Determinants of soil organic matter chemistry in maritime temperate forest ecosystems

While the influence of climate, vegetation, management and abiotic site factors on total carbon budgets and turn-over is intensively assessed, the influences of these ecosystem properties on the chemical complexity of soil organic matter (SOM) remains poorly understood. This study addresses the chemical composition of NaOH-extracted SOM from maritime temperate forest sites in Flanders (Belgium) by pyrolysis-GC/MS. The studied forests were chosen based on dominant tree species (Pinus sylvestris, Fagus sylvatica, Quercus robur and Populus spp.), soil texture and soil-moisture conditions. Differences in extractable-SOM pyrolysis products were correlated to site variables including dominant tree species, management of the woody biomass, site history, soil properties, total carbon stocks and indicators for microbial activity. Despite of a typical high intercorrelation between these site variables, the influence of the dominant tree species is prominent. The extractable-SOM composition is strongly correlated to litter quality and available nutrients. In nutrient-poor forests with low litter quality, the decomposition of relatively recalcitrant compounds (i.e. short and mid-chain alkanes/alkenes and aromatic compounds) appears hampered, causing a relative accumulation of these compounds in the soil. However, if substrate quality is favorable, no accumulations of recalcitrant compounds were observed, not even under high soil-moisture conditions. Former heathland vegetation still had a profound influence on extractable-SOM chemistry of young pine forests after a minimum of 60 year

A bumpy ride on the diagnostic bench of massive parallel sequencing, the case of the mitochondrial genome

The advent of massive parallel sequencing (MPS) has revolutionized the field of human molecular genetics, including the diagnostic study of mitochondrial (mt) DNA dysfunction. The analysis of the complete mitochondrial genome using MPS platforms is now common and will soon outrun conventional sequencing. However, the development of a robust and reliable protocol is rather challenging. A previous pilot study for the re-sequencing of human mtDNA revealed an uneven coverage, affecting predominantly part of the plus strand. In an attempt to address this problem, we undertook a comparative study of standard and modified protocols for the Ion Torrent PGM system. We could not improve strand representation by altering the recommended shearing methodology of the standard workflow or omitting the DNA polymerase amplification step from the library construction process. However, we were able to associate coverage bias of the plus strand with a specific sequence motif. Additionally, we compared coverage and variant calling across technologies. The same samples were also sequenced on a MiSeq device which showed that coverage and heteroplasmic variant calling were much improved

Agro-ecological niche of bacterial wilt (Xanthomonas campestris pv. musacearum) of enset (Ensete ventricosum (Welw.) Cheessman) in Gamo highlands of Ethiopia

In Ethiopia, nearly 20 million people depend on Enset (Ensete ventricosum (Welw.) Cheessman) for food, animal feed and fibre. Most of its cultivation is concentrated in the South and South-Western parts of the country. Enset based farming system is common in the Gamo highlands, with 11, 150 ha currently covered by it. Enset is supplemented with the cultivation of cereals, pulses and other root and tuber crops. Diverse high yielding clones of different ages are available all year round and can withstand dry spells, making Enset the most important food security crop in these densely populated highlands. Despite its relevance, Enset remains very poorly studied. One of the most important problems is Bacterial Wilt disease caused by Xanthomonas campestris pv. musacearum, destructive to Enset at all growth stages and present in all Enset growing areas of the country. As a plant takes up to 8 years to mature, an attack of Bacterial Wilt can leave a family vulnerable to famine for years. It is most likely spread by infected farm tools, harvesting knives, plant debris and repeated transplanting of corms. Adoption of the control package by farmers has been less effective and all known varieties are susceptible, putting a great challenge on controlling the epidemic. Despite being present in the entire Enset belt, the severity of a Bacterial Wilt infection varies greatly from region to region. Hence, this study aims at correlating the distribution and severity of the disease to environmental factors such as soil type, fertility, climate and altitude, and to the socio-economical status of the farm households. A better knowledge of the influence of these factors would help in developing more targeted measures to control the disease

Forest-derived lignin biomarkers in an Australian oxisol decrease substantially after 90 years of pasture

The dynamics of soil organic matter are a key factor in controlling the terrestrial carbon cycle. Compound specific stable carbon isotope analysis has given new insight in to the stability of individual organic molecules in soil. For lignin, one of the major plant compounds, available data suggest the existence of both a labile (turnover time <1 year) and a relatively stable (turnover time in the range of decades) pool. However, these data derive almost exclusively from agricultural soils in temperate climates. In order to extend the range both in ecosystem type and observed time span, we analysed a pasture soil in subtropical Australia that had experienced a land use change from rainforest 90 years earlier. We determined the concentration and isotopic signature of lignin biomarkers and compared them to those in an existing rainforest soil nearby and to samples of the respective vegetation. The land use change shifted both the relative abundance of lignin biomarkers and their isotopic signatures. In particular, the isotope data indicate that the pasture soil contains only small proportions of inherited rainforest-derived lignin biomarkers, which are mostly close to or below detection limit. These drastic changes in biomarker composition indicate that the original lignin structure had little chance to persist in this soil over a century. Thus, the stable soil organic carbon identified an earlier study of this soil is probably highly altered material and lignin biomarkers are not a suitable proxy of this stable carbon