Evaluating the impacts of short and long-term fates of nitrogen additions on forest carbon pools in Earth system models
Abstract
The capacity for terrestrial ecosystems to slow climate change by storing atmospheric carbon dioxide (CO2) depends in part on whether nitrogen (N) inputs via deposition, fixation, and fertilization are retained in aboveground plant or belowground soil pools. Similarly, the accuracy of Earth system model predictions of future carbon stocks relies on how well these models predict the fate, partitioning, and movement of N between plant and soil pools across time. To evaluate the capability of a terrestrial biogeochemical model to accurately simulate the impacts of ecosystem N inputs on forest carbon pools, we compared modeled N fate and subsequent ecosystem carbon response in the Community Land Model version 5 (CLM5) across a set of temperate forests with different climates, plant types, soils, and N conditions against data from long-term 15N tracer experiments. Overall, CLM5 predicts that most added N is immediately recovered and lost slowly from forests on the decadal timescale. Contrary to observations, CLM5 overestimates annual and decadal plant N recovery and is unable to capture soils as the immediate and dominant sink for ecosystem N additions. Although patterns of N fate and partitioning differ between CLM5 and observations, CLM5 predicts whole-ecosystem carbon responses to N additions that are similar to observations—largely because differences in C:N ratios compensate for inaccurate model predictions of N recovery. By evaluating how accurately CLM5 predicts the fate and movement of N in plant and soil pools over short and long timescales, we identify strengths and weaknesses in CLM5's modeling of plant and soil N uptake, and provide directions for improving their representations to better constrain estimates of the land carbon sink.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B31A..02C
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCESDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 0466 Modeling;
- BIOGEOSCIENCES