The biogeochemical processes of carbon (C), nitrogen (N), and phosphorous (P) are fully coupled in the Earth system, which shape the structure, functioning, and dynamics of terrestrial ecosystems. However, the representation of P cycle in terrestrial biosphere models (TBMs) is still in an early stage. Here we incorporated P processes and C‐N‐P interactions into the C‐N coupled Dynamic Land Ecosystem Model (DLEM‐CNP), which had a major feature of the ability in simulating the N and P colimitation on vegetation C assimilation. DLEM‐CNP was intensively calibrated and validated against daily or annual observations from four eddy covariance flux sites, two Hawaiian sites along a chronosequence of soils, and other 13 tropical forest sites. The results indicate that DLEM‐CNP significantly improved simulations of forest gross and net primary production (
Carbon fluxes at the land‐atmosphere interface are strongly influenced by weather and climate conditions. Yet what is usually known as “climate extremes” does not always translate into very high or low carbon fluxes or so‐called “carbon extremes.” To reveal the patterns of how climate extremes influence terrestrial carbon fluxes, we analyzed the interannual variations in ecosystem carbon fluxes simulated by the Terrestrial Biosphere Models (TBMs) in the Inter‐Sectoral Impact Model Intercomparison Project. At the global level, TBMs simulated reduced ecosystem net primary productivity (NPP; 18.5 ± 9.3 g C m−2 yr−1), but enhanced heterotrophic respiration (Rh; 7 ± 4.6 g C m−2 yr−1) during extremely hot events. TBMs also simulated reduced NPP (60.9 ± 24.4 g C m−2 yr−1) and reduced Rh (16.5 ± 11.4 g C m−2 yr−1) during extreme dry events. Influences of precipitation extremes on terrestrial carbon uptake were larger in the arid/semiarid zones than other regions. During hot extremes, ecosystems in the low latitudes experienced a larger reduction in carbon uptake. However, a large fraction of carbon extremes did not occur in concert with either temperature or precipitation extremes. Rather these carbon extremes are likely to be caused by the interactive effects of the concurrent temperature and precipitation anomalies. The interactive effects showed considerable spatial variations with the largest effects on NPP in South America and Africa. Additionally, TBMs simulated a stronger sensitivity of ecosystem productivity to precipitation than satellite estimates. This study provides new insights into the complex ecosystem responses to climate extremes, especially the emergent properties of carbon dynamics resulting from compound climate extremes.
more » « less- Award ID(s):
- 1903722
- NSF-PAR ID:
- 10452503
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 125
- Issue:
- 4
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract R 2: 0.36–0.97, RMSE:1.1–1.49 g C m−2 year−1for daily GPP at eddy covariance flux sites;R 2 = 0.92, RMSE = 176.7 g C m−2 year−1for annual NPP across 13 tropical forest sites). The simulations were also consistent with field observations in terms of biomass, leaf N:P ratio and plant response to fertilizer addition. A sensitivity analysis suggests that simulated results are reasonably robust against uncertainties in model parameter estimates and the model was very sensitive to parameters of P uptake. These results suggest that incorporating P processes and N‐P interaction into terrestrial biosphere models is of critical importance for accurately estimating C dynamics in tropical forests, particularly those P‐limited ones. -
more » « less
Abstract. Future global changes will impact carbon (C) fluxes andpools in most terrestrial ecosystems and the feedback of terrestrial carboncycling to atmospheric CO2. Determining the vulnerability of C in ecosystems to future environmental change is thus vital for targeted land management and policy. The C capacity of an ecosystem is a function of its C inputs(e.g., net primary productivity – NPP) and how long C remains in the systembefore being respired back to the atmosphere. The proportion of C capacitycurrently stored by an ecosystem (i.e., its C saturation) provides informationabout the potential for long-term C pools to be altered by environmental andland management regimes. We estimated C capacity, C saturation, NPP, andecosystem C residence time in six US grasslands spanning temperature andprecipitation gradients by integrating high temporal resolution C pool andflux data with a process-based C model. As expected, NPP across grasslandswas strongly correlated with mean annual precipitation (MAP), yet Cresidence time was not related to MAP or mean annual temperature (MAT). We linksoil temperature, soil moisture, and inherent C turnover rates (potentiallydue to microbial function and tissue quality) as determinants of carbon residence time. Overall, we found that intermediates between extremes in moisture andtemperature had low C saturation, indicating that C in these grasslands maytrend upwards and be buffered against global change impacts. Hot and drygrasslands had greatest C saturation due to both small C inputs through NPPand high C turnover rates during soil moisture conditions favorable formicrobial activity. Additionally, leaching of soil C during monsoon eventsmay lead to C loss. C saturation was also high in tallgrass prairie due tofrequent fire that reduced inputs of aboveground plant material.Accordingly, we suggest that both hot, dry ecosystems and those frequentlydisturbed should be subject to careful land management and policy decisionsto prevent losses of C stored in these systems.
-
more » « less
Abstract Semiarid grasslands are water‐limited ecosystems where precipitation (PPT) controls the onset and duration of the growing season; however, this variable does not fully explain interannual variability of productivity at temporal scales. We examined the relationship between PPT and carbon (C) fluxes in a semiarid grassland at both seasonal and interannual scales, as well as the role of lagged effects of PPT and asymmetric sensitivities of net ecosystem carbon exchange to PPT and its components (gross ecosystem exchange [GEE] and ecosystem respiration [ER]). Six years of continuous net ecosystem C exchange data measured with the eddy covariance technique and GEE estimated with 15 years of enhanced vegetation index and the gross primary productivity of Moderate Resolution Imaging Spectroradiometer were used. The semiarid grassland was a C source and a C sink among contrasting PPT years (114 to −107 g C·m−2·year−1). At seasonal scale, PPT relationship with the 15 years of GEE derived from enhanced vegetation index and gross primary productivity was sigmoidal. Moreover, PPT legacies of the previous dry season determined the C balance of the grassland by affecting the C uptake and ecosystem respiration of the following growing season, but productivity was more sensitive to PPT changes than respiration. Models of climate change for semiarid grasslands in North America predict up to 30% reduction of winter‐spring PPT and slight summer PPT decrease. Thus, our results suggest that future changes in PPT may have a strong impact on the C uptake capacity of this ecosystem due to weakened legacy effects in summer C uptake.
-
more » « less
Abstract The terrestrial carbon sink provides a critical negative feedback to climate warming, yet large uncertainty exists on its long‐term dynamics. Here we combined terrestrial biosphere models (TBMs) and climate projections, together with climate‐specific land use change, to investigate both the trend and interannual variability (IAV) of the terrestrial carbon sink from 1986 to 2099 under two representative concentration pathways RCP2.6 and RCP6.0. The results reveal a saturation of the terrestrial carbon sink by the end of this century under RCP6.0 due to warming and declined CO2effects. Compared to 1986–2005 (0.96 ± 0.44 Pg C yr−1), during 2080–2099 the terrestrial carbon sink would decrease to 0.60 ± 0.71 Pg C yr−1but increase to 3.36 ± 0.77 Pg C yr−1, respectively, under RCP2.6 and RCP6.0. The carbon sink caused by CO2, land use change and climate change during 2080–2099 is −0.08 ± 0.11 Pg C yr−1, 0.44 ± 0.05 Pg C yr−1, and 0.24 ± 0.70 Pg C yr−1under RCP2.6, and 4.61 ± 0.17 Pg C yr−1, 0.22 ± 0.07 Pg C yr−1, and ‐1.47 ± 0.72 Pg C yr−1under RCP6.0. In addition, the carbon sink IAV shows stronger variance under RCP6.0 than RCP2.6. Under RCP2.6, temperature shows higher correlation with the carbon sink IAV than precipitation in most time, which however is the opposite under RCP6.0. These results suggest that the role of terrestrial carbon sink in curbing climate warming would be weakened in a no‐mitigation world in future, and active mitigation efforts are required as assumed under RCP2.6.
-
more » « less
Abstract The Marine Biogeochemistry Library (MARBL) is a prognostic ocean biogeochemistry model that simulates marine ecosystem dynamics and the coupled cycles of carbon, nitrogen, phosphorus, iron, silicon, and oxygen. MARBL is a component of the Community Earth System Model (CESM); it supports flexible ecosystem configuration of multiple phytoplankton and zooplankton functional types; it is also portable, designed to interface with multiple ocean circulation models. Here, we present scientific documentation of MARBL, describe its configuration in CESM2 experiments included in the Coupled Model Intercomparison Project version 6 (CMIP6), and evaluate its performance against a number of observational data sets. The model simulates present‐day air‐sea CO2flux and many aspects of the carbon cycle in good agreement with observations. However, the simulated integrated uptake of anthropogenic CO2is weak, which we link to poor thermocline ventilation, a feature evident in simulated chlorofluorocarbon distributions. This also contributes to larger‐than‐observed oxygen minimum zones. Moreover, radiocarbon distributions show that the simulated circulation in the deep North Pacific is extremely sluggish, yielding extensive oxygen depletion and nutrient trapping at depth. Surface macronutrient biases are generally positive at low latitudes and negative at high latitudes. CESM2 simulates globally integrated net primary production (NPP) of 48 Pg C yr−1and particulate export flux at 100 m of 7.1 Pg C yr−1. The impacts of climate change include an increase in globally integrated NPP, but substantial declines in the North Atlantic. Particulate export is projected to decline globally, attributable to decreasing export efficiency associated with changes in phytoplankton community composition.
