Impacts of tropospheric ozone and climate change on net primary productivity and net carbon exchange of China's forest ecosystems

Abstract

Aim We investigated how ozone pollution and climate change/variability have interactively affected net primary productivity (NPP) and net carbon exchange (NCE) across China's forest ecosystem in the past half century. Location Continental China.Methods Using the dynamic land ecosystem model (DLEM) in conjunction with 10-km-resolution gridded historical data sets (tropospheric O3 concentrations, climate variability/change, and other environmental factors such as land-cover/ land-use change (LCLUC), increasing CO2 and nitrogen deposition), we conducted nine simulation experiments to: (1) investigate the temporo-spatial patterns of NPP and NCE in China's forest ecosystems from 1961-2005; and (2) quantify the effects of tropospheric O3 pollution alone or in combination with climate variability and other environmental stresses on forests' NPP and NCE. ResultsChina's forests acted as a carbon sink during 1961-2005 as a result of the combined effects of O3, climate, CO2, nitrogen deposition and LCLUC. However, simulated results indicated that elevated O3 caused a 7.7% decrease in national carbon storage, with O3-induced reductions in NCE (Pg C year -1 ) ranging from 0.4-43.1% among different forest types. Sensitivity experiments showed that climate change was the dominant factor in controlling changes in temporo-spatial patterns of annual NPP. The combined negative effects of O3 pollution and climate change on NPP and NCE could be largely offset by the positive fertilization effects of nitrogen deposition and CO2. Main conclusionsIn the future, tropospheric O3 should be taken into account in order to fully understand the variations of carbon sequestration capacity of forests and assess the vulnerability of forest ecosystems to climate change and air pollution. Reducing air pollution in China is likely to increase the resilience of forests to climate change. This paper offers the first estimate of how prevention of air pollution can help to increase forest productivity and carbon sequestration in China's forested ecosystems.

Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance

“…Despite this fact, most studies modeling regional and global responses to O 3 (e.g. Felzer et al, 2004Felzer et al, , 2005Ollinger et al, 1997Ollinger et al, , 2002Ren et al, 2011;Sitch et al, 2007) focus primarily on changes in carbon and do not verify the accuracy of stomatal conductance predictions.…”

“…To date, regional and global models that have incorporated O 3 damage to plants change only photosynthesis and assume a tight correlation between photosynthetic rate and stomatal conductance (Felzer et al, 2004(Felzer et al, , 2005Ollinger et al, 1997;Ollinger et al, 2002;Ren et al, 2011;Sitch et al, 2007), allowing photosynthesis to ultimately drive changes in transpiration. Since experimental data suggest O 3 damage to plants…”

“…The calculation for CUO assumes that the [O 3 ] inside the leaf is zero and is calculated as Felzer et al, 2004Felzer et al, , 2005Ollinger et al, 1997;Ollinger et al, 2002;Ren et al, 2011;Sitch et al, 2007). The second method of modifying photosynthesis, denoted here as Rub, impacts the biochemical aspects of photosynthesis directly through altering the V cmax parameter in the Farquhar model.…”

Responses of native broadleaved woody species to elevated ozone in subtropical China

“…Based on the China forest dataset of 1961e2005, a recent model has indicated that ambient O 3 induced a much greater loss of net carbon storage in (sub)-tropical broadleaf evergreen (9.6%) and deciduous (43.1%) forests than that in temperate broadleaf evergreen (7.6%) and deciduous (21.1%) forest, respectively (Ren et al, 2011). Therefore, it is imperative to investigate the response of subtropical broadleaved species to O 3 through field observation in order to protect biodiversity and enhance carbon sequestration in the subtropical forest ecosystem.…”

Impacts of climate variability and extremes on global net primary production in the first decade of the 21st century

“…The observational data used for model calibration are mainly from the Chinese Ecological Research Network, US Long Term Ecological Research (LTER) sites, and AmeriFlux network. After evaluating the model performance at the site level, DLEM has been widely used to simulate the effects of climate variability and change, atmospheric CO 2 , tropospheric O 3 , nitrogen deposition, and LCLUC on the pools and fluxes of carbon and water in China (Lu and Tian, 2013;Lu et al, 2012;Ren et al, 2007;Ren et al, 2011;Tian et al, 2011), the continental United States (Song et al, 2013;Tian et al, 2010a;Zhang et al, 2007;Zhang et al, 2012;Zhang et al, 2010) and North America (Tian et al, 2010c;Xu et al, 2010).…”