Experimental drying intensifies burning and carbon losses in a northern peatland.

For millennia, peatlands have served as an important sink for atmospheric CO(2) and today represent a large soil carbon reservoir. While recent land use and wildfires have reduced carbon sequestration in tropical peatlands, the influence of disturbance on boreal peatlands is uncertain, yet it is important for predicting the fate of northern high-latitude carbon reserves. Here we quantify rates of organic matter storage and combustion losses in a boreal peatland subjected to long-term experimental drainage, a portion of which subsequently burned during a wildfire. We show that drainage doubled rates of organic matter accumulation in the soils of unburned plots. However, drainage also increased carbon losses during wildfire ninefold to 16.8±0.2 kg C m(-2), equivalent to a loss of more than 450 years of peat accumulation. Interactions between peatland drainage and fire are likely to cause long-term carbon emissions to far exceed rates of carbon uptake, diminishing the northern peatland carbon sink.

An impending water crisis in Canada's western prairie provinces.

Canada is usually considered to be a country with abundant freshwater, but in its western prairie provinces (WPP), an area 1/5 the size of Europe, freshwater is scarce. European settlement of the WPP did not begin until the late 19th and early 20th centuries. Fortuitously, the period since European settlement appears to have been the wettest century of the past two millennia. The frequent, long periods of drought that characterized earlier centuries of the past two millennia were largely absent in the 20th century. Here, we show that climate warming and human modifications to catchments have already significantly reduced the flows of major rivers of the WPP during the summer months, when human demand and in-stream flow needs are greatest. We predict that in the near future climate warming, via its effects on glaciers, snowpacks, and evaporation, will combine with cyclic drought and rapidly increasing human activity in the WPP to cause a crisis in water quantity and quality with far-reaching implications.

Excision of group II introns as circles.

Group II introns are usually removed from precursor RNAs as lariats comprised of a circular component and a short 3' tail. We find that group II introns can also be excised as complete circles. Circle formation requires release of the 3' exon of a splicing substrate, apparently by a trans splicing mechanism. After 3' exon release, the terminal uridine of the intron attacks the 5' splice site, releasing the 5' exon and joining the first and last intron residues by a 2'-5' phosphodiester bond. RNA isolated from yeast mitochondria also contains circles, indicating that at least one group II intron (aI2) forms circles in vivo. Furthermore, analysis of RNA and DNA from certain mutant yeast strains shows that circular DNA introns exist and are produced by reverse transcription of RNA, rather than by ectopic homing.

Seamless gene engineering using RNA- and DNA-overhang cloning.

Here we describe two methods for generating DNA fragments with single-stranded overhangs, like those generated by the activity of many restriction enzymes, by simple methods that do not involve DNA digestion. The methods, RNA-overhang cloning (ROC) and DNA-overhang cloning (DOC), generate polymerase chain reaction (PCR) products composed of double-stranded (ds) DNA flanked by single-stranded (ss) RNA or DNA overhangs. The overhangs can be used to recombine DNA fragments at any sequence location, creating "perfect" chimeric genes composed of DNA fragments that have been joined without the insertion, deletion, or alteration of even a single base pair. The ROC method entails using PCR primers that contain regions of RNA sequence that cannot be copied by certain thermostable DNA polymerases. Using such a chimeric primer in PCR would yield a product with a 5' overhang identical to the sequence of the RNA component of the primer, which can be used for directional ligation of the amplified product to other preselected DNA molecules. This method provides complete control over both the length and sequence of the overhangs, and eliminates the need for restriction enzymes as tools for gene engineering.