In:
Earth System Dynamics, Copernicus GmbH, Vol. 14, No. 4 ( 2023-08-14), p. 767-795
Abstract:
Abstract. Terrestrial carbon (C) sequestration is limited by nitrogen (N), an
empirically established constraint that could intensify under CO2
fertilization and future global change. The terrestrial C sink is estimated
to currently sequester approximately a third of annual anthropogenic
CO2 emissions based on an ensemble of terrestrial biosphere models,
which have been evaluated in their ability to reproduce observations of the
C, water, and energy cycles. However, their ability to reproduce
observations of N cycling and thus the regulation of terrestrial C
sequestration by N have been largely unexplored. Here, we evaluate an
ensemble of terrestrial biosphere models with coupled C–N cycling and their
performance at simulating N cycling, outlining a framework for evaluating N
cycling that can be applied across terrestrial biosphere models. We find
that models exhibit significant variability across N pools and fluxes,
simulating different magnitudes and trends over the historical period,
despite their ability to generally reproduce the historical terrestrial C
sink. Furthermore, there are no significant correlations between model
performance in simulating N cycling and model performance in simulating C
cycling, nor are there significant differences in model performance between
models with different representations of fundamental N cycling processes.
This suggests that the underlying N processes that regulate terrestrial C
sequestration operate differently across models and appear to be
disconnected from C cycling. Models tend to overestimate tropical biological
N fixation, vegetation C : N ratio, and soil C : N ratio but underestimate
temperate biological N fixation relative to observations. However, there is
significant uncertainty associated with measurements of N cycling processes
given their scarcity (especially relative to those of C cycling processes)
and their high spatiotemporal variability. Overall, our results suggest that
terrestrial biosphere models that represent coupled C–N cycling could be
overestimating C storage per unit N, which could lead to biases in
projections of the future terrestrial C sink under CO2 fertilization
and future global change (let alone those without a representation of N
cycling). More extensive observations of N cycling processes and comparisons
against experimental manipulations are crucial to evaluate N cycling and its
impact on C cycling and guide its development in terrestrial
biosphere models.
Type of Medium:
Online Resource
ISSN:
2190-4987
DOI:
10.5194/esd-14-767-2023
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2023
detail.hit.zdb_id:
2578793-7
