SUMMARY Human activities are greatly increasing the amount of nitrogen cycling between the living world and the soil, water, and atmosphere. In fact, humans have already doubled the rate of nitrogen entering the land-based nitrogen cycle, and that rate is continuing to climb. This human-driven global change is having serious impacts on ecosystems around the world because nitrogen is essential t...

The study of the metabolism of Azotobacter has been generally approached from the standpoint of the r6le of this organism in the nitrogen cycle in Nature, but the fact that the ability to fix free nitrogen is regulated by the presence or absence of combined nitrogen in the medium has not been given serious attention although it is made plain in the works to be cited. Bejierink and Van Delden (1...

Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrog...

UNLABELLED A major percentage (20 to 40%) of global marine fixed-nitrogen loss occurs in oxygen minimum zones (OMZs). Concentrations of O2 and the sensitivity of the anaerobic N2-producing processes of anammox and denitrification determine where this loss occurs. We studied experimentally how O2 at nanomolar levels affects anammox and denitrification rates and the transcription of nitrogen cycl...

Clear-cutting of forests affects the nitrogen cycle and the nitrogen isotopic composition of bioavailable ammonium and nitrate in the soil. Here, we have used nitrogen isotopic variations of tree-rings in red oak (Quercus rubra) and white oak (Quercus alba) as indicators of changes in the nitrogen cycle on a local scale. The delta15N values of late-wood from trees at two remnant forest stands i...

Nitrogen deficiency severely inhibits leaf growth. This response was analysed at the cellular level by growing Lolium perenne L. under 7.5 mM (high) or 1 mM (low) nitrate supply, and performing a kinematic analysis to assess the effect of nitrogen status on cell proliferation and cell growth in the leaf blade epidermis. Low nitrogen supply reduced leaf elongation rate (LER) by 43% through a sim...

Patterns in nitrogen-fixing activity by Inga jinicuil Schl., a leguminous shade tree in Mexican coffee plantations, were monitored over a three-and-half year period using acetylene reduction. Year to year variation was unexpectedly large; mean annual fixation equalled 35 kg N ha yr, which constitutes a significant nitrogen input to the coffee ecosystem. Nitrogen-fixing activity occurred through...

The stimulation of plant growth by elevated CO2 concentration has been widely observed. Such fertilization, and associated carbon storage, could dampen future increases in atmospheric CO2 levels and associated climate warming1. However, the CO2 fertilization of plant biomass may be sensitive to nitrogen supply2–4. Herein we show that in the latest decade of a long-term perennial grassland exper...