Nitrogen is one of the major nutrients limiting microbial productivity in the ocean, and as a result, most marine microorganisms
have evolved systems for responding to nitrogen stress. The highly abundant alphaproteobacterium “Candidatus
Pelagibacter ubique,” a cultured member of the order Pelagibacterales (SAR11), lacks the canonical GlnB, GlnD, GlnK, and...
Chronic nitrogen (N) fertilization can greatly affect soil carbon (C) sequestration by altering biochemical interactions between plant detritus and soil microbes. In lignin-rich forest soils, chronic N additions tend to increase soil C content partly by decreasing the activity of lignin-degrading enzymes. In cellulose-rich grassland soils it is not clear...
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(Sterner and
Elser 2002).
Our second hypothesis is that in grassland ecosys-
tems where soils receive