Plant species composition influences belowground ecosystem function. However, there are few data on the interactive effects of plant diversity and soil function. We surveyed plant species diversity, and determined soil carbon (C), nitrogen (N) fractions and enzyme activity in five peatlands with different vegetation-types. We also investigated the interactions between plant species diversity and richness, and soil biochemical properties. We found a close relationship between plant species diversity and total carbon (TC) in both surface (0-15 cm) and subsoil (15-30 cm) layers. Plant diversity and richness positively correlated with soil dissolved organic carbon (DOC), NH4+-N in both soil layers and subsoil moisture and total nitrogen (TN), as well as topsoil pH. Plant species diversity and richness were also positively correlated with subsoil moisture, pH, protease, acid phosphatase activity and topsoil urease activity. Soil beta-glucosidase, invertase, urease, protease, and acid phosphatase activity positively correlated with soil TC, TN, DOC, available N and soil moisture. Our findings demonstrate that plant community diversity is linked with soil C and N turnover through soil enzyme activity. These results will improve our ability to more fully understand the linkages between aboveground and belowground components in peatland ecosystems.

Vegetation, active-layer soils, and snow cover regulate energy exchange between the atmosphere and permafrost. Therefore, interactions between changes to tundra vegetation and soil thermal regime will fundamentally affect permafrost in a warmer world. We recorded soil temperatures for approximately 1 year in a Siberian Low Arctic landscape with a known history of alder (Alnus) shrub expansion on disturbed microsites in patterned ground. We recorded near-surface soil temperatures and measured physical properties of soils and vegetation on sorted-circle microsites in four stages of shrubland development: (1) tundra lacking tall shrubs; (2) shrub colonization zones; (3) mature shrublands; and (4) paludified, long-established shrublands with thick soil organic layers. Summer soil temperatures declined with increasing shrub cover and soil organic thickness; shrub colonization suppressed cryoturbation, facilitating the development of continuous vegetation and a surface organic mat on circles. Compared to open tundra, mature shrubs cooled soils by up to 9 A degrees C during summer, but warmed soils by greater than 10 A degrees C in winter presumably because they developed highly insulative snowpacks. Paludified shrublands had the coldest summer active layers, but winter soil temperatures were much colder than mature shrublands and were similar to earlier stages. Our results indicate that although tall shrub establishment dramatically warms winter soils within decades, much of this warming is transient at paludification-prone sites because the buildup of wet peat favors cooling in winter and the stature and snow-trapping capacity of shrubs diminish over time. In the ecosystem we studied, shrub expansion has contrasting effects on active-layer temperatures both seasonally and over longer timescales due to successional processes.