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Title: Chemical Potential of Nitrogen at High Pressure and High Temperature: Application to Nitrogen and Nitrogen-Rich Phase Diagram Calculations
Award ID(s):
1743701
NSF-PAR ID:
10113469
Author(s) / Creator(s):
;
Date Published:
Journal Name:
The Journal of Physical Chemistry C
Volume:
123
Issue:
12
ISSN:
1932-7447
Page Range / eLocation ID:
7054 to 7060
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    As part of a long-term study on the effects of nitrogen (N) loading in a shallow temperate lagoon, we measured rates of N2fixation associated with seagrass (Zostera marina) epiphytes during the summer from 2005 to 2019, at two sites along a gradient from where high N groundwater enters the system (denoted SH) to a more well-flushed outer harbor (OH). The data presented here are the first such long-term N2fixation estimates for any seagrass system and one of the very few reported for the phyllosphere in a temperate system. Mean daily N2fixation was estimated from light and dark measurements using the acetylene reduction assay intercalibrated using both incorporation of15N2into biomass and a novel application of the N2:Ar method. Surprisingly, despite a large inorganic N input from a N-contaminated groundwater plume, epiphytic N2fixation rates were moderately to very high for a seagrass system (OH site 14-year mean of 0.94 mmol N m−2 d−1), with the highest rates (2.6 mmol N m−2 d−1) measured at the more N-loaded eutrophic site (SH) where dissolved inorganic N was higher and soluble reactive phosphorus was lower than in the better-flushed OH. Over 95% of the total N2fixation measured was in the light, suggesting the importance of cyanobacteria in the epiphyte assemblages. We observed large inter-annual variation both within and across the two study sites (range from 0.1 to 2.6 mmol N fixed m−2d−1), which we suggest is in part related to climatic variation. We estimate that input from phyllosphere N2fixation over the study period contributes on average an additional 20% to the total daily N load per area within the seagrass meadow.

     
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  2. Abstract

    Light and soil nitrogen availability can be strong controls of plant nitrogen (N) fixation, but data on how understory N‐fixing plants respond to these drivers are limited despite their important role in ecosystem N cycling. Furthermore, ecosystem N cycling can be altered by the introduction of species with nutrient use patterns that differ from natives. We assessed how N fixation of two exotic, understory species responded to varying light and soil N environments.

    We sampled leaf tissue fromMimosa pudicaL.,Desmodium triflorum(L.) DC., and a nonfixing reference plant (Axonopus) growing in control and two N fertilization treatments under either N‐fixing or non‐N‐fixing trees, which may alter local soil nutrient cycling, across a range of light conditions. We measured N fixation with15N isotope dilution, and ensured that N‐fixing neighbour trees were in fact fixing N. All understory plants were wild‐growing species not native to the study location.

    DesmodiumandMimosaacquired 82.6% and 71.6% of their nitrogen from fixation (%Ndfa) in the control, compared to 66.8% and 58.1% in the +10 g N m−2 year−1treatment and 73.1% and 64.7% in the +15 g N m−2 year−1treatment. These subtle %Ndfadifferences across fertilization treatments were more apparent at low light availability and disappeared at high light availability. The amount of N fixed by neighbouring trees did not influence %Ndfain the understory species.

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  3. null (Ed.)