High nitrogen contribution by Gunnera magellanica and nitrogen transfer by mycorrhizas drive an extraordinarily fast primary succession in sub-Antarctic Chile.

Chronosequences at the forefront of retreating glaciers provide information about colonization rates of bare surfaces. In the northern hemisphere, forest development can take centuries, with rates often limited by low nutrient availability. By contrast, in front of the retreating Pia Glacier (Tierra del Fuego, Chile), a Nothofagus forest is in place after only 34 yr of development, while total soil nitrogen (N) increased from near zero to 1.5%, suggesting a strong input of this nutrient. We measured N-fixation rates, carbon fluxes, leaf N and phosphorus contents and leaf δ15 N in the dominant plants, including the herb Gunnera magellanica, which is endosymbiotically associated with a cyanobacterium, in order to investigate the role of N-fixing and mycorrhizal symbionts in N-budgets during successional transition. G. magellanica presented some of the highest nitrogenase activities yet reported (potential maximal contribution of 300 kg N ha-1  yr-1 ). Foliar δ15 N results support the framework of a highly efficient N-uptake and transfer system based on mycorrhizas, with c. 80% of N taken up by the mycorrhizas potentially transferred to the host plant. Our results suggest the symbiosis of G. magellanica with cyanobacteria, and trees and shrubs with mycorrhizas, to be the key processes driving this rapid succession.

Identity of plant, lichen and moss species connects with microbial abundance and soil functioning in Maritime Antarctica.

BACKGROUND AND AIMS: We lack studies evaluating how the identity of plant, lichen and moss species relates to microbial abundance and soil functioning on Antarctica. If species identity is associated with soil functioning, distributional changes of key species, linked to climate change, could significantly affect Antarctic soil functioning. METHODS: We evaluated how the identity of six Antarctic plant, lichen and moss species relates to a range of soil attributes (C, N and P cycling), microbial abundance and structure in Livingston Island, Maritime Antarctica. We used an effect size metric to predict the association between species (vs. bare soil) and the measured soil attributes. RESULTS: We observed species-specific effects of the plant and biocrust species on soil attributes and microbial abundance. Phenols, phosphatase and ß-D-cellobiosidase activities were the most important attributes characterizing the observed patterns. We found that the evaluated species positively correlated with soil nutrient availability and microbial abundance vs. bare soil. CONCLUSIONS: We provide evidence, from a comparative study, that plant and biocrust identity is associated with different levels of soil functioning and microbial abundance in Maritime Antarctica. Our results suggest that changes in the spatial distribution of these species linked to climate change could potentially entail changes in the functioning of Antarctic terrestrial ecosystems.

A global atlas of the dominant bacteria found in soil.

The immense diversity of soil bacterial communities has stymied efforts to characterize individual taxa and document their global distributions. We analyzed soils from 237 locations across six continents and found that only 2% of bacterial phylotypes (~500 phylotypes) consistently accounted for almost half of the soil bacterial communities worldwide. Despite the overwhelming diversity of bacterial communities, relatively few bacterial taxa are abundant in soils globally. We clustered these dominant taxa into ecological groups to build the first global atlas of soil bacterial taxa. Our study narrows down the immense number of bacterial taxa to a "most wanted" list that will be fruitful targets for genomic and cultivation-based efforts aimed at improving our understanding of soil microbes and their contributions to ecosystem functioning.