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Pekka Vanhala, Kristiina Karhu, Mikko Tuomi, Katarina Bjorklof, Hannu Fritze, Hasse Hyvarinen, & Jari Liski, 'Transplantation of organic surface horizons of boreal soils into warmer regions alters microbiology but not the temperature sensitiviy of decomposition', Global Change Biology, Vol. 17 (1): 538-550, first published 16 December 2009. The version of record is available online at doi: 10.1111/j.1365-2486.2009.02154.x ?? 2010 Blackwell Publishing LtdChanges in soil carbon, the largest terrestrial carbon pool, are critical for the global carbon cycle, atmospheric CO2 levels and climate. Climate warming is predicted to be most pronounced in the northern regions and therefore the large soil carbon pool residing in boreal forests will be subject to larger global warming impact than soil carbon pools in the temperate or the tropical forest. A major uncertainty in current estimates of the terrestrial carbon balance is related to decomposition of soil organic matter (SOM). We hypothesized that when soils are exposed to warmer climate the structure of the ground vegetation will change much more rapidly than the dominant tree species. This change will alter the quality and amount of litter input to the soil and induce changes in microbial communities, thus possibly altering the temperature sensitivity of SOM decomposition. We transferred organic surface soil sections from the northern borders of the boreal forest zone to corresponding forest sites in the southern borders of the boreal forest zone and studied the effects of warmer climate after an adaptation period of 2 years. The results showed that initially ground vegetation and soil microbial community structure and community functions were different in northern and southern forest sites and that 2 years of exposure to warmer climate was long enough to cause changes in these ecological indicators. The rate of SOM decomposition was approximately equally sensitive to temperature irrespective of changes in vegetation or microbial communities in the studied forest sites. However, as temperature sensitivity of the decomposition increases with decreasing temperature regime, the proportional increase in the decomposition rate in northern latitudes could lead to significant carbon losses from the soils. ?? 2010 Blackwell Publishing Ltd

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2000. Survival, colonization and activity of Pseudomonas syringae bacteria inoculated onto the leaf surface of the common bean (Phaseolus vulgaris) was studied. Inoculated Ps. syringae cells shortened by half their size in 100% humidity and by an average of one ®fth in 40± 60% humidity. The respiring portion of the population, measured by the formation of 5-cyano-2,3-ditolyl tetrazolium chloride (CTC)-formazan crystals, decreased more in 40±60% humidity than in 100% humidity. In scanning electron micrographs, the bacterial cells on leaf surfaces were seen embedded in a mucoid matrix. Intraspecies conjugation of plasmid RP1 also occurred in 40±60% humidity conditions. The portion of transconjugants temporally rose higher than the same portion in 100% humidity conditions. Therefore, although only a small proportion of the inoculated cells remained active on the leaf surface in 40±60% humidity, a relatively high rate of conjugation was still seen. Gene spreading was thus ef®cient on the leaf surface also when conditions did not allow bacterial population growth.

The maintenance and transfer of the broad host-range plasmid RP1 in epiphytically growing populations of Pseudomnas syringae was monitored in the phyllosphere of bush bean (Phaseolus vulgaris). When foliage was inoculated with plasmid-containing bacteria, the plasmid was lost from the majority of the cells within 2 d but was stably maintained in 0 8 % of the population. A high frequency of conjugation between added donors and recipients was observed under high humidity conditions. In 1 d, the number of transconjugants rose to 10-1 of the donors and the proportional level of transconjugants continued to increase until 3 d after inoculation. Under these conditions the proportion of plasmid-containing bacteria stabilized at about 0 8 % of the total population. The conjugation rate appeared to be in equilibrium with plasmid loss and the slower growth of the plasmid-carrying cells. A factor that influenced the high conjugation frequency observed was the available nutrients provided by the leaf and also, to a lesser extent, the leaf surface itself. Transfer of the plasmid from added donors to indigenous bacteria was also studied, using a donor-specific bacteriophage for counterselection of the donor. Transfer was observed to 10 different species of Gram-negative epiphytically growing bacteria. The bean leaf surface appears to function as a hotspot at least for intraspecific transfer of plasmids in high humidity. The frequency of transfer was higher than in soil or in rhizosphere habitats. This is likely to be the result of an environment that is nutritionally rich in combination with a limited colonizable surface area which permits close contact between the bacterial cells.