Journal Article
Biogeosciences, vol. 19, iss. 2, pp. 541-558, 2022
Authors
Stephanie G. Stettz, Nicholas C. Parazoo, A. Anthony Bloom, Peter D. Blanken, David R. Bowling, Sean P. Burns, Cédric Bacour, Fabienne Maignan, Brett Raczka, Alexander J. Norton, Ian Baker, Mathew Williams, Mingjie Shi, Yongguang Zhang, Bo Qiu
Abstract
Abstract. The flow of carbon through terrestrial ecosystems and the response to
climate are critical but highly uncertain processes in the global carbon
cycle. However, with a rapidly expanding array of in situ and satellite
data, there is an opportunity to improve our mechanistic understanding of
the carbon (C) cycle's response to land use and climate change. Uncertainty
in temperature limitation on productivity poses a significant challenge to
predicting the response of ecosystem carbon fluxes to a changing climate.
Here we diagnose and quantitatively resolve environmental limitations on
the growing-season onset of gross primary production (GPP) using nearly 2 decades of meteorological and C flux data (2000–2018) at a subalpine
evergreen forest in Colorado, USA. We implement the CARbon
DAta-MOdel fraMework (CARDAMOM) model–data
fusion network to resolve the temperature sensitivity of spring GPP. To
capture a GPP temperature limitation – a critical component of the integrated
sensitivity of GPP to temperature – we introduced a cold-temperature scaling
function in CARDAMOM to regulate photosynthetic productivity. We found that
GPP was gradually inhibited at temperatures below 6.0 ∘C (±2.6 ∘C) and completely inhibited below −7.1 ∘C
(±1.1 ∘C). The addition of this scaling factor improved
the model's ability to replicate spring GPP at interannual and decadal timescales (r=0.88), relative to the nominal CARDAMOM configuration (r=0.47), and improved spring GPP model predictability outside of the data
assimilation training period (r=0.88). While cold-temperature
limitation has an important influence on spring GPP, it does not have a
significant impact on integrated growing-season GPP, revealing that other
environmental controls, such as precipitation, play a more important role in
annual productivity. This study highlights growing-season onset temperature
as a key limiting factor for spring growth in winter-dormant evergreen
forests, which is critical in understanding future responses to climate
change.
