No abstract

Soil organisms provide crucial ecosystem services that support human life. However, little is known about their diversity, distribution, and the threats affecting them. Here, we compiled a global dataset of 60 sampled earthworm communities from over 7000 sites in 56 countries to predict patterns in earthworm diversity, abundance, and biomass. We identify the environmental drivers shaping these patterns. Local species richness and abundance typically peaked at higher latitudes, while biomass peaked in the tropics, patterns opposite to those observed in aboveground organisms. Similar to many aboveground taxa, climate variables were more important in shaping earthworm communities than soil properties or habitat 65 cover. These findings highlight that, while the environmental drivers are similar, conservation strategies to conserve aboveground biodiversity might not be appropriate for earthworm diversity, especially in a changing climate.

Summary• Kalmia angustifolia is an ericaceous shrub that can rapidly spread on recently harvested boreal forest sites, causing a slow-down in soil nutrient cycling and reduced growth of spruce seedlings. It has been hypothesized that tannins released from Kalmia litter suppress soil enzyme activity, and are thus important in controlling ecosystem structure and processes.• Here the effects of different concentrations of tannins extracted from both Kalmia and black spruce ( Picea mariana ) foliage were tested on enzyme activities of soil extracts. Then the effects of various Kalmia -black spruce litter mixtures on soil enzyme activity were investigated. Lastly, the correlation between Kalmia cover in the field and soil enzyme activity was measured.• Both tannin types suppressed β -glucosidase and acid phosphatase activities, and the magnitude of these effects was concentration-dependent. β -glucosidase and amidase activity decreased linearly with an increasing Kalmia : spruce litter ratio added to soil. A field survey of 24 sites revealed a negative relationship between percentage Kalmia cover and β -glucosidase activity.• Collectively, results of the three experiments converge to support the claim that enzyme inhibition by litter tannins has evolved as an important mechanism controlling ecosystem processes and structure following Kalmia invasion on recently disturbed forest sites.

http://dx.doi.org/10.1111/j.1469-8137.2012.04121.x

Biological nitrogen fixation (BNF) performed by moss-associated cyanobacteria is one of the main sources of new nitrogen (N) input in pristine, high-latitude ecosystems. Yet, the nutrients that limit BNF remain elusive. Here, we tested whether this important ecosystem function is limited by the availability of molybdenum (Mo), phosphorus (P), or both. BNF in dominant mosses was measured with the acetylene reduction assay (ARA) at different time intervals following Mo and P additions, in both laboratory microcosms with mosses from a boreal spruce forest and field plots in subarctic tundra. We further used a N tracer technique to assess the ARA to N fixation conversion ratios at our subarctic site. BNF was up to four-fold higher shortly after the addition of Mo, in both the laboratory and field experiments. A similar positive response to Mo was found in moss colonizing cyanobacterial biomass. As the growing season progressed, nitrogenase activity became progressively more P limited. The ARA : N ratios increased with increasing Mo additions. These findings show that N fixation activity as well as cyanobacterial biomass in dominant feather mosses from boreal forests and subarctic tundra are limited by Mo availability.