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Root traits explain observed tundra vegetation nitrogen uptake patterns: Implications for trait-based land models

Topics: Clean Energy Climate and Environmental Systems
ORNL scientists injected a nitrogen-15 tracer into the rooting zone at three targeted depth intervals (organic layer, mineral soil, and permafrost boundary) to characterize nitrogen acquisition for three prevailing plant species (Carex aquatilis, Eriophorum angustifolium, and Salix rotundifolia) at Alaska’s Barrow Ecological Observatory

Root traits and nutrient competition approach explain NGEE-Arctic observations

Arctic warming will release substantial amounts of soil nitrogen that could potentially fertilize plant productivity. However, under the stress of microbial immobilization demand, the amount of nitrogen plants could assimilate is uncertain. This study demonstrates the important roles of plant functional and structural traits and an appropriate nutrient competition representation in explaining plant nitrogen uptake patterns.

The results cast doubt on current climate-scale model predictions of arctic plant responses to elevated nitrogen supply under a changing climate.  The importance of considering essential root traits in large-scale land models was highlighted in a publication in JGR-Biogeosciences titled "Root traits explain observed tundra vegetation nitrogen uptake patterns: Implications for trait-based land models."

Ongoing climate warming will likely perturb vertical distributions of nitrogen availability in tundra soils through enhancing nitrogen mineralization and releasing previously inaccessible nitrogen from frozen permafrost soil. However, arctic tundra responses to such changes are uncertain because of a lack of vertically explicit nitrogen tracer experiments and untested hypotheses of root nitrogen uptake under the stress of microbial competition implemented in land models. We conducted a vertically explicit 15N tracer experiment for three dominant tundra species to quantify plant N uptake profiles. Then we applied a nutrient competition model (N-COM), which is being integrated into the ACME Land Model (ALMv1-ECA-CNP), to explain the observations. Observations using the 15N tracer showed that plant N uptake profiles were not consistently related to root biomass density profiles, which challenges the prevailing hypothesis that root density always exerts first-order control on N uptake. By considering essential root traits (e.g., biomass distribution, nutrient uptake kinetics) with an appropriate plant-microbe nutrient competition framework (called the Equilibrium Chemistry Approximation), our model reproduced the observed patterns of plant N uptake. In addition, we showed that previously-applied nutrient competition hypotheses in earth system land models fail to explain the diverse observed plant N uptake profiles.

Q. Zhu, C. M. Iversen, W. J. Riley, I. J. Slette, H. M. Vander Stel (2016) “Root traits explain observed tundra vegetation nitrogen uptake patterns: Implications for trait-based land models.” 121, doi:10.1002/2016JG003554, 3101-3112, JGR-Biogeosciences

 

This publication was selected by editors of The Journal of Geophysical Research-Biogeosciences as a Research Spotlight for the journal website.

EOS Earth & Space Science News - Tracking Nitrogen in Arctic Plants - Prevailing nutrient uptake models do not fit Arctic plants.  Scientists test a new option that overcomes older models' shortcomings.

Thompson, E. (2017), Tracking nitrogen in arctic plants, Eos, 98, doi:10.1029/2017EO076103. Published on 20 June 2017