Weakening temperature control on the interannual variations of spring carbon uptake across northern lands

Geophysical Research Letters

et al. 2018

Self Cite

Feedbacks from the carbon cycle in boreal and arctic ecosystems can significantly affect climate change, but the effects of climate change on the high‐latitude carbon cycle during the dormant period remain uncertain. By analyzing the long‐term atmospheric CO2 concentration record from Point Barrow in Alaska, we show that warming significantly boosts net CO2 release in autumn over the period 1974–2014. But this warming‐stimulated effect has been attenuated since 1997. This deceleration of net CO2 release with warming is ascribed to the attenuation in respiration response to temperature rather than changing relationship between temperature and productivity or changes in atmospheric transport, fossil fuel emissions, or air‐sea CO2 exchanges. The attenuated respiration response is likely due to decoupling between temperature and plant‐derived carbon inputs to soil for decomposition. Contrary to previous suggestions, warming no longer results in a higher autumn net CO2 release.

Section: Resultssupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Decelerating Autumn CO₂ Release With Warming Induced by Attenuated Temperature Dependence of Respiration in Northern Ecosystems

Liú

Piao

Geophysical Research Letters

et al. 2018

Self Cite

“…The failure to reproduce the positive sign of γ int in wet season and the seemingly oversensitivity of GPP to interannual temperature variations (roughly two times more in the carbon cycle models compared to MTE for GPP) in dry season highlights the need for further model benchmarking and improvements. As drought length and intensity are projected to change (Colins et al,; Park et al., ), the tropical carbon cycle may become more dominated by interannual temperature variations, which is in contrast to the higher northern lands (Piao et al., ). Furthermore, improving model skills in simulating the response to such climatic change is required in order to project the changing tropical carbon cycle accurately.…”

Section: Discussionmentioning

confidence: 99%

Divergent response of seasonally dry tropical vegetation to climatic variations in dry and wet seasons

Ciais

et al. 2018

Global Change Biology

Self Cite

Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p < 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γ ) and to precipitation (δ ). γ is ~1% °C more negative and δ is ~8% 100 mm more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γ can be explained by background moisture and temperature conditions. Positive γ occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine-learning algorithm applied to flux tower measurements, and nine process-based carbon cycle models) were examined for the GPP-climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γ , while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis-climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.

“…Further, the overall warming trend may lead to earlier seasonal plant growth; however, incomplete development of green tissues exposed to colder environments may negatively influence tree growth and carbon storage [6]. To the contrary, some researchers concluded that increased temperature and longer growing seasons will increase the NPP and enhance carbon uptake of boreal forests; this response, however, was weak in interannual variations [64]. Boreal forests store vast amounts of carbon in soil, but the temperature effects on soils are challenging to measure.…”

Section: The Effects Of the Climate Variables On Carbon Cycling In Momentioning

confidence: 95%

Carbon Mass Change and Its Drivers in a Boreal Coniferous Forest in the Qilian Mountains, China from 1964 to 2013

Fang

et al. 2018

Forests

Carbon storage of mountain forests is vulnerable to climate change but the changes in carbon flux through time are poorly understood. Moreover, the relative contributions to carbon flux of drivers such as climate and atmospheric CO 2 still have significant uncertainties. We used the dynamic model LPJ-GUESS with climate data from twelve meteorological stations in the Qilian Mountains, China to simulate changes in carbon mass of a montane boreal forest, and the influence of temperature, precipitation, and CO 2 concentration from 1964 to 2013 on carbon flux. The results showed that the carbon mass has increased 1.202 kg/m 2 from 1964 to 2013, and net primary productivity (NPP) ranged from 0.997 to 1.122 kg/m 2 /year. We concluded that the highest carbon mass proportion for this montane boreal forest was at altitudes 2700-3100 m (proportion of ecosystem carbon was between 93-97%), with maximum carbon density observed at 2700-2900 m. In the last 50 years, the increase in precipitation and in CO 2 concentration is expected to increase carbon mass and NPP of Picea crassifolia Kom. (Pinaceae) (Qinghai spruce). The effect of temperature on NPP was positive but that on carbon mass was not clear. The increase in CO 2 concentration over the past 50 years was a major contributor to the increase in carbon storage, and drought was the foremost limiting factor in carbon storage capacity of this montane boreal forest. Picea crassifolia forest was vulnerable to climate change. Further studies need to focus on the impact of extreme weather, especially drought, on carbon storage in Picea crassifolia forests.