From N2 fixation to N2O emission in a grass-clover mixture

In organic dairy farming, a major N input to the plant-soil system comes from biological N2 fixation by pasture legumes, but knowledge is sparse on how much of the fixed N2 is lost from the pastures as N2O. Nitrifying and denitrifying bacteria are the main contributors to the N2O production in soils. Currently, no contribution from biological N2 fixation in legume pastures is included in the national N2O inventories, partly because of uncertainties in quantifying the N2 fixation in the pastures (Mosier et al., 1998). According to the guidelines issued by The Intergovernmental Panel on Climate Change (IPCC), inventories for N2O emissions from agricultural soils should be based on the assumption that 1.25 % of added N is emitted as N2O (IPCC, 1997). The standard N2O emission factor of 1.25 % could be considerably unrepresentative for biologically fixed N2. Firstly, only a part of the fixed N is mineralised during the lifetime of the crop. Secondly, the release of inorganic N into the soil occurs slowly. A 15N2-tracer-experiment was initiated on grass-clover grown in pots. The aim was to assess: · the contribution of recently fixed N2 as a source of N2O · the translocation of N from clover to companion grass References IPCC, 1997. Greenhouse gas inventory. Reference manual. Vol. 3. Intergovernmental Panel on Climate Change. Bracknell, UK. Mosier, A. et al. 1998. Nutrient Cycling in Agroecosystems 52, 225-248

N2O emission from grass-clover swards is largely unaffected by recently fixed N2

The contribution of biologically fixed dinitrogen (N2) to the nitrous oxide (N2O) production in grasslands is unknown. To assess the contribution of recently fixed N2 as a source of N2O and the transfer of fixed N from clover to companion grass, mixtures of white clover and perennial ryegrass were incubated for 14 days in a 15N2-enriched atmosphere (0.4 atom% excess). Immediately after labelling, half of the grass-clover pots were sampled for N2 fixation determination, whereas the remaining half were examined for emission of 15N labelled N2O for another eight days using a static chamber method. Biological N2 fixation measured in grass-clover shoots and roots as well as in soil constituted 342, 38 and 67 mg N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. The drop in N2 fixation was most likely due to a severe aphid attack on the clover component. Transfer of recently fixed N from clover to companion grass was detected at 26 and 36 weeks after emergence and amounted to 0.7 ± 0.1 mg N m-2 d-1, which represented 1.7 ± 0.3 % of the N accumulated in grass shoots during the labelling period. Total N2O emission was 91, 416 and 259 μg N2O-N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. Only 3.2 ± 0.5 ppm of the recently fixed N2 was emitted as N2O on a daily basis, thus recently fixed N released via easily degradable clover residues appears to be a minor source of N2O

Production of N2O in grass-clover pastures

In organic as well as conventional dairy farming, grass-clover pastures is an important component of the cropping system. This is because grass-clover is an excellent cattle fodder, and because clover has the ability of fixing atmospheric N2. When budgets for N2O emissions are made accord-ing to the IPCC guidelines it is assumed that 1.25 % of added nitrogen is emitted as N2O. This emission factor is used for all nitrogen inputs although the factor relies on experiments with fertilizer and manure, only. The emission factor for biological fixed nitrogen may be lower than 1.25 %, because nitrogen is released only slowly into the soil. However knowledge is very sparse. On the other hand, when the effect of grazing cattle is added the situation might be different. In Denmark organic cattle are supposed to be on grazing fields for at least 150 days a year. Nitrogen returned to the system in urine and dung is likely to locally exceed the needs of the plants and is therefore at risk of being lost as N2O. Thus far, however, there have only been a few detailed estimates of total N2O emissions from grassland livestock productions, and understanding of the factors controlling N2O emissions remains unsatisfactory

From N2 fixation to N2O emission in a grass-clover pasture

In organic dairy farming, a major N input to the plant-soil system comes from biological N2 fixation by pasture legumes, but knowledge is sparse on how much of the fixed N2 is lost from the pastures as N2O. Nitrifying and denitrifying bacteria are the main contributors to the N2O production in soils. Currently, no contribution from biological N2 fixation in legume pastures is included in the national N2O inventories, partly because of uncertainties in quantifying the N2 fixation in the pastures (Mosier et al., 1998). According to the guidelines issued by The Intergovernmental Panel on Climate Change (IPCC), inventories for N2O emissions from agricultural soils should be based on the assumption that 1.25 % of added N is emitted as N2O (IPCC, 1997). The standard N2O emission factor of 1.25 % could be considerably unrepresentative for biologically fixed N2. Firstly, only a part of the fixed N is mineralised during the lifetime of the crop. Secondly, the release of inorganic N into the soil occurs slowly. A 15N2-tracer-experiment was initiated on grass-clover grown in pots. The aim was to assess: * the contribution of recently fixed N2 as a source of N2O * the translocation of N from clover to companion grass References IPCC, 1997. Greenhouse gas inventory. Reference manual. Vol. 3. Intergovernmental Panel on Climate Change. Bracknell, UK. Mosier, A. et al. 1998. Nutrient Cycling in Agroecosystems 52, 225-248

Production of N2O in grass-clover pastures

In organic as well as conventional dairy farming, grass-clover pastures is an important component of the cropping system. This is because grass-clover is an excellent cattle fodder, and because clover has the ability of fixing atmospheric N2. When budgets for N2O emissions are made accord-ing to the IPCC guidelines it is assumed that 1.25 % of added nitrogen is emitted as N2O. This emission factor is used for all nitrogen inputs although the factor relies on experiments with fertilizer and manure, only. The emission factor for biological fixed nitrogen may be lower than 1.25 %, because nitrogen is released only slowly into the soil. However knowledge is very sparse. On the other hand, when the effect of grazing cattle is added the situation might be different. In Denmark organic cattle are supposed to be on grazing fields for at least 150 days a year. Nitrogen returned to the system in urine and dung is likely to locally exceed the needs of the plants and is therefore at risk of being lost as N2O. Thus far, however, there have only been a few detailed estimates of total N2O emissions from grassland livestock productions, and understanding of the factors controlling N2O emissions remains unsatisfactory

Massively parallel determination and modeling of endonuclease substrate specificity

We describe the identification and characterization of novel homing endonucleases using genome database mining to identify putative target sites, followed by high throughput activity screening in a bacterial selection system. We characterized the substrate specificity and kinetics of these endonucleases by monitoring DNA cleavage events with deep sequencing. The endonuclease specificities revealed by these experiments can be partially recapitulated using 3D structure-based computational models. Analysis of these models together with genome sequence data provide insights into how alternative endonuclease specificities were generated during natural evolution

Assessing Fish Communities and Habitat Dynamics at the North Platte River-Lake Mcconaughy Interface: Implications for Conservation and Management

The river-reservoir interface (RRI) provides dynamic habitat heterogeneity that influences fish communities within the reservoir and the tributary upstream. However, little is known about the North Platte River-Lake McConaughy interface. Thus, the objectives of this research were to: 1) describe fish assemblages in the North Platte River and relate their temporal differences to water quality and physical habitat parameters; and 2) compare young fish communities collected with different gears in the upper reservoir. Twenty-nine species were collected across four habitat types in the North Platte River above Lake McConaughy. Main and side channel habitats were more consistently available throughout the summer. Backwater habitats declined in abundance, and back eddies disappeared. Species richness and Shannon’s diversity were highest in backwaters. Fish communities were somewhat similar between the habitat types, but some species were more or less abundant in some habitats. Water quality did not differ between habitat types. However, discharge and water temperature appeared to influence community composition. In upper Lake McConaughy, I captured 21 taxa across four sampling gears. Fewer species were captured with the gears used in the earlier time period compared to the gears used later time period. Species richness, Shannon’s diversity, and relative abundance were highest for seines and lowest for tow nets. Boat-mounted electrofishing appeared to be the most efficient gear. Similarities were noted in fish communities between the two time periods, but abundance of individual species varied between time periods. This study provides updated and new information on fish communities in the North Platte River-Lake McConaughy system. Selecting the sampling gear or gears that best meet sampling objectives is important for understanding fish communities in RRIs. With such sampling information, fisheries managers may be able to identify water management strategies that provide habitats for fish communities in unique ecotones such as the RRI

Efficient Mutagenesis by Cas9 Protein-Mediated Oligonucleotide Insertion and Large-Scale Assessment of Single-Guide RNAs

The CRISPR/Cas9 system has been implemented in a variety of model organisms to mediate site-directed mutagenesis. A wide range of mutation rates has been reported, but at a limited number of genomic target sites. To uncover the rules that govern effective Cas9-mediated mutagenesis in zebrafish, we targeted over a hundred genomic loci for mutagenesis using a streamlined and cloning-free method. We generated mutations in 85% of target genes with mutation rates varying across several orders of magnitude, and identified sequence composition rules that influence mutagenesis. We increased rates of mutagenesis by implementing several novel approaches. The activities of poor or unsuccessful single-guide RNAs (sgRNAs) initiating with a 5′ adenine were improved by rescuing 5′ end homogeneity of the sgRNA. In some cases, direct injection of Cas9 protein/sgRNA complex further increased mutagenic activity. We also observed that low diversity of mutant alleles led to repeated failure to obtain frame-shift mutations. This limitation was overcome by knock-in of a stop codon cassette that ensured coding frame truncation. Our improved methods and detailed protocols make Cas9-mediated mutagenesis an attractive approach for labs of all sizes

The effect of creative psychological interventions on psychological outcomes for adult cancer patients: a systematic review of randomised controlled trials

Objective This systematic review examined the effectiveness of creative psychological interventions (CPIs) for adult cancer patients. In particular, the findings of randomised controlled trials of art, drama, dance/movement and music therapies on psychological outcomes were examined. Methods The review yielded 10 original studies analysing data from a total of 488 patients. Data extraction and quality assessment were conducted by two independent reviewers. Results Four of the papers focused on the use of art therapy, three studies used music therapy, one paper utilised dance therapy, one study used dance/movement therapy and the remaining paper used creative arts therapies, which was a combination of different art-based therapy approaches. Eight papers focused solely on breast cancer patients, and the remaining studies included mixed cancer sites/stages. The studies reported improvements in anxiety and depression, quality of life, coping, stress, anger and mood. However, few physical benefits of CPIs were reported; there was no significant impact of a CPI on physical aspects of quality of life, vigour-activity or fatigue-inertia or physical functioning. One study was assessed as high quality, seven studies were assessed as satisfactory and two studies were assessed to be of poorer quality. Conclusions There is initial evidence that CPIs benefit adult cancer patients with respect to anxiety and depression, quality of life, coping, stress, anger and mood; there was no evidence to suggest that any one type of CPI was especially beneficial. However, more and better quality research needs to be conducted, particularly in the areas of drama and dance/movement therapies