bioavailability of contaminants in soils.     

Nitrogen fixation by free-living heterotrophic bacteria in an oak forest: The effect of liming

Nitrogen-fixing heterotrophic bacteria, mainly Clostridium butyricum and, less frequently, Enterobacter agglomerons and Klebsiella pneumoniae, are found throughout the aerial and soil layers of an oak forest. However they are only active in nitrogen fixation in the soil. Soil slurry experiments show that the main factors limiting N₂ fixation in the forest are low temperature, low pH and shortage of C sources. Raising the pH of the soil with lime to pH 6, which is the optimum for N₂ fixation by C. butyricum in soil slurries, more than doubles the rate of N₂ fixation (as measured by in situ¹⁵N₂ methods) from 7.84 to 16.1 kg N ha^?1yr^?1. The N fixed by C. butyricum can rapidly be taken up by oak seedlings and translocated to the actively-growing leaves.     

Relating microarthropod community structure and diversity to soil fertility manipulations in temperate grassland

We aimed to identify patterns of diversity in a below-ground community of microarthropods (mites and Collembola) after 15 months of a nutrient (calcium and nitrogen) manipulation experiment, located at the Natural Environment Research Council (NERC) Soil Biodiversity Site in Scotland, UK. We found that microarthropod densities increased with elevated soil fertility, but we detected no concurrent change in the diversity of soil microarthropods (mites and Collembola combined). That microarthropod density increased concurrently with improvements in soil fertility and plant productivity suggests that soil microarthropod communities are predominately regulated by bottom-up forces, driven by increased energy transfer via plant inputs to soil, providing increased food resources for fauna. However, that we found no concurrent change in the diversity of soil microarthropods provides little support for the idea that the diversity of soil fauna is positively related to their population density, primary productivity or improvements in soil conditions resulting from nutrient manipulations. However, we did find that microarthropod communities of more fertile sites contained a greater proportion of predators suggesting that more energy was transferred to higher trophic levels under elevated soil fertility. Our findings suggest that unlike plant communities, soil faunal diversity may not be strongly regulated by competition in productive situations, since competitive exclusion might not occur due to increased predation. Whilst we conclude that soil microarthropod diversity at our study site has not been affected by the nutrient additions to date, in the longer term we predict that changes in community composition and diversity could arise, most likely through top-down regulation of the soil food web.     

Fast-track applications: The potential for direct delivery of proteins and nucleic acids to plant cells for the discovery of gene function

In animal systems, several methods exist for the direct delivery of nucleic acids and proteins into cells for functional analysis. Until recently, these methods have not been applied to plant systems. Now, however, several preliminary reports suggest that both nucleic acids and proteins can also be delivered into plant cells by very simple, direct application. This promises to open the way for high-throughput screening for gene function in a range of plant species.     

Deep planting with shelters improves performance of different stocktype sizes under arid Mediterranean conditions

New Forests - Increasing plant size has been considered a way to improve survival and growth of planted containerized stock under dry conditions. Additionally, deep planting provides advantages to...     

Impact of coastal development on mangrove cover in Kilim river, Langkawi Island, Malaysia

We examined the impact of various coastal developments on mangrove cover along the Kilim River, Langkawi Island, Malaysia between 1996 and 2008. We analysed images from Systeme Probatoire d’Observation de la Tarre (SPOT) of Kilim River using supervised classification and Principal Component Analysis (PCA). Over 8% (176.83 ha) of mangrove cover was degraded along the Kilim River from its total area of 2153.07 ha during the past 14 years. We identified several causes of mangrove degradation, including mangrove clearing (38%), mangrove conversion to commercial area (21%), residential area (19%), agriculture (12%), aquaculture (12%) and wake current (6%). Langkawi is one of the main tourism islands in Malaysia. Tthe pace of coastal development throughout the entire island including Kilim River had suppressed the mangroves propagation over the years. Long term monitoring of mangrove ecosystems is essentials to ensure the survival and sustainability of mangrove associated biodiversity.     

Reliability of drip irrigation systems under different operation conditions in Poland

Present crop production in Poland depends on climatic, hydrologic, pedologic, social and economic conditions. Drip irrigation systems will play a significant role in the future by fulfilling the requirements of intensive, energy-saving agricultural production. The total area under micro-irrigation in Poland is estimated to be approximately 3000 ha. Drip irrigation is currently applied mainly in orchards, vegetable farms and greenhouses. The investigations of drip irrigation have shown a high influence of the operating conditions on the reliability and productivity effects of the irrigation system. This paper contains the results of the investigations on the reliability of drip irrigation systems under different operation conditions such as system components, crops, water quality, fertigation and irrigation technology.     

Potential use of rare earth oxides as tracers of organic matter in grassland

Tracing organic matter (OM) in soil is challenging, because runoff and leaching processes are interrelated and have multiple sources. Therefore, multiple tracers with low background concentrations such as rare earth element oxides (REOs) are necessary to delineate the origin of sources of the organic materials in groundwater, rivers or in catchments. The main objective of this study was to examine the potential use of REOs as a tracer in various forms of OM (1) whole slurry, (2) solid, and (3) liquid phase of cattle slurry after mechanical separation. A laboratory experiment was carried out using five REOs (La, Gd, Sm, Pr, and Nd oxides) mixed directly into soil or mixed with various fractions of cattle slurry and then applied to the soil surface. In the additional grassland experiment, Gd oxide was spiked with soil and cattle slurry and then applied to the soil surface. The mineral N in the liquid phase (urine) of the slurry in the grassland experiment was labelled with ¹⁵N urea (16 atom%). In the laboratory experiment, results showed that the five REOs concentration of soil in 0–1 cm soil section after the rainfall simulation was still up to 20 times more than the background values. In 1–2 cm soil section, the concentration of only Gd (two fold higher) and La oxides (50% higher) were significantly higher than the soil background values. Therefore, we hypothesized that Gd and La oxides were associated also with relatively finer organic particles in slurry, thus 1–2 cm soil section were enriched with these oxides. The five REOs concentration below 2 cm soil depth were similar to the background values in all treatments. In line with the laboratory experiment, Gd concentrations in the deeper soil layers (2–4 and 4–8 cm) in the grassland experiment were not significantly affected by any treatment. Both in grassland and laboratory experiment, solid phase of the slurry (dung) was collected from the soil surface after rainfall simulation. Here, about 56% of REOs were measured on the solid phase of the slurry which indicates the strong binding potential of REOs on slurry OM. The present novel study, where REO tagged slurry was uniquely tested to study geochemical cycle of organic fertilizers, clearly highlighted the potential for their use as multiple‐tracers of (animal derived‐) OM in agricultural soils.