Patterns of and controls over N2 fixation by green alder were studied in post-fire, mid-succession, and white spruce upland forests in interior Alaska, focusing on the hypothesis that ecosystem-level nitrogen (N) inputs decrease with successional development. N2-fixation rates tracked plant phenology during the 1997 (drought) and 1998 (normal precipitation) growing seasons. The best model for p...

Functional traits define species by their ecological role in the ecosystem. Animals themselves are host-microbe ecosystems (holobionts), and the application of ecophysiological approaches can help to understand their functioning. In hard coral holobionts, communities of dinitrogen (N2)-fixing prokaryotes (diazotrophs) may contribute a functional trait by providing bioavailable nitrogen (N) that...

Cyanobacterial ; blooms are a regular feature of lakes in central North America, but little is known of their importance to the nitrogen (N) cycle and nutrition of aquatic food webs. We hypothesized that N2-fixing cyanobacteria constitute a significant source of N to prairie lakes, that fixed N is effectively transferred to primary and secondary consumers, and that the importance of fixed N is ...

Multiple strains per plant and root-to-root (not seed-borne) transmission should favor rhizobia that invest in their own reproduction, rather than symbiotic N2 fixation, as analogous factors may favor pathogen virulence. But legumes can select for greater mutualism, controlling nodule O2 supply and reducing reproduction of rhizobia that fix less N2.

The continental shelves are the most biologically dynamic regions of the ocean, and they are extensive worldwide, especially in the western North Pacific. Their area has varied dramatically over the glacial/interglacial cycles of the last million years, but the effects of this variation on ocean biological and chemical processes remain poorly understood. Conversion of nitrate to N2 by denitrifi...

Symbiotic associations occur in every habitat on earth, but we know very little about their evolutionary histories. Current models of trait evolution cannot adequately reconstruct the deep history of symbiotic innovation, because they assume homogenous evolutionary processes across millions of years. Here we use a recently developed, heterogeneous and quantitative phylogenetic framework to stud...

Paraburkholderia nodosa CNPSo 1341 is a N2-fixing symbiont of Phaseolus vulgaris isolated from an undisturbed soil of the Brazilian Cerrado. Its draft genome contains 8,614,032 bp and 8,068 coding sequences (CDSs). Nodulation and N2-fixation genes were clustered in the genome that also contains several genes of secretion systems and quorum sensing.

Biological nitrogen fixation by the nitrogenase enzymes has long been a touchstone for dinitrogen chemists.1,2 Both the enzymatic reduction and protonation of N2 mediated by these metalloenzymes (eq 1)3,4 and the industrial hydrogenation of N2 exemplified by the Haber-Bosch process (eq 2)5-7 employ transition metal-based catalysts to accelerate the thermodynamically feasible production of ammonia.

Fe-mediated biological nitrogen fixation is thought to proceed via either a sequence of proton and electron transfer steps, concerted H atom transfer steps, or some combination thereof. Regardless of the specifics and whether the intimate mechanism for N2-to-NH3 conversion involves a distal pathway, an alternating pathway, or some hybrid of these limiting scenarios, Fe-NxHy intermediates are im...

The predominant input of available nitrogen (N) in boreal forest ecosystems originates from moss-associated cyanobacteria, which fix unavailable atmospheric N2, contribute to the soil N pool, and thereby support forest productivity. Alongside climate warming, increases in atmospheric CO2 concentrations are expected in Canada’s boreal region over the next century, yet little is known about the c...