Understanding effects of varying nitrogen and carbon availability on soil emissions of nitrogen oxides in drylands:
Nitrogen (N) is the main macronutrient limiting primary productivity on Earth. While abundant in the atmosphere, it is inaccessible to living organisms without being fixed to ammonium (NH4+).
N fixation initiates the N cascade in which numerous organic, inorganic, and gaseous forms of N are interchanged, in processes that are mediated by biological and abiotic reactions.
Despite intensive studies during the past ~100 years, our knowledge on specific drivers and rates of N transformations in terrestrial ecosystems is still rather limited due to the difficulty of translating results from the laboratory experiments to the field scale and generalization of results from the field measurements.
The most uncertain part of the N cycle is soil N oxide loss, which is difficult to elucidate since the process is controlled by most of the known biological and abiotic reactions: heterotrophic and autotrophic, aerobic and anaerobic, oxidation and reduction.
In addition, our inability to measure gaseous N emissions at needed temporal and spatial resolutions hampers our ability to predict and model gaseous N release from soils and ecosystems. There are two main forms of N oxides: nitrous and nitric oxides (N2O and NO, correspondingly).
The N2O plays an important role in trapping heat in the atmosphere and ozone destruction in the stratosphere, and NO is the precursor of the ozone in the troposphere.
Study of the processes leading to soil N oxide emissions is vital for understanding drivers and controls of specific reactions controlling their emissions in ecosystems. Specifically, knowledge about the controls of soil emissions of N oxide forms in high-temperature ecosystems, such as deserts, is scarce.
In deserts, an interplay between high temperature and short water availability times can cause high but short-lived emissions that are difficult to measure and predict. In the proposed research, I will use controlled field experiments to study the effects of environmental factors, e.g., water and temperature, as well as the availability of substrates, (carbon (C) and N) on the N oxide fluxes in the high-temperature ecosystem of the central Negev Desert.
While using natural temperature variability, I will manipulate water and soil C and N levels and measure fluxes of N2O and NO to develop predictive relationships between these factors and the gaseous N loss. Specific attention will be given to the inflection points (thresholds) of the emission rates as they are affected by changing soil temperature, water, C, and N availability.
Together with field measurements of the N oxide emissions, I plan to take soil samples and perform laboratory experiments utilizing, among others, stable isotope techniques to explain specific N transformation pathways that affect soil N oxide emissions. Knowledge gained during the proposed research will contribute to our ability to predict soil fluxes of N oxides in high-temperature ecosystems and elsewhere.
This study was funded by the Israel Science Foundation (ISF) for four years with 300,000 per year, 38,000 for international cooperation and 647,000 for instrumentation per year