Title: Weaker land–climate feedbacks from nutrient uptake during photosynthesis-inactive periods

Abstract

Terrestrial carbon–climate feedbacks depend on two large and opposing fluxes—soil organic matter decomposition and photosynthesis—that are tightly regulated by nutrients. Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 represented nutrient dynamics poorly, rendering predictions of twenty-first century carbon–climate feedbacks highly uncertain. Here, we use a new land model to quantify the effects of observed plant nutrient uptake mechanisms missing in most other ESMs. In particular, we estimate the global role of root nutrient competition with microbes and abiotic processes during periods without photosynthesis. Nitrogen and phosphorus uptake during these periods account for 45 and 43%, respectively, of annual uptake, with large latitudinal variation. Globally, night-time nutrient uptake dominates this signal. Simulations show that ignoring this plant uptake, as is done when applying an instantaneous relative demand approach, leads to large positive biases in annual nitrogen leaching (96%) and N₂O emissions (44%). Furthermore, this N₂O emission bias has a GWP equivalent of ~2.4 PgCO₂ yr^–1, which is substantial compared to the current terrestrial CO₂ sink. Such large biases will lead to predictions of overly open terrestrial nutrient cycles and lower carbon sequestration capacity. Both factors imply over-prediction of positive terrestrial feedbacks with climate in current ESMs.

Authors:

Riley, W. J.  ^[1];

• Search DOE PAGES for author "Riley, W. J."
• Search DOE PAGES for ORCID "0000-0002-4615-2304"

Zhu, Q.  ^[1];

• Search DOE PAGES for author "Zhu, Q."
• Search DOE PAGES for ORCID "0000-0003-2441-944X"

Tang, J. Y.  ^[1]

• Search DOE PAGES for author "Tang, J. Y."
• Search DOE PAGES for ORCID "0000-0002-4792-1259"

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+ Show Author Affiliations

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Publication Date:

Mon Oct 29 00:00:00 EDT 2018

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1563979

Grant/Contract Number:  

AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Nature Climate Change

Additional Journal Information:

Journal Volume: 8; Journal Issue: 11; Journal ID: ISSN 1758-678X

Publisher:

Nature Publishing Group

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES