Carbon dioxide balance of subarctic tundra from plot to regional scales

Peer reviewe

Methane dynamics in the subarctic tundra : combining stable isotope analyses, plot- and ecosystem-scale flux measurements

Methane (CH4) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May-October 2008) cumulative CH4 emission of 2.4 (EC) and 3.7 gCH(4) m(-2) (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km(2), the chamber measured flux data yielded a regional flux estimate of 6.7 gCH(4) m(-2) yr(-1). Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 gCH(4) m(-2) yr(-1) were the most dominant CH4-emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH4 release pathway from wetlands to the atmosphere was plant-mediated diffusion through aerenchyma, a process that discriminates against C-13-CH4. The CH4 released to the atmosphere was lighter than that in the surface porewater, and delta C-13 in the emitted CH4 correlated negatively with the vascular plant cover (LAI). The mean value of delta C-13 obtained here for the emitted CH4, 68.2 +/- 2.0 %, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1 degrees C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH4-emitting wet surfaces.Peer reviewe

Mutation analysis of 18 nephronophthisis associated ciliopathy disease genes using a DNA pooling and next generation sequencing strategy

Background Nephronophthisis associated ciliopathies (NPHP-AC) comprise a group of autosomal recessive cystic kidney diseases that includes nephronophthisis (NPHP), Senior-Loken syndrome (SLS), Joubert syndrome (JBTS), and Meckel-Gruber syndrome (MKS). To date, causative mutations in NPHP-AC have been described for 18 different genes, rendering mutation analysis tedious and expensive. To overcome the broad genetic locus heterogeneity, a strategy of DNA pooling with consecutive massively parallel resequencing (MPR) was devised.Methods In 120 patients with severe NPHP-AC phenotypes, five pools of genomic DNA with 24 patients each were prepared which were used as templates in order to PCR amplify all 376 exons of 18 NPHP-AC genes (NPHP1, INVS, NPHP3, NPHP4, IQCB1, CEP290, GLIS2, RPGRIP1L, NEK8, TMEM67, INPP5E, TMEM216, AHI1, ARL13B, CC2D2A, TTC21B, MKS1, and XPNPEP3). PCR products were then subjected to MPR on an Illumina Genome-Analyser and mutations were subsequently assigned to their respective mutation carrier via CEL I endonuclease based heteroduplex screening and confirmed by Sanger sequencing.Results For proof of principle, DNA from patients with known mutations was used and detection of 22 out of 24 different alleles (92% sensitivity) was demonstrated. MPR led to the molecular diagnosis in 30/120 patients (25%) and 54 pathogenic mutations (27 novel) were identified in seven different NPHP-AC genes. Additionally, in 24 patients only single heterozygous variants of unknown significance were found.Conclusions The combined approach of DNA pooling followed by MPR strongly facilitates mutation analysis in broadly heterogeneous single gene disorders. The lack of mutations in 75% of patients in this cohort indicates further extensive heterogeneity in NPHP-AC

Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse

Ecological sustainability and environmental risks of agricultural intensification in inland valleys in Benin

To meet food demand after the failure of irrigation system developments, agricultural intensification is occurring in inland valley agro-ecosystems in sub-Saharan Africa. Agricultural enhancement in inland valleys, which undermines environmental sustainability, was assessed using 'Driving Force–Pressure–State–Impact–Response' approach in four agro-ecological zones of Benin. The survey revealed that inland valleys are largely devoid of ligneous species. Crop residues are mainly transferred from inland valley fields to feed cattle, burnt in situ by the farmers themselves or abandoned to wildfires or to pasture—not mulched. Crop diversification is not universal and is limited to rice and vegetables crops. Monocropping of rice, practised by 83.3% of inland valley farmers, requires large chemical fertilizer application despite their impacts on environment including land degradation and water contamination. A major challenge is to determine means of characterizing entire agro-ecosystems of inland valleys in a way that is simple enough to be effectively and efficiently monitored. Inland valley agricultural development projects might include backstopping activities and policies that enable monitoring of chemical inputs and farming practices in inland valleys to reduce negative impacts on the environment and human health

Failure and success factors of irrigation system developments – a case study from the Ouémé and Zou valleys in Benin

In the period 1960–1980, Chinese and Taiwanese cooperations developed irrigated rice schemes throughout West Africa with variable success. In Benin for instance, schemes in Zonmon and Bamè (Ouémé Valley) were abandoned upon withdrawal of the project developers and have been sub-optimally used ever since, while the neighbouring scheme of Koussin-Lélé (Zou Valley) is still functional (double rice cropping) and well operated and maintained by the farmers. The factors for success and failure were investigated by comparing the two abandoned schemes with the successful one, using field observations and stakeholder surveys. We observed that (i) operation and maintenance costs associated with irrigation were presumably lower in the successful scheme––where irrigation was driven by gravity––compared to the failed ones––where part of the schemes were designed for motor-pump driven irrigation. Moreover, contrary to the situation in the unsuccessful schemes, farmers in the successful scheme of Koussin-Lélé benefit from (ii) external technical support, (iii) a favourable land tenure policy, entailing seasonal redistribution of plots favouring active and motivated producers, (iv) reliable access to credit, and (v) an effective farmer organization. These observations underscore the importance of addressing the longer-term technical and financial needs of the beneficiaries for the successful development of irrigation schemes advancing smallholder farmers in sub-Saharan Africa