Stable isotope ratios from tree rings and peatland mosses have become important proxies of past climate variations. We here compare recent stable carbon and oxygen isotope ratios in cellulose of tree rings from white spruce (Picea glauca), growing near the arctic tree line; and cellulose of Sphagnum fuscum stems, growing in a hummock of a subarctic peatland, in west-central Canada. Results show that carbon isotopes in S. fuscum correlate significantly with July temperatures over the past ~20 yr. The oxygen isotopes correlate with both summer temperature and precipitation. Analyses of the tree-ring isotopes revealed summer temperatures to be the main controlling factor for carbon isotope variations, whereas tree-ring oxygen isotope ratios are controlled by a combination of spring temperatures and precipitation totals. We also explore the potential of combining high-frequency (annual) climate signals derived from long tree-ring series with low-frequency (decadal to centennial) climate signals derived from the moss remains in peat deposits. This cross-archive comparison revealed no association between the oxygen isotopes, which likely results from the varying sensitivity of the archives to different seasons. For the carbon isotopes, common variance could be achieved through adjustments of the Sphagnum age model within dating error.

This study investigated why the susceptible or resistance phenotype to the nematode Heligmosomoides polygyrus was lost when susceptible (C57BL/6) and resistant (Balb/c) strains of mice were housed together in indoor arenas with continuous transmission of the parasite larvae present in peat trays (Scott, 1991). First, both strains expressed their normal phenotype when given a controlled challenge while living in arenas, and when experimentally infected with only 5 parasite larvae. To test whether chronic exposure to peat altered the resistance phenotype, mice were given a challenge infection while living on peat. C57BL/6 mice living on peat had higher egg production and higher worm numbers than Balb/c mice, except at 2 months post-challenge. Finally, natural transmission rates were increased in arena experiments through either regular replacement of arena mice with naïve mice or direct introduction of additional larvae. A transient difference in infection levels between strains was detected in response to a modest increase in transmission whereas a 10-fold increase in transmission allowed C57BL/6 mice to exhibit the typical profile of high egg production and elevated worm numbers. These data indicate that C57BL/6 mice are less able to regulate parasite numbers at high transmission rates compared with lower transmission rates.